Seismic Design Code Of Japan.pdf

JAPAN SOCIETY OF CIVIL ENGINEERS

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January,2000

JAPAN SOCIETY OF CIVIL ENGINEERS

@Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES OF CIVIL ENGINEERING STRUCTURES IN JAPAN

1.

KEY CONCEPTS FOR EARTHQUAKE RESISTANT DESIGN OF CIVIL ENGINEERING

STRUCTURES

AFTER

THE

1995

HYOGOKEN-NANBU

EARTHQUAKE 2.

1996 SEISMIC DESIGN SPECIFICATIONS OF HIGHWAY BRIDGES JAPAN ROAD ASSOCIATION

3.

SEISMIC DESIGN FOR RAILWAY STRUCTURES RAILWAY TECHNICAL RESEARCH INSTITUTE, JAPAN

4.

EARTHQUAKE RESISTANT DESIGN OF PORT FACILITIES BUREAU OF THE PORTS AND HARBORS, IvuNISTRY OF TRANSPORT

5.

BASIC PRINCIPLES OF SEISMIC DESIGN AND CONSTRUCTION FOR WATER SUPPLY FACILITIES JAPAN WATER WORKS ASSOCIATION

6.

RECOMMENDED PRACTICES FOR EARTHQUAKE RESISTANT DESIGN OF GAS PIPELINES JAPAN GAS ASSOCIATION

@Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

THE JAPAN SOCIETY OF CIVIL ENGINEERS

THE PUBLICATION COMMITTEE OF EARTHQUAKE RESISTANT DESIGN CODES OF CIVIL ENGINEERING STRUCTURES IN JAPAN

Chairman:

Masanori Hamada

(r#iseda Unievrsity)

Key Concepts for Earthquake Resistant Design

Members:

Shigeki Unjo

(Public Works Research Institute, Ministry of Construction)

Highway Bridges

Akihiko Nishimura

(Railway Technical Research Institute, Japan)

Railway Structures

Tatsuo Uwabe

(Port and Harbor Research Institute, Ministry ot Trensport)

Port Facilities

Seiji U ne

(Japan Water Works Association)

Water Supply Facilities

Hiroyuki Yamakawa

(Japan Ges Associetion)

Gas Pipelines

@Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

1. KEY CONCEPTS FOR EARTHQUAKE RESISTANT DESIGN OF CIVIL

ENGINEERING STRUCTURES AFTER THE

1995 HYOGOKEN-NANBU

EARTHQUAKE

1.1

Lessons from The 1995 Hyogoken-nanbu (Kobe) Earthquake

1- 1

1.2

Key Concepts for Earthquake Resistant Design

1- 4

1.3

Technical Subjects for Revision of Earthquake Design Code

1- 6

1.4

Diagnosis and Reinforcement of Existing Structures

1- 7

1.5

Future Innovations of Design Codes and Research Subjects

1- 8

@Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

1. KEY CONCEPTS FOR EARTHQUAKE RESISTANT DESIGN OF CIVIL ENGINEERING STRUCTURES AFTERTHE 1995 HYOGOKEN-NANBU EARTHQUAKE the causative fault system with a length of 40km,

1.1 Lessons from The 1995 Hyogoken-nanbu (Kobe) Earthquake At 5:46AM of January 17, 1995, a highly urbanized area of western Japan was jolted by an earthquake with a magnitude of M=7.2. This earthquake affected an extensive area containing major cities, Kobe and Osaka and their surrounding satellite cities which constitute the industrial, commercial and cultural center of western Japan. The areas most heavily damaged by this earthquake extends in a belt-shaped zone along

Table 1.1

particularly the zones identified as JMA intensity scale VII (equivalent to MMI=X). They extend over the entire east -west length of the most densely populated part of Hanshin (meaning Osaka-Kobe) metropolitan region.. Three million

people in this region were seriously affected. A free-field ground acceleration (pGA) exceeded 800cmfs 2 in Kobe city and its response spectrum was over 2000cmfs 2 at a damping coefficient of 0.05. Table.Ll shows loss of human lives, and a

A Summary of Damage Caused by the 1995 Kobe Earthquake (1995 Kobe Earthquake)

Human*

Death: 6306 Missing: 2

Housing and Buildings

Totally collapsed houses:

Injured: 41,527

100,300

Half and partially collapsed houses:

214,000

3,700

Buildings:

Railway:

32

Bridges **

Road (Hanshin Expressway):

Embankment and Landslides

Embankment:

427

Landslides: 367

Water

Customers without service:

1.2 million

Restoration time: 40 days

Gas

Customers without service:

857,000

Restoration time: 85 days

Electricity

Customers without service: Outage of electric power: Restoration time:

2.6 million 2836Mw 7 days

Telecommunication

Customers affected by Switchboard Malfunction: Damaged Cable Line: 19,300

Economic Impact

Private properties: Transportation facilities: Lifelines: Others: Grand total:

*

Toll by Fire Defense Agency May 21, 1995

**

Collapsed and Extensively Damaged

67

¥6.3 ¥2.2 ¥0.6 ¥0.5 ¥9.6

@Seismicisolation @Seismicisolation 1-1

235,000

trillion trillion trillion trillion trillion

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

summary of structural and functional disaster by

been· incorporated into design codes. This is one

the Kobe earthquake to houses and buildings,

of the technical subjects that the earthquake

bridge, lifeline facilities and so on.

showed needs to be promptly studied and

The first point to note about damage to civil

implemented.

engineering structures is that elevated highway bridge piers were completely destroyed. Although there had been RC bridge piers damaged by earthquakes in the past, this was the first experience of total collapse in Japan. Most of the seriously damaged

piers

were

designed

in

accordance with pre-1980 earthquake resistant design codes. The piers of concrete structures having low ductility and low ultimate strength, were shear-fractured, resulting in such major failures. Damage to RC piers designed

Figure 1.3

in

Buckling of A Steel Pier of A

Bridge (1995 Kobe Earthquake)

conformance with the current earthquake resistant design codes after 1980 was not so severe as to result in bridge collapses.

Damage to large underground structures, such as subway structures has also become a focus ofattention. The severest dainage was caused at a subway station in the downtown of Kobe city, which is of box-type

RC structure,

where

reinforced concrete columns were shear- fractured and an upper floor deck slab collapsed along with the overburden soil. Severe damage to other underground subway stations was also reported. Besides subway tunnels, which were constructed Figure 1.2 Elevated

by the cut-and-fill method, many mountain

Collapse of Bridge Piers of A

tunnels

Highway Bridge (1995 Kobe

of railway and highway were also

damaged due to large ground motion in the near

Earthquake)

field of the earthquake fault.

Another point to note is the damage to steel

Another. typical characteristic of damage to civil infrastructures caused by the Kobe

bridge piers. Many steel bridge piers buckled.

earthquake is collapses and large displacements of

Most steel structures were designed by a method

quay walls. Numerous collapses of revetments and

where stresses in steel structural members fell

quay walls had been reported in past earthquakes,

within an elastic region. The characteristics of

but most of them had not been designed to

plastic deformation of steel structures had not

withstand soil liquefaction and had been decaying.

@Seismicisolation @Seismicisolation 1-2

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

This was the first time when recently constructed

of the Shinkansen (bullet trains) shocked not only

quay walls were largely displaced by several

civil engineers, but also the general public. RC

meters or collapsed. All the damaged quay walls

bridge piers were shear-fractured and collapsed,

had been constructed using concrete caissons. The

and

result of the investigation into cause of the

earthquake struck 14 minutes before service hours,

damage to quay walls said that soft clay of the sea

no human life was lost. A serious issue has

bed largely amplified the earthquake motion and

surfaced of how to assure the safety of high speed

girders

fell.

Fortunately,

because

the

the foundation ground of the caissons, which had been constructed by replacing the original sea bed of soft

clay with

liquefiable gravel

sand,

weathered granite, also liquefied besides the filled ground behind the quay walls.

Figure 1.5

Soil Liquefaction of An Artificial

Island in Kobe (1995 Kobe Earthquake)

trains, including Shinkansen, against earthquakes caused by inland faults directly below them. Figure 1.4

Large Movement of Concrete

Caisson Quay walls (1995 Kobe Earthquake)

However, it should be noted that all the so-called earthquake resistant quay walls mostly survived. The construction of earthquake resistant quay walls has been promoted nationwide, mainly in major ports and harbors, through the lessons leamed from the damage to quay walls in Akita Harbor

during

the

1983

Nihonkai-Chubu

earthquake. The earthquake resistant quay walls, which were designed by adopting a higher seismic load than that for conventional quay walls, were constructed to withstand liquefaction. Damage to RC elevated railway bridge piers

Soil liquefaction was extensively caused in the artificial islands and alluvial low lands in Kobe and its neighboring areas, which resulted in a significant damage

to buried pipes

and

structures of lifeline systems, and many port facilities. Most of the artificial islands in Kobe area was reclaimed from the sea by weathered granite which contained large cobbles and fine contents. This revealed a need of revision of the method to evaluate the liquefaction potential of gravel sand with fine contents. The ground behind the quay walls moved several meters towards the sea, resulting from the large displacement of quay walls. These lateral ground movement damaged the foundation piles of bridges, buildings and industrial facilities.

@Seismicisolation @Seismicisolation 1-3

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Furthermore,

large

ground

strain

due

to

factor was that the earthquake struck early in the

liquefaction-induced ground movement ruptured

morning. If the earthquake had struck a few hours

buried pipes of lifeline systems such as gas, water,

later during the rush hour, the results would have

electricity and sewer. A great number of breakages

been much more tragic. Another factor was that

of buried pipes resulted in the out of service to

dawn broke over the disaster-stricken area after

numerous customers during a long period. These

the earthquake. The daylight aided the evacuation

liquefaction-induced ground displacement had not

of victims and the rescue of people trapped under

been taken in the consideration in the earthquake resistant design codes before the 1995 Kobe

collapsed houses. If the earthquake had struck at midnight, the death toll would have been much

earthquake.

greater. It is highly important to investigate into the

causes of damage to the structures and to apply the results in future preventive measures against earthquakes, but we should also pay our full attention on the above-mentioned hidden lessons.

1.2

Figure 1.6

Fall of A Bridge Girder due to

Movement of its Foundation Caused by Liquefaction-Induced Ground Displacement

When we learn the lessons from the Kobe earthquake, we should keep in mind the fact that some conditional factors mitigated the disaster. For one example had the earthquake struck the Shinkansen (bullet train) traveling on elevated railway bridges one hour later, it would have run off the rails and caused disastrous train accidents. The same can be said of the collapse of subway stations. Concrete slabs along with their overburden soil collapsed onto subway tracks. If subway trains had been stopped there or had smashed into the collapsed sections, additional serious damage would have resulted. There were other factors that contributed to lessening the secondary damage. One important

Key Concepts for Earthquake Resistant Design. The JSCE (Japan Society of Civil Engineers) organized a Special Task Committee of Earthquake Resistance of Civil Engineering Structures ill March 1995, about two months after the Kobe earthquake, to discuss various subjects, such as what an earthquake resistant capability of civil engineering structures should be in the future through the lessons from the Kobe earthquake. The committee first discussed whether the strong earthquake motions that had occurred in Kobe area should be taken into account in the future earthquake resistant design of civil engineering structures. According to researchers on active faults, in Japan the return period of the activity of the earthquake fault is 500 to 2,000 years. Assuming that the return period of the fault activity is 1,000 years and the service life of civil engineering structures is about 50 years, a probability that the structures would undergo such strong earthquake motions as those observed at the Kobe earthquake during the serviceable life is

@Seismicisolation @Seismicisolation 1-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

only five percent. The subject of the discussions by the JSCE committee was how to treat great

Level IT ground motion should be taken into

disasters with such low probability of occurrence.

account in the earthquake resistant design is

One of the reasons why JSCE said that the

The JSCE proposed two key concepts for

shown in Figure 1.7. This figure is a list of the

earthquake resistant design of civil engineering structures based on the discussions by the

damaging earthquakes in the last century in Japan and the numbers of casualties, and shows that

committee. Those are two levels of ground

inland earthquakes of magnitude 7 and larger such

motions for earthquake resistant design and so

as the Kobe earthquake, which are surrounded by

called performance-based design.

squares in the figure, occurred 8 times and have a

JSCE said that the resistance of civil

probability of occurrence that can not be neglected in terms of reformation of the design codes.

engineering structures against future earthquakes should

be

examined

by

taking

into

Figurel.7

the

also

shows

that

the

inland

consideration such strong earthquake motions as

earthquakes such as the Kobe earthquake resulted

observed during the Kobe earthquake in addition

in a greater number of causalities in comparison

to the ordinary earthquake motions that have thus

with the plate boundary earthquakes in the pacific ocean, if the 1923 Kanto and the 1900

far been used for earthquake resistant design.

Sanriku-Tsunami earthquake are excepted. In

These two earthquake motions are respectively called Level I and Level IT ground motions. Name of Earthquake Kumamoto

M

5.8

D ate

0

1889. 7.28

~

8.0

1891.10.28

Tokyo

6.7

1894. 6.20

Shonai

6.8

1894.10.22

Sanriku Tsun.

7.1

1896. 6.15

Rikuu

7.0

1896. 8.31

Gono

6.4

1909. 8.14

Akita·-Senpoku

5.9

1914. 3.15

Ch!iiwa-Bay

6.0

1922.12. 8

Great Kanto

7.9

1923. 9. 1

ita-t'Tafima

6.5

1925. 5.23

ita Tango

7.5

1927. 3.7

ita Izu

7.0

1930.11.26

Sanr-iku Tsun.

8.3

1933. 3. 3

Oga-Hanto

7.0

1939. 5.1

~

7.4

1943. 9.10

Tonankai

8.0

1944.12.7

lMikawa

I

Nanka!

IFukui

I

7.1

1945. 1.13

8.1

1946.12.21

7.3

1948. 6.28

Tokecbf-oki

8.1

1952. 3. 4

Chile EQ Tsun.

8.5

1960. 5.23

Niigata

7.5

1964. 6.16

Tokachr-oki

7.9

1968. 5.16

Izu Hanto-roki

6.9

1974

Izu-Oshima

7.0

1978. 1.14

Miyagiken-·oki

7.4

1978. 6.12

Nihonkat--Chubu

7.7

1983. 5.26

INagano-Seibu I 6.8

1984. 9.14

5. 9

Kushiro-oki

7.8

1993. 1.15

Hokkaido SI:

7.8

1993. 7.12

Hyogoken S

7.2

1995. 1.17

~

~

1000

Casualties 2000 3000

(H, Kem!)da Kyoto

4000

5000

20 7273

31 209

1900

~ ~O

these two earthquakes, the main causes of the loss

~-------------~~~

41 94

~ C;;;65······ ..·..···..·················J~~!'~!·

~ 1------------

2925

~

r- 272

" ••••••••• ---..

P

;;::

~ r------

18~6

·1961

...................... 144J

3769

29

1'-196a... -i-as

t:::

3064

27

26 52

-

.

InlandE.Q. ••••••• ' Plate Boundary (in Pacific Ocean) E.Q. _ - _ Plate Boundary (Tsunami)

30 25 28 104 29

~ 2.

230

6308"

2000

Figure 1.7

Damaging Earthquakes and Number of Causalities in Last Century in Japan (c=J: Inland Earthquakes)

@Seismicisolation @Seismicisolation 1-5

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

of human lives were the aftermath fire and the

determined by considering the following items;

tsunami, respectively.

i) effects of collapse of structures on human life

However, JSCE's recommendation does not

and survival, ii) effects on rescue and ambulance

mean that all structures should be designed and

operations and restoration activities immediately

constructed to sustain Level II earthquake motions.

after earthquakes, iii) effects on civic life after

It states that the earthquake resistant capability,

earthquakes, iv) effects on economic activities

namely performance level of a structure should be

after earthquake, and v) effects on reconstruction

determined by comparing the importance of the

works.

structure with the probability of occurrence of the

The above-mentioned key concepts proposed

design earthquake motion. For instance, against

by JSCE were adopted in the National Disaster

earthquake motions having

a probability of

Prevention Program in Japan which was newly

occurrence once or twice during the service life of

revised after the Kobe earthquake and were

structures, e.g. Level I earthquake motions, the

strongly referred for the revision and development

earthquake resistant design should stipulate that

of the earthquake resistant design codes.

the deformation of structure falls within an elastic limit and that any residual deformation does not

1.3

remain after the design earthquake. In contrast to

Technical

Subjects

for

Revision

of

this, against very rare earthquake motions, e.g.

Earthquake Design Code The adoption of the JSCE-proporsed key

Level II earthquake motions, the performance

concepts for earthquake resistant design raised

level of a structure should be changed according

following technical subjects to be resolved for the

to

code developments.

the

importance

of

the

structure.

The

performance of structures after an encounter with

i) Determination of Level II earthquake ground

the design earthquake motion can be varied for an example

as

functional, iii)

follows;

and

ii) Evaluation of elasto-plastic behaviors and

ii) slightly damaged but functional,

ultimate strength of structures against the

heavily damaged

repairable,

i)

non-damaged

motion.

and

Level II ground motion.

unfunctional, but

iv) collapsed and unrepairable.

iii) Evaluation of residual deformation of earth

structures such as embankments, retaining

The degree of importance of a structure is

Probability of occurrence of

Importance of structure

design earthquake motion

I

~

I

Earthquake resistant capability (Performance Level) of structure Figure 1.8

Determination of Performance Level (Earthquake Resistant Capability)

@Seismicisolation @Seismicisolation 1-6

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

walls and quay walls.

January, 2000

behaviors of steel structures in plastic region. The of

same can be said of the ultimate strength of buried

comparatively stiffer soil against Level II

steel pipes of lifeline systems. If large ground

ground motion v) Effects of liquefaction-induced large ground

strain due to liquefaction-induced lateral ground

iv)

Evaluation

of liquefaction

potential

displacement. How to determine the Level II ground motion

flow is incorporated into the earthquake resistant design of buried pipes, strains of the pipes will reach a plastic region. But a small amount of data

was one of the most important subjects in the

has

development of the design codes. There were

characteristics in a plastic region and ultimate

following three kinds of ideas;

strength of buried pipes.

been

accumulated

on

the

deformation

i) Adoption of the maximum ground motion

Further, evaluation of the and ductility of

recorded during past earthquakes including the

earth structures, e.g. embankments, revetments,

Kobe earthquake.

retaining walls, and quay walls, is another subject

ii) Statistical approach of recorded and calculated ground motion.

iii) Numerical Analysis of ground motion directly from the design earthquake fault. The first idea was introduced for the seismic design specifications of highway bridges (Chapter

which needs research and development. These above-mentioned technical subjects have been progressively carried out after the Kobe earthquake and the outcomes of the researches was applied for the revision and the development of the design code.

2) and the Level II ground motion was determined

steel structures has been generally made by the

1.4 Diagnosis and Reinforcement of Existing Structures Although the future earthquake resistant design of civil engineering structures will be based on the concepts described above, an additional problem is diagnosis and reinforcement of existing structures. In large Japanese cities, such as Tokyo and Osaka, there are countless civil engineering structures similar to those damaged in the Kobe area by the Kobe earthquake. Some of them, e.g. highway bridges, Shinkansen lines, subways, and quay walls, were constructed earlier or have decayed more than those damaged in the Kobe area. The earthquake resistant reinforcement of these structures becomes an inevitable problem if disaster preventive measures are taken by

allowable stress method. That is, the design is

predicting that earthquakes of a similar scale of

made, not in a plastic region beyond an elastic

the Kobe earthquake will hit these cities.

based on the ground motions recorded during the Kobe earthquake. The second idea was adopted in the revision of the design codes for the railway facilities (Chapter 3) water facilities and gas supply facilities (Chapters 4, 5). The third idea where the :design ground motion was numerically calculated from the fault movement was also adopted for the railway facilities and gas supply facilities. The adoption of the Level II design ground motion raised another Technical subjects. One is how to estimate the behaviors of the structures in the plastic region and their ultimate strength. For an example, the earthquake resistant design of

region. Research has hardly been done on the

Therefore, reinforcement of concrete piers of

@Seismicisolation @Seismicisolation 1-7

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

highways and railways and concrete columns of

more detailed investigations in future.

subways has been carried out by jacketing the

i) Dynamic failure mechanism of steel and

existing

concrete

with

steel

casting

concrete structures due to severe earthquake

additional concrete, and the other methods while

ground motion, eg Level II ground motion,

the effectiveness of those reinforcements was

shall be investigated through static and

confirmed by loading teats in the laboratory.

dynamic loading tests of structural members

However, the diagnosis and the reinforcement of

and large size structural models. Outcomes of

the foundations of bridges and buildings against

these studies are expected to give significant

the

information to

liquefaction-induced

plates

large

ground

displacement has hardly been conducted.

establish

new

earthquake

resistant design method against extremely

As is clear from the damage caused by the

severe earthquake ground motion.

Kobe earthquake, most critical and urgent issue is

ii) Mechanisms of large deformation and failure of

the reinforcement of structures on reclaimed lands,

foundations against strong earthquake ground

for instance the Tokyo Bay and the Osaka Bay

motion and large ground deformation shall be

areas, where in most of cases no soil improvement

investigated, and effective countermeasures for

has been taken against soil liquefaction, and a

foundations against liquefaction and its induced

huge number of buildings, bridges, and lifeline

large ground displacement are required to be

facilities already exist there. It is urgently required

developed.

to develop technologies of soil improvement of existing artificial grounds.

iii) Mechanisms of occurrence of static large

ground deformation due to liquefaction shall

In addition, because reinforcement should be

be studied by large scale shaking table test.

undertaken in a proper order, it is also necessary to develop a basic idea to decide the priority of

Studies on properties of perfectly liquefied soil is essential for development of a rational

reinforcement.

method

The

previously

mentioned

for

estimation

of

the

ground

importance level of structures may be referred to

displacement. Furthermore, large scale shaking

in deciding the priority of the reinforcement. That

table test on liquefaction-induced ground

is, the effects of structures on human life and

displacement is

survival and on rescue and ambulance operations

mechanism.

and

restoration

activities

immediately

after

earthquake, as well as other effects:

Research Subjects Most of earthquake resistant design codes for

to

clarify the

iv)Reasonable techniques are expected to be developed for diagnosis and reinforcement of existing

1.5 Future Innovations of Design Codes and

expected

structures

Furthermore,

including

foundations.

proper technology

shall be

developed for the soil improvement of existing liquefiable ground.

civil engineering structures have been revised or newly developed under the JSCE's key concepts and based on the outcomes from the researches after the Kobe earthquake. However, the following technical subjects remains unresolved and needs

@Seismicisolation @Seismicisolation 1-8

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

REFERENCES 1)

Japan Society of Civil Engineers: Proposal on Earthquake Resistance for Civil Engineering Structures, 1996

2)

Hamada, M.: Seismic Code Development for Civil

Infrastructures

Hyogoken-nanbu

after

(Kobe)

Proceedings of the 5

th

the

1995

Earthquake,

U.S. Conference on

Lifeline Earthquake Engineering, TCLEE, Monograph No.16, pp922-929, 1999 3)

Japan

Road

Association:

Design

Specifications of Highway bridges, Part I Common Part, Part IT Steel Bridges, Part ill Concrete Bridges, Part IV Foundations, and Part V Seismic Design, 1996

4)

Seismic Design Code for Railway Structures, published by MARUZEN, Oct., 1999. (in Japanese) 5) Japan Water Works Association: Seismic Design and Construction Guidelines for Water Supply Facilities, 1997

@Seismicisolation @Seismicisolation 1-9

@Seismicisolation @Seismicisolation

2. 1996 SEISMIC DESIGN SPECIFICATIONS OF HIGHWAY BRIDGES

JAPAN ROAD ASSOCIATION 2.1

Introduction

2- 1

2.2

Damage Features of Bridges in The Hyogo-ken Nanbu Earthquake

2- 1

2.3

Basic Principle of Seismic Design

2- 3

2.4

Design Methods

2- 4

2.5

Design Seismic Force

2- 6

2.6

Evaluation of Displacement Ductility Factor of a Reinforced Concrete Pier

2- 7

2.6.1

Evaluation of Failure Mode

2- 7

2.6.2

Displacement Ductility Factor

2- 7

2.6.3

Shear Capacity

2- 8

2.6.4

Arrangement of Reinforcement

2- 9

2.6.5

Two-Column Bent

2- 11

Evaluation of Displacement Ductility of a Steel Pier

2.7

2- I I

2.7.1

Basic Concept

2- 11

2.7.2

Concrete Infilled Steel Pier

2- 12

2.7.3

Steel Pier without Infilled Concrete

2- 12

2.8

Dynamic Response Analysis

2- 13

2.9

Menshin Design

2- 14

2.9.1

Basic Principle

2- 14

2.9.2

Design Procedure

2- 15

2.9.3

Design of Menshin Devices

2- 15

2.10

Design of Foundation

2- 17

2.11

Design Against Soil Liquefaction and Liquefaction-Induced Ground Flow

2- 17

2.11.1 Estimation of Liquefaction Potential

2- 17

2.11.2 Design Treatment of Liquefaction for Bridge Foundations

2- 17

2.11.3 Design Treatment of Liquefaction-induced Ground Flow for Bridge Foundations 2- 18 2.12

Bearing Supports

2- 18

2.13

Unseating Prevention Systems

2- 19

2.14

Concluding Remarks

2- 20

@Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

2.1996 SEISMIC DESIGN SPECIFICATIONS OF HIGHWAY BRIDGES JAPAN ROAD ASSOCIATION 2.1 Introduction Highway bridges in Japan had been considered safe even against extreme earthquake such as the Great Kanto Earthquake (M7.9) in 1923, because various past bitter experiences have been accumulated to formulate the seismic design method (Kawashima (1995)). Large seismic lateral force ranging from O.2g to O.3g has been adopted in the allowable stress design approach. Various provisions for preventing damage due to instability of soils such as soil liquefaction have been adopted. Furthermore, design detailings including the unseating prevention devices have been implemented. In fact, reflecting those provisions, number of highway bridges which suffered complete collapse of superstructures was only 15 since 1923 Great Kanto Earthquake. Based on such evidence, it had been regarded that the seismic damage of highway bridges had been decreasing in recent years. However, the Hyogo-ken nanbu Earthquake of January 17, 1995, exactly one year after the Northridge, California, USA, earthquake, caused destructive damage to highway bridges. Collapse and nearly collapse of superstructures occurred at 9 sites, and other destructive damage occurred at 16 sites (Ministry of Construction, 1995a). The earthquake revealed that there are a number of critical issues to be revised in the seismic design and seismic strengthening of bridges in urban areas. After the earthquake the "Committee for Investigation on the Damage of Highway Bridges Caused by the Hyogo-ken nanbu Earthquake" (chairman : Toshio IWASAKI, Executive Director, Civil Engineering Research Laboratory) was formulated in the Ministry of Construction to survey the damage and clarify the factors which contributed to the damage. On February 27, 1995, the Committee approved the "Guide Specifications for

Reconstruction and Repair of Highway Bridges which suffered Damage due to the Hyogo-ken nanbe Earthquake," (Ministry of Construction 1995b) and the Ministry of Construction noticed on the same day that the reconstruction and repair of the highway bridges which suffered damage in the Hyogo-ken nanbu earthquake should be made by the Guide Specifications. It was decided by the Ministry of Construction on May 25, 1995 that the Guide Specifications should be tentatively used in all sections of Japan as emergency measures for seismic design of new highway bridges and seismic strengthening of existing highway bridges until the Design Specifications of Highway Bridges was revised. In May, 1995, the "Special Sub-Committee for Seismic Countermeasures for Highway Bridges" (chairman Kazuhiko KAWASHIMA, Professor of the Tokyo Institute of Technology) was formulated in the "Bridge Committee" (chairman : Nobuyuki NARlTA, Professor of the Tokyo Metropolitan University), Japan Road Association, to draft the revision of· the Design Specifications of Highway Bridges. The Special Sub-Committee drafted the new Design Specifications of Highway Bridges, and after the approval of the Bridges Committee, the Ministry of Construction released it November 1, 1996. This chapter summarizes the damage feature of highway bridges by the Hyogo-ken N anbu earthquake and the new Design Specifications of Highway Bridges issued in November 1996. 2.2 Damage Features of Bridges in The Hyogo-ken Nanbu Earthquake Hyogo-ken Nanbu earthquake was the first earthquake which hit an urban area in Japan since the 1948 Fukui Earthquake. Although the magnitude of the earthquake was moderate (M7.2), the ground motion was much larger

@Seismicisolation 2-1 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

than anticipated in the codes. It occurred very close to the Kobe City with shallow focal depth. Damage was developed at highway bridges on Routes 2, 43, 171 and 176 of the National Highway, Route 3 (Kobe Line) and Route 5 (Bay Shore Line) of the Hanshin Expressway, the Meishin and Chugoku Expressway. Damage was surveyed for all bridges on National Highways, Hanshin Expressways and Expressways in the area where destructive damage occurred. Total number of piers surveyed reached 3,396 (Ministry of Construction, 1995a). Fig.2.1 shows Design Specifications referred to in design of the 3,396 piers. Most of piers (bridges) which suffered damage were designed according to the 1964 Design Specifications or older Design Specifications. Although the seismic design methods have been improved and amended several times since 1926 based on damage experience and progress of bridge earthquake engineering, only a requirement for lateral force coefficient was provided in the 1964 Design Specifications or older Specifications. 1980 Design Specifications

January, 2000

or no damage). Substructures of the Route 3 and Route 5 were designed with the 1964 Design Specifications and 1980 Design Specifications, respectively. It should be noted in this comparison that the intensity of ground shaking in terms of response spectra was smaller at the Bay Area than the narrow rectangular area where JMA Seismic Intensity was vn (equivalent to Modified Mercalli Intensity of X-XI). The Route 3 was located in the narrow rectangular area while the Route 5 was located in the Bay Area. Keeping in mind such difference of ground motion, it is apparent in Fig.2.2 that about 14% of the piers on Route 3 suffered As or A damage while no such damage was developed in the piers on the Route 5. A

s

B

o

1990 Design Specifications (a) Route 3

(b) Route 5

Fig.2.2 Comparison of Damage Degree between Route 3 and Route 5 (As: Collapse, A : Nearly Collapse, B : Moderate Damage, C : Damage of . Secondary Members, D : Minor or No Damage)

1971 Design Specifications

Although damage concentrated on the bridges designed with the older Design Specifications, it was thought that essential revision was required even in the recent Design Specifications to prevent damage against destructive earthquakes such as the Hyogo-ken nanbu earthquake. The main points requiring modifications were; (1) it was required to increase lateral capacity and ductility of all structural components in which seismic force is predominant so that ductility of a total bridge system be enhanced. For such purpose, it was required to upgrade

1964 or Older Design Specifications

Fig.2.1 Design Specifications Referred to in Design of Hanshin Expressway Fig.2.2 compares damage of piers on the Route 3 (Kobe Line) and Route 5 (Bay Shore Line) of the Hanshin Expressway. Damage degree was classified as As (collapse), A (nearly collapse), B (moderate damage), C (damage of secondary members) and D (minor

@Seismicisolation @Seismicisolation 2-2

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

the "Check of Ductility of Reinforced Concrete Piers," which has been used since 1990, to a "Ductility Design Method," and to apply the Ductility Design Method to all structural components. It should be noted here that "check" and "design" is different; the check is only to verify the safety of a structural member designed by other design method, and is effective only to increase the size or reinforcements if required, while the design is an essential procedure to determine the size and reinforcements, (2) it was required to include the ground motion developed at Kobe in the earthquake as a design force in the Ductility Design Method, (3) it was required to specify input ground motions in terms of acceleration response spectra for dynamic response analysis more actively, (4) it was required to increase tie reinforcements and to introduce intermediate ties for increasing ductility of piers. It was decided not to terminate main reinforcements at mid-height for preventing premature shear failure, in principle, (5) it was suggested to adopt multi-span continuous bridge for increasing number of indeterminate of a total bridge system, (6) it was suggested to adopt rubber bearings for absorbing lateral displacement between a superstructure and substructures. It was

important to consider correct mechanism of force transfer from a superstructure to substructures, (7) it was suggested to include the Menshin design (seismic isolation), (8) it was required to increase strength, ductility and energy dissipation capacity of unseating prevention devices, and (9) it was required to consider the effect of lateral spreading associated with soil liquefaction in design of foundations at the site vulnerable to lateral spreading.

2.3 Basic Principle of Seismic Design Table 2.1 shows the seismic performance level provided in the revised Design Specifications in 1996. The bridges are categorized into two groups depending on their importance; standard bridges (Type-A bridges) and important bridges (Type-B bridges). Seismic performance level depends on the importance of bridges. For moderate ground motions induced in the earthquakes with high probability to occur, both A and B bridges should behave in an elastic manner without essential structural damage. For extreme ground motions induced in the earthquakes with low probability to occur, the Type-A bridges should prevent critical failure, while the Type-B bridges should perform with limited damage .

Table 2.1 Seismic Performance Levels

Importance of Bridges Type of Design Ground Motions

Type-A (Standard Bridges)

Type-B Equivalent (Important Static Lateral Bndges) Force Methods

Ground Motions with Prevent Damage High Probability to Occur Ground Motions with Low Probability to Occur

Type-I (Plate Boundary Earthquakes) Type-II (Inland Earthquakes)

Design Methods

Seismic Coefficient Method

Dynamic Analysis Step by Step Analysis or

Prevent Critical Damage

Limited Damage

Ductility Design Method

@Seismicisolation @Seismicisolation 2-3

Response Spectrum Analysis

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

In the Ductility Design Method, two types of ground motions must be considered. The first is the ground motions which could be induced in the plate boundary-type earthquakes with magnitude of about 8. The ground motion at Tokyo in the 1923 Kanto Earthquake is a typical target of this type of ground motion. The second is the ground motion developed in earthquakes with magnitude of about 7-7.2 at very short distance. Obviously the ground motions at Kobe in the Hyogo-ken nanbu earthquake is a typical target of this type of ground motions are called as Type-I and Type-Il ground motions, respectively.

(

Start

January, 2000

The recurrence time of the Type-IT ground motion may be longer than that of the Type-I ground motion, although the estimation is very difficult.

2.4 Design Methods Bridges are designed by both the Seismic Coefficient Method and the Ductility Design Method as shown in Fig.2.3. In the Seismic Coefficient Method, a lateral force coefficient ranging from 0.2 to 0.3 has been used based on the allowable stress design approach. No change was introduced since the 1990 Specifications in the Seismic Coefficient

)

Design for

Principal Loads

Seismic Design by Seismic Coefficient Method

>--~

:heck the Safety by Dynamic Response Anal sis

Unseating Prevention Devices

Seismic Design by Dynamic Response Analysis (Type I and II Ground Motions

Seismic Design by Ductility Design Method (Type J and II Design Force) Check the Safety by Dynamic Response Analysis (Type I and II Ground Motion)

I End

Fig.2.3

Flowchart of Seismic Design

@Seismicisolation @Seismicisolation 2-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Method. In the Ductility Design Method, assuming a principle plastic hinge formed at the bottom of pier as shown in Fig.4(a) and the equal energy assumption, a bridge is designed so that the following requirement is satisfied. Pa > he W (1) where he

khe = -.fZjJ.a-1 = Wo--c» Wp

(Z)

W (3) in which, Pa = lateral capacity of a pier, he = equivalent lateral force coefficient, W = equivalent weight, kne = lateral force coefficient, jJ. a = allowable displacement ductility factor of a pier, Wu = weight of a part of superstructure supported by the pier, Wp = weight of a pier, and cp = coefficient depending on the type of failure mode. The cp is 0.5 for a pier in which either flexural failure or shear failure after flexural cracks are developed, and 1.0 for a pier in which shear failure is developed. The lateral capacity of a pier Pa is defined as a lateral force at the gravity center of a superstructure. In the Type-B bridges, residual displacement developed at a pier after an earthquake must be checked as (4) R< aa where

a

a

January, 2000

OR = CR (jJ. R-l) (l-r) a y jJ. R = 1/2 {(he' W /Pai+ l ]

(5) (6) in which R = residual displacement of a pier after an earthquake, Ra = allowable residual displacement of a pier, r = bilinear factor defined as a ratio between the first stiffness (yield stiffness) and the second stiffness (post-yield stiffness) of a pier, CR = factor depending on the bilinear factor r, jJ. R = response ductility factor of a pier, and y = yield displacement of a pier. The a aa should be 11100 of a distance between the bottom of a pier and a gravity center of a superstructure. In a bridge with complex dynamic response, the dynamic response analysis is required to check the safety of a bridge after it is designed by the Seismic Coefficient Method and the Ductility Design Method. Because this is only for a check of the design, the size and reinforcements of structural members once determined by the Seismic Coefficient Method and the Ductility Design Methods can only be increased if necessary. It should be noted however that under the following conditions in which the Ductility Design Method is not directly applied, the size and reinforcements can be determined based on the results f a dynamic response analysis as shown in Fig.2.3. The conditions when the Ductility Design Method should not be directly used include: (1) principle mode shapes which contribute to

a

a

Principal Plastic Hinge

(a) Conventional Design

(b) Menshin Design (c) Bridge Supported by A Wall-type Pier

Fig.2.4 Location of Primary Plastic Hinge

@Seismicisolation @Seismicisolation 2-5

a

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

most cases excessive. Therefore if a foundation has sufficiently large lateral capacity compared with the lateral seismic force, the foundation is designed assuming a plastic hinge at the foundation and surrounding soils as shown in Fig.2A(e),

bridge response are different from the ones assumed in the Ductility Design Methods, (2) more than two modes significantly contribute to bridge response, (3) principle plastic hinges form at more than two locations, or principle plastic hinges are not known where to be formed, and (4) response modes for which the equal energy assumption are not applied. In the seismic design of a foundation, a lateral force equivalent to the ultimate lateral capacity of a pier Pu is assumed to be a design force as h p = Cdf PuIW (7) in which hp = lateral force coefficient for a foundation, Cdf = modification coefficient (=1.1), and W = equivalent weight by Eq.(3). Because the lateral capacity of a wall-type pier is very large in transverse direction, the lateral seismic force evaluated by Eq. (7) becomes in

2.5 Design Seismic Force Lateral force coefficient he in Eq.(2) is given as he = cz : heO (8) in which cz = modification coefficient for zone, and is 0.7, 0.85 and 1.0 depending on zone, and heo = standard modification coefficient. Table 2.2 and Fig.2.S show the standard lateral force coefficients heo for the Type-I and the Type-Il ground motions. The Type-I ground motions have been used since 1990 (1990 Specifications), while the Type-Il ground motions were newly introduced in the 1996

Table 2.2 Lateral Force Coefficient heo in the Ductility Design Method (a) Type-I Ground Motions Lateral Force Coefficient fuco

Soil Condition Group I

2J hco=0.876T / for T > 1.4

fuco=0.7 for T < 1.4

(stiff) Group II (moderate) Group III (soft)

fueo=1.51TI/J (fueo > 0.7) for T 0.18 I/J beo=1.51T (beo > 0.7) for T 0.29

<

<

fueo=0.85 for 0.18

< T < 1.6

fueo=1.0 for 0.29

< T < 2.0

fueo=1.16T2/J for T> 1.6 fueo= 1.59T2/3 for T> 2.0

(b) Type-Il Ground Motions Lateral Force Coefficient fueo

Soil Condition Group I (stiff) Group II

fueo=4.46T/J for T

< 0.3

heo=3.22T

< 0.4

(moderate)

for T

Group III

hco=2.38T

(soft)

for T

/J

/3

< 0.5

beo=2.00 for 0.3

< T < 0.7

heo=1.75 for 0.4 ~ T

< 1.2

beo=1.50 for 0.5

< T < 1.5

@Seismicisolation @Seismicisolation 2-6

beo=1.24T

4/J

for T> 0.7 beo=2.23T4/J for T> 1.2

beo=2.57T'3 for T> 1.5

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

u

2.5

.Y

....., c a;

2

I I

U <;:: ~

a;

a

1.5

--

accelerations excursion is longer in the Type-I ground motions than the Type-II ground motions. As will be described later, such a difference of the duration has been taken into account to evaluate the allowable displacement ductility factor of a pier.

- - - - - Group I - Group II Type I Group III

..c ~

--.

- - - - - Group I - Group II Type II Group 111

U

a; U

L-

a

2.6 Evaluation of Displacement Ductility Factor of A Reinforced Concrete Pier

u.,

ro

L-

a; .....,

0.5

---

ro -..l

2.6.1 Evaluation of Failure Mode In the ductility design of reinforced concrete piers, the failure mode of the pier is evaluated as the first step. Failure modes is categorized to 3 types based on the bending capacity and shear capacity of the pier as : bending failure 1) Pu < Ps 2) Ps < Pu < Pso : bending to shear failure 3) PsO < Pu : shear failure in which Pu == bending capacity, Ps == shear capacity in consideration of the effect of cyclic loading, and Pso == shear capacity without consideration of the effect of cyclic loading. The ductility factor and capacity of the reinforced concrete piers are determined according to the failure mode as described later.

0 0

3

2

4

Natural Period T (5) Fig.2.S

Type I and Type II Ground Motions in the Ductility Design Method

Specifications. It should be noted here that the heO at stiff site (Group I) has been assumed smaller than the heO at moderate (Group II) and soft soil (Group III) sites in the Type-I ground motions as well as the seismic coefficients used for the Seismic Coefficient Method. The Type-I ground motions were essentially estimated from an attenuation equation for response spectra that was derived from a statistical analysis of 394 components of strong motion records. Although the response spectral accelerations at short natural period are larger at stiff sites than at soft soil sites, the tendency has not been explicitly included in the past. This was because damage has been more developed at soft sites than at stiff sites. To consider such fact, the design force at stiff sites has been assumed smaller than that at soft sites even at short natural period. However being different from such a traditional consideration, the Type-II ground motions were determined by simply taking envelops of response accelerations of major strong motions recorded at Kobe in the Hyogo-ken nanbu Earthquake. It was considered appropriate to set realistic ground motions. Although the acceleration response spectral intensity at short natural period is higher in the Type-II ground motions than in the Type-I ground motions, the duration of extreme

2.6.2 Displacement Ductility Factor The allowable displacement ductility factor of a pier j.J. a in Eq.(2) is evaluated as j.J. a

== 1 +

a

ay ay

u -

Q:'

(9)

a

in which Q:' = safety factor, y == yield u = ultimate displacement of a pier, and displacement of a pier. As well as the lateral capacity of a pier Pa in Eq.(I), the a y and u are defined at the gravity center of a superstructure. In a reinforced concrete single pier as shown in Fig.2.4(a), the ultimate displacement u is evaluated as a u== a y+ (et> u- et> y) Lp(h - Lp/2) (10) in which et> y = yield curvature of a pier at bottom, et> u == ultimate curvature of a pier at bottom, h == height of a pier, and Lp == plastic hinge length of a pier. The plastic hinge length is given as

a

a

a

@Seismicisolation @Seismicisolation 2-7

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Lp= 0.2h - O.lD (O.lD < Lr < 0.5D) (11) in which D is a width or a diameter of a pier. The yield curvature ¢ y and ultimate curvature ¢ u in Eq.(10) are evaluated assuming a stress-strain relation of reinforcements and concrete as shown in Fig.2.6. The stress (J' e - strain t: e relation of concrete with lateral confinement is assumed as Ee

e

e{l _

1 n

~)n-l} C

ee

(0 < C e < e cc ) Edes( c e - c cc) (c cc < e e < E cu) (12) Ee e ee n= (13) Ee E ee - (J' ee in which a cc = strength of confined concrete, Ee = elastic modules of concrete, e cc = strain at maximum strength, and Edes = gradient at descending branch. In Eq.(12), (J' cc, C ee and Eses are determined as a ee = (J' ek + 3.8 a p s (J' sy (14) (J'e=

[

ee -

C

ee = 0.002+0.033 j3

P s (J' sy (J' ek

Edes = 11.2

(J' ek 2

(15)

(16) p s (J' sy in which (J' ek = design strength of concrete, (J' sy = yield strength of reinforcements, a and j3 = coefficients depending on shape of pier ( a =1.0 and j3 =1.0 for a circular pier,

and a = 0.2 and j3 = 0.4 for a rectangular pier), and p s = tie reinforcement ratio defmed as

Stress

Stress (}s

=

4Ah

< 0.018 (17) sd in which Ah = area of tie reinforcements, s = space of tie reinforcements, and d = effective width of tie reinforcements. The ultimate curvature ¢ u is defmed as a curvature when concrete strain at longitudinal reinforcing bars in compression reaches an ultimate strain e eu defined as for Type I ground motions C ee C ell = ( 0.2 (J' ee C ee + Edes for Type II ground motions (18) It is important to note here that the ultimate strain c eu depends on the types of ground motions; the c eu for the Type-II ground motions is larger than that for the Type-I ground motions. Based on a loading test, it is known that a certain level of failure in a pier such as a sudden decrease of lateral capacity occurs at smaller lateral displacement in a pier subjected to a loading hysteresis with more number of load reversals. To reflect such a fact, it was decided that the ultimate strain e eu should be evaluated by Eq.(18), depending on the type of ground motions. p

0.80' cc

s

O'c

I

- - - - --

_____ L

_

I

I I I

I I

Strain e,

I

I I

I I

r

£cu

(a) Reinforcing Bars

(b) Concrete

Fig.2.6 Stress and Strain Relation of Confined Concrete and Reinforcing Bars

@Seismicisolation @Seismicisolation 2-8

Strain E.c

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Table 2.3

January, 2000

Safety Factor a in Eq.(9)

Type of Bridges

Type-I Ground Motions

Type-II Ground Motions

Type-B

3.0

1.5

Type-A

2.4

1.2

Table 2.4

Modification Factor On Scale Effect for Shear Capacity Shared by Concrete Effective Width of Section d (m)

Coefficient

d ;;:;; 1

1.0

d::::3

0.7

d::::5

0.6

~

0.5

d

10

Therefore, the allowable ductility factor u a depends on the type of ground motions; the u a is larger in a pier subjected to the Type-IT ground motions than a pier subjected to the Type-I ground motions. It should be noted that the safety factor a in Eq.(9) depends on the type of bridges as well as the type of ground motions as shown in Table 2.3. This is to preserve higher seismic safety in the important bridges, and to take account of the difference of recurrent time between the Type-I and the Type-IT ground motions. 2.6.3 Shear Capacity Shear capacity of reinforced concrete piers is evaluated by a conventional method as Ps :::: Sc + Ss (19) Sc :::: 10 Cc Ce Cpt reb d (20) Ss > Aw a sy d (sin e +cos e) (21) 10 x 1.1Sa in which Ps :::: shear capacity, Sc :::: shear capacity shared by concrete, Ss :::: shear capacity shared by tie reinforcements, t: c = shear stress capacity shared by concrete, Cc = modification factor for cyclic loading (0.6 for Type-I ground motions, 0.8 for Type-II ground motions), Ce = modification factor for scale effect of effective width, Cpt :::: modification factor for longitudinal reinforcement ratio, b, d

Ce

:::: width and height of section, Aw :::: sectional area of tie reinforcement, (J' sy:::: yield strength of tie reinforcement, = angle between vertical axis and tie reinforcement, and a = spacing of tie reinforcement. The modification factor on scale effect of effective width, Ce, was based on the experimental study of loading tests of beams with various effective height and was newly introduced in the 1996 Specifications. Table 2.4 shows the modification factor on scale effect.

e

2.6.4 Arrangement of Reinforcement Fig.2.7 shows suggested arrangement of tie reinforcement. Tie reinforcement should be deformed bars with a diameter equal or larger than 13 mm, and it should be placed in most bridges at a distance of no longer than 150mm. In special cases such as the bridges with pier height taller than 30m, the distance of tie reinforcement may be increased at height so that pier strength should not be sharply decreased at the section. Intermediate ties should be also provided with the same distance with the ties to confine the concrete. Space of the intermediate ties should be less than 1m.

@Seismicisolation @Seismicisolation 2-9

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

~~

u

u

u

u

u

p

(

(

~

~~

~

(b) Semi-square Section

(a) Square Section

(c) Circular Section (d) Hollow Section Fig.2.7. Confinement of Core-concrete by Tie Reinforcement

n

Lp

Lp

r:

o--6--r--o---(c)}-+----------j--
LPC o @

Node Plastic hinge

Lp

Plastic Hinge Length Rigid Member

o.

o

Fig.2.S Analytical Idealization of A Two-Column Bent

@Seismicisolation @Seismicisolation 2-10

Elastic Member

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

2.6.5 Two-Column Bent To determine the ultimate strength and ductility factor for two-column bents, it is modeled as the frame model with plastic hinges at the both end of lateral cap beam and columns as shown in Fig.2.8. Each elastic frame member has the yield stiffness which is obtained based on the axial load by the dead load of the superstructure and the column. The plastic hinge is assumed to be placed at the end part of a cap beam and the top and bottom part of each column. The plastic hinges are modeled as spring elements with bilinear moment-curvature relation. The location of plastic hinges is half distance of the plastic hinge length off from the end edge of each member, where plastic hinge length LP is assumed to be Eq.(ll). When the two-column bent is subjected to the lateral force in the transverse direction, axial force developed in the beam and columns is affected by the aoolied lateral force. Therefore, the horizontal force-displacement relation is obtained through the static push-over analysis considering axial force N - moment M interaction relation. The ultimate state of each plastic hinges is obtained by the ultimate plastic angle pu as pu = (¢ uI ¢ y -1) Lp ¢ y (22) in which ¢ u = ultimate curvature and ¢ y = yield curvature.

e

January, 2000

The ultimate state of the whole two-bent column is determined so that all 4 plastic hinges developed reach the ultimate plastic angle.

2.7 Evaluation of Displacement Ductility of A Steel Pier 2.7.1 Basic Concept To improve seismic performance of a steel piers, it is important to avoid specific brittle failure modes. Fig.2.9 shows the typical brittle failure mode for rectangular and circular steel piers. The followings are the countermeasures to avoid such brittle failure modes and to improve seismic performance of steel piers: 1) fill the steel column with concrete 2) improve structural parameters related to buckling strength • decrease the width/thickness ratio of stiffened palates of rectangular piers or the diameter/thickness ratio of steel pipes • increase the stiffness of stiffeners · reduce the diaphragm spacing · strengthen comers using the comer plates 3) improve welding section at the comers of rectangular section 4) eliminate welding section at the comers by using round comers

e

(b) Elephant Knee Buckling

(a) Fracture of Comers

Fig.2.9 Typical Brittle Failure Modes of Steel Piers

@Seismicisolation @Seismicisolation 2-11

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

2.7.2 Concrete Infilled Steel Pier In a concrete infilled steel pier, the lateral capacity Pa and the allowable displacement ductility factor jJ. a in Eqs.(l) and (2) are evaluated as Pu - Py Pa == Py + --'-'----'-(23)

be idealized as reinforcing bars and that only steel section resists axial force. A stress vs. strain relation of steel and concrete as shown in Fig.2.10 is assumed. The height of infilled concrete has to be decided so that. bucking is not developed above the infilled concrete.

(]I

-(1 jJ.a-

+ O'u-O'y)~

2.7.3 Steel Pier without Infilled Concrete A steel pier without infilled concrete must be designed with the dynamic response analysis. Properties of the pier need to be decided based on a cyclic loading test. Arrangement of stiffness and welding at comer must be precisely evaluated so that brittle failure should be avoided.

(24)

ay

Pa in which Py and Pu == yield and ultimate lateral y and u == yield and capacity of a pier, ultimate displacement of a pier, and (]I == safety factor (refer to Table 2.3). The Pa and the jJ. a are evaluated idealizing that a concrete infilled steel pier resists flexural moment and shear force as a reinforced concrete pier. It is assumed in this evaluation that the steel section (]I

a

a

ay

o

0 Of.]

'" .....l-< 1;1) ~

0.01

0.02

0.03 0.04

Strain

0

0.05

iO. 05

iEy

0.02

0.04

Strain

t: s

.

E

a= 2a,
o

!

!

0.01

0.02

Ec

)

0.00827

!

t

0.04

0.05

!

0.03

Strain

Fig.2.10

t: s

(b) Steel (Compression Side)

(a) Steel (Tension Side)

o

0.06· 0.08

t: c

(c) Concrete Stress-Strain Relation of Steel and Concrete

@Seismicisolation 2-12 @Seismicisolation

0.10

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

2.8 Dynamic Rresponse Analysis Dynamic response analysis is required in the bridges with complex dynamic response to check the safety factor of the static design. Dynamic response analysis is alas required as a "design" tool in the bridges for which the Ductility Design Method is not directly applied. In dynamic response analysis, ground matins which are spectral fitted to the following response spectra are used; S I = cz ' CD' S I 0 (25) S II = cz ' CD • SilO (26) in which S I and S II = acceleration response spectrum for Type-land· Ty6e-II ground motions, S I 0 and SilO = standard acceleration response spectrum for Type-land Type-Il ground motions, respectively, CZ = modification coefficient for zone (refer to Eq.(8», and CD =

Table 2.5

Group II

Group III

CD

=

coefficient for 1.5 40hi + 1

damping

+ 0.5

Table 2.5 and Fig.2.ll show the standard acceleration response spectra (damping ratio h=0.05) for the Type-I and Type-Il ground motions. It is recommended to use at least three ground motions per analysis, and take an average to evaluate the response. In the dynamic analysis, modal damping ratios have to be carefully evaluated. To determine themodal damping aratios, a bridge may be divided into several sub-strucctures in which energy dissipating mechanism is essentially the same. If one can specify a

2

Response Acceleration S10 (gal=cm/sec ) SIO=700 for Ti SJo=1,505T."3 (SJO ~. 700) for Ti < 0.18

SJO=1,511T."3 (SJO ~ 700) for T; < 0.29

~

1.4

SIO=980!Ti for Ti

~

Ti

~

~

Ti

~

>

for Ti

1.6

1.6

SJO=2,000/Ti

SIO=l,OOO for 0.29

1.4

SJO=1,360!Ti

S1O=850 for 0.18

>

>

for Ti

2.0

2.0

(b) Type-Il Response Spectra SilO 2

Response Acceleration Suo (gal=cm/sec )

Soil Condition

SII0=4,463Ti Group I for Ti

2/3

~

0.3 13 Sno=3,224T/ Group I!

for T,

<

0.4 213

3no=2,381Ti Group III for Ti

<

0.5

ratio (27)

Standard Acceleration Response Spectra (a) Type-I Response Spectra SIO

Soil Condition Group I

modification given as

January, 2000

SII0=1,104/Ti

SII0=2,000 for 0.3

~

T;

~

SII0=1,750 for 0.4 ~ Ti ~ 1.2 SII0=1,500

>

for Tj

0.7

513

0.7

SJJO=2,371/T/'3 for T ;

>

1.2

SII0=2,948/T;513

for 0.5 ~ Ti ~ 1.5

@Seismicisolation 2-13 @Seismicisolation

for T;

>

1.5

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

2.5

2.9 Menshin Design 2.9.1 Basic Principle Implementation of the Menshin bridges should be carefully decided from not only seismic performance but function for traffic and maintenance point of view, based on the advantage and disadvantage of increasing natural period The Menshin design should not be adopted at the following conditions; 1) sites vulnerable to lose bearing capacity due to the soil liquefaction and the lateral spreading, 2) bridges supported by flexible columns, 3) soft soil sites where potential resonance with surrounding soils could be developed by increasing the fundamental natural period,and 4) bridges with uplift force at bearings. It is suggested that the design should be made with an emphasis on an increase of energy dissipating capability and a distribution of lateral force to as many substructures as possible. To concentrate the hysteretic deformation at not piers but bearings, the fundamental natural period of a Menshin bridge should be about 2 times or longer than the fundamental natural period of the same bridge supported by the conventional bearings. It should be noted that an elongation of natural period aiming to decrease the lateral force should not be attempted.

- - - - - Ground I -;)

..

;:;

,

2

1.5

'-' '-'

" I

'-'

\

• Ground IJ

-

Type I

- - Ground III

..

"I :I :I

<

-

\

, \ ,_-"", __ \

----- Ground I -

,,

\

-

- Ground II Type U

\

r-r-r-r-r-r-it-r-r-r-r-c-: \ _ _ _ ..J.. _ _

~

- -- - - - - - - - ....- , \.

<, "-

' ... --....

;:: '-'

...

c::

...........

-...

--- """'---~~~~~~~~~~~j r

0 0

2

3

4

Natural Period (5)

Fig.2.ll Type I and Type II Standard Acceleration Response Spectra damping ratio of each sub-structure for a given mode shape, the modal damping ratio for i-th mode, hi, may be evaluated as n

L ¢ ij T. hij . Kj' ¢ ij hi =

j=l

(28)

iT'K' i

January, 2000

in which hij = damping ratio of j-th substructure in i-th mode, ¢ ij = mode vector of j-th substructure in i-th mode, kj = stiffness matrix of j-th substructure, K= stiffness matrix of a bridge, and i = mode vector of a bridge in i-th mode, and is given as cP iT = {¢ u", ¢ iZT , • • • • • • , ¢ inT } (29) Table 2.6 shows recommended damping ratios for major structural components.

Table 2.6 Recommended Damping Ratios for Major Structural Components Structural Components Superstructure

Elastic Response Steel

0.02

~

Concrete

0.03

Rubber Bearings Mensbin Bearings

Substructures Foundations

Nonlinear Response

0.03

~

0.05

Steel

0.02

~

Concrete

0.03

0.02

~

0.05 0.1

0.05 ~

~

0.05

0.02

Equivalent Damping Ratio by Eq.(26)

0.03

0.03

0.3

~

Equivalent Damping Ratio by Eq.(26)

0.1

0.1

rv

0.2 0.2

@Seismicisolation @Seismicisolation 2-14

0.12 rv

0.4

~

0.2

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

2.9.2 Design Procedure Menshin bridges are designed by both the Seismic Coefficient Method and the Ductility Design Method. In the Seismic Coefficient Method, no reduction of lateral force from the conventional design is mae. In the Ductility Design Method, the equivalent lateral force coefficient kbcm in the Menshin design is evaluated as

= hcm =

hcm

hem

reduced, as large as 30%, by the modification coefficient CE depending on the modal damping ratio of a bridge. Modal damping ratio of a menshin bridge h for the fundamental mode is computed as Eq.(32). In Eq.(32), hsi = damping ratio of i-th damper, hPi = damping ratio of i-th pier or abutment, hFui = damping ratio of i-th foundation associated with translational displacement, hF e i = damping ratio of i-th foundation associated with rotational displacement, Kn = equivalent stiffness of i-th pier or abutment, KFui = translational stiffness of i-th foundation, KF e i = rotational stiffness of i-th foundation, UBi = design displacement of i-th Menshin device, and. H = distance from a bottom of pier to a gravity center of a deck. In the Menshn design, the allowable displacement ductility factor of a pier jJ. m in Eq.(30) is evaluated by

(30)

.["2 jJ. m-1

January, 2000

hc (31) in which hcm lateral force coefficient in menshin design, jJ. m = allowable ductility factor of a pier, CE = modification coefficient for energy dissipating capability (refer to Table2.7), and knc = lateral force coefficient by Eq.(8). Because the hc is the lateral force coefficient for a bridge supported by the conventional bearings, Eq.(31) means that the lateral force in the Menshin design can be CE'

=

2 "'K L. B i

·u

2(h B i . B i

+

hPi'KBi

K

h=

L K

B j'U B

j

Pi

+

Fui

KBi KBi + -+ -+

2(1

KPi

a

hFui'KBi K

ay

KFui

+

hFBi'KBi'H TT

)

..L"'!t..~81

KBi'H

2

(32)

)

KFBj

O~

smaller allowable ductility factor in the menshin design is to limit the hysteretic behavior of a pier at the plastic hinge zone so that principle hysteretic behavior occurs at the menshin devices as shown in Fig.2.4(b).

where a is the safety factor in the conventional design (refre to Table 2.3). Eq.(34) means that the allowable displacement ductility factor in the menshin design jJ. m should be smaller than the allowable displacemnent ductility factor u a by Eq.(2) in the conventional design; The reason for the

2.9.3 Design of Menshin Devices Simple devices stable against extreme earthquakes have to be used. The bearings have to be anchored to a deck and substructures with bolts, and should be replaceable. The clearance has to be provided

jJ.

m

=1 +

u -

(33)

_---=--_-'---L.-

amoy

in which a m is a safety factor used in Menshin design, and is given as jJ.m=2a

Table 2.7 Modification Coefficient for Energy Dissipation Capability Damping Ratio for 1st Mode h h

<

Coefficient c

0.1

1.0

0.1 ~ h

<

0.12

0.9

0.12 ;;;;;; h

<

0.15

0.8

h ~ 0.15

E

0.7

@Seismicisolation @Seismicisolation 2-15

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

between a deck and an abutment or between adjacent decks. Isolators and dampers must be designed for a desired design displacement us. The design displacement UB is evaluated as khem Wu UB :::: (35)

January, 2000

The equivalent stiffness KB and equivalent damping ratio hs of a Menshin device are evaluated as F(UBe) - F(-uBe) (36) 2UBe ~W

hs ::::

K:e

2 7C W

(37)

use :::: cs : UB

(38) in which F(u) :::: restoring force of a device at a displacement U , UBe :::: effective design displacement, ~ W = energy dissipated per cycle, W = elastic strain energy, 'and CB :::: coefficient to evaluate effective displacement

in which hem :::: equivalent lateral force coefficient by Eq.(3l), KB :::: equivalent stiffness, and Wu :::: dead weight of a superstructure. It should be noted that because the equivalent lateral force coefficient hem depends on the type of ground motions, the design displacement us also depends on it.

(=0.7).

Vertical Force at Pile Top P

...

Ultimate Bearing Capacity -r-r_

P" -

KVE,~~ ,

kHE _ _ _ _ _...L -

: :

,

,

1

' I ' ... _..l

,

I I ...

PT'

Ultimate Pull-out Force

/:v~ ti'\~ ,

:

Vertical Displacement

(b)Vertical Force YS. Vertical Displacement Relation

I~

" I

I I 1 _ _ .J

_.J

(a) Analytical Model

OJ

<.J 1-0

o

~

c

~<.J ~

P::

PHU

Max. Horizontal Reaction Force

B c

E C

o ~

l: Mu - ••••••• _.- •••••• --- •••• -.-.------

y My.-.----

C b.O Ma ---

C

o

:ac

N

'J: o

.....

OJ

:I: 0 ' - - - ' - - - - - - - - Horizontal Displacement

C: Crack Y: Yield U : Ultimate :

~

c E

v:

M.

i---------

o

;'8

My - _ . :

Y : Yield - Mp: Plastic Moment

OJ)

c

"t:l C

OJ

~

Curvature

o

Curvature

(c) Horizontal Force vs, (d) Moment vs. Curvature (e) Moment vs. Curvature Horizontal Displacement Relation of Reinforced Relation of Steel Pipe Relation Concrete Piles Piles Fig.2.12Idealized Nonlinear Model of A Pile Foundation

@Seismicisolation @Seismicisolation 2-16

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

2.10 Design of Foundation The evaluation methods of ductility and strength of foundations such as pile foundations and caisson foundations was newly introduced in the 1996 Specifications. In a pile foundation, a foundation is so idealized that a rigid footing is supported by piles which are supported by soils. The flexural strength of a pier defined by Eq.(7) shall be applied as a seismic force to foundations at the bottom of the footing together with the dead weight superstructure, pier and soils on the footing. Fig.2.l2 shows the idealized nonlinear model of a pile foundation. The nonlinearity of soils and piles is considered in the analysis. The safety of the foundation shall be checked so that 1) the foundation shall, not reach the yield point of a foundation, 2) if the primary nonlinearity is developed in the foundations, the response displacement shall be less than displacement ductility limit, and 3) the displacement developed in the foundation shall be less than allowable limit. The allowable ductility and allowable limit of displacement were commented as 4 in displacement ductility, 40cm in horizontal displacement and a.025rad in rotation angle. For a caisson type foundation, the foundation is modeled as a reinforced concrete column which is supported by soil spring model and the safety is checked in the same way as the pile foundations. 2.11 Design Against Soil Liquefaction and Liquefaction-induced Ground Flow 2.11.1 Estimation of Liquefaction Potential Since the Hyogo-ken nanbu Earthquake of 1995 caused liquefaction even at coarse sand or gravel layers which had been regarded invulnerable to liquefy, a gravel layer was included in the soil layers that require liquefaction potential estimation. Soil layers that satisfies the following conditions is estimated to be potential liquefaction layers: 1) saturated soil layer which is located within 20m deep under the ground surface and in which ground water level is within 10m deep.

January, 2000

2) soil layer in which fine particle content ratio Fe is equal orless than 35% or plasticity index IF is equal or less than 15. 3) soil layer in which mean grain size Dso is equal or less than 10mm and 10% grain size DIO is equal or less than Imm. Liquefaction potential is estimated by the safety factor against liquefaction FL as FL = RJL (35) where, FL = liquefaction resistant ratio, R = dynamic shear strength ratio and L = share stress ratio during an earthquake. The dynamic shear strength ratio R may be expressed as R = cw Rc (36) where, Cw = corrective coefficient for ground motion characteristics (1.0 for Type-I ground motions, 1.0-2.0 for Type-IT ground motions), and Rc = cyclic triaxial strength ratio. The cyclic triaxial strength ratio was estimated by laboratory tests with undisturbed samples by in-situ freezing method. The shear stress ratio during an earthquake may be expressed as L = ru kne a via v' (37) where, ra = modification factor shear stress ratio with depth, :he = design seismic coefficient for the evaluation of liquefaction potential, (J" v = total loading pressure, (J" v' = effective loading pressure. It should be noted here that the design seismic coefficient for the evaluation of liquefaction potential :he is ranging from 0.3 to 0.4 for Type-I ground motions, and from 0.6 to 0.8 for Type-IT ground motions.

2.11.2 Design Treatment of Liquefaction for Bridge Foundations When the liqeufaction occurs, the strength and the bearing capacity of a soil decreases. In the seismic design of highway bridges, soil constants of a sandy soil layer which is judged liable to liquefy are reduced according to the FL value. The reduced soil constants are calculated by multiplying the coefficient DE in Table2.8 to the soils constants estimated on an

@Seismicisolation @Seismicisolation 2-17

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Table 2.8

Reduction Coefficient for Soil Constants due to Soil Liquefaction Depth from the Present

Range of FL Ground Surface x (m) FL~

0~x;;;;'10

1/3

January, 2000

Dynamic Shear Strength Ratio R R

~

0.3·

0.3
a

1/6

----------------------- ----------------- ---------------10<x ~ 20 1/3 1/3

1/3
a ~x;;;; 10 1/3 2/3 ----------------------- ----------------- ---------------10<x ~ 20 2/3 2/3

2/3
0 ~x;;;; 10 2/3 1 ----------------------- ----------------- ---------------10<x ~ 20 1 1

assumption that the soil layer does not liquefy.

2.11.3 Design Treatment of Liqeufaction-Induced Ground Flow for Bridge Foundations When the liquefaction-induced ground flow that may affect bridge seismicity is likely to occur, this influence was included in the revised Design Specifications in 1996. The case in which the ground flow that may affect bridge seismicity is likely to occur is generally that the ground is judged to be liquefiable and is exposed to biased earth pressure, for example, the ground behind a seaside protection wall. The effect of liquefaction-induced ground flow is considered as the static force acting on structure. This method premises that the surface soil is of the non-liqeufiable and liquefiable layers, and the forces equivalent to the passive earth pressure and 30% of the overburden pressure are applied to the structure in the non-liquefiable layer and liquefiable layer, respectively. The seismic safety of a foundation is checked by confirming the displacement at the top of foundation caused by ground flow does not exceed an allowable value, in which a foundation and the ground are idealized as shown in Fig.2.l2. The allowable displacement of a foundation may be taken as two times the yield displacement of a foundation. In this process, the inertia force of structure is not necessary to be considered simultaneously,

because the liquefaction-induced ground flow may take place after the principle ground motion. 2.12 Bearing Supports The bearings are classified into two groups; the first is the bearings which resist the seismic force of Eq.(2), and the second is the bearings which resist the seismic force considered in the Seismic Coefficient Method. The first and the second bearings are called as the Type-B bearings and the Type-A bearings, respectively. Seismic performance of the Type-B bearings is, of course, much higher than the Type-A bearings. In the Type-A bearings, a displacement limiting device, which will be described later, has to be co-installed in both longitudinal and transverse directions, while it is not required in the Type-B bearings. Because of the importance .of bearings as one of the main structural components, the Type-B bearings should be used in the menshin bridges. The uplift force applied to the bearing supports is specified as 2 Ru :::: R» Rhe q + Rvec{ (38) in which Ru = design uplift force applied to the bearing support, RD = dead load of superstructure, Rheq and Rveq are vertical reactions caused by the horizontal seismic force and vertical force, respectively. Fig.2.13 shows the design forces for thebearing supports.

.r

@Seismicisolation @Seismicisolation 2-18

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Center of gravity

1

jh B

.-

!

_----Jr==F=...Jc..J..

+

--'r-iL..Ji.-!:,

r=..-==...-.L.l:.-,

I

.:t.... _.

±RV E Q RHEQI (i- )

Fig.2.13

Design Forces for Bearing Supports

2.13 Unseating Prevention Systems Unseating prevention measures are required for the highway. bridges. The measures required for the highway bridges are as: 1) the unseating prevention systems have to be so designed that unseating of a superstructure from their supports can be prevented even if unpredictable failures of the structural members occur, 2) the unseating prevention systems are consisted of providing enough seat length, a falling-down prevention device, a displacement limiting device, and a settlement prevention device, 3) enough seat length must be provided and a falling-down prevention device must be installed at the ends of a superstructures against longitudinal response. If the Type-A bearings are used, a displacement limiting device has to be further installed at not only the ends of a superstructure but each intermediate support in a continuous bridge, and 4) if the Type-A bearings are used, a displacement limiting device is requested at

each support against transverse response. The displacement limiting device is not generally required if the Type-B bearings are used. But, even if the Type-B bearing is adopted, it is required in skewed bridges, curved bridges, bridges supported by columns with narrow crest, bridges supported by few bearings per piers, and bridges constructed at the sites vulnerable to lateral spreading associated with soil liquefaction. The seat length SE is evaluated as SE = UR +UG > SEM (39) SEM = 70 + 0.51 (40) UG =100' C G'L (41) in which UR = relative displacement (cm) developed between a superstructure and a substructure subjected to a seismic force equivalent to the equivalent lateral force coefficient he by Eq.(2), UG = relative displacement of ground along the bridge axis, SEM = minimum seat length (cm), C G = ground strain induced during an earthquake along the bridge axis, and is 0.0025, 0.00375, and 0.005 for Group-I, II and ill sites, respectively, L= distance which contributes to the relative displacement of ground (m), and 1 = span length (m). If two adjacent deck are supported by a pier, the lager span length should be 1 in evaluating the seat length. Inthe menshin deisgn, in addition to the above requirements, the following

@Seismicisolation @Seismicisolation 2-19

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

copnsiderations have to be made. 1) To prevent collisions between a deck and an abutment or between two adjacent decks, enough clearance must be provided. The clearance between those structural components SB shall be evaluated as UB + LA between a deck and an abutment CB"UB + LA between two adjacent decks

January, 2000

of the new Seismic Design Specifications of Highway Bridges issued in 1996 as well as the damage features of highway bridges in the Hyogo-ken nanbu earthquake. The Hyogo-ken nanbu earthquake was the first earthquake which developed destructive damage in an urban area since the 1948 Fukui Earthquake. Because it had been considered that such destructive damage could be prevented due to the progress of construction technology in recent years, it provided a large impact on the earthquake disaster prevention measures in various fields. The "Part V Seismic Design" of the "Design Specifications of Highway Bridges" (Japan Road Association) was totally revised in 1996, and the design procedure moved from the traditional Seismic Coefficient Method to the Ductility Design Method. The revision was so comprehensive that the past revisions in the last 30 years look minor. Major point of the revision was the introduction of explicit two-level seismic design consisting of the Seismic Coefficient Method and the Ductility Design Method. Because the Type-I and the Type-Il ground motions are considered in the Ductility Design Method, three design seismic forces are totally used in design. Seismic performance for each design force was clearly stated in the Specifications. The fact that lack of near-filed strong

(42)

in which UB = design displacement of menshin devices (em) by Eq.(35), LA =:: redundancy of a clearance (generally + 1.5cm), and CB = modification coefficient for clearance (refer to Table 2.9). The modification coefficient CB was determined based on an analysis of the relative displacement response spectra. It depends on a difference of natural periods 6. T = T. - T2 (T. > T2), in which Ti and T2 represent the natural period of the two adjacent bridge systems. 2) The clearance at an expansion joint LE is

evaluated as LE = us + LA (43) in which UB = design displacement of men shin devices (cm) by Eq.(35), and LA = redundancy of a clearance (generally -+- 1.5cm).

Table 2.9 Modification Coefficient for Clearance

c. TIT,

CB

CB

o ~~ TlTl < 0.1 0.1 ~ ~ TIT, < 0.8

-V2

0.8 ~ ~ T(I\ ~ 1.0

1

1

2.14 CONCLUDING REMARKS The preceding pages presented an outline

motion records prevented to seriously evaluate the validity of recent seismic design codes is

@Seismicisolation @Seismicisolation 2-20

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

important. The Hyogo-ken nanbu earthquake revealed that history of strong motion recording is very short, and that no near-field records have yet been measured by an earthquake with magnitude on the order of 8. It is therefore essential to have enough redundancy and ductility in a total bridge system. It is hoped that the revised Seismic Design Specifications of Highway Bridges contributes to enhance seismic safety of highway bridges.

N anbu Earthquake, 1995

ACKNOWLEDGMENTS

Drafting of the revised version of the "Part V Seismic Design" of the "Design Specifications of Highway Bridges" was conducted at the "Special Sub-committee for Seismic Countermeasures for Highway Bridges" and was approved by the Bridge Committee, Japan Road Association. The first and other authors of this paper served as chairman and executive members in the Special Sub-committee. The authors thank ail members of the Special Sub-Committee and the Bridge Committee. REFERENCES 1) Japan Road Association Design Specifications of Highway Bridges, Part I Common Part, Part II Steel Bridges, Part ill Concrete Bridges, Part IV Foundations, and Part V Seismic Design, 1996 2) Kawashima, K.: Impact of Hanshin/Awaji Earthquake on Seismic Design and Seismic Strengthening of Highway Bridges, Report No. TIT/EERG 95-2, Tokyo Institute of Technology., 1995 3) Ministry of Construction: Report on the Damage of Highway Bridges by the Hyogo-ken N anbu Earthquake, Committee for Investigation on the Damage of Highway Bridges Caused by the Hyogo-ken Nanbu Earthquake, 1995 4) Ministry of Construction: Guide Specifications for Reconstruction and Repair of Highway Bridges Which Suffered Damage due to the Hyogo-ken

@Seismicisolation @Seismicisolation 2-21

@Seismicisolation @Seismicisolation

3. SEISMIC DESIGN FOR RAILWAY STRUCTURES

RAILWAY TECHNICAL RESEARCH INSTITUTE, JAPAN 3.1

Basic Principles of Seismic Design for Railway Structures

3- 1

3.2

Setting of Design Earthquake Motions

3- 3

3.3

3.2.1

Setting of Earthquake Motions for Bedrock

3- 3

3.2.2

Setting of Design Earthquake Motions on the Ground Surface

3-11

Seismic Performance of Structures 3.3.1

Setting of Seismic Performance Levels for Structures

3.3.2

Consideration on the Damage Levels of Member, the Stability Levels of Foundation as well as their Limit Values

3-13

3-13

3-14

3.4

Concept ofImportance Degree of Structure

3.5

Evaluation of Surface Ground and Calculation of Displacement and Stress ofStructure3-17

3.6

3.7

3-17

3.5.1

Evaluation of Surface Ground

3-17

3.5.2

Calculation of Responses of Structures

3-24

Safety (Seismic Performance) Checking of Structures

3-25

3.6.1

Checking Damage Levels of Members

3-27

3.6.2

Checking Stability Levels of Foundation

3-27

3.6.3

An Example of Safety Checking of Pile Foundation

3-27

Conclusions

3-29

@Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

3. SEISMIC DESIGN FOR RAILWAY STRUCTURES RAILWAY TECHNICAL RESEARCH INSTITUTE, JAPAN 3.1

Basic Principles of Seismic Design for Railway Structures

A new code, "Seismic Design Code for Railway Structures" (in Japanese), drawn up by Railway Technical Research Institute, has been published recently, which reflects the recent advances in earthquake engineering'{ In the code some new thought for seismic design have been adopted by drawing the lesson of the HyogokenNanbu Earthquake of January 17, 1995 that caused the devastating damage including the large-scale cave-in of many railway structures. In order to introduce a methodology for the seismic design that can effectively prevent reappearance of the kind of damage happened in the HyogokenNanbu Earthquake, elucidation of the damage mechanism has been conducted. As the results, the following causes of the damage are inferred based

on

the

damage

reconnaissance

and

columns. This situation with different damage pattern might be mainly due to the difference in dynamic behavior of the surface ground, which was inferred through the dynamic analysis by considering both the properties of structures and ground. @As to the damage of cut and cover tunnel, both bending and shear stresses occurred in columns , but since the shear strength was lower than that of bending which is same as the case of viaducts, the shear failure occurred and caused the collapse under the weight of overburden. The

facts

above

indicate

the

following

procedures are important to seismic design. CDTaking inland earthquakes into account ®Evaluating the safety of members by considering the failure modes of structures @The necessary to

use

dynamic

analysis

methods and consider the dynamic behavior of

analysis".

CDMany of the structures damaged possessed the seismic capacity that was designed by only considering

totally and the other side with only cracks in

a

horizontal

design

seismic

coefficient of 0.2. However, the acceleration level of the Hyogoken-Nanbu Earthquake was far over such a design level and caused the

surface

ground

in

response

analysis

of

structures. Moreover, the level of design earthquake motion has become dramatically large because of consideration

of

the

inland

earthquakes.

Generally the return period of the intense earthquake may be several hundred years long.'

large damage. ®Viaducts of the Shinkansen that suffered serious damage including the collapsing of structures, were originally designed to be less safety against shear loads than bending loads. This imbalance aggravated the damage degree of the structures. This was partly due to the fact that allowable stress against shear force was set larger in the design code of those days. @Some situation of the damage showed a great gap in the damage degree between two adjoining viaducts, where one side collapsed

Therefore, it is reasonable to abandon the elastic design method and adopt the performance-based design method in which the seismic performance of structures is evaluated and the damage of structure is allowable in some extend, but never the collapse. Seismic design of a railway structure should therefore be carried out following

procedures.

according to the Firstly,

from

the

viewpoint of damage control, the degree of damage to a structure (seismic performance) should be identified. Secondly, the responses of

3-1 @Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

the surface ground are analyzed by inputting the

resulting from an earthquake should be made to

design earthquake motion in the base ground.

satisfy

Thirdly, the response waves of the surface

Which performance the structure should be

ground are inputted to the structure and the

endowed

responses of the structure are analyzed. Finally,

importance of the structure.

basing on the obtained responses of the structure the seismic performance can be checked.

the

seismic

with

performance

basically

objective.

depends

on

the

As the reasons described above, in order to check the seismic performance properly, a

There are two types of design earthquake

dynamic analysis method for calculating the

motion are determined in this code. One is the

responses of a structure is generally adopted in

so-call L1 earthquake motion, which has a

seismic design.

recurrence probability of a few times during the

analysis method is also used depending on the

service life of the structure. .The other is L2

type of structure.

earthquake motion with high intensity, which is

design for bridges or viaducts based on the

caused by a near-land-large-scale interplate

approaches above is shown in Fig.3.1.1.1.

However, some times a static The procedure of seismic

earthquake or an inland earthquake near to the

As what indicated in the figure, there are two

Comparing with Ll earthquake, the

types of approaches can be used for the seismic

structure.

occurrence probability of L2 earthquake is low.

design. One is the simplified method (nonlinear

For the earthquake motions, by considering the

spectrum method) that can be easily applied for

of the

the calculation of the responses of a structure by

foundations, the seismic performance of a

i) selecting the soil profile type based on site

structure is set to 3 grades corresponding to the

geological conditions; ii) using the demand yield

presumed levels of repair or reinforcement that

strength spectrum that is calculated with the

may be required following an intense earthquake.

earthquake motion corresponding to the soil

In the seismic design, responses of a structure

profile type selected. The other is the detailed

damage of members

and

stability

Setting input earthquake motion

Evaluation of surface ground

Calculation of responses of structures

Examination of seismic performance

Selection of Ll , L2 earthquake motions (Spectrum I, Spectrum II)

Selection of earthquake motions according to Soil Profile Type

Simplified dynamic analysis (Nonlinear spectrum method)

Members : Damage Level Foundation; Stability Level

Fig.3.1.1.1 Procedure of seismic design for bridges or viaducts

@Seismicisolation @Seismicisolation 3-2

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

method (time-history dynamic analysis method)

may happen in most areas of Japan. Consequently,

with which the time history of responses of the

the motion due to this type of earthquake is also

ground and structure can be analyzed detailed.

covered by Spectrum I, therefore this spectrum is

For

a

common

structure,

spectrum method is suitable.

the

nonlinear

However if a

structure can not be modeled as a system with

regarded as the minimum earthquake motion to be verified in the seismic design.

®

SpectrumII : acceleration spectrum based

single degree of freedom, as described later, the

on the statistic analysis of the earthquake data

detailed analysis method should be applied to.

recorded in the past inland earthquakes caused

In the following pages, major procedures for

the seismic design, such as the setting of design

by active faults.

@ Spectrumill:

also

representing

the

of

motions caused by active inland faults, but based

displacements and stresses of structures, and the

on the analysis of the active faults, if such a

checking of structural safety are described.

model of active fault is available.

3.2

motion from the 3 types above is a difficult, but

earthquake

motions,

the

analysis

Setting of Design Earthquake Motions

3.2.1

Setting of Earthquake Motions for

important task in the seismic design, because the presumed earthquake may be affected by a great

Bedrock

amount of uncertainty. (1) Types

and

Determination

of

Design

Spectra

It

is

desirable

to

determine

the

design

earthquake motion for a specific site according to

As what described previously, in order to

the risk factors such as the return period of

consider the effects of surface ground to the

earthquake from certain seismic faults. However,

responses of a structure, either LIar L2

the return period of earthquake related to an

earthquake motion is set on the surface of

inland active fault is not accurate enough at

bedrock.

present, when compared with the service life of

Ll earthquake motion has about the same level

structure. Therefore, an extreme event associated

as the acceleration spectrum corresponding to the

with an inland active fault should be taken into

high quality ground that used to be adopted in

account, unless it is evident that the fault will not

the allowable stress design. The maximum value

move during the life of structure.

of

the

response

acceleration

is

250

gal

corresponding to the damping coefficient of 5 %. L2 earthquake motion is classified into the SpectrumI

corresponding

acceleration to

the

near-land

site, the geological and seismological information on inland active faults, historical activities of earthquakes

around

spectrum

earthquakes

near

interplate

carefully'). A general flowchart is given in

following 3 types.

CD

To determine the design earthquake motion of a

earthquakes of magnitude 8.0 and epicenter distance of 30 to 40 kilometers.

the land

site must

and

interplate

be

analyzed

Fig.3 .2.1.1. There are a number of ways to define the design

In addition, the inland active fault, which will

earthquake motion. The design earthquake motion

cause an earthquake of magnitude less than 6.5, is

is defined below by the response spectra of

difficult to be found since its size is not big

acceleration on a free surface of bedrock, the

enough to reach the ground surface. According to

shear wave speed of which is over 400m/s. The

the historical earthquakes, this type of earthquake

choice of bedrock is to avoid the influences from

@Seismicisolation 3-3 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

local effects of specific site on the ground motion,

objective response spectra of acceleration and

such as the amplification due to the soft surface

modeling the phases to reflect the non-stationary

soil and irregular topography of ground. The

property of earthquake motions.

influence due to geological conditions is very

Which spectrum should be used as the design

remarkable, as recognized in seismic records, and

earthquake motion depends on the results of

can be evaluated by calculating the responses of

investigation of inland active faults. There could

surface soil using a proper numerical model of

be three possibilities shown following from the

surface ground with the design earthquake motion

investigation (Fig.3.2.1.1).

as the incident motion. A corresponding artificial

The first (the left route in Fig.3.2.I.1), if there is

seismic wave can be generated by adjusting

no active fault near the site, the earthquake motion

Fourier amplitudes of the wave according to the

of Spectrum I is to be used as design earthquake

T No

Doubtful

Analysis with source model?

No

Yes, Computation of ground motions

Determine local seismic risk factor

,

,I

,

Spectrum I modified by risk factor

Determination of spectrum ill

Determine local seismic risk factor

~-----'

,

Speetrum Il attenuated with distance

Spectrum TI modified by risk factor

I

Compared with odified spectrum

,

,

Artificial wave

I

c? Fig.3.2.1.1 General flowchart to determine the design earthquake motion

@Seismicisolation @Seismicisolation 3-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

motion after modified by the risk factor of the

with each other. Hence, the design earthquake

area.

motion is Spectrum IT modified by the risk factor

The second (the middle route in Fig.3.2.1.1),

of the area.

there are cases where one or more active faults

(2)Near-Source Earthquake Motions Induced by Inland Active Faults

existing near the site. When the parameters of seismic source for the faults can be properly decided, the design earthquake motion can be

There are still many problems to be solved

determined by the fault analysis with source

when using a seismic source model of fault to

model (Spectrum III). Otherwise, the earthquake

predict the earthquake ground motion at a site for

motion of Spectrum IT attenuated according to the

the purpose of seismic design, such as the

distance between the fault and site, will be used as

distribution of the asperity on the fault plane, the

the design earthquake motion. Because the power

start point of rupture, etc.

of the motion decreases as the distance between

uncertainties of it, it is effective to evaluate the earthquake

motion

To consider these

near inland

fault

from

attenuated results of Spectrum IT and III should be

statistical analyses of near-source strong seismic

compared with that of Spectrum I modified by the

records

risk factor of the area, then the larger one will be

summarized is a method to determine Spectrum IT

taken as the design earthquake motion.

based on strong seismic records.

The third (the right route in Fig.3.2.1.1), there

observed

in

recent

years.

Below

are sites where the existence of active fault is very

1) Seismic records Table 3.2.1.1 shows the list of records observed

doubtful and difficult to confirm due to very deep

in recent earthquakes in the United States and

sedimentary deposit, or there exists a complex

Japan, Hyogoken-Nanbu (1995,M7.2), Coyote

tectonic structure beneath the site, such as the

Lake (1979, MS.9), Loma Prieta (1989,M7.1),

Kanto area in Japan where three plates encounter

Landers (1992, M7.5) and Northridge (1994,

Table 3.2.1.1 Near-source seismic records from recent earthquakes "S

]

Max. Ace. (gal)

tU LL

r!:::

Ol

No

-""

Ol

::::>

""0

'" 0-

£;

ffi

.8

Ol

3

Name of seismic record NS

EW

W

~

....J

Ol ""0

3

'5> c

0 ....J

'-' o

Ol

c.. c> .>, c; .c ro

-05 C._

Ol""O Cij

>

'5 0-

UJ

2 3 4

Hyogoken-

5

Nanbu

Ol

o c ro

05 0 05 Ol

'"

a

_

Ol

>

Ol

c 0

:.=

Soil condition

ro

-2:

""OOl C en

::::>.0

eo

at the position of seismometer

o

0

U

679.8

302.6

135.208

11.64

3.24

GL-83

Vs=450 (m/s)

86.0

109.3

134.783

32.75

27.08

GL·100

Vs=460 (m/s)

293.9

319.8

135.442

34.57

24.65

GL-97.0

Vs=455 (m/s)

272.0

306.5

135.240

14.99

6.90

GL·9.5

0.5m (240m/s) layeroverVs=590 (m/s) Vs=780m/s

185.3

200.4

135.427

38.03

25.03

GL-30

6

445.9

425.3

135.296

20.00

12.38

GL-33

Layerof N=18 aboveGL-45

7

683.6

600.9

135.344

29.93

16.88

GLO.O

N over63, 1.5m surfacelayerwith N=5

16.52

7.53

GLO.O

Vs=300m/s, 4msurface layerVs=200m/s

1.0

GLO.O

Rock

12.19

GLO.O

Limestone

8 9 10

Coyote Lake Loma Prieta

11 12 13

::;]

Landers Northridge

510.7

584.2

135.250

314.6

408.8

121.484

433.1

401.5

122.06

18.01

426.6

433.6

121.572

26.56

12.21

GLO.O

Franciscan Sandstone

268.3

278.4

116.314

16.90

10.79

GLO.O

Shallow alluvium over granite bedrock

GLO.O GLO.O

@Seismicisolation 3-5 @Seismicisolation

Thin alluvium oversiltstone

IRock

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

4000

2000

1000 800

---.

600

'"2 400 eo <::»

:::: 0

.~

200

'-

<1)

a:5 <:) o

~

100 80 60 40

20

10 0.1

0.2

0.3

0.4

0.5

0.6 0.7 0.80.9 1

Period (sec)

2

3

4

5

Fig.3.2.1.2 Acceleration response spectra of observed records at near-source area of inland earthquakes

M6.7).

The records are chosen to satisfy the

soil at all sites is higher than 450m/s anywhere, except at the Great Bridge of East Kobe.

following requirements. CDThe soil condition at the station of seismometer

The

acceleration response spectra of the

meets the condition of the aforementioned

selected records are illustrated in Fig.3.2.1.2. It

bedrock.

can be found that the response accelerations vary

®The maximum acceleration is greater than

from 200(gal) to 3000(gal) in the range of short period and from tens of gals to lOOO(gal) in the

lOOgal. @The Closest Distance to Fault is less than 30km.

range of long period. As the soil conditions at the

The list shows that the records of Hyogoken-

observation stations have been carefully chosen,

Nanbu Earthquake are all within the ground.

this wide variation may be attributed to the

Theoretically, deconvolution shall be carried out

following.

to separate the incident wave from the record. The

CDDifferencein the mechanism of seismic sources

original records are used here instead, because it

®Difference in the propagation of seismic waves

is difficult to get a result that is reasonably closer

@Influence of irregular topography

to incident wave than original record, as there are a

number

of

unsolved

problems

in

the

The influence of irregular topography can be avoided only by selecting records according to the

deconvolution analysis for strong ground motion.

geological condition if available.

Besides, the influence of the surface soil would

careful investigation, it is found that the records at

not be too strong since the shear wave speed of

Tarzana, Northridge earthquake (1994, M6.7),

@Seismicisolation @Seismicisolation 3-6

Through a

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

New Kobe substation and Takaratuka, Hyogoken-

On the other hand, Ohno et al.7 ) proposed

Nanbu earthquake (1995,M7.2), are influenced

another type of attenuation relation based on

strongly by special topography4),S), so that these

Equivalent

records are excluded from the statistical analyses.

determined by the energy radiated from the finite

As to the influence of the propagation of

Hypocentral

Distance,

this

is

fault plane.

seismic waves, the profiles in deep ground in the range of several kilometers as well as the Q factor (quality factor)

are considered to be

logS(T) = a(T)Mw -logXeq - b(T)Xeq + c(T) + &(T)

very

(3.2.1.2) 2 N 2 2 IN"d x-eq2 = "d i..J x:.t...

important, but they are out of the scope of this study.

I

However, a number of attenuation

1

j=l

(3.2.1.3)

I

j=l

functions of ground motion have been proposed,

x;

in which influences on propagation are all

where

denotes the Equivalent Hypocentral

considered in an average sense.

By using the

Distance; N, Xi, and d, are the number of small

recorded earthquake motions to a same distance

site and the center of the area i, and the seismic

from the seismic source so that the variation of

moment on the area i, respectively.

to propagation can be

The Closest Distance to Fault and Equivalent

minimized. The rest variation of ground motion

Hypocentral Distance given in Table 1 for every

in statistics is attributed to the properties of the

site of record are calculated according to the fault

seismic source or other unclear reasons.

models published by USGS for earthquakes in

ground motion due

2) Compensation by attenuation function Among the attenuation functions proposed, the measurement of the distance between the site and the seismic source is very important to decide the near-source strong ground .motion, where the extent of fault plane must be considered properly. To satisfy the above requirement, the Closest Distance to Fault (CDF) has been widely used recently. The following is an attenuation function of response spectra of ground motion based on

USA

and by Irekura for Hyogoken-Nanbu

Earthquake, respectively. There is an important phenomenon for the ground motion in near-source area, in that it tends to saturate as the site is getting close to fault presumably for the following reasons.

Firstly,

most of active fault planes are nearly vertical to the ground surface. Secondly, the thickness of the crust of the earth is from 15 to 20km. In consequence, the size of the fault in the horizontal direction will increase as the scale of the

CDF which is proposed by Fukushima6 ).

earthquake gets larger, so that the affected area logS(T)

= aj (T)M~ -

becomes larger too.

az(T)M w + b(T)· R

-log(R +O.025xlOo.4zMw) + [,cj(T)l j

(3.2.1.1)

However, the intensity of

ground motion at the near-source area will not increase because the energy does not concentrate but widely spreads on the whole plane of the fault.

in which M w , R and T are the moment magnitude, the Closest Distance to Fault and the period, respectively; al, az and b are coefficients of regression; Cj is the coefficients related to site properties.

Since we need to infer the ground motion right above the fault, we can omit the influence of the magnitude while taking into account only the distance

between

the

site

and

the

fault,

compensating for the observed records by the aforementioned attenuation relation.

@Seismicisolation 3-7 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

After all fault models are examined,

January, 2000

the

Equivalent Hypocentral Distance of destination is taken as 12lan in this study. With the attenuation relation using the value of Equivalent Hypocentral Distance, all the acceleration response spectra of observed records are then compensated, the results are shown in Fig.3.2.1.3.

1000

800 600

t:<_.....

"lO

---=~~

.]: 200

~

=~:::::;:

3100

~

_=1

·"-_"";'''''';;;Mm",-H-.p..:;c~H~~~~~-H

~

_1oI._a.-Jo

=:-='~':If]l

80

_··_$o.:r._.... _1o.r.... ,..1

-.~.~"')j

40

_ ••__ e-UCl:ca ..

__ -to_C_UOC"I

Because, overall, the compensation from the attenuation function gives a ground motion closer

__

~l_.c.u;w

=:=~::-c..&)Q H-+-t-++++----1----+":-H

2D

_1.'.t_NS __ ,.. .....w

10

_","l,I.~

0.1

.4

0.5

o.e 0.70.80.91 Period (sec) 2

4

5

to the fault than original records, all spectra become larger. The upper limit is about 2000gal, except those of SGK EW97 Gravilan Coll.EW records.

Fig.3.2.1.3 with

and Gilroy#l

np.v1:ltlcm crrrrrmri monon frorn thp. -_..--.. -- of --- 0------- ----- staristir-al

4000

mean value becomes smaller for all periods.

2DOO

When compared with those in the short period,

1000

~---~---

.'

BOO

the improvement in the long period is slight, to

the

attenuation

relation

of

Equivalent Hypocentral Distance

As expected, the

~-

Observed spectra compensated

~'~r~"" ...... ....

1

i---.~ _.~ '" f· "'-

.

BOO

"

I

.

,,,·..•......·i·.

...~'.,

imply the existence of dominating effects from

~

...--... mean(Kobe)

v-,

-_.. 90%

---= -

ground.

llnsurpass (US)

-mean 90% Unsur

40

I

", ·1·:··..··. ~..I ",

unsurpass (Kobe) ......... mean(US)

the seismic source and the structure in deep

~"

,.~~

" ~ >-\

-,

I

ss

Fig.3.2.1.4 compares the statistical results based 2D

on the seismic records of USA and Kobe. They 10

0.2

0.1

satisfactorily agree with each other for the period

0.3

0.4

0.5 0.6 0.7 OBO.g 1 Pedodfsec) 2

4

5

up to 1.0 second. For the period longer than 1.0

Fig.3.2.1.4 Comparison of the statistical results

second, the records at Kobe give larger response

based on the seismic records in USA

spectra This difference would be a major cause

and Kobe, respectively

of larger deviation of total statistical results in the long period range.

Meanwhile, it can also be

found that the statistical results become smoother as the number of records increases.

4000

2000

~

V' 1000 800 600

The attenuation function based on CDF is also

400

used, where the distance of destination is taken as

200

2lan. The point of 2km from fault is the place

100

---

I

1'--.. i J--.....

rt- I

~

I

<,

'" 1"'- "\

1'----.

r-.

80

right above it, because little portion of energy will

1

60

40

be radiated from the range within 2km from the 20

ground surface, even though the fault reaches and 10

appears on the ground surface. There is not much difference between the mean of response spectra

0.2

0.1

Fig.3.2.1.5

0.3

0.4

0.5 0.6 0.70.80.91

Comparison

of

4

the

5

statistical

and that based on the Equivalent Hypocentral

results using Closest Distance to Fault

Distance, but the values of 90% unsurpassed

and equivalent hypocentral distance

probability show a little difference (Fig.3.2.1.5).

attenuation relations

This illustrates that the statistical result of ground

@Seismicisolation @Seismicisolation 3-8

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

motion right above the fault is almost independent

2"'0

of attenuation relation of the Closest Distance to

,,'"

Fault or the Equivalent Hypocentral Distance.

3) Spectrum for earthquake motion straightly above the inland fault In view of the limited number of records

~

y

I

900 800 700

~

I

sao

-,

$500

.,g"

I

400

~

'E

:<

300

I Damping ratio h=5%

adopted at present as well as unknown properties of earthquakes in the future, it is wise and

-, I

II

'00 0.1

0,2

0.3

0.4

5

0.5 0.6 0.70.80.9 1 Penod (sec) 2

reasonable to determine the design seismic motion according to a certain unsurpassed value, rather

Fig.3.2.1.6 Response spectra of acceleration for design earthquake motion straightly

than by taking the envelope of the maximum

above an inland fault (Spectrum II)

values. To what degree the unsurpassed probability should be taken is very important but difficult to determine.

It usually depends on a subjective

judgment. For railway structures, the following

acceleration for the design earthquake motion (Fig.3.2.1.6) called Spectrum II.

Its values

corresponding to the ranges of period are shown

considerations are necessary.

CD Railways

log plot to define the response spectra of

are means of mass transportation

directly related to the safety of passengers. @ A failure at one point of a railway system will

affect the whole route, and it is very costly and impossible to have a bypass for the same railway. @The seismic records used are limited possibly with unknown factors. In the light of above considerations, a high

unsurpassed probability is strongly expected, but the value 90% is believed to be acceptable and adequate when the accuracy of the whole process of seismic design is taken into account.

below. CDllOOgal at O.ls in period ®1700gal between 0.2s and 0.7s in period @154galat 5.0s in period. This spectrum express the motion just above a fault straightly.

Therefore, it's values can be

reduced by the attenuation relationship according to the distance between the seismic fault and the site.

Here Formula (3.2.1.2) based on the

Equivalent Hypocentral Distance is recommended.

(3)Earthquake Motions due to Near-Land Interplate Earthquakes In the codes of seismic design used before the

It is not difficult to get the value of a certain

Hyogoken-Nanbu earthquake, the seismic motion

unsurpassed probability if we assume that the

of interplate earthquake was provided. The values

response spectra at the given period is normally

of the response spectra of acceleration for the

distributed. The 90% unsurpassed value is given

design were about 1000gal on a standard ground

in thick dot line in Fig.3 .2.1.3.

Due to the

surface. In order to treat the earthquakes due to

influence of the records at SGK (Hyogoken-

inland faults and interplates on a same basis, the

Nanbu earthquake) and Gilroy Gavilan Coll.

same

(Lama Prieta earthquake), the apparent value near

compensation carried out so far are applied to the

0.3s in period is over 2000gal, which may be

seismic records of interplate earthquakes. A brief

attributed to some local effects of two sites.

outline about the determination of Spectrum. I is

Therefore, we use three straight lines on the log-

summarized bellow.

methods

for

@Seismicisolation 3-9 @Seismicisolation

statistical

analysis

and

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Table 3.2.1.2 Seismic records from recent interplate earthquakes in Japan <;

"o

~

Earthquake

No

Recorded site

Latitude

Longitude

<;

2

.b~

c~

"o 0

0,

c-,

::r: 40.55 . 141.483

Tokacbi-Oki (May 16,1968)

1

Hacbinohe

Off NemnroPen. (June 17,1973)

2

Otanoshike Brg.

43.0083

Off Miyagi Pref. (June 12,1978) W off N Tohoku (May 26,1983)

Kusiro-Oki (Jan. 15, 1993)

Hokkaido Nansei-Oki (July 12,1993) Hokkaido Tohoku-Oki (Oct 4,1994)

144.271

= g 2

.8

"

~~ ::c~

'"

'"

<.l~

§ ."§

o c '" .£c U;

2 0

.~

'0

Cl

.-

C' ~

Direction of records

:~

~0

;>-0

.::;

" § a

<5

~

,,~

;.0,,-...

....

= '"

.b

0

U

P-.

179.4

130

88.6

GL

NS,EW

136.9

163.7

109.7

GL

LG

3

Kaihoku Brg.

38.445

141.313

81.6

70.2

56.5

GL

LG,TR

4

Ofunato- Bochi

39.00

141.733

101.7

86.8

71.6

GL

N41W,E41N

5

Kamitorizawi Brg.

42.1014

140.563

231

190.8

144.5

GL

LG,TR

6

Urakawa

42.158

142.781

151.6

174.4

149.1

GL

NS,EW

7

Hanasaki Port

43.2800

145.589

109.4

156.4

131.3

GL

N20E,E20S

8

Tokachi Port

42.2889

143.324

106.5

141.7

121.8

GL

NS,EW

9

HirooBrg.

142.2792

143.319

107.5

142.4

122.4

GL

LG,TR

10

Otanosbike Brg.

143.0083

144.271

19.8

105.2

100.1

GL

LG,TR

11

Chiyocla Brg.

42.9197

143.389

81.5

123.3

108.2

GL

LG,TR

12

Muroran Port

42.3167

140.967

153.3

149.0

129.3

GL

NS,EW

13

Kamitorizawi Brg.

42.1014

140.563

124.6

120.1

91.4

GL

LG,TR

14

Hanasaki Port

43.2800

145.589

168.4

123

58.5

GL

N20E,E20S

1) Seismic records of interplate earthquakes The recent interplate earthquakes occurred near Japan are shown in Fig.3.2.1.7, from which over a hundred records with the maximum acceleration larger than 100gal have been collected.

The

distances between the site of seismometer and the source

are

mostly

from

100

to

200km 0.1

(Fig.3.2.1.8). From these data, 27 records have been chosen,

Fig.3.2.1.7 Interplate earthquakes occurred in Japan recently

according to the following requirements, their detail information is given in Table 3.2.1.2.

16

(DBoth Equivalent Hypocentral Distance and

14

Closest

Faults

Distance

are within

~ Hypocentrai

200

distance

SiI EquivalentHypocentral distance

r---

r-----

o Closest distance to fault

12

kilometers. ®The soil condition of the observation station is good. @There is no unnatural peak existing in the Fourier spectra of the records.

I~

II

n 11m

~

~

,~

~

.~~ II~~ n~111

~ ~

Distance (km)

The acceleration response spectra of those records are shown in Fig.3.2.1.9.

I

Fig.3.2.1.8 Distribution of distance between seismometer and seismic source

@Seismicisolation 3-10 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

2) Spectrum

compensated

for

interplate

shown in Fig.3.2.1.10, which possesses the following values.

earthquakes The attenuation relations

used for inland

earthquakes are also used here.

As we have to

take the scale of earthquake into consideration

(1) 1100gal between O.ls and LOs in period

(2) 154gal at 5.0s in period For comparison, Spectrum IT is also plotted in In order to make the design

because the earthquake motion to be inferred is at

Fig.3.2.1.10.

the site a little far from the seismic source, the

simplified, the values of Spectra I are defined as

motion becomes very sensitive to the scale of

the same as the Spectrum IT for the period longer

earthquake.

than 1.0 second.

After investigating the effect of scale of

When compared with the

original records in, Fig.3 .2.1.9, the design spectra

attenuation

are larger in the period longer than 0.2 seconds.

functions .based on the Equivalent Hypocentral

In general, the vibration of high frequency

Distance as well as the Closest Distance to Fault

decreases much quicker due to the damping in

respectively, the final compensated result is

structure and soil as ,:veil as the displacement

obtained. Through analysis of the characteristics

associated with it is small too.

of this compensated spectrum, the Spectrum I is

design,

defined by two straight lines in log-log plot as

underestimate the actual ground motion for the

earthquake

with

the

different

spectra

defined

Therefore, the

here

does

not

seismic design. Besides, the level of Spectrum I, even when -S-ZS2NS

~ktro~~~~~ =~~EW _It!o~n~s

multiplied by the smallest risk factor, can cover

_IXH_W

_OO-l_W

~,,=----"~"-+--+--1 =~~~~

=;:~

+--f'-,:-"'f-.j

_P_61Il:tS

_00'-

_ 0 0....

~l&"+'rl--i =~:~;:=~: -oo-6U> _oo-ou

_OO_IIHA -OO-11lUl -OQ-11HA. _OO_11Wl

the ground motion due to an earthquake with the magnitude less than 6.5 which may occur inland without making its fault reach the ground surface. This can be easily verified through the attenuation

_CXi_lJlU..

-oo-1.ltlB

-!'-ss.,..s

_1"_llol'lW _~'l"':lltS

function given above, where the depth of a fault

-J,(-I4f38W

center is assumed as 10km from the ground aa

(1.<1

surface".

Period (sec) 2

1).5 G.6 U-1l>.8'O.9 1

Fig.3.2.1.9 Acceleration response spectra of observed

records

of

interplate

3.2.2

on the Ground Surface

earthquake near Japan

While calculating responses of a structure to

'000

l~

I

.... ... ... -

.......... "1"" .....

.400 300

I·......

I,

100

90

eo

60

I

<,

r-,

I

200

10

"'

Spectrum I Spectrum If

1i .::

surface

I

I

I , i I I' I

I

between

structure

can

be

where

then

the

inputting

foundation the

is

previously

mentioned design earthquake motion into the

r-,

bedrock, and using a dynamic analysis method to perform a nonlinear analysis which can take the

I

4

0.1

Comparison

the

I

"

Fig.3.2.1.10

ground

embedded,

I

,

I

I

I

motions,

modeled as an overall system including the

I

~: ]

earthquake

··j··l

,

3500

.9

Setting of Design Earthquake Motions

of

the interplate

the

,

spectra

and inland

effect

of

soil-foundation-superstructure

interaction into account. .This kind of procedure, however, at this time is considered overly

@Seismicisolation 3-11 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

3000

2000 r--,

ca

tlJ)

"-"

Q)

1000 900 800 700

()

600

('j

..... (l)

o


500

;::: 0 0.. UJ (l)

""'-

,

2"3

~q5 .

~v-;>~ - -------- -.- -.- "K ........j-.......... -....... I~ I"" _._.u.. ...... 'G6 ~l~~-----r-, .. .. , , .» -, " ---', r-, <, --" .-' .' .' . . --, ,"", , , -~ ...... <, .-, !'-.-'-'>- , . . - .. .' -, <, '

.'

~

-,

.- .. .... ..

400

--.

.- -

.., ....

--. . . -

.'

,

(l) UJ

G2

,

..~z~:.~.~

;:::

.9 .....,

I

l.--/

-, <,

.G7

~" '

"

,, '

., ,

"GO"" J" Gl".~'~ ~ -,

--.

,

",

"

-, .

""~ ~

200

0.2

,,

,

~~"'"'-."-"

,~

~ ~I ~

0.1

,

....' \."........

300

~

,

0.4

0.3

0.5

0.6

2

0.7 0.8 0.9 1

c:;

4

5

Period (sec) Fig.3.2.2.1 Design response spectra of acceleration on ground surface for Spectrum II (damping coefficient of 5%)

complicated and impractical for general use. As a general rule, in order to simplify the design procedure, the foundation of a structure will be replaced

by

supporting

springs

and

the

Table 3.2.2.1 Soil Profile Types Soil Profile Type

Period (sec)

Soil Profile Name/Generic Description

superstructure modeled as a multiple mass

GO

-

Hard Rock

system. In this case, the earthquake motions on

Gl

-

Bedrock

the ground surface are needed, which can be

G2

-0.25

Diluvium

But, in reality, there are difficulties in this

G3

0.25-0.5

Dense Soil

dynamic analysis of surface ground such as

G4

0.5-0.75

Dense to Soft Soil

setting of relationships between the strain and

G5

0.75-1.0

Soft Soil

G6

1.0-1.5

Very Soft.Soil

G7

1.5-

Extremely Soft Soil

calculated from dynamic analysis of the ground.

shear modulus of ground, damping coefficient of soil and so on. To overcome such difficulties, design earthquake motions on ground surface corresponding to various types of soil profile were investigate in an amount of parametric

to G7. Moreover, the soil profile types indicated

studies. As the results, the acceleration response

in the figure are categorized based on the natural

spectra on ground surface due to Spectrum I and

periods of ground that are calculated with the

Spectrum II are determined. Fig.3.2.2.1 gives the

velocities of elastic shear wave in surface ground.

design response

spectra of acceleration on

The relations between the soil profile types and

ground surface for Spectrum II, which are

the natural periods of ground are summarized in

corresponding to the soil profile types from GO

Table 3.2.2.1.

@Seismicisolation 3-12 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

In summary, there are 8 types of soil profile

used in this code. profile,

the

@Seismic Performance II (SPIT): capability of

With respect to each soil

design

response

spectra

making

of

quick

recovery

of

the

original

functions with repairs after an earthquake

acceleration on ground surface are determined

@Seismic Performance ill (SPill): capability of

corresponding to the L1 earthquake motion,

keeping the overall structure in place without

Spectrum I and Spectrum II of L2 earthquake

collapse during an earthquake

motion.

These performance levels are mainly defined by the ease degree of recovery of the structures

3.3

after an earthquake. Therefore, the relationship

Seismic Performance of Structures

3.3.1

between the levels of earthquake motions and

Setting of Seismic Performance Levels for Structures

seismic performances has been established as follows.

Corresponding to the presumed levels of repair

For L1 earthquakes, the structural seismic

and reinforcement of structures that may be required after an intense earthquake, the seismic

structures designed.

performance can be categorized into 3 levels as

For L2 earthquakes, SPII should be satisfied by

follows.

the structures with greater importance, and SP ill

CDSeismic Performance I (SPI): capability of

by other structures.

maintaining the original functions without any repair

and

no

excessive

Furthermore, the seismic performance levels

displacement

are also connected with the state of damage of

occurring during an earthquake

Seismic Performance I (SPI) Capability of maintaining the original functions without any repair and no excessive displacement occurring during an earthquake Seismic Performance II (SPII) Capability of making quick recovery of the original functions with repairs after an earthquake Seismic Performance III (SPill) Capability of keeping the overall structure in place without collapse during an earthquake

Fig.3.3.1.1

member as well as the stability of foundation

Damage Level 1: no damage Damage Level 2: damage that may require repair depending on situation Damage Level 3: damage requiring repair Damage Level 4: damage requiring repair, and replacement of members depending on situation

Stability Levell: no damage (loading smaller than bearing capacity) Stability Level 2: damage requiring repair depending on situation Stability Level 3: damage requmng repair, and correction of structure depending on situation

Relationship among seismic performance levels, damage levels of member and

stability levels of foundation (bridges and viaducts)

@Seismicisolation @Seismicisolation 3-13"

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Maintaining yield load

Reinforcing bar yielding in axial direction

Cracks occurring

Skelton curve for analysis

Envelop curve of test results

Deformation

Fig.3.3.2:1

Relationship of lateral load-deformation relationship for reinforced concrete

member, with a generai ievei of compressive axiai force

which are constituted in the overall structure.

relation among the property of the member, state

Since the damage level of member and the

of damage, and repairing methods. Moreover the

stability level of foundation will influence the

relationship between the damage levels and the

structural seismic performance level much, how

displacements on the load-displacement curve

to determine them properly is important. ill this

should also be taken into account.

code, the damage level for each member which

example, the following shows how to set the

composes

damage levels for a member of reinforced

a

structure

is

set

properly

by

considering the role played by the member for the overall structure. ill regard to the stability of

As an

concrete. ill case the bending failure mode occurs firstly

on

under the condition that the exerting compressive

should be

axial force is of a general level, the load-

determined by considering the bearing capacity

deformation relation of the member is shown in

or the deformation of the foundation involved.

Fig.3.3.2.1. It is considered that some physical

foundation,

as

it

has

a

big

displacement of a structure, it

impact

shows the relationships among

phenomena reflecting the stress-strain condition

seismic performance levels required for bridges

of the member, as shown in this figure, occur at

and viaducts, the damage levels of member, and

the changing points of the envelop curve.

the stability levels of foundation.

Taking

Fig.3.3.1.1

this

member's

characteristics

into

consideration, each damage level of the member

3.3.2

Consideration on the Damage Levels of

is determined corresponding to the deformation

Member, the Stability levels of Foundation as Well as Their Limit Values

range as the following. CDDamage Levell: before the point of B ®Damage Level 2: from B to C @DamageLevel3:fromC to D

(1)Damage Levels of Member

@Damage Level 4: after D

It is considered appropriate to determine a

Once the relationship between the damage

damage level to a member by considering the

level and the deformation is established, the

@Seismicisolation @Seismicisolation 3-14

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Table 3.3.2.1 Relationship between the damage levels of member and rotational angles

------------

Limit Value of Rotational Angle

Damage Level 1

eyd

Damage Level 2

emd :

Rotational angle of member corresponding to the maximum deformation resulting from the peak lateral loading

Damage Level 3

end

Rotational angle of member corresponding to the maximum deformation being able to resist the yield lateral load

Damage Level 4

eud: Rotational

Yielding rotational angle of member

:

angle of member for limiting the excessive deformation in axial direction

p Level 1 p p

m ...........•................._._..•......_

y

_

Level 3

Level 2

B

P y: Yield bearing capacity . Pm: Maximum bearing capacity COy: Yield displacement

:.:; _ - - - - - - - .

A.

Om: Displacement corresponding to maximum load u : Ultimate displacement

o

Oy

Om

Ou

Fig.3.3.2.2 Imagine of load-displacement curve as well as stability levels offoundation

In order to ensure the

value of deformation becomes a suitable index

properly is important.

for checking the damage level, which may be

seismic performance for an overall structure, the

directly calculated from a response analysis. If

stability

the member's nonlinear behavior is evaluated

determined in term of two aspects.

with a mechanical model of bar, generally, the

damage levels with respect to the stability of the

rotational angle or the curvature for the section

foundation itself. The other is the damage level

of plastic hinge is taken as the index for the

to the members constituting the foundation. For

member checking.

the latter one, the procedure to determine the

The relationship between

levels

of

foundation

should

be

One is the

damage levels of member is same as what

them is shown in Table 3.3.2.1.

described previously.

(2)Stability Levels of Foundation

As to the procedure for

determination of damage levels to the foundation

Since the stability levels of foundation have a

stability, the following items should be taken into

great impact on the seismic performances of

account.

overall

CDThe effects on the usage property of structure

structure,

how

to

determine

them

@Seismicisolation @Seismicisolation 3-15

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

due to the displacement of foundation

January, 2000

the foundation should be less than its yield

®The variation of bearing capacity of the

bearing

capacity

and

no

excessive

foundation after an earthquake

displacement occurs.

As indexes for evaluating these items, response

members composing the foundation should not

ductility ratio as well as residual displacement of foundation should be used.

The former is

Stress

resultant of

exceed yield strength. @Stability Level 2: Either subgrade supporting

defined as the ratio of the foundation's seismic

the

response displacement to yield displacement that

foundation or both are deformed plastically, but

is determined by the load-displacement curve of

yet maintain sufficient bearing capacity.

the foundation.

Fig.3.3 .2.2 gives a general

displacement detrimental to maintenance of the

illustration of the load-displacement curve as

structure's functions nor residual displacement

well as the stability levels of the foundation.

should be allowable after an earthquake.

Using the indexes of displacement in this figure, the

stability levels

of foundation

can

be

foundation,

members

composing

the No

@Stability Level 3 : Sufficient bearing capacity should be maintained to protect the structure

determined as follows.

from collapse by damage of the bearing

G)Stability Levell: In principle, load acting on

subgrade or members.

8 j : Damage parts Fig.3.3.2.3 Illustration of damaged parts of a rigid frame viaduct Table 3.3.2.2

An example of the relationship among the limit values of structure's seismic

performance levels, member's damage levels and foundation's stability levels (rigid frame viaduct)

SPI

SPIT

SPill

Superstructure Girder and Underground Beam

1

2

3

Other Beam

1

3

4

Column

1

3

3

Stability Level of Foundation

1

2

3

Structure

Damage Level of Member

@Seismicisolation @Seismicisolation 3-16

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Besides the values of stability level are set corresponding to the types of foundation.

Therefore, how to evaluate the nonlinear effects of ground and structure becomes an essential task in seismic design.

(3) Limit Values Based on the consideration explained above,

3.5.1

Evaluation of Surface Ground

the parts where the damage may occur to a rigid frame viaduct are illustrated in Fig.3.3.2.3, and an example of the relationship among the limit values of structure's seismic performance levels, member's

damage

levels

and

foundation's

Characteristics of the surface ground must be carefully analyzed because of its big impact on the seismic performance of the structure to be built.

Generally there are 3 kinds of problems

that may be encountered and difficult to handle

stability levels is shown in Table 3.3.2.2.

in design practice: irregularity in topography or 3.4

Concept

Importance

of

Degree

of

geology, liquefaction, and soft or very soft soil profile.

Structure

In this section, the consideration and

analysis approaches adopted in the code to deal Determination of the importance degree of a railway structure requires consideration various

with these special kinds of surface ground are described.

factors, for example, the possible influences on human life, society, neighborhood, operating

(1) Irregular Surface Ground

speeds and timetable of trains, and the difficulty

From the past damage reconnaissance after

degree of recovery in case of damage. Based on

earthquakes, it is often observed that severe

this concept, greater importance has been given

damage happened on a ground with irregularity in

to the following structures.

topography or geology.

(DStructures of the Shinkansen bullet lines and

phenomenon is obvious that the superposition of

those of passenger railway lines in major

reflection waves resulting from the irregularities

metropolitan cities

of surface ground make the response amplified.

The cause for this

@Structures whose recovery after an earthquake

At this time even though there are some analysis

is considered very difficult, for example a cut

methods with rigorous numerical models may

and cover tunnel, etc.

evaluate such irregularity effects precisely, the necessary of large amount of precise input

3.5

Evaluation

of Surface Ground

and

Calculation of Displacement and Stress of Structure

I Groundmodel for 2D analysis I Inclination

e

According to what shown in Fig.3.1.1.1, the procedure for seismic design of a viaduct is, inputting the L2 earthquake motions on the bedrock firstly, evaluation of surface ground, calculation of response of the structure and evaluation of its seismic performance.

In this

'I """'_"""-,. II

case, since the L2 earthquake motions are so intense, both the ground and the structure are expected to

behavior strongly

nonlinearly.

Fig.3.5.1.1 Ground models used for 10 and 20 analyses

@Seismicisolation 3-17 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

parameters makes such analysis impractical for

The incident wave is input at the bottom of the

general use. Therefore, a simplified method that

hard layer and the response analysis method used

can estimate the amplification of earthquake

in the investigation is FEM.

The time-history

motion caused by irregularity and satisfy the accuracy for seismic design is needed. 1) Ground models Since ground motion amplification is affected by various factors, such as the scale of irregular

,

,

l,x=<sU(

I"(}In

H

•••••••

,

6Qlin

is

considered

in

this

investigation. As what illustrated in Fig.3.5.1.1, there are. two types of models prepared for analysis, one is the two-dimensional (2D), and the other is the one-dimensional (1D).

.:

modeled by the 3 key parameters: the inclination angle ((J) of hard layer (bedrock), the thickness (If) of soft layer, and the impedance ratio (IC ) of

the two layers.

,'., ... ,

.:

.-:

..:

TT

,.,

,

'·"1"'"

,

,

... '. .'

,' .. <

.:

... ' ...

:

,.. , ... .:... ,

IT

... ,

'

'.

<.

"~ .

....

"

"

. '.,'

"

,.

",". 160:in

"

~bv

••••••••

.'.

,

20

For 2D

analyses, the property of surface ground is

-:

'.' ...'.

...

For this reason, a ground model with rather irregularity

...'"'

.. '.

AUlm

simple

.,,'.. '. ,,"

,

it is almost impossible to take all the factors into

<

,

" ,

shape and the characteristics of input motion, etc. account in the response analysis of surface ground.

,.

.,"

I~~I~ iT> ,-

Time(s)

Fig.3.5.1.2

Responses

acceleration

obtained

of from

H~m)

horizontal 20-FEM

analysis (normalized by peak value of input wave)

In ID analyses, all conditions

such as the properties of soil profile and the thickness of soft and hard layers are set equal to those of the corresponding 2D models as shown in the Fig.3.5.1.1. 2) Effects of geological irregularity In order to elucidate the mechanism of amplification of earthquake motion due to the geological

irregularity,

some

numerical

investigations have been conducted as follows. Firstly, the responses of 2D and 1D modeled grounds were calculated, respectively. Then the differences of the response between the 2D and

ID models were extracted by subtracting the results of 1D from those of2D. These differences represent the effects of geological irregularity, because the responses

due to the laterally

10

15

20

H=20(m)

Time(s)

Fig.3.5.1.3

Responses

acceleration

of

horizontal

obtained by subtracting

propagating waves that rebound on the inclined

values of 10 from 20 (normalized by

boundary of hard layer are included in the results

peak value of input wave)

of2D.

@Seismicisolation 3-18 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

response acceleration on the ground surface calculated by 2D FEM are shown in Fig.3.5.1.2, whose incident wave is a SH Ricker wavelet with a predominant period of O.8sec that is the same as the fundamental resonance period of the soft layer. Since the soft layer is

rather thick,

the

amplification property of the irregular ground is obvious with the normalized peak value of 2.4 in the vicinity of the edge of basin (x=40m).

3) Simplified methodology for evaluation of geological irregularity CDFormulae for estimating ground motion Based on the results of numerical investigation above, the influence of the irregularity upon the earthquake motion on the ground surface is possible to be modified with the following expressions.

The

G(CtJ, x) = F(CtJ)+ a .F(w)- e-imAt =F(CtJ). ~ +a .e-i~t}= F(w)·r;(w)

duration time of response becomes longer at places remote from the edge of basin,

These

characteristics are attributed to both the thickness

(3.5.1.1)

of soft layer and the irregularity in geology. Then,

f'(t) f(t)

a=-,-,

the responses purely caused by the irregularity can

be obtained by subtracting the results of ID from those of 2D (See Fig.3.5.1.3).

The response

waves shown in Fig.3.5.1.3 are caused by a

Where,

G(CtJ,x)

wave is nearly equal to that of Raleigh wave, the major component

included in

ground; a:

the amplitude ratio between the horizontally propagating wave l' (t) and the vertically

the laterally

propagating wave is presumed to be Raleigh wave.

propagating SH wave J(t);

From these results of the numerical investigations,

the Fourier spectra of SH wave

a phenomenon is revealed that the earthquake motions on the surface of the ground with

the Fourier spectra of earthquake motion on the surface of irregular

laterally propagating wave that is generated at the edge of the basin. Since the phase velocity of this

(3.5.1.2)

LJ.t

irregularity are synthesized from two parts, one is

J(t) ; the delay time between

J' (t)

and

J(t) ;

the SH wave propagating directly form the bedrock,

the

other

one

propagating horizontally.

is

Raleigh

wave

®Determination of a andLJ. t It is easy to be conjectured that the coefficient

a: and LJ. t in Formula (3.5.1.1) are dependent on

+

Fig.3.5.1.4 Definition of the parameters for irregular ground

@Seismicisolation @Seismicisolation 3-19

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

the properties of geometry and material of the

formulae.

irregular ground.

Fourier amplitudes calculated by 2D-FEM and the results of Gem, x) obtained by the empirical

Through

an amount

of

parametrical studies, the relationship among a and the geometrical parameters

e (the inclination

formula

Fig.3.5.1.5 gives the comparison of

(3.5.1.1).

As to the time-history

angle of hard layer), H (the thickness of soft

responses

layer), and the material parameter

(the

between the two methods are shown in Fig.3.5.1.6.

impedance ratio of soft and hard layers) is

The good agreement between them proves that the

empirically expressed as the following".

accuracy degree of the empirical formulae is

x

a = 0.3 exp( -

K

of

sufficient

7~OJxJr xexp(-O.44X)

to

acceleration,

the

level

the

comparisons

of seismic

design.

Accordingly, in practice it is adequate to apply the simplified methodology for general use.

(3.5.1.3)

Where, X

=xIH

represents the normalized

distance from the origin at the edge point as

1500 x=20(m)

shown in Fig.3.5.1A.

---2D FEM

.-

With the same procedures the empirical formula for delay time,.,d t is obtained as follows.

Proposed method

.-+.. ,.

-t-t-t-tf-l

:iJ.000 I-······..;-·~ ..

eeo ...

.2:

a o

r;.;.

500 1-'-"';-'.".

(3.5.1A)

Where,

as

illustrated

in

Fig.3.5.1.4,

the

o'---'--'--'--'-'---'---"-''-=-'....... 0.1 0.5 1 5 10

meanings of the main parameters are as the

Frequency(Hz)

following.

Vb

Fig.3.5.1.5 Comparison of Fourier amplitudes

shear velocity of the hard layer;

between the 2D-FEM and the empirical

shear velocity of the soft layer; travelling horizontally

velocity

of

propagating

method (x=20 m)

the wave

within the range where the hard

1500 , - - - - - . , - - - - - . , - - - - - - , - - - - - - - - , :;

CJ!...OJ) : phase velocity of the Raleigh wave; CDAdequacy of the simplified methodology In the code, the simplified methodology described above is proposed for evaluation of the ground irregularity in general use. According to this methodology, in a general case a 2D response analysis of irregular ground can be omitted and the irregularity effect is taken into account by modifying the response of ID analysis with the empirical formulae. Therefore, it is necessary to

·1500

--;;---J - - . .

1\

tx=O(m)----.:

.=9 ~. ~ 0

layer slants;

.

I !lA1

;..,/

..

.n ""

,

V..... ~

_

-i\l\rl~ '1/

V

:

~~~= method

---

fr~-l

rS}--+~__4~

'1500~'

.

10

Fig.3.5.1.6

. 20

Time(sec)

Comparison

of

time-history

responses between the 2D-FEM and the empirical method (x=O, 20, 40 m)

grasp the calculation accuracy of the empirical

@Seismicisolation @Seismicisolation 3-20

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Since the intense level of the earthquakes which

(2) Liquefied Surface Ground Liquefaction is a very serious problem to consider in seismic design.

During the past

earthquakes, there were an amount of damages to infrastructures

caused

by

subsequent lateral flow.

liquefaction

or

Therefore, for the

ground with liquefaction possibility, if any financially feasible measure is available, such as ground

improvement

that

can

prevent

liquefaction to happen, it should be implemented. If not, the overall

superstructure,

structure, including the

should

be

taken

care

of

comprehensive measures to prevent collapse or other

disastrous

response

the

damage

against

structure may

excessive

incur due to

occurred before the Hyogoken-Nanbu Earthquake was not so high, the relative density of the soil profile

incurred

liquefaction

was

low.

Accordingly the relationship between R and N c was obtained based on experimental results that correspond to the values of relative density below 60%.

Furthermore,

this

relationship

was

determined independent to the relative density of soil profiles. After the Hyogoken-Nanbu Earthquake, the intensity level of design earthquake as well as the density

level

of

the

soil

profile

needed 1-.~_1-.1 •• 1.1J.bll-'-

liquefaction judgement arc promoted

Therefore,

the

hitherto

applied

s-

relationship

liquefaction or lateral flow. In this code, the procedures for liquefaction

o~

~10 ~

judgment as well as decrease in coefficient of 2.S

subgrade reaction to consider the effect of liquefaction and subsequent lateral flow are determined.

2.0

.€.~ 1.5

~ + '1\ -, ~ r-, + 4ill

:r. --::::I:-l" -

design, the following expression is applied.

+

~\~

I

. +

!, •

I

0.0

• + ,.~

•

O.S

r-t-

I

10

1

Or<SQ'X; Dr=::70$

.Or-SO'!. • Or-9O$

\

1.0

1) Liquefaction judgement In liquefaction judgement for railway structure

• ...

~

I

--

100

1000

Nnber of cycle(Nc)

( 3.5.1.5)

Fig.3.5.1.7 Relationship between the ratio of liquefaction

Where, FL

factor of liquefaction resistance;

R

ratio of liquefaction strength;

(R)

and

the

number of cycles (Nc)

\[1\ ~

3.0

L maximum shear stress ratio; The ratio of liquefaction strength (R) is determined by correcting the standard values of liquefaction strength ratio that are obtained from cyclic triaxial tests or in-site tests. In this correction the concept of accumulated damage index is introduced to reflect the irregularity effect of earthquake motion. Therefore, the relationship between R (ratio of liquefaction strength) and N, (number of alternative cycles of earthquake motion) becomes required.

strength

2.5

~I\ DA=5~ 1\

I

DA-"""2Q%

2.0

t!.~ 1.5 '---......

~ DA=5~

1.0

I--

~ t - - t--t-

0.5

0.0 1

10

100

1000

NootIer of. eyels(Ne)

Fig.3.5.1.8 Relationship between the ratio of liquefaction strength and the number of cycles (DA=10% to15%)

@Seismicisolation 3-21 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

between R and N; corresponding to the low relative density is considered too conservative, in which it mistakenly leads to judgement that even soil at

a high relative

density

ground surface + - - ground

surface properties for- seismic design

free from

liquefaction will liquefy. On the other hand, the influence of liquefaction on the dynamic response of structure is taken into account by reducing the coefficient of subgrade reaction according to the situation ofliquefaction. Accordingly, the decrease in coefficient of

Structures are designed by seismic defomation method.

subgrade reaction should be formulated varying with the degree of liquefaction and the depth from ground surface. Fig.3.5.1.7 shows the relationship between R and N, corresponding to different relative density obtained from cyclic triaxial tests of dense sandy - - ground surface properties for seismic design

soil. This result reveals a fact that the sandy soil with relative density below 50% its relationship between R and N, can be considered independent to relative density, but if the density over the value of 50%

the relationship

should

be

_

range to reduce the coefficient of subgrade reaction

Ground surface properties for se iseric design set up the shallowest layer to reduce the coefficient of subgrade reaction.

determined by taking the effect of relative density 20
into account. So far, the double amplitude (DA) of axial strain used as index for liquefaction judgement is set to 5% as the critical value. This is proper to L1 design earthquake motion, but for L2 earthquake the critical value of DA is promoted to 10% or 15% by

considering

the structural

_ _ ground surface pruper-t.ies for seismic design

seismic

performance levels and the return period of

~ ~

range to reduce the coefficient of subgrade reaction

earthquake'?', In the strain range of 10 to 15%, dense soil will

Ground surface properties for seismic design set up the deepest layer to reduce the coefficient of subarsde reaction.

show cyclic mobility or positive dilantancy,

Fig.3.5.1.9 Range to reduce the coefficient of

recover the effective stress and present high

subgrade reaction and ground surface

stiffness against cyclic shear stresses. In this

properties for seismic design

situation,

the dynamic

shear strength

ratio

becomes larger as shown in Fig.3.5.1.8, which range for lowering the coefficients of subgrade

means that the soil will not liquefy.

and the parameters concerning ground properties

2) Reducing

the

coefficient

of

subgrade

is judged by using the liquefaction coefficient, an

reaction as the effect of liquefaction Basing on some researches, in this code the

index of the degree of liquefaction, for different values of liquefaction resistance given by the

@Seismicisolation @Seismicisolation 3-22

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

equation

.(3.5.1.6),

where

the

weighting

coefficient for the depth is set to reflect the effect

3) Liquefaction-induced lateral flow From mechanism elucidation of foundations

on structures.

damaged by liquefaction-induced lateral flow of

PL

20 = Jor (1 - FL )wdz

ground in past earthquakes, it is understood that (3.5.1.6)

force due to liquefaction layer and load due to

=1O-0.5z

W

loads existing at foundation are composed of drag ground displacement of non-liquefaction layer.

in which PL is the liquefaction potential; FL is

However, this kind of investigation needs precise

the factor of liquefaction resistance; and z is the

analysis models and sophisticated technology for

depth in meters.

numerical computation.

Fig.3.5.1.9 shows the range to reduce the coefficient of subgrade reaction and ground surface properties for seismic design by referring

It is impractical for

seismic design, especially, estimating the drag force is very difficult. Since the most important task in seismic design

to the calculation result of the liquefaction potential of a few ground models.

This

structure, the methods for evaluating the drag

formulation considers sudden changes of ground

force and the load due to ground displacement in

condition for liquefaction.

this

Moreover, this covers soft ground at the

code,

consideration

are

determined

that

the

based

calculated

on

the

response

liquefaction potential of less than 5, and structures

displacements of structure can fit well to those

are designed by the seismic deformation method.

obtained by experiments. The illustration of this

Because the ground strain considered by the

concept is shown in Fig.3.5.1.11, where the

seismic deformation method is 0.1 %, this is a case

effects of the lateral flow are expressed with the

of liquefaction potential of less than 5. Namely,

loads exerted to the upper and lower parts of the

this is a state where the strain has risen a little in

foundation, respectively. The upper part load is

excess pore water pressure in Fig.3.5.1.10. It is

transferred equivalently from the displacement of

the state of just before liquefaction.

the non-liquefaction layer through the spring constants of subgrade. The lower part load is due to the lateral flow of liquefaction layer. Displacements of structure calculated with this model are a little bit larger than those obtained in experiments. Therefore, this design methodology is considered in the safety side.

(3) Surface Ground with Soft Soil Profile The amplification property of surface ground with soft soil profile has been testified in many past earthquakes. o

-4

10

Fig.3.5.1.10

~2

-1

0

10 10 10 Shear strain (%)

1

10

Relationship between excess

pore water pressure and shear strain

This property will cause big

effects on structure design. For this reason, response analysis of surface ground under an intense earthquake should be conducted carefully and precisely. For dynamic analysis of surface ground, a shear

@Seismicisolation @Seismicisolation 3-23

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

stress-strain model used should be satisfied to the following conditions.

3.5.2

Calculation of Responses of Structures

Dynamic analysis should be the main method

The model,

for seismic design of bridges. In this case, how

(Dcan express the stress-strain relationship ('" "-'

r ) for various geo-materials ranging

from soft

clay to hard rock over a wide pre-failure strain range;

to setting the nonlinear behavior for structural members is very important.

In the code, the

member's non-linearity is prescribed according to what shown in Fig.3.3.2.1 and Fig.3.3.2.2. In

®has a minimum possible number of parameters to describe the model, each possessing clear physical meaning;

loops for determining damping constant are also required. In the code, they are given with respect

@can express the damping-strain relationship (h

"-' r ) over

addition to the skeleton curves, the hysteresis

a wide strain range obtained from

laboratory tests;

to the types

This

model fits dynamic deformation characteristics G/Gmax~

r , hr- r relationships over a wide strain range, and reflects failure limit stress r

»

Furthermore,

the adequacy of the model was examined by model ground test with shaking table.

(the

simplified

dynamic

calculate the ductility ratio of structure for a

In this code, a model of shear stress-strain

obtained from laboratory tests, such as

method

analysis method as shown in Fig.3.1.1.1) to

@can easily be applicable to seismic design. satisfy the conditions above is proposed.

foundations.

Moreover, it is very convenient to use nonlinear spectrum

@)can reflect the concept of failure strength;

of material and

general case. Fig.3.5.2.1 gives an example of the demandyield-seismic-coefficient spectrum that is applied in nonlinear spectrum method. The spectrum is applicable to a general structure, and the procedure for making out it is: i) modeling the structure to a single-degree-of-freedom system, ii) calculating the maximum nonlinear response displacement of the structure under the design earthquake motion; iii) plotting the relationship

("

!

....

,

j

load as lateral flow of non-Iiqufaction layer

model of analysis

non effective

ranp of lateral flow

I

non-Iiquifaction layer

Fig.3.5.1.11 Illustration of design methodology for lateral flow induced by liquefaction

@Seismicisolation @Seismicisolation 3-24

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

between the yield seismic coefficient and the

ground displacement caused by an earthquake

natural period corresponding to each ductility

will generate curvature of deep foundation and

ratio.

subsequently bending moment along its whole

For

such

structures

as

multiple-spanned

length, which makes stress resultant increase

bridges, structures with long natural periods, or

within the foundation's members. Therefore the

new types of bridges whose behavior cannot be

design method considering only initial force is at

expressed with the system of single degree of

unsafe side,

freedom, detailed dynamic analysis method using

earthquakes.

the model of multiple degrees of freedom should

especially in

case of intense

The seismic deformation method prescribed in

be chosen.

the

code is

a cost-effective one that can

With regard to foundation structures, dynamic

conveniently combine the both effects coming

response analysis should also be chosen as main

from the inertial force of superstructure and the

way for design. In case of surface ground with

displacement of ground according to relationship

soft soil profile,

between the natural periods of structure and

the ground displacement

ground.

resulting from an earthquake is generally beyond negligible levels, especially when the earthquake is intense the ground displacement may cause

3.6

severe damage to a deep foundation embedded.

of Structures

In this code, therefore, it is prescribed that the

effect

on deep

foundation

due to

Safety (Seismic Performance) Checking

In checking seismic performance of a structure,

ground

the prescribed procedure in the code specifies

displacement should be taken into account by

that responses calculated as in Section 3.5 should

using so-called seismic deformation method.

satisfy the limit values of the member's damage

Until now only this code has the stipulation,

levels and the foundation's stability levels, both

and in other codes deep foundations are designed

mentioned in Section 3.3.

The flowchart for

merely against seismic inertial force. However,

InputWave: L2 Earthquake Motion; Objective Structure: Surperstructures of RC or SRC

c

Q)

'(3

~o

o

o

:~ 0.5 -------------------_-----~--§--§~~~ ~

----------------------------------------pT~rOr

(j)

---------------------------:---------------,----------,--------,------r-----'- -, Nonlinear Behavior: Clough model

>=

~ ~

i

.

'

Stif ness:

I-----------------------~-------------.L-------j--------L-----:-----f--..L ~::s:x~::::~;~~~:~~::~~g 0.1 . I Type of Soil Profile: G3 i i ' Initial Damping Coefficienth=0.04/T, (0.10~h~0.20) j

0.1 1 0.1

i

0.5

1

5

Equivalent Natural Period (sec)

Fig.3.5.2.1

An example of Demand-Yield-Seismic-Coefficient Spectrum (Earthquake Motion:

Spectrum II, Surface Ground: G3 Type)

@Seismicisolation @Seismicisolation 3-25

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Setting design earthquake motion and soil profile

•

Modeling structure foranalysis

i.-

Static nonlinear analysis (Pushoveranalysis): Lateral load-displacement relationship

~

"""""

Setting nonlinear property for members and subgrade

~ Grasping seismic performance of structure (khy : yield seismic coefficient; Teq: equivalent natural period; deformation property)

~ Calculating response of structure; Ductility ratio

I~

Demand-yield-seismic-coeff cient spectrum or Detailed dynamic analysis method

~ Checking seismic performance of structure (Members: damage level; Foundation: stability level)

Fig.3.6.1.1

Procedure of seismic performance checking for bridges and viaducts

curve.

such a procedure is shown in Fig.3.6.1.1. Static nonlinear analysis method (pushover

Such critical steps include the steps

where the structural capacities reach to the limit

Analysis method), in the code, is stipulated to

values of yield, maximum and ultimate.

apply in the checking process. The procedure of

ultimate displacement can be determined by

pushover

comparing the calculated displacement with the

analysis

is,

i)

modeling

overall

The

structure (from superstructure to foundation) to a

limit values listed in Table 3.3 .2.1.

frame structure, and sub grade supporting the

superstructure

foundation to a system composed of springs; ii)

member's capacity of whichever reaches to the

setting the strengths and deformation behaviors

limit value of ultimate state, the displacement is

for the structural members and the subgrade

determined as the ultimate displacement for the

reaction according to what described previously;

overall structure.

iii) calculating the displacement of structure by

Therefore,

and

if the

foundation,

For the

when

value of the

the

ultimate

increasing seismic load step by step and plotting

displacement determined as above is larger than

the relationship between the seismic load and the

response displacement calculated by a dynamic

displacement. In this way, the failure process of

analysis method, it means that the structural

the overall structure can be grasped by indicating

seismic

the various critical steps in the load-displacement

objective of seismic performance level, and a

performance

@Seismicisolation @Seismicisolation 3-26

designed

satisfy

the

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

safety judgement is obtained. Furthermore, the

the allowable values of residual displacement

judgement of each member's damage level and

should be limited within a small range.

foundation's stability level should be conducted

All the items above are checked according to

by checking the deformation state of the step in

the results obtained by the static nonlinear

the pushover analysis, whose displacement is as

analysis.

same as that calculated by the dynamic analysis method. The main contents about this checking

3.6.3

An Example of Safety Checking of Pile

are described as follows. 3.6.1

Foundation

Checking Damage Levels of Members

In checking the damage levels of members

made of concrete, failure mode should be judged

(1) Seismic

Performance

Levels

of

Pile

of

pile

Foundation The

seismic

performance

levels

at first, namely, if shear stress calculated is

foundation are determined by the stability levels

smaller than

or pue foundation,

shear strength

when bending

The stability levels of pile

strength is reached, the failure mode is defined as

foundation are determined by considering the

bending failure mode, inversely shearing failure

strength and deformation properties of subsoil and

mode. In the code, it is stipulated that the real

pile members. Table 3.6.3.1 shows the definition

strength of reinforcing bar should be used in the

of the state of pile foundation corresponding to

failure mode judgement.

the seismic performance.

In case of bending failure mode, the damage

(2) Pushover Analysis

levels can be judged with the deformation results calculated from static nonlinear analysis. For the case of shearing failure mode, however, the judgement can only be conducted according to the strength.

Table 3.6.3.1 State of pile foundation corresponding

to the seismic performance levels

That is to say the deformation

behavior of the member with shearing failure mode should be set to linearity in the overall

Seismic Performance Level

Stability Level of Foundation

State of Pile Foundation

SPI

Level 1

Pile foundation do not yield.

SPII

Level 2

Although pile foundation yields, it maintains a sufficient bearing capacity.

Level 3

Although pile foundation reaches the ultimate state, super structure does not collapse.

structural model for the static nonlinear analysis. 3.6.2

Checking

Stability

Levels

of

Foundation In the code, the following items are stipulated

for the checking of stability levels of foundation. CDThe response ductility ratio of foundation;

SPill

®The damage levels of the members composing the foundation; @The residual displacement of foundation. The residual displacement above is taken as a main

index

for

checking

the

Seismic

Performance II. That is to say in order to make quick recovery of the function for train operation,

1) Structural analysis model In the pushover analysis, super structures and pile foundations

are modeled

as a overall

structural system (Fig.3.6.3.1), which includes the

@Seismicisolation @Seismicisolation 3-27

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

nonlinear properties of both the subgrade and structures. The springs expressing the subgrade

Ell

reaction are attached to the nodal points, and the

i

parts connecting the pile to the spread footing and the pile to the embedded lateral beams are

EIs

LKhf

Elr

I

il i

assumed to be rigid.

i------

Elp

!

i

K.h

Elp

I

2) Characteristics of ground resistance The property of ground resistance of pile

I

foundation is assumed to be represented by an elasto-plastic model (bilinear type).

Kv : Vertical subgrade reaction of pile point

Fig.3.6.3.2

Ksv : Vertical subgrade reaction of pile surface K.h : Horizontal resisitance of pile .Khf : Horizontal resisitance of footing

shows an example of the ground resistance model that becomes plastic when the subgrade reaction of each ground resistance reaches the upper limit. 3) Yield point of pile foundation Yield point of a pile foundation is established according to the load-displacement curve of an overall

structure,

where

the

displacement

(a) Pier type

(b) Rigid frame type

Fig.3.6.3.1 Structural model for viaducts

Vertical subgrade reaction of pile skin

Vertical subgrade reaction of pile point Indentation side Rp f--~---

Indentation side

increases rapidly mainly because of the subgrade reaction reaching the upper limit values or the stiffness of pile members decreasing due to the

Pulling side

liw Displacement of pile skin

Displacement of pile point

strength yielding. However, the yield point where

Pulling side ---'----I-U n h

the displacement rapidly increases in the 1000displacement curve varies for different types of foundations. This makes it difficult to judge the yield point from i) the degree to which the

(a) Vertical at pile tip

(b) Vertical on pile surface

Horizontal resiaitance of pile I Effective resistance earth pressure

subgrade reaction exceeds the upper limit values and ii) the number of members damaged over the

Rp: Design point bearing capacity of single pile Re: Design skin friction capacity of single pile Pe : Effective resistance earth pressure

0'---'------Iih Horizontal displacement

total number of members. In order to investigate the causes of yield point,

(c) Horizontal on pile surface

some common prototype pile foundations were chosen for trial designing.

As a result, it was

Fig.3.6.3.2 Models for ground resistance

confirmed that the yield point appears when i) the subgrade reaction yields at the outermost edge of the indentation in side of pile group and ii) half of

criterions.

the total number of pile members yields.

determined by taking into account the causes

In the code, therefore, it is stipulated that the

yield point of pile foundation with a common

In this case, the yield point can be

which intensify the displacement rapidly in the load-displacement curve.

shape can be determined as the point when it reaches one of the states shown in Table 3.6.3.2. If a pile foundation has too many piles, it is

difficult to determine the yield point by these

@Seismicisolation @Seismicisolation 3-28

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Table 3.6.3.2 Yield point definition for pile foundation

January, 2000

of the foundation. Table 3.6.3.3 gives the limit values of response ductility ratio corresponding to

Subgrade in the indentation-in side of pile group

When the vertical resistance of pile head atthe outermost edge reach the upper limit value of design vertical capacity

When the vertical resistance of the Subgrade in the head of a half (ignoring fractions) of pulling-out side of total piles reach the upper limit of pile group design pull-out resistance When the strength of a half (ignoring fractions) ofthe total piles yield

Pile members

various stability levels for cast-in-place pile, which are prescribed in the code. Furthermore, the limit values of ductility ratio are based on the results of loading experiments.

If there is the

sufficient strength left for pile members, the limit values can be determined by other methods while taking the damage process into account. Table 3.6.3.3 Stability Levels and Limit Values of Ductility Ratio Limit value of ductility factor

(3)Response Analysis of Pile Foundation

jL

To check the stability levels of pile foundation, the response values of pile foundation due to the design earthquake motion should be calculated firstly. Then the stability level can be determined

L

Stability level 1

Stability level 2

Stability level 3

1

5

8

Cast-InPlace Pile

by comparing the response values with the indexes of ductility, damage level and response displacement.

The response analysis should be

conducted by using the dynamic analysis method which is chosen by the designer out of the following by taking into account the ground and

In the seismic design, it is necessary to confirm that the demanded damage level of each pile member is satisfied. Referring to some studies'", it is understood that even when the damage level of one part of a pile group exceeds the damage

structure conditions.

level 1 or 2, the strength remaining for the overall

CDNon-linearspectra method ®Analysis method with

2) Damage levels of members

springs

supporting

structural system is enough. Therefor, in the code, the limit values for the damage levels of pile

foundation @Analysis method considering the soil-pilestructure interaction

members have been relaxed.

CD or ® above, the procedure of

3) Response displacement It is confirmed that the values of response

pushover analysis is needed. But for the method

displacement or residual displacement should be

@, only the member's properties and the

less than the limit values corresponding to various

properties of ground resistance as illustrated in

stability levels.

For the method

Fig.3.6.3.2 are needed. 3.7 (4) Checking

Stability

Levels

of

Pile

Conclusions

The outline of the new seismic design code for railway structures has been described above.

Foundation

Because of the limited space in this article, only 1) Response ductility ratios

the basic principles and some.important advances

In the code, the safety checking of pile

foundation is stipulated to check the ductility ratio

for the seismic design are introduced. The adequacy of seismic design methodology

@Seismicisolation @Seismicisolation 3-29

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

should be confirmed through precise analysis of

of earthquake resistance of civil engineering

real

structures, Japan

damage

examples

incurred

in

past

earthquakes. The methodologies introduced here

4) "Report on the investigation of disaster of

are based on the results of damage analyses

Earthquake in Hanshin-Awaji", Committee on the

concerning to the Hyogoken-Nanbu Earthquake.

investigation

Since these damage analyses are still being

Hanshin-Awaji,

conducted by each organization, currently, some

Society. (in Japanese)

new

knowledge

or

disaster The

of Earthquake

Japanese

in

Geotechnical

be

5) Gotou, Y, Ejiri, J.: "The characteristics of

Consequently, by

amplification at the Tarzana observation station in

consideration

obtained in the near future.

of

may

absorbing that information, the current seismic

Northridge

design methodology can become as perfect as

Amplification of Ground Motion on Soft Ground

possible.

Symposium, Japan, 1994.

Moreover, the methodology for seismic design L_~____

ucco.urcs

__.4-L__

_

1.: __ .4-_..1

1 <1Wc;l

I,;VllljJlll,;<1lc;U

1-.

_.&

~_

Uc;l,;<1U1\C'

Vi.

earthquake",

Proceedings

of

6) Yoshimitsu Fukushima: "Empirical prediction for .J

_.&......

1\UVllg

gIVUllU

_ _ .l.':

lllVUVll

J:1 __ .l._..J

__

"-L

lCJ.lCl,;lCU

Vll

WCVIC'U'-'''-l

...: __ l

consideration of the both non-linearity corning

backgrounds of source and propagation of seismic

from the structures and the subgrade. In order to

wave", ORr Report 93-07, Ohsaki Research

avoid meaningless complication, the described

Institute, March 1994. (in Japanese)

approaches taken in the seismic design are the

7) Susumu 0000, Katsuya Takahashi: "Evaluation

essential ones that can express the damage levels

of strong-motion attenuation relation using near-

these

source data in California", Proceedings of the 9th

approaches the state of damage to designed

Japan Earthquake Engineering Symposium, 1994.

structures during an intense earthquake can be

(in Japanese)

of structures.

predicted

Therefore, by using

corresponding

to

the

seismic

8) Haibo

Wang,

Akihiko

Nishimura:

"Determination of design seismic motion by

performance levels. At last, there is a notice that the precision of

considering inland and interplate earthquakes",

the input parameters concerning structures and

Quarterly Report of RT.RI., Vol.40, No.3 ,

subgrade and the computing accuracy should be

pp.130-138, 1999.

appropriate to the execution of computer. Even

9) Yoshitaka

Murono,

Akihiko

Nishimura:

though the level of design method is promoted, a

"Characteristics of Local Site Effects on Seismic

design using incorrect input data can not be

Motion, --Non-linearity of Soil and Geological

considered as a good one.

Irregularity--", Quarterly Report of R T.RI., Vo1.40, No.3, pp.139-l45, 1999.

REFERENCES

lO)Ryo Sawada, Akihiko

1) Seismic Design Code for Railway Structures, published by MARUZEN,

Oct,

1999.

(in

Nishimura: "Design

Method of Structure Considering Liquefaction and Subsequent Lateral Flow" , Quarterly Report of RT.RI., VolAO, No.3, pp.146-l51, 1999.

Japanese) 2) Akihiko Nishimura: "Earthquake resistant design for Railway Structures", Quarterly Report of RT.RI., VOl.37, No.3, pp.128-138, 1996.

11)Kimura, Okoshi, et al : An Experimental Study on The Ductility of Pile Foundations, Journal of Study Engineering, Vol.44A, 1998.3 (in Japanese)

3) "Proposal on Earthquake Resistance for Civil Engineering Structures", Special task committee

@Seismicisolation @Seismicisolation 3-30

4. EARTHQUAKE RESISTANT DESIGN OF PORT FACILITIES

BUREAU OF THE PORTS AND HARBORS, MINISTRY OF TRANSPORT 4.1

History or Revisions of Design Codes

4- 1

4.2

Damage to Port Facilities by Past Earthquakes

4- 3

4.3

4.4

4.2.1

Gravity Type Quaywalls

4- 3

4.2.2

Sheetpile Bulkheads

4- 4

4.2.3

Pile Supported Piers

4- 6

4.2.4

Breakwaters

4- 6

Evaluation of Seismic Performance 4.3.1

General

4- 7

4.3.2

Seismic Performance Requirement for Port Facilities

4- 7

4.3.3

Pseudo-static Method

4- 8

4.3.4

Earthquake Response Analysis

4- 9

4.3.5

Seismic deformation method

4- 16

Earthquake Load 4.4.1

4.5

4.6

4- 18

Design Seismic Coefficient

Lateral Earth Pressure and Water Pressure during Earthquake

4.8

4- 18 4- 22

4.5.1

General

4- 22

4.5.2

Apparent Seismic Coefficient (Seismic Coefficient of Submerged Soil Layer)

4- 22

4.5.3

Dynamic Water Pressure During Earthquake

4- 22

Liquefaction Prediction/Determination Method

4- 22

4.6.1

General

4- 22

4.6.2

Grain Size Distribution and SPT-N Value

4- 22

4.6.3

Undrained Cyclic Triaxial Test and Seismic Response Analysis (Sensitive Assess Method)

4.7

4- 7

Seismic Design of High Seismic Resistant Quaywalls

4- 24 4- 25

4.7.1

Evaluation of Seismic Performance of High Seismic Resistant Facilities

4- 26

4.7.2

Design Seismic Coefficient of High Seismic Resistant Quay Walls

4- 26

New Seismic Design of Open Piled Piers

4- 31

4.8.1

General

4- 31

4.8.2

Seismic Performance Requirements

4- 31

4.8.3

Design Earthquake Forces

4- 32

4.8.4

Structural Analysis Procedures

4- 32

@Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

4. EARTHQUAKE RESISTANT DESIGN OF PORT FACIILITIES BUREAU OF THE PORTS AND HARBOURS MINISTRY OF TRANSPORT 4.1 History of revisions of design codes

factors were classified into three groups respectively,

with the regional seismic coefficient

Having been established in 1951, the Port and

ranging from 0.05 to 0.15, the factor for subsoil

Harbour Law in Japan has been revised many

condition ranging from 0.8 to 1.2, and the im-

times so far. The important revision in view of

portance factor ranging from 0.5 to 1.5. The re-

the design of port and harbour facilities was made

sultant value, the design seismic coefficient, was

in 1974, in which it was noticed that the port and

rounded off to the nearest 0.05 or 0.00. As to the

harbour facilities must be constructed, maintained

design of the reinforced concrete structures, al-

and rehabilitated in accordance with the Techni-

lowable stress method was applied.

cal Standard of Port and Harbour Facilities. In

Significant modification had not been made as

1975 the engineering requirement was established

to the earthquake resistant design procedures ever

as the Ordinance of the Ministry of Transport and

since the first edition thus far, however, the pro-

it was prescribed in the ordinance that the faciliti-

cedure of assessing the liquefaction potential was

es in ports and harbours must be stable against

not stated in the 1973 edition, and was firstly

the loads such as earthquake loads, dead weights,

stated in the 1979 edition.

wave forces, impacts due to ships andso on.

In 1999, the order of the Director General of

The Technical Standard of Port and Harbour

Bureau of the Ports and Harbours was repealed

Facilities was established in 1973 as the order of

for variety of reasons, and the Ministry of Trans-

the Director General of Bureau of the Ports and

port notified the new detailed Technical Standard.

Harbours, Ministry of" Transport, in which the

In the new Technical Standard, some significant

details on earthquake resistant design, such as

revisions have been made based on the outcome

design procedures, factor of safety and allowable

of the recent research after the 1995 Hyogoken-

stresses, were specified.

Nambu earthquake. Those are summarized as

In 1979 the Technical Standard of Port and

Harbour Facilities and its Commentary was com-

follows: (1) Principles of design

piled under the supervision of the Bureau of the

The concept of performance-based design

Ports and Harbours, Ministry of Transport, and

has been introduced. The principles are:

has been revised in every ten years after the 1979 edition.

CDAil

the level 1 earthquake motions whose return periods are about 75 years.

Seismic stability of the port and harbour structures was to be examined only by the

the structures must be stable against

® High

seismic resistant facilities should

pseudo-static method in the 1979 edition and

keep the required performance against the

1989 edition of the Technical Standards. The

level 2 earthquake motions whose retum

pseudo-static method is called the seismic coeffi-

periods are over some hundred years.

cient method, and the earthquake load is obtained by the multiplication of the design seismic coeffi-

(2) Seismic coefficient method

CD

The regional seismic coefficient and the

cient and the vertical load. The design seismic

importance factor have been modified,

coefficient is obtained by the multiplication of the

while the factor for subsoil condition has

regional seismic coefficient, the factor for subsoil

remained as it was. The number of region-

condition, and the importance factor. Those three

al groups for the regional seismic coeffi-

@Seismicisolation @Seismicisolation 4-1

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

cient has come up to five, coefficient

motions has been introduced.

ranging from 0.08 to 0.15. Range of the

(4) Assess of liquefaction potential

importance factor has become from 0.8 to

Assessing way of liquefaction potential has

1.5. In addition, the resultant value has

been modified. (5) Design method of open piled piers

been considered down to three decimal

Modified pseudo-static design method, whi-

places.

(2) The equation for the apparent seismic

ch is called the modified seismic coefficient

coefficient, which is the seismic coeffi-

method, has been introduced for the design

cient used for the calculation of earth

of open piled piers.

pressure below groundwater level, has

(6) Design method of reinforced concrete struc-

been modified.

®

tures

Consideration of the dynamic water pres-

Limit state design method has been intro-

sures acting at the front of vertical walls

duced, and safety factors for the design have

has been stated.

been established.

(3) Assess of earthquake-resistant performance Assessing way of the earthquake-resistant

The history of revisions of design codes

performance in view of level 2 earthquake

summarized in Table 4.1.1.

Table 4.1.1 Summary of history of revisions of design codes

1973

1979

1989

Earthquake design level

One level

Seismic coefficient method

0

1999 Two levels

0 modified

Performance-based design principles

Assess of liquefaction potential

0

-

-

0

0

modified Design of open piled piers

Seismic coefficient method

Modified seismic coefficient method

Design of reinforced concrete structure

Allowable stress method

Limit state design method

@Seismicisolation @Seismicisolation 4-2

IS

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

4.2 Damage to port facilities by past earthquakes

January, 2000

the evidence of ground liquefaction and the ground liquefaction behind the caisson might have a major effect on the deformation of the

Port facilities

ill

Japan has been suffering

caisson and the settlement at the apron. _______. before

severe damage by earthquakes, such as the 1964

- - after

Niigata earthquake, the 1968 Tokachi-Oki earth-

20.0

~t""'r',...,,-------.-------- muJ

quake, the 1978 Miyagiken-Oki earthquake, the 1983 Nipponkai-Chubu earthquake, the 1993 Kushiro-Oki

earthquake,

the

1993

l~ I: \\

L WL. ± 0.0

Hokkaido-

\:;.J---l.... ' -------.-,

~

Nansei-Oki earthquake, the 1995 HyogokenNambu earthquake, etc. Earthquakes that induce

Concrete Caisson

severe damage for port facilities have been occurring approximately once in five years in Japan.

13.0

The details of the damage caused by those earthquakes were carefully surveyed and summarized in the reports. The observation of the strong-motion earth-

FigA.2.1 Cross section and deformation of a

quake at major ports in Japan has been conducted

quaywalI at Gaiko District in Akita port

since 1962 and strong ground motions by these earthquakes were recorded at various ports. Therefore, the relationship between ground mo-

The 1993 Kushiro-Oki earthquake A typical cross section of a gravity type quay-

tion and damage of port facilities has been ex-

wall at Kushiro port is shown in FigA.2.2. As

amined carefully since

1962. Although the

shown in the figure, a caisson wall was put on a

mechanism and pattern of the damage depend on

firm foundation with SPT N-values ranging from

the type of facilities, strong ground motion char-

30 to 50, with a loose backfill. Shaken with a

acteristics and geotechnical properties of founda-

peak bedrock acceleration of O.28g, residual dis-

tion have a major effect on the extent of damage.

placement of the caisson walls ranged from Om to

In this section, typical damage of various types

OA3m, on average 0.24m.

of port facilities and its mechanism are summarized considering the ground motion characteris-

- - - Before earthquake ---- After earthquake

~

tics and geotechnical background.

a

;;rIi

.tl2

+3.

vH.W.L+1.§ I

i L.W.L+0.5

4.2.1 Gravity type quaywalls

.

The 1983 Nipponkai-Chubu earthquake Figure 4.2.1 shows a cross section of a quay-

:.. _ -

I

I I I I

wall at Gaiko district in Akita port. A typical

-

-

-

"",

-

I I

0.43

Caisson L

B

H

15.0x12.0XO.6

= .....

..........

..

,.,,--=-

.....

I "-~< I Rubble "I Backfill -, ..... I >-

-9.11 I 1. "\) -- -_-..1---------.....:...< »>: - <: __-J~6_ B.u.!?ll!.el'1E.ull d__ .»>: Unit (m)

feature of the damage was a large settlement at the apron in an order of 1.0 to 1.5m, and the cais-

FigA.2.2 Cross section and deformation of a quaywall at Kushiro port (West port District No.2 West quaywaIl-9m)

son wall inclined toward the sea by 1.6 degree. Maximum horizontal displacement at the top of the caisson was lAm. Observed was 0.22g of maximum acceleration in Akita port. There was

@Seismicisolation @Seismicisolation 4-3

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

The 1995 Hyougoken-Nambu earthquake

- - - before - - after

Gravity type quaywalls in Kobe port slid to

+2.37

offshore side 1m to Sm and subsided 1m to 2m,

r,---~~~-------~~~r------­

subsidence behind the quaywalls of 3m to 4m due

I

\

I

~\

_

\7±O.

to the lateral deformation of the quaywall as indicated in Fig A .2.3. As shown in this figure, a caisson wall was put on loosely deposited decom-

Tie Rod 1=11.0

E E

~

0 0

tti

"S-

c::

posed granite. A peak acceleration of 0.55g at a

~

Ol

s: Ul

depth of GL-32m was recorded at the Port Island

~~

vertical seismic array site in Kobe port.

FigA.2A Cross section of a sheetpile bulkhead in Yamanoshita Revetment in Niigata port T:'.: C .rlgUlC '"t • .L . .J ~l'"

_L

snows a

........:

1:'

(.;1U::;::; ::;C(.;l.!UH Ul

.....L

_

anouier

sheetpile bulkhead in Yamanoshita wharf Con-

Alluvial Clay Layer

Backfillin Sand for Replacing Clay Layer

struction of this wharf was completed about one year before the earthquake. The earthquake resistance design of the wharf was carried out using the design seismic coefficient of 0.12. As seen in

Sand Drain

'V-34.00~-36.00

Unil(m}

the figure, no appreciable damage was observed, except for a local sinking of the fill behind the

FigA.2.3 Cross section and deformation of a quaywall in Kobe port (RC-5, Rokko Island -14m)

anchor plate.

4.2.2 Sheetpile bulkheads The 1964 Niigata earthquake Tie Rod

The majority of quaywalls in Niigata port were sheetpile bulkheads. A typical damage of the sheetpile bulkheads was their swelling and tilting toward the sea. This type of damage was observed mostly in bulkheads with poor anchor resistance. In such cases, the swelling of bulkheads was accompanied by a horizontal shear at a joint

FigA.2.5 Cross section of a sheetpile bulkhead

of the top concrete and the upper end of sheet-

in Yamanoshita wharf in Niigata port

piles. The 1968 Tokachi-oki earthquake

A cross section of a sheetpile bulkhead in

As shown in FigA.2.6, the Konakano No.1

Yamanoshita Revetment is shown in FigA.2A. A characteristic feature of the damage was an over-

quaywall in Hachinohe port was heavily damaged

all settlement. A face line of the walls swelled

by the earthquake. The walls tilted 5 degrees and

more or less toward the sea and some of the top

swelled toward the sea by O.6m at maximum due

concrete blocks sank completely under the water.

to insufficient anchor resistance. Tension cracks in the direction parallel to the face line and set-

@Seismicisolation @Seismicisolation 4-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

tlement in an order of several 10cm occurred in

January, 2000

The 1973 Nemuro-hanto-oki earthquake

the backfill surface. The maximum acceleration

As shown in FigA.2.8, the sheetpile bulkhead

of the earthquake was observed to be 0.26g in

was severely damaged by the earthquake. Ac-

this district.

cording to the investigation after the earthquake, - - - l:efore

-after

the tie rods were not cut and the damage was estimated to have been caused by the decrease of anchoring capacity due to the seismic effect. - _. before aIler

L - 068.0 I~~

H.WL+~ ~itf

LWL ±O.ro

15.0

__ . [+250 :::

1

1\

TIe Rod

The sheetpile bulkhead with batter anchor piles, the quaywall of Kitahama pier in Hakodate port, was damaged by the earthquake as shown in FigA.2.7. The fixation point of sheetpiles and anchorpiles was broken and the face line of the quaywall swelled toward the sea by 59cm at maximum.

Tumbuclde

""

Tlrrber Pile I

]~

-5.0

s:

-4.5

FigA.2.6 Cross section of a sheetpile bulkhead in Konakano No.1 quaywaII in Hachinohe port

\

~

VV

FigA.2.8 Cross section of a sheetpile bulkhead

in Hanasaki port The 1983 Nipponkai-chubu earthquake The severe damage occurred on the sheetpile bulkhead at Ohama NO.2 wharf of -10m depth. Typical features of damage in the quaywall were a large settlement at the apron and a tilting of the coping. Through the investigation after the earth-

- - - before - - after

+3.00

quake, the sheetpile damage was summarized as shown in Fig.4.2.9. These damages were estimat-

HWL +1.04 ~ , L WL ± O.00 "1\\~:;:Ll:u"

+2.73

ed to be caused mainly by liquefaction of the backfilling sand.

+2.0 -7.00

LWL

~

±o.oo

-12.00 -14.50

-

-10.0 -1.lV..t.?;t--

Fig.4.2.7 Cross section of a sheetpile bulk-

Fig.4.2.9 Cross section of a sheetpile bulkhead

head in Kitahama pier in Hakodate port

at Ohama No.2 pier in Akita port

@Seismicisolation 4-5 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

4.2.3 Pile supported piers

January, 2000

Composite breakwaters consisting of concrete

The 1964 Niigata earthquake

caissons and the foundation rubble in Kobe port

The severe damage was observed on the tres-

suffered damage as shown in Fig.4 .2.12. These

tle type quaywalls at Rinko district in Niigata

breakwaters were constructed on loose decom-

port. The ground having consisted of very loose

posed granite, which was filled into the area after

sandy alluvial layer, a typical feature of damage

the excavation of the original alluvial clay layer.

in this area was a large settlement. The quaywall

TIle breakwater settled about 1.4 to 2.6m through

shown in FigA.2.10 sank completely under the

the earthquake. The horizontal displacements of

water.

the breakwater, however, were less than tens of em. The mode of deformation suggests that the

+2.40 l7

caisson was pushed into the rubble foundation and the rubble was also dragged down and

+0.00

pushed into the loose deposit beneath it.

-1.50

- - - before -after

II II II II II

,

FigA.2.10 Cross section of a trestle type pier in B Berth in Niigata port -·16.7

The 1995 Hyogoken-Nambu earthquake FigA.2.11 Cross section and deformationlfailure of a pile supported pier at Kobe port

A pile supported pier suffered damage at Takahama wharf in Kobe port. The horizontal residual displacement of the pier ranged from 1.3 to 1.7m. A typical example of the cross section and deformation of the pile supported pier is

before -afler

shown in FigA.2.ll. As shown in this figure, the

.g L.W.L

pier was constructed on a :firm foundation deposit consisting of alternating layers of Pleistocene clay and sandy gravel. The steel piles having a ....

diameter of 700mm buckled at the pile heads exClay

cept for the piles located most landward. A crack

.... -!-'~s

Backfill Soil, after Excavating Clay Layer

...........

///

......<::~::. -40.00.:::':'-;;':'-1-15}0- J

was observed at the connection of the pile cap

c; /"

'j'> /" Clay

Unit(m)

and the concrete beam located most landward.

Fig.4.2.12 Cross section and deformation of a 4.2.4 Breakwaters

breakwater at Kobe port (Breakwater No.7)

The 1995 Hyogoken-Nambu earthquake

@Seismicisolation @Seismicisolation 4-6

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

4.3 Evaluation of Seismic Performance 4.3.1 General

In the design of port facilities, the effect of earthquakes should be taken into account so that they possess appropriate amount of seismic resistance. Explanation (1) Earthquake resistant design should be applied to port facilities as explained :in this chapter. Seismic resistance of bridges, oil be examined based on other appropriate regulations and guidelines. (2) In the examination of seismic resistance, following factors should be taken into account. (a) Seismicity of the region, target earthquake and target ground motion. (b) Subsoil conditions. (c) Importance of the facility, which should be determined based on various factors including it's role in the society or economy. (d) Seismic resistance of the facility. (3) Following factors should be examined to assure the seismic resistance of the facility. (a) Stability of the whole structure. (b) Stability of the subsoil against failure. (c) Effects of liquefaction on the stability of subsoil and upper structure. (d) Stress of the members of the structure. (e) Relative displacements between various portions of a structure, between structures or between structure and soil. This factor may be important for the purpose of maintaining the functions of the structure after the earthquake. (4) At Kobe Port, the type of structures were quite uniform during the 1995 HyogokenN anbu earthquake. This is why almost all of the structures suffered similar damage. If the type of structures had been more diverse, the amount of damage for each structure should not have been uniform because their response characteristics should have been different.

January, 2000

Based on this experience, in the choice of the structural type of port facilities, it is recommended to adopt various type of structures as long as possible. Related information Seismic performance of port facilities should be examined with pseudo-static method, earthquake response analysis and/or seismic deformation method depending on the dynamic characteristics of the structure. Seismic resistance of structures which are relatively rigid and will not show much amplification during earthquake, should be design seismic coefficient designated in 4.4 and 4.7. Gravity type quay wall is a typical example of such structure. For structures which has a small damping factor and a natural period close to predominant period of ground motion or for the structures which has a relatively long natural period, modified pseudo-static method should be applied, taking into account the dynamic characteristics of the structure. The application of modified pseudo-static method to the design of piled piers is explained in 4.8. The seismic resistance of buried line structures such as tunnels and pipelines should be examined with seismic deformation method because the safety of these structures are controlled by the deformation of surrounding soil. If the facility is especially important or the type of structure is rare and there is no similar conventional structure, it is recommended that it's seismic resistance should be examined by using earthquake response analysis together with . conventional pseudo-static method, modified pseudo-static method or seismic deformation method. The earthquake response analysis should be based on appropriate modeling of related conditions including the structure and the earthquake. 4.3.2 Seismic performance requirement for port facilities.

@Seismicisolation 4-7 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

the importance of the liquefaction mitigation. (1) Port facilities should sustain their structural stability and maintain their functions for a level-1 ground motion, which by definition occurs with high probability during the facility's duration. (2) High seismic resistant facilities, which are especially important and require high seismic resistance, are allowed to suffer only slight damage for a level-2 ground motion, which by definition occurs with relatively low probability during the facility's duration but which is very intense. In other words, high seismic resistant facilities should be prepared for rapid restoration to sustain their intended functions after a level-2 ground motion.

Seismic coefficient (Level-I ground motion)

I Seismic coefficient -Regional seismic coefficient X

Factor for subsoil condition

x Importance factor

I Cross section of the facility

I Assessment of liquefaction and mitigation

Explanation

I

In the seismic design :of port structures, a level 1 ground motion, which has a return period of 75 years and a level 2 ground motion, which is a ground motion due to intra-plate earthquake with a return period of more than several hundred years or a ground motion due to a subduction zone earthquake, should be taken into account. High seismic resistant facilities include high seismic resistant quay walls, which are specially designed for the transportation of emergency cargo or for the maintenance of economic or social activity just after the earthquake, and the revetments of the disaster prevention base, which is intended to keep the safety of the citizen just after the earthquake. While 'to maintain their functions' means to sustain their structural stability, 'to sustain intended functions' means to suffer only a slight damage and to be prepared for a immediate restoration.

Detailed design

Figure 4.3.1 Design process applied to

all port facilities (2) During the 1995 Hyogoken-Nanbu earthquake, the lateral movement of the ground caused significant damage to piles. In the earthquake resistant design of port structures, the mitigation of liquefaction is always required when necessary. Therefore, it is only in very limited case that that the liquefaction or related lateral movement of the ground is allowed and used as a given condition of the design of structures. In these limited cases, the design should be performed adequately based on the earthquake response analysis as a part of the examination of earthquake resistance of soilstructure system or based on the references regarding lateral movement of the ground.

Related information (1) Fig. 4.3.1 shows the design procedure required for all of the port facilities. In this procedure, after determining the structural parameters, the evaluation of liquefaction potential and the mitigation of liquefaction is requested. This is based on the appreciation of

4.3.3 Pseudo-static method

@Seismicisolation @Seismicisolation 4-8

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

I

(1) In principle, seismic load for port structures with relatively short natural period and relatively high damping' factor should be designated as a design seismic coefficient for pseudo-static approach. In this case, the design seismic coefficient designated in 4.4 and 4.7 should be used. Seismic inertia force should be the larger of the following (a) and (b) and should be assumed to act on the gravity center of the structure. (a) (Seismic force):::: (Self weight) x (Seismic coefficient) (b) (Seismic force)=(Self weight + Surcharge) x (Seismic coefficient) (2) For structures for which pseudo-static method is not applied, seismic load should be designated in an appropriate manner, taking into account the characteristics of the structure.

Explanation (1) For quay walls and other similar port

structures, pseudo-static method is applied as for other wide range of structures 1) • Because natural periods of these structures are generally higher than predominant periods of ground motions, the response of these structures during earthquake are similar to those of rigid bodies on a rigid table. In this case, it is assumed that the seismic load is proportional to the structure's weight, The seismic coefficient is defined as the seismic load divided by the weight. In pseudostatic method it is assumed that the seismic load acts as if it were a static load at the gravity center of the structure. (3) Because the seismic load is assumed to act as a static load in the pseudo-static method, it is necessary to take into account the difference between the real phenomena and the assumptions in the method. To appreciate this difference, the safety factor and the allowable stress for dynamic loads are different from those for static load. (3) It is preferable to examine the seismic resistance of those structures which has a longer natural period compared to predominant periods of ground motion or for which the distribution of acceleration is not uniform along the height. In this case, seismic load should be assumed to be

the product of the weight of the portions of the structure and the seismic coefficient of the particular portion depending on the response characteristics of the structure. In modified pseudo-static design of port structure, design seismic coefficient designated in 4.4 is used for the calculation of seismic load. Therefore, the only difference of modified pseudo-static method compared to original pseudo-static method lies in the computation of the distribution of seismic coefficient along the height of the structure. See 4.8 for details of the modified pseudo-static method for piled piers. (4) The effect of the vertical component of ground motion depends on the type of structure and on strict to consider vertical seismic coefficient, the vertical seismic coefficient is not required to be considered in the design code because of following reasons. First, it is preferable to avoid the complexity of the computation. Second, according to the observation of ground motion, the vertical component is usually smaller than the horizontal component except for near-source region. Thirdly, the horizontal design seismic coefficient designated in 4.4 includes the effect of vertical seismic ground motion-.Because of these reasons, the consideration of horizontal design seismic coefficient is sufficient for the design of usual port structures. 4.3.4 Earthquake response analysis

If the facility is especially important or the type of structure is rare and there is no similar conventional structure, it is recommended that it's seismic resistance should be examined by using earthquake response analysis together with conventional pseudo-static method or seismic deformation method.

Explanation (1) General explanation

@Seismicisolation @Seismicisolation 4-9

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Recently, new type of port facilities or extremely large port facilities have been designed and constructed. On the other hand, it is sometimes required to construct port structures at a site with a poor subsoil conditions. Furthermore, as explained in 4.7, it is requested to examine whether a high seismic resistant facility will maintain their functions after a near-source ground motion such as the ground motion at Kobe Port during the 1995 Hyogoken-Nanbu earthquake. It is recommended to examine earthquake resistance of structures-by conducting earthquake response analysis to understand the performance of structures during earthquake more precisely jf -LL _

.L-

.f!

_.J..

~~_~_

:.

~_~

:..J'! .L-l- __ .L-..._w

...... J...

...

.; ....

January, 2000

conditions at the observation site and the construction site are different, the surface records should be deconvolved to obtain incident wave at the bedrock, which can be used as a incident wave to compute surface motion at the construction site. For this process, response analysis of the ground based on multiplereflection theory can be used. Multiple reflection method, however, is based on equivalent-linear theory. Therefore, the method can be applied only when the shear strain in the soil is less than 1%. It should be noted that if the target ground motion is of level-2, the method is not applicable in many cases. (d) To determine the peak amplitude or the ~.~•• _-J

_~-<-:~_

.f'~~...~ .. ~ .. 1-.~ .. ~.~_~ .!.a.\';iJUJ..~ ltL!.aL vv,ac;

~ .. ~.;.~~ ~~

th\

"oJ!

Lilt: LYIJl::: UJ. ::;L.I:UCLUJ.-t: L:5 ilew U.I: .ll I,llt: ::;L.l:U{.;l>UJ.1:: -'-'"

~.!l.uu.uu

especially important.

should be considered. Following equation has been presented to estimate peak amplitude of ground motion at engineering-oriented bedrock",

(2) Implementation of earthquake response

analysis. When earthquake response analysis is conducted, first, appropriate method should be selected. Then the structure should be modeled for that particular method and the material properties should be determined. Furthermore, input ground motion should be determined. The validity of the results should be examined carefully in the light of the limitation of the method, the limitation of the modeling and the accuracy of the material property; Related Information (1) Input ground motion (a) In the design of structures, it is recommended to determine input ground motion based on past observations or earthquake response analysis of the ground. Strong motion records at Japanese ports have been accumulated and published since 1963 2). (b) For determining peak amplitude and waveform of the ground motion, the size and the source-mechanism of the earthquake, the distance and the site effects should be taken into account. (c) When past records are used, if the soil

.1..llV W.Vll ,

Log l oAcoR=O.55M -loglO(X+O.0050 X lOD.05M) - O.00122X+O.502. Log l A MAC=O.53M -loglO<X+O.0062 X lOo.53~ - O.00169X+O.524. Log lOV=0.48M -loglO<X+O.014 X - O.00060X-O.324.

~LoGUJtJ\A.

J.L.I.

(4.3.1)

(4.3.2)

100.43M)

(4.3.3)

Here, AcOR is the corrected peak ground acceleration (Gal), ASMAC is the peak ground acceleration measured with SMAC-t-ype accelerograph (Gal), V is the peak ground velocity (kine), M is the magnitude, X is the closest distance from the fault to the site (km). Strong motion observations. at Japanese ports have been conducted with SMAC-type and ERStype accelerographs, Because of the different characteristics of these types of seismographs, they give different waveforms. SMAC-type accelerograph gives smaller peak ground acceleration. Therefore accelerograms from these two different manner should be treated in a different way. In the standard process of the

@Seismicisolation @Seismicisolation 4-10

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

strong motion observation at Japanese ports, records are corrected for their characteristics of the accelerographs and published as "corrected records". Corrected records can be treated in the same way irrespective of the type of accelerographs. This is the reason why usually corrected records are used in the earthquake response analysis. Although almost all of the accelerographs at Japanese ports are of ERS-type, most of the past earthquake records were obtained by SMACtype accelerographs. Therefore, past research were based on the SMAC records. Because the determination of design seismic coefficient of high seismic resistant quay walls and liquefaction assesment is based on research, SMAC PGA is used for these examinations. (e) Most commonly used seismograms in the design of port structures are shown in FigA.7.3. These waveforms, however, are equivalent to SMAC-type accelerographs. In the earthquake response analysis, corrected waveforms should be used. (f) Alley observations of strong motion have been conducted, which are useful in measuring the . strain of the ground during earthquake. In general strong motion accelerations are directly observed and the displacement can be obtained by integrating the records. This integration often fails in error because of the error during the digitization. A method to avoid the error during the integration was presented. Displacement waveforms based on this method are displayed in reference 2). (g) In pseudo-static design, the vertical component of ground motion is usually neglected. In the earthquake response analysis, however, vertical component of ground motion should be sometimes taken into account. The peak vertical ground motion divided by peak horizontal ground motion usually ranges between 1/31/23),4 ) . (11) According to the examination of past strong-

motion records, the attenuation of peak ground acceleration is dependent on the region. The regional attenuation was examined for the Pacific coast of Tohoku area. The results are

given in FigA.3.2 and expressed in EqA.3A. Log 1oA=3.159+0.234M- l.4781oglDX. (4.3.4) Here, A is the peak ground acceleration of engineering-oriented bedrock (Gal), M is the magnitude, X is the shortest distance from the site to the fault (km). (2) Methods for earthquake response analysis Methods for earthquake response analysis can be divided into two categories, that is, numerical analysis with computers and vibration tests. 1000.-

It J.iI:: 7. .:1. oM' 7.2

x M>6.7 .c. M-6.5-6.0 a M = .5.9_5. .5

500

..-.

--;

Q. <: 0

0.-

•

M·5.4-~.O

..

M ::4.9-4,0

100

,,~

J5~ J 10

M :r6.0

( 50

100

I

, I I 500

I Ii 1000

Fault distance [km]

Figure 4.3.2 Attenuation relations for Pacific side of Tohoku (a) Numerical analysis Table 4.3.1 shows various methods for numerical earthquake response analysis. 1) Effective stress analysis and total stress analysis When the soil is liquefied, the pore water pressure is induced in the soil and the effective stress decreases. As a result, rigidity and damping of the soil change. Effective stress analysis can treat these situations and the

@Seismicisolation 4-11 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Table 4.3.1 Methods of numerical earthquake response analysis

Treatment of excess pore water pressure

Dimension

I

Effective stress

I

I-D, 2-D. 3-D

Total stress

i

,

I

i

Modeling

I I

Material

Linear. Equivalent-linear, Nonlinear

Time domain, Frequency domain

Domain

-liH"~ i

(rnJ

.

6

I

(kN/JJI")

! 19.5

i

I

4119.3

I

t

a

: !

I I

!

16.1

Multiple reflection model. :MDQIi'. FEM

I'J Time 07 05 0.3 , I I ~======S=4;=C:;:;~=::::::~==01

0.2

O~

i 12~j fmJ'$J i

"Ii

200

'!='

I

I'~O!'

ef l : : ;i 1 14

JO.7! '20

,

I

I

J

!

i

i

1 1a. 5 I .

'20 I

I

I"

'"

!

I

r

(a) Material properties

(b) Reflection and transmission

Figure 4.3.3 Multiple reflection model

@Seismicisolation @Seismicisolation 4-12

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

excess pore water 'pressure in the soil can be computed directly, On the other hand, in total stress analysis the pore water pressure is not computed and the effect of pore water pressure on the response is not considered. Therefore, in the case of high pore water pressure (the pore water pressure ratio of 0.5 or greater), the results of total stress analysis is not accurate. In the practical design, however, total stress analysis is often utilized because of it's simplicity. In many cases, stress or acceleration given by effective stress analysis is smaller than those given by total stress analysis. 2) Dimension of the domain The dimension ranges from 1 to 3. In general the response of horizontally layered soil is treated as a I-D problem. On the other hand, structure-soil system such as quay walls which satisfies plane-strain condition is 'treated by 2-D analysis. Although there are some cases in which 3-D analysis is more appropriate, 3-D analysis is mainly used for especially important structures or research purposes because of the limitations of computers. 3) Modes for computation a) Multiple reflection model In this model, the soil layers are considered to be horizontally homogeneous as shown in FigA.3.3 and vertical incidence of a shear wave is assumed. In this method, stressstrain relation is usually assumed to be equivalent-linear. SHAKE 5) adopts this algorithm. b) MDOF model In this model, the soil is considered to be a combination of masses, springs and dampers as shown :in. Fig.4.3A. The algorithm of this method is simple. It is also possible to consider nonlinear restoring force. c) FEM, etc. In this model, the soil is divided mto finite elements as shown in FigA.3.5. This method is applicable not only soils but also many types of materials. The main feature of this method is that the 2-D characteristics of the soil is easily taken into account. Practical program for this method includes FLUSH6), BEAD?) and FLIPS).

January, 2000

d) Cantilever model Structure (or soil) is modeled as a cantilever with a constant or linearly varying material properties. Shear beam model is most commonly used. Information regarding the shape of the structure, density, rigidity and damping is necessary for computation. 4) Evaluation of material properties. In the earthquake response analysis, modeling of the soil nonlinearity is also important. In the low strain range, stress-strain relation of the soil is linear. In the middle or high strain range, however, this relation is nonlinear, In such cases, nonlinearity of the soil has to be taken into account. Today, besides linear analysis, equivalent-linear analysis, which uses material parameters corresponding to the level of strain, and nonlinear analysis, which reproduces actual stress-strain relation at large strain to some extent, have been developed and used. The effect of the deference of modeling among these analysis can be summarized as follows. Fig. 4.3.6 shows the comparison among linear, equivalent-linear (SHAKE), Bi-linear, Tri-linear, Hardin-Drnevich and Ramberg-Osgood models as applied to I-D soil response problem in which the amplitude of input ground motion is 100Gal. G/Go- 'l' and h- 'Y curves from these models are set to be consistent with experimental results at the strain level of 0.3%. The figure shows the distribution of peak acceleration, peak stress and peak strain. In this range of the input motion amplitude, the models which considers soil-nonlinearlity has a tendency to give smaller response acceleration / stress and larger strain. Difference between equivalent-linear model and nonlinear model are small as long as the peak strain is less than 1%. In the case of level-2 ground motion, however, peak shear strain often exceeds 1%. At our current state of knowledge it is difficult to determine whether above mentioned tendency applies to' such cases. In the earthquake response analysis, G/Go- "I . and h- 'Y curves from the models should be consistent with the results of experiment at the strain level of concern. In general, masing-rule is used for representing the stress-strain loop. It has been revealed that this rule overestimates

@Seismicisolation 4-13 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

H Vs

{ml si

M 5

~::!:~C!!/){'------=-I I

7.5

/6.7

I

37 ,

In

M 4

~=:::::j

'5.6

(b)

(a) Material properties

M 3

K4

M 2

K 3

M

K2

I

Multiple degree of freedom system

Figure 4.3.4 Multiple degree of freedom (J\1DOF) system

30.50

v H.W.L+1.7m

'¥¥ LW.L""*"O.om Basement of crane Backfill soil Gravel /'"1.< I , v-6.0

11.J 9-14.50

,,;/1 l;

Gravel ~=='------7

v-IH.sn

Replaced soil

Cohesive soil

Cohesive soil

Sand drain 7-:tlJXl-3S.0': 2-l.lY./

(.!jilli : rn)

(a)"Cross section of the target structure

Inclination 4.1"

\l

Horizontal displacement 3.5m

\'ertical displacement I 5m

,

T ............. ...,..."'T'"-r

I

,I

~ .....

_

J

-!--'_ -H-\-;i..(:· eJ.:I.:.l''- ~U X t

,

______ • __

I

I

I

...... ,._

_

_

_

-- - ---- --"'---... -

..

- -

-

....... _to .. _

L~

"_.1

-~~

~

.

"

, I

"I

i

, I I I ' i I i I I I i

, , ,

I I 1I ; ; (b)

I

Results of FEM analysis'

Figure 4.3.5 FEM analysis

@Seismicisolation @Seismicisolation 4-14

I

,

I

I ;

Iii i

I I ;

+4.0m

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Acceler-ation a (Gal)

a

12.3

100

,

200 <,

'\',B 1'1)

i '

x -'- I>

E

~

..------;--

~P'"

l

'/

'I

!\

'-"<.,

I

%

0--QLin 0---08- L Lr--6T- L V---'V H - D

I

o-'~R

- 0 --SHAKE

:

,

I

'1. ,//1\ :

i i

,

T~

i..:

400

300

r~

I

I

I

.

;

S - 252 NS Bose

I

Cl mcx =' 100Gai

j),o' >!::;l>,.u

'"

V

iI

\

I

"

:Ii

,

-73.6

I

i

I

Shear strain y (%) 12.3

o

05

1.0

0

~~---=-~-~ .

q .

~

i i

q71 Lf.~

;

!

JI:

~

i

!

9

I

!WoP

S-252 NS Base Omex = IOOGal

I

:

-,

C!

i

;)#>'1\

!

,

~.->J~

,J:r If' Iti'f

i

!

i

i

Shear stress

0 0

10

-r: (Him')

20

,

a;:a... o.,

i\\

Ii

~'::J

"",~

!

-,

1"< \7

QI

.!

:;.;0

(

'
'-[

'-<

?J;

i

I i

i

, !

....-

Lin o--oS-L Lr---6. T - L v---v H - D o-.-¢ R - a - - SHAKE 0--0

, i

ii

s- 252 NS

?

I

Omex ='IOOGol

~~""

I

f'..

__ 0 ~=t

I

\ItS

u.:.

<s. \Zl' !

I I

~

.,~ l;;:(, L>:

~

:

c>-

50

I

I

-\'R~ .~

.~-~

40

30 I

-c;

~

-73.6

I

!

i

"",4

~

12.3

o--oLin o--oS - L is--'£:' T - L y--"7 H - D <>---¢ R - 0 --SHAKE

--~ i

-0

~.,---:~

-73.6

1.5

'$>-.

L~

~>~

~L:,.+-\

«~\I ~

I 'Qy

\----=-~, --¥0

-.

Figure 4.3.6 Comparison ofthe modeling of soil noninearitv (l) 4-15 @Seismicisolation @Seismicisolation

Base

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

the damping in the case oflarge strain. Today an approach to mitigate this discrepancy has been presented, in which the thickness of stressstrain loop is controlled to give more realistic damping factors". FLIP is one of the programs which use this approach. Fig. 4.3.7 compares the results of SHAKE, DESRA (hyperbolic model) and CHARSOIL (Ramberg-Osgood model) for the same ground motion (El Centro-1940NS, PGA=O.lG) and for the same soil layers'?', SHAKE gives larger surface acceleration and shear stress. Today there is a consensus to think that equivalentlinear analysis such as SHAKE gives safe-side results, although the situation will depend on the soil and ground motion characteristics. 5) TIme domain and frequency domain. Nonlinear analysis including effective stress analysis is usually implemented in time domain. If the excess pore water pressure is small (pore water pressure ratio less than 0.5), effective stress analysis may be implemented in frequency domain in a similar manner as equivalent-linear analysis. 6) Effect of water In FEM programs, the effect of water should be properly taken into account by using fluid element. For example, FLIP has a fluid element by which sea water can be treated as a noncompressional fluid.

January, 2000

Effective stress analysis is a method to consider this nonlinear properties relatively accurately. Now effective stress analysis has been proved to be a efficient method to evaluate seismic performance of structure including residual deformation and residual stress. On the other hand, equivalent-linear analysis has been used widely because of it's simplicity, Material properties for this analysis should be determined by conducting experiment or by referring to past analysis. (5) The effect of water should be taken into account if the structure has an interface with water. (6) Sometimes large and temporal response appears in the results of earthquake response analysis. These phenomena can be evaluated by referring to the past design of similar structure or related research results. 4.3.5 Seismic deformation method Because the deformation of line structures etc. buried in the soil during earthquake is controlled by surrounding soil, it is preferable that such structures should be designed by using seismic deformation method.

Explanation (b) Vibration tests

This is a test in which model soil-structure system is subject to ground motion. This is a convenient method to understand the global performance of soil-structure system. High skill. is required, however, to conduct vibration tests. Vibration tests include log shaking table tests, centrifuge tests and in-situ vibration tests. (3) FOl' dynamic characteristics of the structure (vibration mode, natural period and damping), it is convenient to refer to the results of in-situ measurement and/or numerical analysis. (4) Earthquake response analysis requires the evaluation of nonlinear material properties.

(1) In the examination of earthquake resistance of line structures such as tunnels or oilpipelines, the relative displacement of the ground is important. The relative displacement is dependent on the characteristics of ground motion and the soil conditions. (2) Besides line structures buried in the soil, seismic deformation method has been applied to dams. Seismic deformation method can be applied to structures other than line structures as long as the residual displacement of the structure can be appropriately evaluated.

@Seismicisolation @Seismicisolation 4-16

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

(kg/lem')

'mol

01

C

j

'" -

II J

5

-,

03

", ,',

'C,

CHARSOIL

/SHAKE

\\ \\

10

I

DESRA/

».

\,

\\ \ \,

(,)

J ! [

\\

2

Period

05

-,

~.

~

0.4

\\

-=

I

~"

0.2

~

I

"

15

Figure 4.3.7 Comparison of the modeling of soil nonlinearity (2)

References

of Approximate 3-D analysis of Soil-Structure Interaction Problems" by J. Lysmer, T. Udaka, C.F. Tsai and H.B.Seed, Report No.EERC 75-30, University of California at Berkley, 1975. "Coupled Hydrodynamic Response Characteristics and Water Pressures of Large Composite Breakwater" By T. Uwabe, S. Noda, T. Chiba and N. Higaki, Report of the Port and Harbour Research Institute, Vo1.20, No.4, 1981 (in Japanese with English abstract). "Strain Space Plasticity Model for Cyclic Mobility" by S. Iai, Y. Matsunaga and T. Kameoka, SOlIs and Foundations, Vo1.32, No.2, pp.1-15. "Modeling of Stress-Strain Relations of Soils in Cyclic Loading" by K. Ishihara, N. Yoshida and S. Tsujino, Proceedings of the {fh Conference on Numerical Methods in Geomechenics, Nagoya, Vol.L, 1985, pp.373380. "Comparison of Dynamic Analysis for Saturated Sands" by W.D.L. Finn, G.R. Martin and M.K.W. Lee, Proc. of ABeL Earthquake Engineering and Soil Dynamics, VoLI. pp.472-491, 1978. ........nnnntOl" ...... "' .......... 1:-' ....................

1) "Earthquake Resistant Design of Civil Engineering Structures" by N. Mononobe, 1952 (Revised Edition in Japanese). 2) "Annual Report on Strong-motion Earthquake Records In Japanese Ports (1995 & 1996) ,i by Yukihiro Sato, Koji Ichii, Susumu Iai, Yuko Hoshino, Yoko Sato, Masafumi Miyata and Toshikazu Morita, Technical Notes of the Port and Harbour Research Institute, No.909, 1998 (in Japanese with English abstract). 3) "Relation between Seismic Coefficient and Peak Ground Acceleration Estimated from Attenuation Relations" by A Nozu, T. Uwabe, Y. Sato and T. Shinozawa, Technical Note of the Port and Harbour Research Institute, No.893, 1997 (In Japanese with English abstract). 4) "Characteristics of Vertical Components of Strong Motion Accelerograms and Effects of Vertical Ground Motion on Stability of Gravity-type Quay wall" by T. Uwabe, S. Noda and E. Kurata, Report of the Port and Harbour Eesearcb Institute, Vol. IS, No.2, 197G. 5) "SHAKE-A Computer Program for Earthquake Response Analysis of Horizontally Layered Sites" by P.B. Schnabel. J. Lysmer and H.B. Seed, Report No. EERC 72-12. Col. of Eng., University of California at Berkeley, December 1972.

7)

8)

9)

10)

@Seismicisolation @Seismicisolation 4-17

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

4.4 Earthquake Load 4.4.1 Design Seismic coefficient

(1) For pseudo-static design of port structures, horizontal design seismic coefficient should be determined with following equation. Seismic coefficient =Regional seismic coefficient.x Factor for subsoil condition X Importance factor (4.4.1) Horizontal design seismic coefficient should be rounded to obtain two places of decimals. Standard values for regional seismic coefficient are: ReID-on A: 0.15 Nemuro, Kushiro, 'Iokachi and Hidaka districts of Hokkaido, Saitama, Chiba, Tokyo (Except for Hachijo and Ogasawara Islands), Kanagawa, Yamanashi, Shizuoka, Aichi, Gnu, Fukui, Shiga, Mie, Nara, Wakayama, Osaka and Hyogo. Recion B: 0.13 Pacific side of Aomori, Iwate, Miyagi, Fukushima, Ibaragi, Tochigi, Gunma, Nagano, Kyoto, Kochi and Tokushima. Region C: 0.12 Iburi, Oshima and Hiyama districts of Hokkaido, Aomori (except for Pacific side), Nata, Yamagata, Niigata, Toyama, Ishikawa, Tottori, Hiroshima, Ehime, Oita, Miyazaki, Amami Islands of Kagoshima and Kumamoto. Region D: 0.11 Abashiri, Goshi, Ishikari, Sorachi, Rumoi and Kamikawa districts of Hokkaido, Okayama, 'Iottori, Kagawa, Nagasaki (except for Goto, Iki and Tsushima Islands), Saga, Kagoshima (except for Amami Islands) and Okinawa (except for Daito Islands). Region E: 0.08 Sorachi district of Hokkaido, Hachijo and Ogasawara Islands of Tokyo, Yamaguchi, Fukuoka, Goto, Ik:i. and Tsushima Islands of Nagasaki and Daito Islands of Okinawa. Factor for subsoil condition should be determined as shown in Table 4.4.1 and 4.4.2.

Table 4.4.1 Factor for subsoil condition ==--====--===--=====

Classification Factor

l"t kind

0.8

1.0

1.2

Table 4.4.2 Classification of subsoil Thickness of Quaternary Deposit

Gravel

Sand or clay

Soft ground

less than 5m 5-25m more than 25m

@Seismicisolation @Seismicisolation 4-18

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Importance factor should be determined according to Table 4.4.3. Table 4.4.3 Importance factor Category Factor

Special 1.5

A

B

C

1.2

1.0

0.8

========--===--=== Category Special: The structure has significant characteristics described by items (1)~(4) of category A. Categorv A: (1) If the structure is damaged by an earthquake, a large number of human life and property will possibly be lost. (2) If the structure is damaged by an earthquake, economic or social activity of the region will be severely suffered. (3) The structure will perform an important role in the reconstruction work of the region after the earthquake. (4) The structure handles a hazardous or a dangerous object and it is anticipated that the damage of the structure will cause a great loss of human life or property. (5) If the structure is damaged, it is supposed that the repair work is considerably difficult. Category B: The structure does not belong to categories Special, Anor C. Category C: The structure does not belong category Special nor A and is easy to repair or, even if the structure is damaged by an earthquake, the effect on economic or social activity is small. (2) If vertical seismic coefficient is required in the pseudo-static design, the vertical seismic coefficient should be determined appropriately, taking into account the characteristics of sn..u cture and subsoil.

Explanation (1) In general, factors that has to be considered in the determination of design seismic coefficient are regional seismicity, subsoil conditions, dynamic characteristics of the structure and the importance of the structure. Most of the port structures, however, have relatively short natural period and relatively large damping factor. Therefore, in general, the design seismic coefficient for pseudo-static design is determined without considering the dynamic characteristics of the structure. (2) When the design seismic coefficient can be accurately determined by investigating regional seismic activity; characteristics of ground motion, site response, etc., it is preferable to use this design seismic coefficient instead of the value designated here. For example, when the design ground motion is determined based on the information regarding regional seismic activities or based on strong ground motion

observations or when seismic response analysis of the structure is conducted, design seismic coefficient can be determined based on these results. (3) Th determine importance factor of the structure, it is necessary to consider not only the purpose, type or size of the structure but also social or economic aspects of the structure. Following factors also should be taken into account. 1. The extent of damage in the future earthquake, the difficulty of restoration work 01' the residual strength after the earthquake. 2. The cargo-handling capacity of the other facilities of the same port. Therefore, it is possible to use different importance factors for the structures for the same cargo in the same port when desired. (4) When computing seismic load, it is not allowed to subtract buoyancy from the weight of the structure. In the computation of soil

@Seismicisolation 4-19 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

pressure, however, unit weight is usually modified to include the effect of buoyancy. Therefore, in the computation of soil pressure, apparent seismic coefficient should be used as describes in 4.5. (5) For structures other than high seismic resistant quay walls, the upper limit of design seismic coefficient should be 0.25 for several reasons. First, in the past, the upper limit of design seismic coefficient was 0.25. Second, there has been no port structures with design seismic coefficient of 0.25 that suffered significant damage. Thirdly, high seismic resistant quay wall has been constructed in many ports.

coefficient was obtained based on past quay wall damage and peak ground acceleration was obtained from either observation or attenuation relations. For sheet-pile quay walls, similar result have been obtainedv". Application of the results to other structures require prudent examinations. By the way, peak ground acceleration in FigA.4.1 is a value obtained with SMAC-type accelerograph. Peak ground acceleration which is obtained with another type of accelerograph should be converted to that of SMAC-type accelerograph before comparison. (3) Level-l ground motion for all port facilities (a) Regional seismic coefficient has been ..J~ .. ~.~~_~A

uC:;lIt:a,U1...U..J,C;U

Related information (1) Design seismic coefficient for

modified pseudo-static method should be determined based on the response characteristics, response spectrum of ground motion and the relation between response acceleration and design seismic coefficient. The dynamic characteristics of the structure can be obtained by appropriately modeling the structure as described in 4.3.4. Response spectrum of ground motion can be obtained by appropriately modeling earthquakes or by averaging observed response spectra. By using these response spectra, peak response acceleration natural periods of corresponding to fundamental and higher orders can be obtained. By superposing these peak accelerations, response acceleration can be obtained, from which design seismic coefficient is determined. Observed acceleration response spectra from strong motion observations in Japanese ports are displayed in reference 3). For the purpose of assessing dynamic characteristics of the structure, not only the structure itself but also soil and water surrounding the structure have to be appropriately modeled. Also the dissipation of vibration energy ha-ve to be considered appropriately. (2) The relation between seismic coefficient and peak ground acceleration 1),2) for gravity quay walls is shown in FigAA.l, in which seismic

January, 2000

.t'..~_

.LLV.lll

...l..~

VUC

...:l~~ ..... ;'l..... .h~_

\Lli)lo.l.~JJu.w..U.1.L

N{: VJ.

_~_1~

VCQ..fi.

ground acceleration with a return period of 75 years 2),5) . Here, return period is defined in a probabilistic way and it does not necessarily imply that the particular ground motion occurs every 75 years. For example, a structure with a duration of 50 years encounters a ground motion with a return period of 75 year or longer with a probability of approximately 50%. For structures with a shorter duration, it may be reasonable to reduce the return period of design ground motion. (b) Table 4.4.4 shows peak ground acceleration with a return period of 75 years. Regional seismic coefficients have been obtained from averaged relation between seismic coefficient and peak g-round acceleration. Reference 1) "Relation Between Seismic Coefficient and Ground Acceleration for Gravity Quay Wall" S. Noda, T. Uwabe and T. Chiba, Report of the P01"t and Harbour Research Institute, Vol. 14, No.4, 1975 (in Japanese with English abstract). 2) "Relation between Seismic Coefficient and Peak Ground Acceleration Estimated from Attenuation Relations" by A Nozu, T. Uwabe, Y: Sato and T. Shinozawa, Technical Note of the Port and Harbour Research Institute, 1'10.893, 1997 (In Japanese with English abstract), 3) Annual Report on Strong-motion Earthquake Records In Japanese Ports (1995 & 1996) " by

@Seismicisolation @Seismicisolation 4-20

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Table 4.4.4 Regional seismic coefficient and

Yukihiro Sato, Koji Ichii, Susumu Iai, Yuko Hoshino, Yoko Sato, Masafumi Miyata, Toshikazu Morita, Technical Note of tile Port and Harbour Research Institute, No.909, 1998 (in Japanese with English abstract). 4) "Analysis on Seismic Damage in Anchored Sheet-Piling Bulkheads" by S. Kitajima and T. Uwabe, Report of the Port and Harbour Research Institute, Vol.18, No.1, 1979 (in Japanese with English abstract). 5) "Expected values of Maximum Base Rock Acceleration along Coasts of Japan" by S. Kitazawa, T. Uwabe and N. Higaki, Technical Note of the Port and Harbour Research Institute, No.486, 1984 (in Japanese with English abstract).

.peak acceleration with a return 'period of 75 years

seismic

Peak ground acceleration with return period of,

coefficient

75 years(Gal)

Regional Area

0.15 0.13 0.12 0.11 0.08

A

B C D E

350 250 200

ISO 100

-1--------------------7

--.:.-----------r-- ---·-----------·-r---------- -------- ---1-------":'----------

). 3 0 ";---~--- -- - ~--- --- -:-----~

Ii

Vertical bar indicates the estimated range ~f seismic coefficient

'if:

.------- --- ---- -------7---- -------.-- ----i-------- ------:v--L-

: TTL

'----------f~

1_

6:

:

,

---------··-·~l~-H A;- )f.------:

~t~--- f--~~-J------------------L------~

i i---------,--t ·:-~~~:l)t-±+---T------------L----f 0"

y ---:-

0"

.

.

0,00 . ----•. _-----------.,---------

o

100

..

:

: • 200

LV

Seismic coefficient estimated for ports ; __• •. --1 ..__..;

--:

300

GOD

ASMAC

400

500

(Gal)

Figure 4.4.1 Relation between peak. ground acceleration and seismic coefficient

@Seismicisolation @Seismicisolation 4-21

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

4.5

Lateral

earthpressure

and

water

In the case ·of using equation(4.5.2), it should

be

included the dynamic water pressure during earthquake

pressure during earthquake

when overall seismic stability calculation. The dynamic water pressure is applied in the seaward direction.

4.5.1 General In static conditions, earth pressures are calculated by ordinary More-Coulomb earth pressure theory. On the other

hand,

earthpressures during

earthquakes

are

calculated by the Mononobe/Okabe method (Mononobe 1957, Okabe 1924) with special treatment where beneath

Apparent

of civil

engineering structures',(Revised edition), 1957. Okabe, S.,'GeneraI theory on earthpressure and seismic of

stablility

retaining

walls

and

dams',J.

JSCE, Vol.] O,No.6, 1924.

the water table soil layers. 4.5.2

Refernces: Mononobe, N.,'Emthquake resistant design

seismic

coefficient

(Seismic

coefficient of submerged soil layer)

4.6 Liquefaction Prediction/Determination Method

The concept of the apparentseismic coefficient k'

is

indicated in following equation.

4.6.1 General Saturated loose sandy deposits tend to liquefy during

y,xk=(y-]O)xk'

(4.5.1)

earthquakes, causing damage to structures. Currently, liquefaction phenomenon is a major keyword for seismic

A product of unit weight of a soil layer and seismic

coefficient over the water table equals a product of submerged unit weight of a soil layer and the apparent coefficient.

design of port and harbor facilities. Past big earthquake disaster reports show that liquefaction should be taken into

consideration

in

design

and

construction

of

structures. Liquefaction potential should be assessed by

The apparent seismic coefficientofsubmerged soil layer can be evaluated by equation (4.5.2).

two step procedures as follow with

considering the

condition of construction site, a degree of importance, etc .. (J ).Grain Size Distribution and SPT- N value

If the results obtained by (I) is not sufficient, following procedure should be conducted. Where: Y, =unit weight of a soil layer over the water table (kl-l/rrr'), y =unit weight of saturated soil layer at submerged area(kN/rri\ m=uniform external load at the ground surfacefkl-l/rrl), h =thickness of arbitrary soil layer(m), suffix i=over the

water table and

suffix

j=submerged area.

(2).Undrained Cyclic Triaxial Test and seismic response analysis

4.6.2 Grain Size Distribution and SPT-N value A soil

is

classified according to

the grain size

distribution by Fig.(4.6.1). The soil of which gr.ain size distribution falls outside of the liquefaction possibility zone in Fig.(4.6.1) is considered non liquefiable.

4.5.3 Dynamic water pressure during earthquake In case of sea walls during an earthquake, external forces can be summarized as shown in Figure(4.5.]).

For

the soil of which the distribution curve falls inside the liquefaction possibility zone the following procedure is conducted

using

standard

penetration

test

blow

counts(SPT N value). (l).Equivalent N Value Dynamic Water Press.

Dynamic Earth Press.

An equivalent N value is calculated by the following equation.

Fig. 4.5.1 Schematic diagram of external forces (

N)

N - 0.0]9(d v -65) 65 - 0.0041(d v -65)+ 1.0 _

@Seismicisolation @Seismicisolation 4-22

(4.6.1)

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Where: (N)65 =Equivalent N value, N =SPT N value of a soil layer,

(J'

l'

= effective overburden pressure of a

January, 2000

gives a critical N value ofa soil under a given equivalent acceleration.

soil layer (kN/m") (The effective overburden pressure

Zone 1 has a very high possibility of liquefaction.

should be calculated with respect to the ground surface

Zone

n has a high possibility

elevation at the time ofthe standard penetration test).

Zone

ill has a low possibility of liquefaction.

Zone

N

of liquefaction.

has a very low possibility ofliquefaction.

;j SAND WITH LOW COEFFICIENT OF UNIFORMITY Ucd.5

f-

:c 100,----,-----,---,---:---.---::------:--,--

30

o

Ui

IV

3 75

>-

'"ffi

z

r;: uJ

c

25 UJ

:::J

:i

25

-c

20

>

iiif-

0L-.---:"':-:---~-7:---___:_"::_------,0:_-

OJ

U

c:<:

CLAY I 0.005

lJJ

c,

1.0

10

GRAIN SIZE (rnrn) I SAND SILT 0.Q75 2.0

GRAVEL

Z JZ I., UJ -l

:::J 10

iii

5

SAND WITH HIGH COEFFICIENT OF UNIFORMITY Uc>3.5 :c I00,-----,-----=----,...----:--.---,,---o

C! UJ

3 75

>'"B} 50 r;:

o

o''-'----:-':-.,-----;!-;------:-'-:-------:!-;:--0.01 0.1 1.0 10

u

c:<:

CLAY I

uJ

c,

100

III

V

J

V

200

300

400

500

600

EQUIVALENT ACCELERATION (Gal)

25

~ 15

~

00

z

/; ~

/

!

..

1/

«: 2:

~

f-

lJJ

/

50

D.W5

GRAIN SIZE (111m) I SAND SILT 2.0 0.075

GRAVEL

Fig. 4.6.2 Classification of soil layer for liquefaction prediction based

011

equivalent acceleration and

eq uivalent N-values.

Fig. 4.6. J G radation of soil having the possibility of (4).Correction of the equivalent N value (The fine

liquefaction.

content «O.075mm) ofa soil is not less than 5%) The equivalent N value of a soil of which the fine

(2).Equivalent acceleration An equivalent acceleration is estimated by the following

content is not less than 5% is corrected as in the

equation based on the maximum shear stress obtained

following three cases:

from earthquake response analysis.

Casel:The plasticity index ofa soil is less than 10 or the fine content is less than 15%. An equivalent N value . obtained from Eq.(4.6.1) is corrected by the following (4.6.2)

Where:

(Xeq

= equivalent acceleration,

shear stress (kN/m"), (kN/m

2 )

(J'" =

rroax

= maximum

equation. (N)65corrected = (N)65 / c N

(4.6.3)

effectiveoverburden pressure

(The effective overburden pressure should be

calculated with respect to the ground surfaceelevation at the time of earthquake), g = acceleration of gravity (980Gal). (3).Check by the critical N value (The fine content of a

where: (N)65corrected = a correctedequivalent N value, c N = a correction factor obtained from, Fig.(4.6.3) based on

the fine content. The corrected equivalent N value is plotted in Fig.(4.6.2) with an equivalent acceleration and the zone to which a soil layer belongs is determined. Case2: The plasticity index is not less than 10 and not

soil is less than 5%) The zone in Fig.(4.6.2) to which a soil layer belongs is determined from the equivalent N value and the equivalent acceleration. The boundary line of the zones

more than 20, and the fine content is not less than·15%. Two corrected equivalent N values are calculated as follows:

@Seismicisolation @Seismicisolation 4-23

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

(N)65corrected = (N)65

/0.5

January, 2000

(4.6.4)

can be evaluated by the relationship between cyclic stress

(4.6.5)

ratio and number

(4.6.6)

liquefaction initiated state as shown in Fig.(4.6.4). The

N+M M = 8 + 0.4(1p - 10)

(N)65corrected =

of cycles(=20)

to the

defined

in-situ liquefaction strength ratio Rrnax is given by the Where: (N)65 =an equivalent N value obtained from

following equation,

Equation(l), N =SPT N value of a soil layer, I p = a plasticity index ofa soil. (4.6.7)

=> "' ..J

-c >

z

b:

~1.0r----.....

In this equation, several corrections are included as listed

-c

u

in followings.

1=

'" o '" u

(1).Stress condition correction: The stress conditions

~ 0.5

between at site( Ko) and

13

in the triaxial cell(isotropic

;;:

~

5

"' '"

01 0

--'--

-'-

5

10

-'--__---',

(2).Type of Input motion correction: The applied stress

15

condition

20

FINE CONTENT (BELOW 0.075I11m) ('To)

Fig. 4.6.3 Reduction facto!" for critical STP-N value based on the fine content.

between at

a site high/low degree of

irregularity of input motion(impact type/vibration type) and in case case of cyclic triaxial test(harmonic). Impact type input motion

C, =0.55

Vibration type input motion C, =0.7 The two corrected equivalent N values are plotted in 0.5

Fig.(4.6.2) with acceleration and the zone to which c

a soil layer belongs is determined as follows. In

l2;:> 0.4

the case that the (N+ D N) is inside of the zone ] , the

o f::: -c 0.3 p::

soil layer belongs to the zone 1 . In the case that the

(N+ D N) is inside ofthe zone II, the soil layer belongs to the zone II . In the case that the (N+ D N) is inside ofthe zone III or N, and the

(N\5

/0.5 is outside ofthe

N, the soil layer belongs to the zone ill. In the N, and the (N)65 / 0.5 is inside of the zone N, the soil layer belongs to the zone N. zone

case that the (N+ 6.N) is inside of the zone ill or

Case3: The plasticity index is not less than 20 and the fine content is not less than 15%. A corrected equivalent N value is calculated by Eqs.(4.6.5) and (4.6.6). The

corrected equivalent N value is plotted in Fig.(4.6.2)

Undrained Cyclic Triaxial Test Results

CI) CI)

~ 0.2 f~------':"'_----6 Rrnaxtvibration type) ' " CI)

0.1 O!:-:-----'-----:-'::-~--:-:':-::------:-:-:!

0.1

10 20

100

1000

NUMBER OF CYCLES NI

Fig. 4.6.4 Correction of Rmax Applied stress ratio L max =

T"max / (5'

I'

is calculated by

seismic response analysis. The liquefaction potentiahsafetyfactorjf'., is given as,

with an equivalent acceleration and the zone to which a soil layer belongs is determined.

(4.6.8)

4.6.3 Undrained Cyclic Triaxial Test and seismic response analysis (Sensitive assess method)

In case ofF L < 1.0, the soil layer should liquefy.

When the liquefaction potential cannot be determined from the grain size distribution and SPT N value,

Reference:(the text mentioned above is revised in 1998 )

liquefaction prediction is made by performing undrained

POIi and Harbour Research Institute ed., 'Handbook on

cyclic triaxial tests using undisturbed soil samples. The

Liquefaction

index of a degree of liquefaction strength R max of a soil

Balkema, 1997.

Remediation

@Seismicisolation @Seismicisolation 4-24

of

Reclamimed

Land',

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

4.7 Seismic Design of High Seismic Resistant Quaywalls 4.7.1

Evaluation of seismic performance of high seismic resistant facilities.

(1) In the design process of high seismic resistant facilities, it is requested that their seismic performance should be evaluated for a level-2 ground motion to assure that their seismic resistance is satisfactory. (2) Seismic performance should be evaluated by appropriately modeling the soil and the structure of the facility, with a method which is appropriate for the particular type of the structure.

Ground motion which is used for the evaluation of seismic performance should be determined with response analysis of the ground in principle. Explanation (1) Evaluation of the residual deformation of high seismic resistant facilities, which is based on a earthquake response analysis, is required for the purpose of verifying that they will sustain their intended functions after a level-2 ground motion. The reason is that, for the examination of the stability of the structure or the soil for a large ground motion such as a level-2 ground motion, conventional pseudostatic method is not sufficient. (2) The judgement whether the high seismic resistant facilities will sustain their intended functions based on the results of earthquake response analysis should be based on the combined considerations on the stability of the structure after the earthquake, the functions and the difficulty of restoration work. Although the allowable residual deformation should be defined for this judgement, it is not easy to specify the allowable deformation at the present state of knowledge. Tables 4.7.1 and 4.7.2, in which the possibility of temporal use just after

January, 2000

the earthquake is presented, should be useful for the judgement. It should be noted, however, that these tables cannot be applied to a quaywall with cranes because the stability or the function of the cranes is not addressed in Tables 4.7.1 and 4.7.2. In the case of the 1995 Hyogoken-Nanbu earthquake, some of the caisson quaywalls with a normalized deformation (lateral residual displacement I height of the quaywall) of over 10-20% was temporary repaired and offered for immediate use just after the earthquake. . Related information for

seismic resistant quaywalls. 4.7.2 Design Seismic coefficient ofhigh seismic resistance facilities

(1) When pseudo-static design is applied to high seismic resistant quaywalls, the design seismic coefficient should be determined by a global judgement base on the seismic coefficient determined by EqAA.l with importance factor 1.5, by following equations for which peak ground acceleration should be calculated with ground response analysis for level-2 ground motion, and by other appropriate methods. 1. If a is smaller than or equal to 200Gal, Kh=a/g (4.7.1) 2. If a is larger than 200Gal, x, =(113) X ( a Ig)(lJ3) (4.7.2) Here, Kh is horizontal seismic coefficient, a is peak ground acceleration at free surface and g LS the acceleration of gravity.

Explanations (1) When the design seismic. coefficient can be accurately determined by investigating regional seismic activity, characteristics of ground motion, site response, ete., it is preferable to use this design seismic coefficient instead of the value designated here. For example, when the design ground

@Seismicisolation 4-25 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Table 4.7.1 Allowable residual deformation from the viewpoint of availability i

Type of structure.

Depth of water

'Available: N at available

Amount of deformation

I II

Gravity quay wan

Sheet-pile quay wall

More than 7.5m

Less than 7.5m

More than 1.5m

Less than 7.5m

o -30cm

o -20cm

o-30cm

o -20cm

30-l00cm

20-S0cm

30-S0cm

20-30cm

Table 4.7.2 Allowable residual displacement from functional point ofview

Subsidence of whole apron Main structure

20-30cm 3- 5

Inclination

0

20-30cm

Irregularity of the horizontal displacement offace line Irregularity of subsidence Apron

Gap between apron and backyard: Inclination

normal: 3-5%

3 -lOcm 30-70cm

reverse: 0%

(5) From the experience of significant damage at Kobe Port during the 1995 Hyogoken-Nanbu earthquake, minimum design seismic coefficient for high seismic resistant facilities should be 0.25 if the site is ill a near-source region. (6) When it is desired, seismic resistant qua walls should be designed for level-2 ground motion with a method other than pseudo-static method such as earthquake response analysis. In this case, it is necessary to make sure that seismic resistant facilities will sustain their structural stability for level-I ground motion.

motion is determined based on the information regarding regional seismic activities or based on strong ground motion observations or when seismic response analysis of the structure is conducted, design seismic coefficient can be determined based on these results. (2) In the design of high seismic resistant facilities. target earthquake has to be selected from earthquakes including hypothetical earthquake in the disaster prevention plan set by local government. (3) One way of calculating peak ground acceleration at free surface is to use multiple reflection model for the response analysis of the ground. (4) Refer to the reference 1) and 2) for the details ofEq.4.7.1 and Eq.4.7.2.

Related information (1) Level-2 ground motion for high seismic

@Seismicisolation @Seismicisolation 4-26

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Regional seismic coefficient, XF'actor for subsoil condition >< Importance factor O. 5)

Requirement of performance

I I

Ground motion

; Seismic coefficient

I Size of earthquake

I

I

I Type and parameters of structure,

soil improvement, function of facility Selection of target earthquake

I

, (Near-source or not?) Cross section of the facility

PGA at bedrock

l-

I Examination of residual, deformation for level-2 ground motion

Earthquake response analysis of ground

-

I Assessment of liquefaction and mitigation

Selection of waveform

I-

r--

I Detailed design

Figure 4.7.1 Design process of high seismic resistant facilities

resistant facilities (a) If hypothetical earthquake is not designated in the regional disaster prevention plan or if the hypothetical earthquake in the disaster prevention plan is not appropriate for determining level-2 ground motion, it is recommended to select an earthquake which brings the largest ground motion to the site among earthquakes in the past and hypothetical earthquakes on active faults. Magnitude of hypothetical earthquake on active faults can be estimated with following equation. Log1oL=O.6M-2.9. (4.7.3) Here, L is the length of the fault (kID) and M is the magnitude. Sometimes several active faults are closely located to each other in the fault map. In such cases, if one fault is within 51an

£rom another fault, these faults should be considered as one long fault m the determination of magnitude. If there is difficulty in the application of EqA.7.3, the magnitude 7.2 can be used, which is the same as the 1995 Hyogoken-Nanbu earthquake. (b) Following equation" can be used to determine peak ground acceleration at engineering-oriented bedrock. Log lOAsMAC=O.53M . -loglO(X+O.0062 x lOo.53~ - O.00169X+O.524. (4.7A) Here, A SMAC is the peak ground acceleration measured with SMAC-type accelerograph (Gal), M is the magnitude, X is the closest distance from the fault to the site (km). The relation is shown in Fig.4.7.2. If the dip angle of the fault

@Seismicisolation 4-27 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

0;

Q.
""'U
100 9

7

;:;; UJ

"

10 :3

~

:s

6

3

'0

04 5

G

100

Fault distance X [km]

Figure 4. 7.2 Attenuation relations for peak acceleration for engineering-oriented bedrock 200

;;a Q. <:: 0 +J

...'"

i

o

...:

I a) 5-252 NS

a...

MAX. 170 Gel

------------~---------------.1--------.------

100

° -100

;

!

,

.

--------1---------~------·----__:_------·----

1

-200

Time

:::;'

..

(b) 5-1210 E 041S

MAX, 161

8

...:

,

-.- -----}-------------1--------------

-100

.

-200 0

Time

;;a

60O

Q.

"00

<::

200

Gal

---------r-------------.t----------

°

j

20

[s]

200

'" Q. <:: 0 +J

!

10

0

(c) Pi-7S

us

I

•

10

15

: 20

[s]

Bue

.S

.......

-400

<

-600

8

---+----------------r--------------

-200

'"

Qj

-'---'----:'---------'------------

°

10

Time

I.

20

[s]

Figure 4.7.3 Time history of representative strong motion records

@Seismicisolation @Seismicisolation 4-28

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

80r-------,-------,--------,-----, e-.

Ill} S-252. NS

-------r-------r-----.-----

:

:

i:

;:

10

,5

Frequency [Hz]

'Or---~---,--------,-------,-----..,

i

(b) 5-1210 e.1 S

:

------

-------~--t--~-------r·-------;

60

. een-i--+-_== -v

f

i. -+

Vf\A

~

':_-i~

'0 Frequency [Hz] i (e) Pf-7R N&

'ai'

• en

Q.

a

:

'" ....

<)

'"so0-

:

s.--UHz

---~------+--_._

100

:

.~....

~'"

a-

---j-'------+----:-J=i------l-----:----

200

! ~O

. _-+-_._-: :

:

:

!

:

-----~--.----! --~-----

•• - - - - - . -

oL_ _---'-_ _-=::::::::::::::::=h====d c

20

10

Frequency {Hz]

Figure 4.7.4 Fourier spectra of representative strong motion records 30 ,

,

2S

a

c:.

20

~ r.:.'"

•

I

I

,

I I

:

:

:

I

,

,

I

I

l

:

:

I

liB

--1---------;----.. :

1 ------~---

l

:

J

~

: :

5

0

1

----t----------+-----~ i"

-r-~=~r 5

6

;

T------I

! ! "

/0

II

1/

: II ,: , ,; -----;----------;-------;--------- T-----------

C 1S

I

I

: : J ! ,/ ---r------l--------r-----:------T-l--------

$(

.:l '5'"

I

I

,

-+,

w_

-i-r-IA

I

:

e

7

9

MagnitudeM

Figure 4.7.5 A diagram presented for determining whether near-source effects should be considered

@Seismicisolation @Seismicisolation 4-29

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

is unknown, the distance from the site to the updip projection of the fault can be used in EqA. 7 A. If the location of the fault cannot be determined, the distance from the site to a sphere with a radius determined from following equation can be used. Log lOr=0.5M-2.25. (4.7.5) Here, r is the radius (km) and M is the magnitude. Engineering oriented bedrock is defined as a soil layer with shear-wave velocity over 300m/s, a sandy soil with SPT-N value over 50 or a cohesive soil with qu over 650kN/m2 . (c) Hypothetical earthquakes can be divided into intra-plate earthquaJre and inter-plate earthquake. Strong monon records at POIt Island during the 1995 Hyogoken-Nanbu earthquake can be used as a representative ground motion from intra-plate earthquake. Records at Hachinohe Port during 1968 'Iokachi-oki earthquake or at Ofunato during the 1978 Miyagi-ken-oki earthquake can be used as a representative ground motion from inter-plate earthquake. It is recomended to use Port Island records when it is necessary to take into account near-source effects even when the earthquake is a inter-plate earthquake because near-source ground motion from inter-plate earthquake has not been obtained yet. Time history of these records are shown in Fig. 4.7.3 and Fourier spectra of these records are shown in FigA.7A. (d) FigA.7.5 can be used to determine whether the site is in near-source region. If the site is located in A of Fig. 4.7.5, then the site is in near-source region. (e) Sometimes design seismic coefficient obtained from EqA.7.1 and EqA.7.2 is smaller than those obtained from regional seismic coefficient, etc. This is partly because the factor of subsoil conditions are not necessarily consistent with the amplification factor obtained from response analysis. In the case of weak soil, peak ground acceleration at the surface is often smaller then expected form linear theory due to nonlinear effects during large earthquake. It should be noted that ground motion at weak soil site sometimes

causes large deformation of structures even when peak ground acceleration is small. Reference 1) "Relation Between Seismic Coefficient and Ground Acceleration for Gravity Quay Wall" S. Noda, T. Uwabe and T. Chiba, Report of the Port and Harbour Research Institute, Vol.14, No.4, 1975 (in Japanese with English abstract). 2) "Relation between Seismic Coefficient and Peak Ground Acceleration Estimated from Attenuation Relations" by A. Nozu, T. Uwabe, Y. Sato and T. Shinozawa, Technical Note of the Port and Harbour Research Institute, No.893, 1997 (In Japanese w-ith English abstract).

@Seismicisolation @Seismicisolation 4-:30

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

4.8 New Seismic Design of Open Piled Piers

unforeseen external forces and caused buckling of

4.8.1 General

steel pipe piles and cracks in concrete superstructures.

The seismic design of open piled piers described in

Since it should be rather difficult to estimate the

this section is basically to verify if they possess the

magnitude of such external forces, the design method

required structural performance during earthquakes.

for open piled piers assumes that liquefaction does

At first, the fundamental dimensions of structural

not occur.

members to be verified are designed with the

prevented.

allowable stress method against loads except seismic forces.

Therefore, liquefaction should be However, the effect of liquefaction

. should be considered for very important facilities.

Then structural performance of the pre-

determined section under seismic actions is checked considering seismic energy absorption due to plastic deformation of steel pipe piles. structural

performance will

be

The required determined

m

4.8.2 Seismic performance requirements _It should be examined appropriately whether open

piled piers will perform as required when earthquakes happen.

For common piers, structural performance

consideration of the importance and the role of

should be verified against Level 1 ground motions.

structures, and will be expressed in terms of

Both of Levels 1· and 2 ground motions should be

horizontal displacement and the place and the timing.

taken into consideration for high seismic resistant

of local damages.

piers.

Seismic performance requirements depend on

Open piled piers were damaged by liquefaction of

the importance of piers and can be described with

the base ground or the backfilling soil of retaining

indices such as extent of damage, maximum

structures behind them due to the 1995 Hyogoken-

displacement,

Nambu earthquake.

earthquakes.

The liquefaction produced

and

residual

displacement

The difficulty of· repair to damages

Natural period of pier

Dynamic analysis of ground

after

Maximum acceleration of the base Model for Frame model, etc.

Ground response anafsis (SHAKE, etc.) Acceleration at 1/ below the seabed

Seismic coefficient Fig. 4.8.1 Calculation flow of seismic coefficient

@Seismicisolation @Seismicisolation 4-31

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

should be considered well at the same time.

Region A

I. 00 I-~~~~---"----------'

Resonance will make the response of a pier higher than that expected when the natural periods of the structure and the ground are close to each other. In

......

such a case, dimensions, geometry, etc. of the

'0

c

(!)

original structure should be modified to achieve different natural periods.

:i= (!) o

o O. 10 r---:----'---~+--~~-~~

Alternatively, the ground

(.)

should be improved so that the natural period of the

E (f) 'CD

ground is changed.

(f)

For the structure of an access bridge to link a pier to the land, the following should be taken into

O. 01

account: (a) In case large seismic force acts on the

~

O. 1

---'-,-.J

1. 0

10

Period (s)

pier towards the retaining structure, possible contact between the pier and the retaining structure, through

'---..L-_-,-

Fig. 4.8.2 Standard seismic coefficient

the access bridge, should be avoided by checking the available

clearance

displacement.

against

the

maximum

(b) In case the seismic force acts

towards the sea, the maximum displacement should be checked to prevent the access bridge from falling

where Tg is the natural period of the ground, Hi is the thickness of zth stratum, and velocity.

Vsi is the shear wave

Vsi can be assumed using N value of the

ground.

down. If case that cargo handling machines such as container cranes are equipped on piers, the interactive

The natural period of the wharf can be calculated using Eq. 4.8.2:

vibrations between them should be well examined. (4.8.2) 4.8.3 Design earthquake forces

Figure 4.8.1 shows the sequence for calculating the seismic coefficient.

Level 1 ground motions are

defined as those with a 50-percent probability of exceedance in 75 years.

Expected values of the

base ground acceleration depend on the region where piers .are constructed.

Acceleration response that

corresponds to the natural period of pier is obtained as shown in Fig. 4.8.1.

The design seismic

coefficient will be given by dividing the response acceleration by the acceleration of gravity.

seismic coefficient can be obtained using the standard

acceleration, and Kh is the,horizontal spring constant of each pile. The seismic coefficient for Level 2 ground motions is obtained using the same procedure shown in Fig. 4.8.1. Dynamic analysis of the ground is necessary because charts like Fig. 4.8.2 are not available for Level 2 ground motions at present. 4.8.4 Structural analysis procedures

Seismic performance of an open piled pier should be examined with appropriate analytical. models to

spectrum shown in Fig. 4.8.2 as an example. of the ground

weight of the wharf and surcharge, g is the gravity

Instead

of performing the dynamic analysis of the ground, the

The natural period

where T, is the natural period of the wharf, W is the

can be

simulate its non-linear behavior as close as possible. Plastic deformation of steel piles provides excellent

approximately calculated by Eq. 4.8.1:

seismic structural capacity particularly during Level (4.8.1)

2 ground motions, but also initiates local minor

@Seismicisolation @Seismicisolation 4-32

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

damages.

Therefore,

requirements

regarding

moments can reach their fully plastic moments in

locations and extent of these damages should be

about a half of all piles, and after that, horizontal

specified at the verification.

displacement may rapidly increase.

For verification of the seismic capacity of a pier,

P-a is the ratio of the allowable maximum

the ductility design methods recommended to be

horizontal displacement to that at the elasticity limit.

applied are: (a) simplified analysis, (b) elasto-plastic

On the basis of analytical and experimental results,

analysis, or (c) non-linear dynamic analysis.

/-la

(a) Simplified analysis

motions and presented in Eq. 4.8.5 for Level 2

The superstructure of a pier is considered to be a

is summarized in Table 4.8.1 for Level 1 ground

ground motions.

rigid body, and the capacity of the pier is evaluated as Table 4.8.1 Standard values of u; for Levell

the overall capacities of each pile. This method is applicable to piers supported on vertical piles with

ground motions Classification of pier Special class A class B class C class

small variety of their rigidities. (b) Elasto-plastic analysis A pier and its surrounding ground are modeled by a frame and springs, which represent their non-linear properties.

P-a

1.0 1.3 1.6 23

This method is suitable for complicated !-La

structures whose capacities might be overestimated

=

1.25 + 62.5 (t / D)

:s; 2.5

(4.8.5)

by the simplified analysis. The seguence of local

where P-a is the allowable horizontal displacement

failures (generation of plastic hinges, damage of

ductility factor, t is the thickness of pipe pile, and D

superstructures, etc.) and the maximum and residual

is the diameter of pipe pile. Instead of performing elasto-plastic analysis, the

displacements will be verified.

elasticity limit P, can be given by Eqs. 4.8.6 and

(c) Non-linear dynamic analysis The pier structural system is analyzed by the finite

4.8.7 based on parametric studies: O.8 2-p.all

(4.8.6)

element method considering non-linear and dynamic

P,

properties.

Paall = L {2M pi /(hi + 1/ f3i )}

This method is applied when the whole

=

(4.8.7)

structural system is complicated or large deformation

where

of the ground is predicted.

moments at the pile head and the assumed fixed point

PI/all

is the horizontal force when bending

In the ductility design method, the Newmark law

under the ground of all piles reach their fully plastic

of constant energy is assumed. The basic equation

moments, M p i is the fully plastic moment of each pile,

for the verification' is presented as Eg. 4.8.3:

and (hi +1/(3;) is the length between the head and the (4.8.3)

assumed fixed point of each pile. The residual horizontal displacement of a pier can

where R; is the load carrying capacity during earthguake, K; is the design seismic coefficient, and

be

W is the vertical loads including self-weight and

load-displacement relationship during unloading has

surcharge. Ra is given by Eg. 4.8.4:

the same gradient as that during initial loading.

s, = ~2/-1-a -1+8(/-I-a-1)2

Py

(4.8.4)

e is

calculated

on

the

assumption

that

the

The structural behavior of high seismic resistant

the

piers should remain within elastic regions during

ratio of the secondary gradient to the primary

Level 1 ground motions, and it should be controlled

gradient in the load-displacement relationship, and P,

with horizontal displacement, as mentioned above,

is the horizontal force corresponding to the elasticity

during Level 2 ground motions.

limit.

capacity R; in Eg. 4.8.4 can be calculated with

where P-a is the allowable plasticity ratio,

At the elasticity limit, pile-head bending

@Seismicisolation 4-33 @Seismicisolation

The load carrying

e and

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

methods.

bending failure.

Allowable ultimate stage "'0
CO .....

i

Pp

The shear failure should not occur prior to

The properties of piles pushing into or pulling out from the ground should be modeled taken into

P)'

consideration their non-linear behaviors.

c

Lateral

0 N

resistance of the ground should also be modeled as

0

the same way above.

'C

I

Buckling of piles often dominates the ultimate

0

0p

(5!'

state of a pier.

Displacement

may cause local buckling in steel pipe piles: C ma• =

Fig. 4.8.3 f-L. and

Equation 4.8.14 gives the strain that

0.44t / D

(4.8.14)

where t is the thickness of the steel pipe and D is the

e

diameter of the steel pipe. f-La obtained by the result of elasto-plastic analysis as

The moment at the strain of

Either a bi-linear or a tri-linear model can be used for the constitutive law of steel pipe piles.

commonly used dimensions.

Fully

plastic moment Mp , yielding moment My, and their respective curvature ¢>p and ¢y can be given by Eqs. 4.8.8 to 4.8.11. cos(an /2)

p

=

M

My

=

(Jy -N / A)Ze

¢y

=

pa

(4.8.8)

(4.8.9)

My / £1

(4.8.10)

¢p =(Mp-MJrf>y (4.8.11) where M po is the fully plastic moment of the steel pipe without axial force expressed as follows:

«; =Zpfy

(4.8.12)

Zp is the plastic sectional modulus of the steel pipe,

which can be obtained as follows: Zp =~{r3

-(r -tJ}

is not much

different from Mp in Eq. 4.8.8 for steel pipe piles with

shown in Fig. 4.8.3.

M

Cmax

(4.8.13)

where r is the radius of the steel pipe, t is the thickness of the steel pipe, a is the ratio of applied axial force N to yield axial force No (No = A h) when bending moment is not applied, A is the area of the cross section of the steel pipe, fy is the yield strength of the steel pipe, Z, is the elastic sectional modulus of the steel pipe, and EI is the flexural rigidity of the steel pipe. The concrete superstructure is represented by the tri-linear bending moment-curvature relationship. Cracking moment, rebar-yielding moment, ultimate moment should be calculated with appropriate design

@Seismicisolation @Seismicisolation 4-34

5. BASIC PRINCIPLES OF SEISMIC DESIGN AND CONSTRUCTION FOR WATER SUPPLY FACILITIES

JAPAN WATERWORKS ASSOCIATION

5.1

Basic Concept of Anti-Seismic Measures for Water Supply Facilities 5.1.1

General

5- 1

5.1.2

Planning, Designing and Implementation

5- 1

5.1.3

Geotechnical Survey of the Foundation

5- 2

5.1 A

The Employment of Highly Earthquake Resistant Materials and Joints

5- 3

5.1.5

Anti-Seismic Design of Water Supply System

5- 3

5.1.6

Maintenance and Planned Improvements

5- 4

5.1.7

Assumption of Earthquake Damage

5- 5

5.1.8

The Order of Restoration Works and Relationship Between Emergency Restoration Works and Permanent Restoration Works

5.2

53

5- 1

Basic Concept of Anti-Seismic Design

5- 5 5- 5

5.2.1

General

5- 5

5.2.2

Seismic Motion Levels for Anti-Seismic Design

5- 6

5.23

Importance Ranking of Facilities

5- 6

5.2A

Anti-Seismic Level Which Water Supply Facilities Must Maintain During and Earthquake

5- 6

5.2.5

Earthquake Effects on Anti-Seismic Designs

5- 7

5.2.6

Sequence of Anti-Seismic Design Works

5- 7

5.2.7

Related Regulations

5- 8

Seismic Motion Input for Anti-Seismic Design 53.1

Anti-Seismic Calculation Methods and Objective Structures

53.2

Seismic Intensity Used in Anti-Seismic Design under the Seismic Intensity Method for Ground Structures (Seismic Motion Levell)

533

5- 10

5- 10

Seismic Motion Level Used in Anti-Seismic Design by the Seismic Intensity Method for Ground Structures (Seismic Motion Level 2)

5.3A

5- 10

5- 11

Seismic Intensity Used in Anti-Seismic Design by the Seismic Intensity Method for Buried Structures (Seismic Motion Levell)

@Seismicisolation @Seismicisolation

5- 15

5.3.5

Design Seismic Intensity Used in Anti-Seismic Intensity Method for Buried Structures (Seismic Motion Level 2)

5.3.6

Seismic Motion Level Used in the Response Displacement Method for Buried Structures (Seismic Motion Levell)

5.3.7

5.3.8 5.4

5.5

5.6

5.7

5-16

5- 16

Seismic Intensity Used in Design of Buried Structures by the Response Displacement Method (Seismic Motion Level 2)

5- 17

Seismic Motion Input Used in Design Using the Dynamic Analysis

5- 19

Geotechnical Surveys, Ground Displacement, and Ground Distortion

5- 19

5.4.1

Primary Subjects of Geotechnical Survey

5- 19

5.4.2

Methods of Geoetchnical Survey

5- 20

5.4.3

Soil Liquefaction and Lateral Spreading

5- 21

5.4.4

Ground Displacement and Ground Strain Caused by Liquefaction

5- 21

5.4.5

Ground Strain at the Incline of Artificially Altered Ground

5- 21

5.4.6

Reduction in Reaction Force and Ground Friction Force due to Soil Liquefaction 5- 22

Soil Pressure During an Earthquake

5- 23

5.5.1

General

5- 23

5.5.2

Calculation of Horizontal Soil Pressure During an Earthquake

5- 23

5.5.3

Calculation of Vertical Soil Pressure During an Earthquake

5- 23

5.5.4

External Pressure due to Lateral Spreading

5- 24

5.5.5

Buoyancy Generated by Soil Liquefaction

5- 24

Hydrodynamic Pressure During an Earthquake and the Water Sloshing

5- 24

5.6.1

Hydrodynamic Pressure During an Earthquake

5- 24

5.6.2

Water Sloshing

5- 25

Safety Check

5- 25

5.7.1

Combination of Loads

5- 25

5.7.2

Safety Check of the Structures Fabricated with Steel, Concrete, etc

5- 25.

5.7.3

Safety Check of Pipeline in their Anti-Seismic Calculations

5- 26

5.7.4

Safety Check ofthe Foundation Ground in its Anti-Seismic Calculations

5- 26

5.7.5

Safety Check of Foundation, Earthen Structures and Retaining Wall in Anti-Seismic Calculations

5.7.6

5- 27

Safety Check in Anti-Seismic Calculations in Consideration of Critical State under Seismic Motion Level 2

@Seismicisolation @Seismicisolation

5- 27

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

5. BASIC PRINCIPLES OF SEISMIC DESIGN AND CONSTRUCTION FOR WATER SUPPLY FACILITIES JAPAN WATER WORKS ASSOSIATION 5.1 Basic Concept of Anti-Seismic Measures for

of the disaster must be properly assumed; the reinforcement works must be implemented based

Water Supply Facilities

on rational anti-seismic designs; and everyday

5.1.1 General

facility maintenance must be carried out with For developing anti-seismic measures in water supply, the following basic plans must be drawn beforehand: (1) Proper

consideration of the anti -seismic measures. In the immediate post-earthquake period, it is

essential to collect quick and accurate information, damage

estimates

before

the

and establish a communication network.

A plan

occurrence of an earthquake, and preventive

must be drown. before-hand for calling out

measures based on such estimates,

personnel for their deployment for initial response

(2) Plans on emergency relief measures to be

activities,

undertaken immediately after an earthquake,

important.

and disaster prevention measures including

During

effective emergency repair works and

which the

are

considered

reconstruction

the

most

period,

in

coordination with the police and fire departments

(3) Detailed plans on the organization for the

and under the rescue operations provided by other

implementation of permanent restoration

water utilities, an emergency water service must

works in the period from temporary works

be implemented until restoration of regular water

in above (2) to the completion of the

supply; restoration works must efficiently be

permanent works

implemented and manpower and materials and equipment required for such activities must be

The underlying goal of implementing anti-

procured.

seismic measures for water supply systems is to save human lives. established

To this end, a plan must be

to

provide

well-balanced,

comprehensive measures to be implemented under adequate

mutual understanding

organizations, during:

5.1.2 Planning, Designing and Implementation

with

related

(1) the pre-earthquake

For preparation of plans and designs of water supply sufficient

facilities

and

their

implementation,

consideration should be given

to

period; (2) the immediate post-earthquake period;

earthquakes in accordance with various conditions

and (3) the reconstruction period.

in which the water utility is actually situated.

In the pre-earthquake period, the potential scale

For important facilities, their structures must be

@Seismicisolation @Seismicisolation 5-1

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

rationally designed with adequate consideration to

January, 2000

carried out.

the effects from earthquakes. The construction of water supply facilities must

For the construction of the water supply

be so implemented that the water supply system as

facilities, it is essential to that a good ground site

a whole retain as much capability to do water

be chosen.

service even though the system has sustained

construction of key facilities such as water intake

certain damage.

facilities, reservoirs, delivery facilities, treatment facilities,

Water supply facilities are fundamental to the infrastructure supporting a city and to the lives of the city's citizens.

This is particularly true for the

service

reservoirs,

and

main

sending/receiving lines. The power of an earthquake's force on building

For earthquake disasters,

differs greatly depending on various ground

maximum effort to develop countermeasures must

foundations, even ground foundations in the same

be taken in order to insure that the water suppiy is

region.

In addition, the scale of an earthquake's

protected.

motion

may

This is true regardless of the size of

the facility.

also differ, depending on

the

topographical and geological differences of a

Restoration of emergency water supplies is crucial immediately after an earthquake disaster.

particular region. For

the

construction

of

key

facilities,

Implementation and execution of an effective

architectural designs for main buildings and their

reconstruction plan must be applied in conjunction

foundations must be based on data gathered by a

with earthquake countermeasure upgrades.

detailed survey of ground conditions.

In order to implement and execute adequate

plans

for

different

distribution

facilities,

examination of local earthquake records and accurate predictions and .estimates of future

These

detailed surveys of the construction site must include an analysis of the site's dynamic behavior during an earthquake. When: the ground conditions are not the most

earthquakes based on changes in the earth's crust

desirable,

improving

(from geological surveys) must be completed.

substructure work or additional slope stabilization work must be applied.

5.1.3 Geotechnical Survey of the Foundation

the foundation

through

Preventative measures,

such as the use of flexible structures which respond to ground 'floating' or displacement

It is desirable that water supply facilities are founded on location where the foundation is firm and the landscape is stable.

during an earthquake, must also be used. For ground foundations in areas with high

Prior to the

ground water levels, such as sandy soil (which

construction of specially important facilities a

easily generate ground Fluidization), suitable

careful and detailed geotechnical survey must be

measures must be adopted.

@Seismicisolation @Seismicisolation 5-2

These methods

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

include flexible ground structures that absorb

be used.

ground displacement

capable of absorbing earthquake displacement

and

reinforced

ground

In addition, flexible materials that are

foundations.

may also be used to avoid structural damage.

5.1.4 The Employment of Highly Earthquake

5.1.5 Anti-Seismic Design of Water Supply

Resistant Materials and Joints

System

For construction of main water supply facilities, earthquake resistant materials should be employed

For anti-seismic design of water supply systems, the followings are prerequisites:

in structurally important locations.

1) Earthquake damage is localized

For water containing facilities,

as much as

possible.

structures,

which can absorb structural strain and abate stress,

2) The damage is easily repaired.

must be designed with the provision of earthquake

3) Measures, which will prevent secondhand

resistant

joints,

which

absorb

expansion,

disasters as a result of an earthquake, must

contraction and distortion must be provided

be provided. To meet

between interfacing structures which may move,

these

conditions, redundancy in

when an earthquake occurs, and leave relative

important facilities,

displacement.

systems, grouping of such systems, separation of a

interconnection of block

pipe network into blocks, and installation of Underground pipelines will bend as a result of the ground earthquake.

displacement

produced

by

emergency cut-off valves must be implemented.

an When

Such displacement tends to escalate

water conveyance

and

distribution

in areas where the geography or topography is

pipelines receive earthquake damage, the water

subject to

supply in an entire distribution area may be cut off

sudden

change.

As

a

result,

connections between the structure and related pipes are subject to great distortion.

ad severe conditions may result. When the system of water conveyance pipelines

This

distortion results from the difference between the

is

rigidity of the structures and the related pipes.

In

distribution of water may be cut off when one

addition, the alteration of fluid ground also

portion of the system is cut off or out of service.

produces irregular and uneven ground surfaces.

Therefore, it is desirable to have a system which is

This results in movement and distortion of

capable delivering water even after sustaining

structural bulkheads.

damage.

On such ground, flexible,

interconnected,

the

transmission

and

Using an interconnected system with

capable of absorbing the

different functioning lines is the most effective

displacement generated during an earthquake must

method of supplying water when an earthquake

anti-seismic joints

@Seismicisolation @Seismicisolation 5-3

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

disaster occurs.

This method is also effective for

responding to other common disasters and for providing raw water for regular usage. to other water works

neighboring vicinities.

facilities

Positive anti-seismic diagnostic inspections in accordance with this manual must be conducted. Facilities with low anti-seismic ratings must

It is desirable to connect the main water supply pipeline

January, 2000

undergo improvement works through planning.

in

In order to minimize the

Planning upgrades to existing water works

damage during an earthquake, construction of

systems (in order to make them more earthquake

pipeline networks must take into consideration the

proof)

following issues:

diagnosis.

1) Minimizing the range of water delivery failure

existing

must

utilize

competent

anti-seismic

Such diagnosis in necessary for facilities

in

order

to

execute

after an earthquake by adequately spacing

reinforcement or renovation.

gate valves in the pipeline network, making

perform diagnosis, a water works system must be

the distance between them

broken down, with each facility being categorized

the shortest

First, in order to

and listed in order of its importance.

possible.

Second,

2) Limiting the depth of underground pipes in

initial diagnostic inspections must be conducted

order to insure that they are not buried too

and the priority of work must be decided upon.

deeply. In addition, properly locating access

Third, improvements or reinforcement must be

and work station doors in the facilities to

proceeded with.

make restoration work swift and easy.

To create anti-seismic water work facilities,

3) Using preventative measures, such as setting

design and execution must be carefully carried out.

gate valves both in back and in front of a pipe

After completing construction, constant inspection

when the pipe crosses over a railroad or a

and maintenance of the facility must be carried

large river and installing chlorine neutralizing

out.

devices.

and maintenance must be set and routinely

These preventative measures must

be utilized because damage to a water work facility may generate secondary damage to

To fulfill this purpose, listed inspections

followed. For the improvement of the existing facilities,

important public and private facilities or to

earthquake resisting

measures

neighboring residences.

aimed at the prevention of numerous, everyday accidents must be taken.

5.1.6 Maintenance and Planned Improvements

and measures

These improvements

must be carried out after a comprehensive and integrated evaluation.

Adequate inspection and maintenance of water supply facilities must be undertaken at a basis to insure their anti-seismic integrity.

@Seismicisolation @Seismicisolation 5-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

5.1.7 Assumption of Earthquake Damage Each part of water supply facilities must be Based

and

designed to retain its respective capacity even

magnitude of damage to the water supply systems

after an earthquake with the design intensity of

as a result of an earthquake, plans for emergency

seismic tremor.

water

on assumptions

service

on the

and

repair

established.

To

facilitate

information

networks,

mobilization

plans,

type

works

must

such

works,

The more important the facility, the more the need for such consideration.

manpower

For anti-seismic design of facilities, the design

cooperation

method must be employed, which is suitable to the

system must be established; and comprehensive

characteristics of respective facilities and the

preparation

nature of their founding and surrounding soil.

must

emergency

be

and be

mutual

made

for

stockpiling

materials and equipment required for restoration works, preparation of complete sets of facility drawings

and

decentralization

of

5.2.2 Seismic Motion Levels

their

Design

management. For an anti-seismic design,

5.1.8 The Order of Restoration Works and Relationship Restoration

Between Works

and

two different

magnitudes of intensity must be employed:

Emergency

Seismic Motion Levell, which has a return

Permanent

probability of once or twice in the service lie of the facility, and Level 2, which has a smaller

Restoration Works

probability than the former but is greater in As a general rule, restoration work after an

magnitude.

earthquake disaster should start with raw water intake facilities, followed by, in sequence, water

Seismic Motion Levell (Ll) is equivalent to

treatment facilities, transmission and distribution

the conventional seismic motion level set by many

facilities, and finally water service connections.

civil

To realize early resumption of water service, sufficient consideration should

be made

engineering

construction

guidelines.

Seismic Motion Levell may be generated once or

on

twice during the in service period of a structure.

relationship between emergency restoration works

Seismic Motion Level 2 (L2) is the equivalent of

and subsequent permanent restoration works.

the seismic motion generated in areas with faults or areas with big scale plates bordering. inland

5.2 Basic Principles for Anti-Seismic Design

areas, such as the earthquake which struck the southern area of Hyogo Prefecture in 1995.

5.2.1 General

The probability of a water works system

@Seismicisolation 5-5 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

experiencing Seismic Motion Level 2 is very low.

It is not realistic to demand the highest level of

Nevertheless, the influence of a Seismic Motion

earthquake durability every component of a water

Level

supply system.

2

enormously

great.

seismic

motion

planning for a facility, the facility's degree of

parameters for a fault may be used to search for an

significance must be categorized into either Rank

appropriate location. If a seismic motion caused

A or Rank B.

by active faults is clearly understood using

importance must be combined with the two

preliminary surveys, a construction design can be

Seismic Motion Levels, Level 1 and Level 2.

However,

is

considered

information

on

When implementing anti-seismic

In addition, the degree of

Through these combinations, it is possible to

directly evaluated.

create different designs with different anti-seismic

5.2.3 Importance Ranking of Facilities

capabilities.

Refer to 5.2.1 (general concept) and

5.2.4 (anti-seismic levels for water works facilities In principle, for planning anti-seismic design of

water supply facilities, they must be categorized

during an earthquake). The

significant

degrees

are

decided

by

individual work groups, based on their own

into two: (1) facilities at a high level of importance

judgment, experience, locallspecialized reasoning, and consideration of local disaster prevention

(Rank A), and (2) other facilities (Rank B).

programs.

Factors effecting a facility's degree of

Each water utility must sort the Rank A

significance are grouped in two categories: those factors

system, and with consideration to the following

influence non-water works facilities and those

conditions:

factors

1) Facilities which possess the potential to

which,

which

during

may

an

effect

earthquake,

may

facilities based on the actual position of their

the

conventional

functions of awter works facilities.

generate serious secondary disasters. 2) Facilities located up stream of water supply

5.2.4 Anti-Seismic Level Which Water Supply Facilities Must Maintain

system. 3) Main facilities which do not have backup

During an

Earthquake

facilities. 4) Feeder mains to important facilities. 5) Main facilities which are difficult to restore

Water supply facilities should maintain either one of the following anti-seismic standards, which are set by combining the Seismic Motion Level

if damaged 6) Facilities which will become the center for gatheringinformation during a disaster.

(Ll and L2) and the importance ranking (Rank A and Rank B) of the facilities.

@Seismicisolation @Seismicisolation 5-6

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

ground located above an active fault, must be given sufficient consideration due to the potential for disaster.

In particular, new housing on slopes

which have been artificially altered are especially subject to ground distortion and displacement generated by a Seismic Motion Level 2. \ Indhdd:u~r

•

fa¢lllM".Q~Y

··r~;"t~H$p:t; ,Islil~~ d~~:g#!!'l:rtd

rllil'llktl I$ayt\4l:b¢ahl~

t\)$j;;nltJan, 'B~kt

This earth load stress can be evaluated using methods based on the response displacement method. There are two types of hydraulic water force: one which exerts inertial force directly against a

r~t4rnHi:ln

facility

?¢1I$ibl¢.

and

one

which

exerts

secondary,

osciliating force on the surface of free water. Facilities 5.2.5 Earthquake Effects on

Anti-Seismic

Designs

abut

reservoir

structures,

underground water storage tanks, dams, or water intakes receive dynamic water pressure during an

For anti-seismic design, the following effects of earthquake must be taken into consideration: 1) Displacement

and

distortion

of

the

foundation soil during an earthquake, 2) Inertial force owing to the weight of structures, water

pressure

during

earthquake. facilities

As a result, the design of such

must

take

into

consideration

the

influence of this pressure. The effects of surface oscillation in water on a structure must be determined by analyzing the oscillation characteristics of a structure and the frequency of surface water.

3) Soil pressure during an earthquake, 4) Dynamic

which

an

earthquake, 5) Water surface sloshing, 6) Lateral soil movements due to liquefaction of the soil, and 7) Soil distortion on a slope of reclaimed land. Facilities which are built on ground that is clearly subject to rapid/dynamic change, such as ground subject to horizontal, fluid displacement or

5.2.6 Sequence of Anti-Seismic Design Works As a general rule, anti-seismic designs of water supply facilities must be carried out in the following order: 1) Selection of the construction site, 2) Geotechnical survey at the site 3) Selection of the type of structure and the study

on

geotechnical

foundation,

@Seismicisolation @Seismicisolation 5-7

conditions

of

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

4) Anti -seismic calculation, 5) Examination of anti-seismic level

Figure 5.2.1 illustrates the method for antiseismic calculation.

This method may differ

according to the structural characteristics and ground conditions involved.

The appropriate

calculation. method must match the structure's propose and condition. A facility belonging to Significance Rank B must designed by matching it to Seismic Motion Level 1.

Depending on the facility's necessity,

evaluation under Seismic Motion Level 2. must be made.

5.2.7 Related Regulations

When designing water supply facilities, existing laws and related regulations whichever applicable, must be followed.

In addition, it is desirable that

technical standards established by institutions or associations are followed.

@Seismicisolation @Seismicisolation 5-8

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

S

TAR

T

SELEcrION OF CONSTRUcrION SITE DECISONOF SIGNIFICANT RANKING OF FACILITIES

SOILSURVEY

STRUcrURE DESIGN ANDl'KAMiNG

STATIONARY LOAD CALCULATION

ANTI-SEISMIC CALCULATIONS FORSEISMIC MOTIONLEVEL 1

No

ANTI-SEISMIC CALCULATIONS FORSEISMICMOTIONLEVEL2 No No

Yes

E

N

D

fiGURE· 5.2.1 ANTI-SEISMIC STRUcrURE DESIGNORDER

@Seismicisolation 5-9 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

5.3 Seismic Motion Input for Anti-Seismic Design

dynamic analysis method must be applied when required.

5.3.1 Anti-Seismic Calculation Methods and

For an anti-seismic design of a massive, partially buried structure (such as a settling basin),

Objective Structures

the seismic intensity method may be used. 1. The following are standard anti-seismic design methods to be applied for water supply facilities.

Their selection must be based on the

structural nature of the objective structures and other factors.

5.3.2 Seismic Intensity Used in Anti-Seismic Design

under the Seismic Intensity

Method for Ground Structures (Seismic Motion Levell)

Depending on the structural nature and special subsoil conditions, the result of calculation by

1. The horizontal seismic intensity to be used for

means of either 1) or 2) must be cross-checked

design or structures on the ground surface

with that obtained by mean of 3).

shall be determined as follows:

1) Seismic intensity method

K h1 ::::: C, . K h01

2) Response displacement method

Where:

3) Reference to the

results

by

dynamic

analysis

(5.3.1)

Cz : Region-specific correction factor. Values are 1.0-0.7.

2. For ground structures, an anti-seismic design.

K h01 :

Standard

horizontal

seismic

must be implemented using the seismic intensity

intensity at the center of gravity of the

method.

structure.

Because the effects of inertial force and

dynamic water pressure, in the case water levels

Values are shown in Table

5.3.1 by the type of subsoil.

are full, cannot be neglected, verification of the

The value of KhOl shall be set at 0.16, 0.2,

safety, using the dynamic analysis method, is

and 0.24 for ground type I, IT, and ill

recommended after the seismic intensity method

respectively.

is applied.

2. Ground types for an anti-seismic design must

3. Buried structures must be designed using the seismic

intensity

method

displacement method.

or

the

response

For the anti-seismic

design of a structure whose movements are

be classified based on proper period obtained by the equation 5.3.2.

foundation conforms to the ground surface, the ground type must be Type I.

complex at the Seismic Motion Level 2, to verify

~..................................

the results calculation using the seismic intensity method or the response displacement method, the

If the base of the

Where:

@Seismicisolation @Seismicisolation 5-10

(5.. 3 2)

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

TAlltE

}'(n$T.rj,'"PE•• qltOUNtJ··O'il",i!;2)·.ViHEEE··TaXS·THg·. NKl'LlRALPERJfJDOW THEGROU~l1(lt~

TG: Proper period of ground(s)

layer.

Hi: Thickness of the I th stratum (m)

either Type I ground or Type II ground.

Vsi: Average elastic wave velocity (rills)

Instead, Type II belongs to either diluvial or

Type II ground does not belong to

alluvial

categories.

The

alluvial

ground

3. Should the vertical seismic intensity (K.vl) be

mentioned here includes new sedimentary

taken into account, the following formula

layers created by landslides, landfills, and

shall be used.

other weak ground.

The Diluvial layers

mentioned here include hardened sandy soil layers and layers of boulders.

1. The behavior of water works in reaction to a

5.3.3 Seismic Motion Level Used in Anti-

seismic motion is dependent on factors such

Seismic Design by the Seismic Intensity

as the earthquake's strength, its periodic

Method for Ground Structures

characteristics, its duration, the ground type,

(Seismic Motion Level 2)

the type of structure involved, the type of foundation,

etc..

Standard

design

for

1. Horizontal seismic intensity (K h2 ) used for

horizontal seismic intensity takes these factors

anti-seismic design based' on Seismic' Motion

into account.

Level 2 shall be determinedas follows:

2. Ground classification is used to determine the horizontal seismic intensity value (Kh1) on a construction

design,

using

the

seismic

KhZ = C, . K hoz · · · ·

(5.3.3)

Where: Cz : Structure specific factor, which must

intensity method.

properly be determined based on the

As a "rule of thumb," Type I ground is made

magnitude of diminution due to the

up of ideal diluvial ground and a proper rock

response of the

bed.

Type ill ground is considered poor

ground and is located at or around the alluvial

structure and

the

capability of plastic deformation of the structure.

@Seismicisolation @Seismicisolation 5-11

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

--_.. .•. "

January, 2000

lAn'lI:.5,;;l;:~ tJ:RPE~LIM:IT.YP:i;.I.JE.··O~'.THE • STAN[DRD··:Eii€iE1Z0NTAL•• SEIS'MIC•• ·rWTENSI':fTJRtiL DESIG1\!.OJi'~OY$GROtJ'l'fU STRUttt'tJ.R$t$ElSMlCrNTENSl'1'Y$;1B:T.HOP)

I

,.~~~----.,..

GROUNtlT'l"BE

··'1'YrE·"j·· ['ra~D;2J·

...

..w

J£ho2vPJ.;"tt"EAGP-,lNST STRl1C)",f'UP,;Jl:.J.. NNl'tJ1't.4.L 'f'BBIDT{Sl

'1'<0,2

.... ,....

'O~·IT'l·G'":r'~'T'tl."r"·'1\.f:,,'\:·~t"~:;4-''f''':

;~;~';~~;~~~:ir;~;'; • .

~C;;i¥E\ZB;;;~KkQ!l'~030 "'··..'''"..,,,,.··'' 1.• .• •

T
1"Y?EIlKhM=~.lSi)1'Q,aC7 [0;2&1'o<05J

O,.z;G.'1'';;l.l)

1..0<:'1'

J£hoz==·l)}

KM2=LOOO·f" lAM

1'n:.:~~'r:.=. ::_~:~.~t.q:_::~.-·.:0.'~S::l5

'H;,·:]'::f".....

B:O\VEVER; .·KhC;;,~(Ulfl

""-·.."1.. .

'··...... 'O;2$!1;i'~1

...'

. .. KhG2= 1.4

1..0<.'1'

j

1{h(;~""lAQ(J1'__ lA(I~

T\?B ill [O,G~'l'GJ

tAanL 5,3:$

I E'OT1'M:tilM.l,£ViililJE{$'EI$M1CMOXION tJil'\tEt. 2) OF'STANtJAt1.D.HOR1Z()NT.~...LS:ElSMlt!lNmENSIt$tY, tiSEnt0:R,GrtOiJNn··S11nU£"tUlte.DESrCN·.?'.a0M·.l'nB.SE~S~~n:c··rtiF:t'ENSln··M)o;'10D .....

,

', . .

--.

..

" .. "': ... : ..... : -... _.,.:.. ~._- ... -.,,.: .... _--.- .... : .... : .. " .. ".:.,: ..... :,.:..:.,.:.: .. ,:': ..... ,'.".:': ......-, .. ,'-''':-···-··:----CC":··

TYP.E 1 Ctc< 0.21 Tt>JS THE 'NAT{JRlib GROUND PERIOD

'.t')9E'·Il·.'OEQVN'P··· t(l,a;~Td
Khoz:

Standard

horizontal

seismic

3. If there is a possibility that the seismic motion

intensity at the center of gravity of the

is largely amplified by such irregularities of

structure, the values

are

ground as the titled ground surface, the design

derived from Table 5.3.2, Table 5.3.3

seismic intensity shall be increased by 1.2

depending on the importance of the

times at maximum.

of which

structure and the soil type. However, KhZ shall not be less than 0.3.

These guidelines were decided to be designed

The standard horizontal seismic intensity

horizontal seismic intensity and acceleration

(KhZ) at the ground surface must be: 0.7

response spectrum by the following methods.

(upper limit) - 0.6 (lower limit), 0.8 - 0.7, 0.60.4 respectively for Type I, Type II, and Type ill subsoil classifications.

2. When taking vertical seismic intensity (K,Z), the equation is:

CD

Maximum acceleration on the ground surface. Using the seismic

motion

records

which can be accepted as based on engineering standards (Kobe University [NS EW]; East Kobe Ohashi [GL-33m, N78E, N12W]; Port Island (GL-83m,

@Seismicisolation @Seismicisolation 5-12

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Nl2E), the ground surface response

(acceleration response value) of the

acceleration

was

ground surface seismic intensity which is

equivalent

linear

derived

by

method

the with

considering the flexibility dependence of of

modulus

CD

transverse

flexibility

gathered

from

approximately

150

checking sites were surveyed at each I, IT, and ill type grounds.

Same as the

(modulus of rigidity) and dampening

design

coefficients based on total 150 points of

described before, the value equivalent to

boring data from the Hanshin District.

the acceleration response value was

Based on these results, divided into three

derived at each 90% and 70% of non-

ground types: Type I ground (TG < 0.2s),

over probability and was shown in

Type IT ground (0.2 < TG < 0.6s), and

Figure 5.3.1 x 1.

Type III ground (0.6 < TG) according to

horizontal seismic intensities, the value

its

the

equivalent to the acceleration response

generation frequency distribution of each

value was set within the limits of the

ground type.

significant ranking

natural

period

and

asked

With this results, set non-

horizontal

seismic

intensity

As same with design

of the facilities.

over probability 90%, 70% and decided

Also, concerning the area which periodic

the upper and lower limit values of the

zone is above LOs (Type ill ground must

surface

For example,

be above 1.5s), on the logarithmic graph

surface acceleration of Type I ground

the spectrum value is shown as a

600-700 gal is equivalent to non-over

'declining straight line.

probability of 70%-90%.

Further, the

spectrum value has set to coincide to the

intensity is derived by dividing ground

maximum ground surface acceleration

surface

value as shown in (1).

acceleration.

acceleration

by

gravitational

Also, 0.1 second

Also, the

acceleration and it is used to measure for

response spectrum shows a result of

anti-seismic structural design by seismic

attenuation coefficient 5% and if the

intensity method and judgment of the

structural attenuation coefficient may

liquidation.

horizontal

differ from this result, the acceleration

seismic intensity must be set between

response value will be assumed to

upper limit value and lower limit value of

reverse proportion of the 2 root of

the significance rank of the facilities.

attenuation coefficient, and correct the

Structural acceleration spectrum.

spectrum value.

Before

This

design

mentioned

generation

frequency distribution of the structural acceleration

response

spectrum

For example, in the

case of an acceleration response value of 10%, it may become 5% of the value:

$/.JW = 0.707

@Seismicisolation 5-13 @Seismicisolation

(times).

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

@ Standard Horizontal Seismic Intensity (K hoz)·

The

standard

horizontal

seismic

intensity (K hoz) is derived from dividing the acceleration response value at the center of gravity of the structure by gravitational acceleration.

Based on the

Figure 5.3.1 the result of formulating upper and lower limit values of the standard horizontal seismic intensity is shown in Table 5.3.2 and 5.3.3. Upper and

lower

limit

values

The are

equivalent to the bore mentioned at 90% and 70% of non-over probability.

This

means depending on the water supplier's judgment on the significant degree of water works facility may reflect choice. @ Design

Horizontal

Seismic

Intensity

(Khz)'

III

The design horizontal seismic intensity

I

(Khz) is derived

by multiplying the

standard horizontal

seismic

intensity

STRtiC1'UK41. NATr.7R.tiJ,.PROPF.l{TY(S) SECQNlJ1"'ll{,,: GROU1:T".
(K hoz) with the structural characteristic

factor

(C s) '

This

structural

characteristic factor (Cs) is derived by multiplying the dampening characteristic (D). Figure 5.3.1 shows the response spectrum derived at with a structural attenuation coefficient of 5%.

If, the

structural attenuation coefficient differs from this value, it can be corrected and D '1

can be derived from this graph.

10.t

1

5T1WCTl:W:AL ~UmJI'.AL PROPEJ'SOr

Further, the D'1 value is considered the

(CtntmtiT,(1'r;"'Hf)u.l>ln:CGN\)'?
structural flexibility factor. Thus, it is

ACCELf.r",~T l'o;~rRES?ONS£S?EC'ffiUI>;(,

HGtlRfS~3+

.

($ElSMICMOT!ON LJ-:V'l::L2)

@Seismicisolation @Seismicisolation 5-14

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

equivalent with factors which are used

(K' hOI) and (K hOl) shall be derived using Table

for

5.3.4.

calculating

seismic

equivalent horizontal

intensity

"Road

in

Bridge

Specifications. " This is defined

as

follows:

The standard horizontal seismic

intensity at the objective depth may be derived by linear interpolation between K hOl and K'hOI' 2. The design horizontal seismic intensity, when applying Seismic Motion Level 1, shall be

D

determined as follows:

= J5

hJh

1) The design horizontal seismic intensity at ground surface

=

D 17

't'lTL

1

s;

~1+417

at the base ground surface

VVUC>1C>

h = attenuation coefficient (%)

s;

=durability ratio

=

Cz

'

K'hOi

Where:

The structural characteristic factors

C; Region-specific correction factor. Values are 1.0-0.7.

(Cs) can only be used for seismic motion Level 2.

Cz ' K hOI

2) The standard horizontal seismic intensity

_

7]

=

They cannot be applied to

seismic motion Level 1 anti-seismic construction design.

3) When considering the vertical design seismic intensity (KVI ) K Y1

5.3.4 Seismic Intensity Used in Anti-Seismic

=

K h/2.

Design by the Seismic Intensity Method

·.·rAJHES,3L4 ·STANDARlJHORlZ0f4i1;j\n.SlEtSMlCIN1""Et4Sfl')'{UEVEDll

for Buried Structures

DEsIG1'j'.·.BiX·.1fJ3,$••$EISMlY.·.INTlU-iSIlT'Y·••METH0D

WH1£ff.jS·.TJSED•. FnR't$i$ .•$tJE~D$TRtle'TURA:E

(Seismic Motion Levell) GROIl'1>J"DTi:PB

1. When

anti-seismic

design

for

buried

..... $TAh1)AiRril-to~6NS1AlmAlU)ffd~f1jtf SmlSM1CIh'1'ENSlT'i': •.• .•

CLASSJElCATlom

structures is carried out using the seismic intensity method, seismic

intensity

the standard horizontal shall

be

determined

employing the standard horizontal seismic intensity (K' hOI) at the base ground level assumed for the design and the ground surface seismic intensity (K hOI)'

The values of

@Seismicisolation 5-'15 @Seismicisolation

.•....·N$l'm"· . .

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

When the buried structures are designed by the

3. If there is possible amplification of seismic

seismic intensity method, the standard horizontal

motion due to such irregularities of the ground

seismic intensity which will act on the buried

as tilted ground surface, the design seismic

structure can be considered as the standard

intensity shall be increased by 1.2 times at

horizontal seismic intensity at the center of the

maximum.

gravity of the structure. Also for the underground standard horizontal

Similar to seismic motion Level 1, the

seismic intensity will be assumed that it will

design horizontal seismic intensity, which acts

change linearly between the base ground of the

on buried structures, may be acceptably

anti-seismic

derived using linear interpolation at the

design

and

ground

surface.

Therefore, it will be obtained the value at the

structure's center of the gravity.

center of the gravity of structure by the linear

design horizontal seismic intensity Kh2 is not

interpolation.

necessarj when considering the structural

Here the

characteristic factor. 5.3.5 Design Seismic Intensity Used in Anti-

tAaH15.35

Seismic Intensity Method for Buried

DESIGNfORHORlZONTAI..>SElSMIG.. rNTENSITY

Structures

{S£lSMiCM01'lONLEVU2JWJ:liCHU$ED FOR mJRISD$t~VC:nJltAL. hEsl(iN(SE1SMIC tN'Tt~i$nY

METHOD

(Seismic Motion Level 2) 1. In the case anti-seismic design for an Buried 't'fPR dMJUND

·t1C
structure is carried out by the seismic intensity method,

the

design

horizontal

seismic

intensity shall be determined by the design

,VHE1'l:E'l'G is GRDlfNf.1.·NA'ttlH.i\L '?ERJOD(s) TYPEll

[O.Z1iil'c
horizontal seismic intensity (K 'h2) at the base ground surface used for anti-seismic design

I

Tl'Ps.m

[t.?~5:,$:T~:J

and the ground surface seismic intensity (Kh2) . The values of (K 'h2) and (Kh2) shall be deri,:ed from Table 5.3.5.

The design horizontal

5.3.6

seismic intensity at the objective depth may

Seismic Motion Response

be determined by linear interpolation between

Level Used

Displacement

in

the

Method

for

Buried Structures

K h2 and K h2 '.

(Seismic Motion Levell)

2. In the case vertical seismic intensity (Kv2 ) is taken into account, shall be set as follows: K V2

=

K h12.

1.

For anti-seismic design of buried structures, whose response characteristics during

@Seismicisolation 5-16 @Seismicisolation

an

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

earthquake are chiefly affected by movements of

surrounding

ground,

the

response

displacement method shall be used.

Velocity response(s) per unit seismic intensity is derived using Figure 5.3.2 according to the

Cross-sectional force, stress, strain, etc.

basic natural period for the ground surface layer.

working on the structures shall be computed

Figure 5.3.2 shows the maximum relative

based on the displacement or deformation of

velocity generated by modeling a system with one

the

ground displacement

degree of freedom for the natural period T G'

amplitude to be generated under Seismic

Reduction of the constant hG (20%) for the surface

Motion Level 1 shall be derived by the

ground layer was accomplished.

following formula at the distance x(m) from

derived value together with seismic records

the ground surface.

expanded the maximum velocity to 1.0 g.

ground.

The

u, (x) = -;-SvTGK~l cos ~ Jr

With this

(5.3.4)

~11

Where,

U h (x): the horizontal displacement amplitude (m) of the ground at the depth x from the ground surface.

Sv: seismic motion velocity response spectrum (cmls) of the ground per unit seismic

intensity. TG : the natural period(s) for the surface layer

1 H) Nt:rtJEAV·.r:'E1HOn.·(l'e)(sJOP·SUl'l.%'iGE e..·I'."~H".E•••• "...,. 2·i CRQtJND ROb NDA'1'HJN F:~·~..f>.".~-",,;j. .. ,",_. ,'" .': , _ ' -" , _.' _." . . " •. < SPEED RE:'H>0NSESFECTRUMfORCONSTRUGT1QUI]E$fOW· i$El$~tlC

M01'JON·LKVE:L2'l

of the ground. K 'h1: the design horizontal seismic intensity at

foundation

ground

surface where

the

5.3.7 Seismic Intensity Used in Design of

design is based (Refer to 5.3.4 Seismic

Buried Structures by

Intensity Used in Anti-Seismic Design by

Displacement Method

the Seismic Intensity Method for Buried

the Response

(Seismic Motion Level 2)

Structures (Seismic Motion Levell))

H: the thickness of surface ground layer (m)

Similar to the case of Seismic Motion Levell,

response

like Buried structures, anti-seismic design of

displacement amplitude is taken into account,

structures whose response characteristics during

the following formula is used:

an earthquake are chiefly affected by displacement

ill

the

1 U v =-U 2 h

case

the

vertical

of surrounding ground, the response displacement

@Seismicisolation 5-17 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

method shall principally be used.

January, 2000

foundation and rock bed surface observations

Cross-sectional force, stress and strain, etc.

within 20 km from the Hyogo fault.

Figure

working on the structures shall be computed

5.3.3 represents the velocity response spectrum

based on the displacement or deformation.

obtained

The ground displacement amplitude generated

spectrum of the ground surface.

under Seismic Motion Level 2 is derived by

judgment was added.

the following formula at the distance x(m)

different kinds of values - 200 cm/s (upper

from the ground surface.

limit) and 70 cm/s (lower limit) - as the

U'; (x)

2

1lX

I

= 7r 2 S; To cos 2H

(5.3.5)

the

U; (x): the horizontal displacement amplitude

response

Engineering

Figure 5.3.3 shows two

The system was

modeled with one degree of freedom for natural Each of these values is

compatible to a probability not exceeding 90% and 70%.

ground surface.

acceleration

maximum response velocity.

periods above 0.7(s).

Where,

The desigu value is increased or

decreased within the scope of the upper limit

Sy: seismic motion velocity response spectrum (cm/s)

from

and the lower limit, according to significance rank of the structure.

[See Figure 5.3.3]

To: the natural period(s) for the surface ground layer. H : the thickness of the surface ground layer (m)

When

the

ground

vertical

response

displacement amplitude Uv is considered, the formula is:

1 U =-U 2 h y

If there is possible amplification of seismic

motion due to such irregularities of the ground as tilted ground surface, the design seismic intensity shall be increased by 1.2 times at

r

10

FA'1'tiJLAiL l"B.RIOD(n:;){flFOR•.S.tJf\.f,....c·~:GR0lJND rPUNDATI0N

maximum.

These records were from the 1995 Hyogoken Nanbu earthquake. These records took into account five wave forms obtained from ground

@Seismicisolation 5-18 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

5.3.8 Seismic Motion Input Used in Design Using the Dynamic Analysis

January,2000

Soil surveys here include all surveys related to topography,

geology,

ground,

and

soiL

Generally, less damage due to earthquakes is The seismic waves used for dynamic analysis

found on good ground, that is firm and uniform

must fit the founding ground surface velocity

ground.

response spectrum is shown in Figure 5.3.3, the

be required to be built on such stable ground.

ground surface acceleration response spectrum is

The following are not good ground conditions:

Therefore, water works facilities must

observed in the vicinity of inland faults such as

CD ®

ones caused by the 1995 Hyogo-ken Nanbu

@ Slopes;

earthquake.

@ Different soil layer interfaces;

shown in Figure 5.3.1, or the seismic waves

Sliding; Mountainous slope toes and slope shoulders;

@ Weak ground; When selecting seismic wave observation sites for dynamic analysis against seismic motion Level 2, the ground types for the sites must be well considered.

@ Reclaimed ground;

(J) Ground subject to fluidization or lateral floating during an earthquake.

In particular, whether or not the

observed seismic wave response spectrum is similar to the design response spectrum in Figure

5.3.1 must be check. The maximum value of the inputted seismic wave for dynamic analysis must be for a ground surface that is 6,000 - 7,000 cm/s"

1. Survey using existing records Rough soil conditions at the facility construction site can be studied. 2. Common soil survey Study of required items for construction

and 400 - 600 cm/s 2 against the first ground type,

planning and

second ground type, and third ground type.

facilities will be conducted.

Similarly, the base ground must be 400-500 cm/s".

earthquake resistance of

3. Survey of dynamic properties of soil The physical properties of soil

5.4 Geotechnical Surveys, Ground Displacement,

represented by the N value.

are

Cohesion, C,

and the internal friction angle 1>, are for

and Ground Distortion

static behaviors.

5.4.1 Primary Subjects of Geotechnical Survey

However, the velocity

effect of stress to the constants of the ground and the effects of stress during an

For

anti-seismic

design

of water supply

earthquake must be discussed.

For these

facilities, geotechnical survey at locations, where

studies, the following constants shall be

construction works are situated, depending on the

determined.

importance of the facilities.

@Seismicisolation 5-19 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODESIN JAPAN

1) Modulus of dynamic distortion;

January, 2000

The geotechnical survey methods shall be based

2) Attenuation coefficient;

on the following:

3) Dynamic poison ratio;

1. Follow the standard or criteria which are set

4) Dynamic shear strength.

forth in the Japan Industrial Standard (JIS)

4. Survey of dynamic physical properties of

or the Japan Geology Society (JGS) for

the ground

various survey and laboratory test.

1) Velocity of elastic wave;

2. In principle, measurements shall be actually

2) Ground predominant period; and

conducted for dynamic soil constants and

3) Other.

dynamic physical properties of the ground. When it is impossible to do so, they may be obtained from the results of other surveys.

5.4.2 Methods of Geotechnical Survey

Vfu-lOliS

test-methods and soil Constants related

to ground and soil are shown in Table 5.4.1.

o

01

~.

iO fJ

i

10 .10

o

o Jh7Klli/OR.BODY StAWIC'1'ESTS UNIJl...'t.J'AL.C(tMPRESSI0t'i SMfPtt"1C•.'l'E);.r·· ·.·.Tlo:;sT'l"~lA.."{lAX. . CDM:?RESSrO.NTh:S't~ •. DlRECtSflEAroNGT$tirt ..... ·lixiNA.lV!lC'l'Rb\XIAt

.",.",_.."-_ _....;..

j

. COMPR~S$!ON'T:m$T .

i

o

··.·PYNi><MIC••stMPLl:l.·

. sHE~il:lNGT£b'"1) •..RE.so.N.• AJ.'l·1'EST ~..,,.•

O~.!stHE't!i:ST.:tl:ES't.r..;T •.PI~tC'fl,;';{REQ~rES
O·M,A1U{.mlNPH~EGTW;'.REQ!1ES'!Eb··oa··tJSES··!N·.PtSCtlSS10N

'ON:l..;Y·':l'HEJ~ONG1'1'tml.N¥'.L ""~'l':.rE. S\?EEO\'tIl:;.L.BRDERrilED

··{)NLY'THES.H!EAR!NG ELAS'I'ICCOEl1'FICIEN'T:\'IlLLJUlDERr\I1i:!)

@Seismicisolation @Seismicisolation 5-20

o

o

o o 0 .:

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

5.4.3 Soil Liquefaction and Lateral Spreading

January, 2000

displacement and strain due to such lateral spreading must be taken into account.

Liquefaction of the soil is a phenomenon whereby sandy soil loses its strength and rigidity

Large-scale lateral movement of a revetment,

rapidly and the whole body of soil behaves like

caused by an earthquake, is possible in reclaimed

liquid.

areas.

Since the soil liquefaction causes damage to

This occurs when the tensile strain of the

ground, in a direction perpendicular to revetment

water supply facilities such as flotation of buried

line, is in the range of 1.2 - 2.0%.

structures, and subsidence and/or tilting of other

shows the frequency of ground strain occurrence

structures,

100m from the revetments in the Hyogo-ken

anti-seismic

design

with

due

consideration to such aspects must be provided. In the ground near the embankment bordering a

Figure 5.4.1

Nanbu and Niigata earthquakes. Based on this distribution, the probability was calculated and ~~

reclaimed land and slopil1.g ground, a phenomenon

tabulated in the Figure.

of lateral movements, of liquefied soil may occur

1.2 - 2.0% was obtained from the 70% and 90%

and may damage foundation of structures and

non-exceeding probability.

water mains.

For the examination of anti-

design of underground pipelines, an appropriate

seismic safety of such lateral soil movements shall

ground strain may be selected within this range,

be taken into account.

depending on the pipeline's degree of importance

Judgment on the

possibility of soil liquefaction shall be made if the

ground strain value of

For anti-seismic

and difficulty in restoring.

soil possesses all the following conditions: (1) Saturated soil layer thinner than 25m from the ground surface.

5.4.5

Ground

Strain

at

the

Incline

of

Artificially Altered Ground

(2) Average grain size Dso is less than lOmm. (3) Content by weight of small grain particles

In the case, the surface of artificially altered

(soil grain size of less than 0.075mm) is less

ground (such as in a housing estate) is inclined,

than 30%.

displacements downwards along the slope may occur during a severe earthquake with such

5.4.4 Ground Displacement and Ground Strain

seismic intensity as the Seismic Motion Level 2. The effects of such ground displacement must

Caused by Liquefaction

be taken into account for anti-seismic design of In the ground near the embankment or sloping

buried pipeline.

ground, there is a possibility of lateral spreading due to liquefaction.

For anti-seismic design

buried

water

pipelines

for

supply,

ground

Ground

strain

for inclined ground

(non-

fluidized) during the Seismic Motion Level 2 is

@Seismicisolation 5-21 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

·0$1% Q)7Q$4

filt'5lJRE ·,s.4L..l C~0~*bitg#Stka. brST(n~!T1QN F'RtQttt>CY bl$TRlIHPTlQNNBAR BFL1;l4B;Att

:<EJCHBORHOQDARE:A

within a range of 1.0 - 1.7%.

and foundation structures is reduced when ground

Anti-seismic design for buried pipelines for the Seismic Motion Level 2 must be taken into account.

The types of ground subject to

is fluidized.

Reducing ground reaction greatly

effects

behavior

the

earthquakes.

of

structures

during

The ground reaction coefficient

investigation are: valleys filled with ground,

and ground friction force must be reduced as

ponds, and embankments with more than 10%

shown in Table 5.4.2.

average slope.

according to the degree of fluidization.

5.4.6 Reduction in Reaction Force and Ground

Friction Force due to Soil Liquefaction If there is a possibility of soil liquefaction, the ground reaction force coefficient for the design of buried pipeline and foundation structures must be reduced according to the degree of liquefaction. Ground reactions which act on buried pipelines

@Seismicisolation 5-22 @Seismicisolation

This must be done

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

ACAU1Sl'•• LIQJJlW1>H;nON

ntlrt:H1I'B0M GThOlJ:ND S'l;JE'

GEMEHAtllJN

f'AC~m}

SCOP2bF$AJ:'WtYRAT!t'}j"'L

'~=-,,~---'---;""'-+~

January, 2000

,.;..,.:.........=-"f-..---~-+=-"=-"~.-.-+-- . . . . . ~........., . . . . . _=-"~

5.5 Soil Pressure During an Earthquake 5.5.1 General

For anti-seismic design of structures attached to the earth, the soil pressure during an earthquake shall be determined according to the following: 1. The horizontal soil pressure during an earthquake must be derived by the MononobeOkabe soil pressure formula. 2. In case vertical seismic intensity for the surcharge

load

during

an

earthquake,

the

surcharge load must be multiplied by (1 +Kv ) . 5.5.2 Calculation of Horizontal Soil Pressure During on Earthquake For calculation of the horizontal soil pressure during an earthquake, the cohesiveness of soil, if

5.5.3 Calculation of Vertical Soil Pressure During an Earthquake

any, shall be taken into account. The vertical soil pressure on buried pipeline 1.

Soil

calculation.

classification

for

earth

pressure

For soil classification and for

must be calculated taking into account, the influence of lateral friction, if any.

various numerical soil values of earth pressure, refer to Table 5.5.1.

@Seismicisolation @Seismicisolation 5-23

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

5.5.4

External

Pressure

due

to

Lateral

5.5.5 Buoyancy Generated by Soil Liquefaction

Spreading ill case the liquefaction resistance coefficient,

On the ground, which may be subject to lateral

FL , refer to Explanation of 5.4.3 (Soil Liquefaction

spreading due to liquefaction, anti -seismic design

and Lateral Spreading) of soil surrounding such

of foundation structures must be carried out with

buried structures as pipeline is smaller than 1.0,

consideration to the external force caused by such

the safety of the structure in regard to buoyancy

spreading.

In this case, the influence of inertia

shall be examined.

force from the super-structure and the base structure don't have to be considered.

Specific gravity of fluidized soil is 18 - 20 kN/m3 (1.8 - 2.0 X 10-3 kgf/cnr').

Great concern about the external pressure

If the actual

specific gravity includes the content volume or

created by lateral ground flow exists, especially, with regards to water works facilities built on

it will become smaller than this value and the

suspect ground.

buried structure will have a tendency to balloon.

Anti -seismic structural design

must consider earth and flow pressure.

The upper portion of the non-fluidization layer,

It is shown in the experiments that fluidization

the weight of the road surface pavement materials,

flow pressure (which acts on the buried structure)

and the shearing resistance will usually block out

in the liquefied ground layer is below 30% of the

the

total load pressure.

(Niigata earthquake, etc.) illustrate that floating up

The lateral flow of the external pressure is stated in Figure 5.5.1.

floating

up.

However, past examples

bad broken pipelines or manholes.

Careful

examination is necessary.

5.6

Hydrodynamic

Pressure

During

an

Earthquake and the Water Sloshing

5.6.1

Hydrodynamic

Pressure

During

an

design

of

Earthquake For

anti-seismic

construction

structures that come into contact with water, dynamic water pressure during an earthquake must be considered.

@Seismicisolation 5-24 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Structures which contact water (such as a dams,

January, 2000

sloshing is induced during an earthquake.

The

water tanks, etc.) and are subject to an earthquake

effects of sloshing bring about overflow or impact

must be considered.

pressure against the roof.

These structures receive

dynamic water pressure during an earthquake.

Whether such sloshing cause damage, or not, it

The action of dynamic water pressure during an

depend on the close relationship between the

earthquake must take into account two factors: (1)

natural period of water sloshing in the tank and

whether free surface water is present and (2)

the periodic characteristic of the seismic motion.

whether the complacability of the water can be

The sloshing of water inside of the tank shall be

ignored.

checked by following methods.

Dynamic water pressure action created during an earthquake can be dived into two factors: (1) inertial action which interacts proportionality with

a: Response spectrum method based on the potential theory. b: n wave response method. c: Response spectrum method based on the

secondary dynamic water pressure generated by free surface water oscillation. inertial

force

of

dynamic

Generally, the water

pressure

interaction is more significant and, therefore, will be taken into account by the design.

potential theory. However, when the competent seismic wave has

inputted,

dynamic

response

analysis

is

acceptable.

The action

of surface water oscillation is a supplemental issue

5.7 Safety Check

for dynamic analysis. The complacability of water, with regards to

5.7.1 Combination of Loads

structures like water tanks and water intake towers in water works facilities, can be ignored without creating

problems.

However,

for

Structure safety in anti-seismic calculations

pipeline

must be checked by combining the normal load

structures, the complacability of water must be

(dead weight and live load at ordinary times) and

considered. It is not, an excessive load for the

seismic effects.

design may result. 5.7.2 Safety Check of the Structures Fabricated with Steel, Concrete, etc.

5.6.2 Water Sloshing For anti-seismic design of water tanks, water sloshing must be considered when necessary.

For safety checks of structures fabricated with concrete, steel bars, structural steel pre-stressed concrete(pC) etc., the following related standards

For water tanks with free

surface water,

must be used.

@Seismicisolation 5-25 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Specifications for Highway Bridges (Japan Road Association);

Concrete

characteristics is summarized in Table 5.7.1.

For

either the seismic motion Level 1 or seismic

Standard

Specifications

(Japan

Society of Civil Engineers);

motion Level 2, the pipeline component stress will not exceed the allowable stress of the pipe

Iron Sluice Valve Technology Standard (Iron Sluice Valve & Pipe Society).

materials.

With jointed pipeline structures under

live loads and under ordinary conditions, the jointed component expansion capacity will not

5.7.3 Safety Check of Pipeline in their Anti-

exceed the maximum expansion capacity of the design.

Seismic Calculations

This is the main point for anti-seismic

checking. As a general rule, safety of pipeline during an earthquake must be checked with consideration to

With safety checks against seismic motion

I the strength and flexibility of the pipeline.

under live loads, must basically be below yield A pipeline structure for a water works facility varies in types.

If roughly categorized, the

following two types would emerge:

Distortion, which corresponds with the yield point stress, is:

Here, most of

1. Jointed pipeline structures -

point stress for the pipe component material.

E

=

(J

IE

= 2,400/2,100,000 = 0.11 %

After field condition are completely considered,

the flexibility is dependant on the joint. Here, most

appearances seem better, since distortion of the

of the flexibility is dependent on material the pipe

pipe component is below 23t/D (%) (about 0.15 -

is made of.

0.20)% and the anti-seismic capability can be

2. Continuous pipeline structure -

The anti-seismic calculation method

for the direction of principal buried pipelines is

checked.

described in this edition of the guidelines.

the diameter of the pipe.

Anti-seismic

Level 2, the distortion of the component, even

This method is

considering the stationary free load, is below

based on the behavior of the pipeline. behavior

is generated

through

the

This relative

46tID (%) (about 0.3 - 0.4)%.

capability can be checked.

displacement of pipeline and the ground. The pipelines, which possess the characteristics of (1), are represented by ductile iron pipe.

The

pipeline which possess the characteristics of (2) are represented by steel pipe.

With seismic motion

the

ability is checked using

response displacement method.

Here, t is the pipe thickness and D is

The basic concept

of the safety check on pipelines with these

@Seismicisolation 5-26 @Seismicisolation

The anti-seismic

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

5.7.4 Safety Check of the Foundation Ground in its Anti-Seismic Calculations

January, 2000

so that no plastic yield shall occur until the structures have reached te critical state. 3. For the anti-seismic design based on the

As a general rule, safety of the foundation

critical state, an appropriate safety factor

ground in anti-seismic calculations must be

must be employed with reference to the

checked in accordance with "Supporting Ground

critical displacement.

and Allowable Bearing Force".

5.7.5 Safety Check of Foundation, Earthen and Retaining

wall

in

Anti-Seismic

Calculations As a general lule, safety check of foundation,

earthen structures, and retaining wall in antiseismic

calculation

accordance

with

must

be

"Anti-Seismic

checked

in

Calculation

Methods for Foundations" and "Anti-Seismic Calculation Methods for Earthen Structures and Retaining Wall".

5.7.6 Safety Check in Anti-Seismic Calculations in Consideration of Critical State under Seismic Motion Level 2 Safety check in anti-seismic calculations in consideration of critical state must be carried out using the following rules: 1. Based on the results of proper analyses or testing the anti-seismic safety of structures must be checked with reference to the critical state found in such analysis and testing. 2. In anti-seismic design based on the critical state, tenacity of structures must be secured

@Seismicisolation 5-27 @Seismicisolation

@Seismicisolation @Seismicisolation

6. RECOMMENDED PRACTICES FOR EARTHQUAKE RESISTANT DESIGN OF GAS PIPELINES (DRAFT)

JAPAN GAS ASSOCIATION 6.1

Introduction

6- 1

6.2

High-Pressure Gas Pipelines

6- 1

6.3

6.4

6.2.1

Basic Policy on Earthquake-Resistant Design

6- 1

6.2.2

Earthquake-Resistant Design against Seismic Motions of Level 1

6- 3

6.2.3

Earthquake-Resistant Design against Seismic Motions of Level 2

6- 4

Medium- and Low-Pressure Gas Pipeilnes

6-17

6.3.1

Basic Policy on Earthquake-Resistant Design

6-17

6.3.2

Earthquake-Resistant Design Procedure

6-17

6.3.3

Design Ground Displacement

6-17

6.3.4

Ground Condition

6-19

6.3.5

Pipeline Capability to Absorb Ground Displacement

6-20

6.3.6

Allowable Strain and Allowable Displacement

6-22

Appendix

6-24

6.4.1

Earthquake-Resistant Design ofHigh-Pressure Gas Pipeline

6-24

6.4.2

Improvement of Earthquake Resistance of Pipelines

6-29

6.4.3

Block System of Pipeline Networks

6-29

@Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

6.RECOMMENDEDPRACTICESFDREARrHQUAKE-RESfSTANTDESIGNOFGASPIPELINES (DRAFT) JAPAN GAS ASSOCIATION 6.1 Introduction

Design of High Pressure Gas Pipelines, be-

The presently used "Recommended Practices

cause its official issue may be after the publi-

for Earthquake-Resistant Design of Gas Pipe-

cation of the English version, it is hoped to

lines" was established as the recommended

recognize it as based on a "Draft" of the revised

practices for earthquake-resistant design of

recommended practice.

high-pressure gas pipelines

(See Appendix

The presently used Recommended Practices

6.4.1.) and medium- and low-pressure gas

for Earthquake-Resistant Design of Gas Pipe-

pipelines in March 1982, after the Miyagiken-

lines has not been revised in the medium- and

Oki Earthquake (June 1978),

low-pressure gas pipelines section, since it has

The Hyogoken-N anbu Earthquake occurred in January 1995.

Since the earthquake far

been confirmed that the recommendations therein

are

reasonable

for

earthquake-

exceeded conventional theory, the Central Dis-

resistant design, judging from the results of

aster Prevention Council reviewed its Basic

investigation of the Hyogoken-Nanbu Earth-

Plan for Disaster Prevention and the Japan

quake.

Society of Civil Engineers presented a proposal. These actions showed the necessity for and

6.2

concept of containing the recommended prac-

6.2.1

.tices for the earthquake-resistant design of important structures in methods of design for

High-Pressure Gas Pipelines Basic Policy on EarthquakeResistant Design

(1) Basic Concept of Earthquake-Resistant

seismic motions of a higher level, level 2 seis-

Design

mic motions, which correspond to the shocks

For the earthquake-resistant design, two

generated by the Hyogoken-Nanbu Earth-

levels of seismic motions are assumed to se-

quake in the Kobe District.

cure the earthquake-resistant performance

The gas utilities are also now revising the Recommended

Practices

for

Earthquake-

Resistant Design of Gas Pipelines in the highpressure gas pipelines section, mainly for the purpose of improving the resistance of highpressure gas pipelines to seismic motions of level 2, especially in the concept of design input seismic motions. This revision is aimed at achieving a more carefully-formulated response to advanced seismic needs worldwide in the light of technological findings since the presently used Recommended Practices were established 17 years ago.

Regarding this re-

specified for the respective levels of seismic motions in principle. (Description) (a) The Basic Plan for Disaster Prevention of the Central Disaster Prevention Council was reviewed based on the HyogokenNanbu Earthquake which occurred on January 17,

1995, and it now stipulates

that the earthquake-resistant design of structures, facilities, etc. to be constructed in the future shall not suffer any serious loss of function even should general seismic motions with a probability of occurring once

vised edition of Recommended Practice for

@Seismicisolation 6-1 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

or twice within the service life of the pipeline occur,

and shall not have any serious

January, 2000

(Description) (a) Seismic Motions of Level 1, and Earth-

influence on human life even should a

quake-Resistant

higher level of seismic motions of low prob-

Them

ability occur, due to an inland type earthquake or trench type huge earthquake. equipment, two levels of seismic motions and considering the influ-

ence of structures, facilities, etc. on -human life, the influence on relief activities and on the prevention of secondary disasters,

against

[Seismic Motions] Seismic motions specified in the previous

(b) For the earthquake-resistant design of gas

are assumed,

Performance

and

the influence on economic activities, gas

Recommended Practices

for

Earthquake-

resistant design of High Pressure Gas Pipelines (March 1982). [Earthquake-Resistant Performance] The earthquake-resistant performance required for the seismic motions of level 1 is

equipment must have earthquake-resistant

such that "Operation can be resumed imD:1e-

performance suitable for its respective

diately without any repair." based on the Re-

kinds and degree of importance.

port of the Committee for Preventing Seismi-

(c) Based on the above basic concept; earthquake-resistant design is performed to se-

cally Caused Gas Disasters. (b) Seismic Motions of Level 2, and Earth-

cure the earthquake-resistant performance

quake-Resistant

required for the two levels of seismic mo-

Them

tions, as described in the following chapter. (2) Seismic Motions to be Assumed for

Performance

against

[Seismic Motions] A proposal concerning the seismic standard,

Design, and Earthquake-Resistant

etc. of the Japan Society of Civil Engineers

Performance

presents concrete images as "seismic motion

The seismic motions to be assumed for de-

near the hypocenter fault of an earthquake

sign, and the earthquake-resistant perfor-

caused by any internal strain of a plate of

mance required of them are shown in Table

magnitude 7 class (hereinafter called an in-

6.2.1.

land type earthquake)" and "seismic motion

Table 6.2.1

Seismic Motions and EarthquakeResistant Performance

Seismic Motions to be Assumed for Design General seismic motions Seismic with a probability of motions occurring once or twice of during the service life of level 1 gas pipeline are assumed.

Eart hquake- Resistan t Performance Operation can be resumed immediately without any repair.

Very strong seismic motions due to an inland type earthquake or trench type earthquake likely to occur at a low probability rate during the service life of gas pipeline are assumed.

The pipeline does not though leak. deformed.

Seismic motions of leve12

in the hypocenter region by a large-scale inter-plate earthquake occurring near land (hereinafter called a trench type earthquake)",

and the present "Recommended

Practices" assumes the seismic motions of these two earthquake types; inland type earthquake and trench type earthquake. Further, even if there -is no active fault found in the existing documents, there is a possibility that an inland type earthquake may occur.

Thus, it was decided to adopt a

@Seismicisolation @Seismicisolation 6-2

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

concept that a lower limit level is set when

March 1982)*.

seismic motions are assumed.

propagationvelocity of seismic motion", the

[Earthquake-Resistant Performance]

value stated in "Apparent wavelength of

However, for the "apparent

The earthquake-resistant performance re-

seismic motion" is used, and for the "ground

quired for the seismic motions of level 2 is

spring constants in the axial direction ofthe

such that "the pipeline does not leak, though

pipe and in the transverse direction of the

deformed." based on the Report of the Com-

pipe",

mittee for Preventing Seismically Caused

of ground" are used.

the values stated in "Confining force

Gas Disasters.

* See Appendix 6.4.1.

(3) Evaluation of Earthquake-Resistance

(Description)

Since seismic motions repetitively forcibly

For earthquake-resistant design against

displace the pipeline, the fatigue damage at

seismic motions of levell, Recommended Prac-

a very low frequency caused by them is

tices for Earthquake-Resistant Design of High

evaluated for earthquake-resistant design,

Pressure Gas Pipelines* (Japan Gas Association, March 1982) is applied.

When the ground of the planned pipeline is likely to be greatly deformed by liquefac-

However, the following portions among the

tion, etc., it must be examined adequately.

latest results of research concerning the earthquake-resistant design, especially among

(Description) The method for evaluating earthquake-

the findings obtained after the 1995 Hyogo-

resistance was decided, considering that seis-

ken-Nanbu Earthquake inclusive should also

mic motions have the following characteristics:

be applied, in view of their nature, to the.

a) the loads are short-term ones, and

earthquake-resistant design against seismic

b) since the strains (or relative displacements)

motions of level 1.

So, for the following val-

caused in the ground by seismic motions are

ues stated in the 1982 Recommended Practices,

repetitively applied to the pipeline, the loads

those stated in the present Recommended

are periodically displacement-controlled, and

Practices are used. (1) "Apparent propagation velocity of seismic

also in reference to the concepts of existing

motion" in "Design seismic motion"

standards(ASME Sec. III, etc.) which specify

(2) "Ground spring constants in the axial di-

these loads.

rection of the pipe and in the transverse di6.2.2

Earthquake-Resistant Design

rection

of the

pipe"

in

"Earthquake-

against Seismic Motions of Levell

resistant design of straight pipe in uniform

The earthquake-resistant design against

ground", "Earthquake-resistant design of

seismic motions of level 1 is performed ac-

straight pipe in roughly varying Ground"

cording to the Recommended Practices for

and "Earthquake-resistant design for bend

Earthquake-resistant design of High Pres-

and tee".

sure Gas Pipelines (Japan Gas Association,

@Seismicisolation @Seismicisolation 6-3

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

6.2.3

Earthquake-Resistant Design

plying the design seismic motion II stated

against Seismic Motions of Level 2

in "[E] Design seismic motion II" by the

(1) Entire Flow of Earthquake-Resistant Design

seismic zone coefficient stated in "[G] Seismic zone coefficient" is used as the

(a) The procedure for setting the design seismic motion is shown in Fig. 6.2.1. (b) The earthquake-resistant design flow

based on the set design seismic motion is

design seismic motion. 3) When it has been concluded that the existence of any active fault is unknown: . The seismic motion obtained by multiplying the design seismic motion I stated

shown in Fig. 6.2.2. (2) Setting of Design Seismic Motion [A] Procedure and Method for Setting Design Seismic Motion I, II and III The design seismic motion is set as follows based on "[B] Investigation of active fault" and "[C] Judgment as to existence of

in "[D] Design seismic motion I" by the seismic zone coefficient stated in "[G] Seismic zone coefficient" is used as the design seismic motion. (Description) (1) The seismic motion of level 2 to be applied

active fault".

for design is set using any of the three kinds

1) When it has been concluded that the ex-

of seismic motion described below based on

istence of any active fault is positive:

the conclusion as to whether the existence

· The seismic motion obtained by multi-

of any active fault is positive or negative.

plying the design seismic motion I stated

Design seismic motion I: Seismic motion

in "[D] Design seismic motion I" by the

decided for the inland type earthquake

seISmIC zone coefficient stated in "[G]

based on the observation records of

Seismic zone coefficient" is used as the

Hyogoken-Nanbu Earthquake

design seismic motion.

Design seismic motion II: Seismic motion

· Alternatively if fault analysis can be per-

decided for the trench type earthquake

formed, the seismic motion calculated ac-

based on past earthquake observation

cording to the fault analysis stated in "[F]

records

Design seismic motion III" is used as the

Design seismic motion III: Seismic motion

However, if the

based on analytical decision for the in-

calculated design seismic motion is smal-

land type earthquake by modeling the

ler than the seismic motion obtained ac-

hypocenter fault and using the hypocen-

cording to the procedure of 2), the seismic

ter parameter and the information on

motion of 2) is used as the design seismic

the ground and physical properties of

motion.

propagation routes

design seismic motion.

2) When it has been concluded that the existence of any active fault is negative: · The seismic motion obtained by multi-

(2) If it is concluded that the existence of any active fault likely to greatly affect the planned pipeline is positive,

@Seismicisolation @Seismicisolation 6-4

it can be con-

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

sidered to analytically calculate the seismic

(3) When it has been concluded that the exis-

motion by modeling the hypocenter fault

tence of any active fault is negative, it is re-

and using the. fault parameter and the in-

quired to take only the trench type earth-

formation onthe ground and physical prop-

quake into consideration, and the design

erties of propagation routes (this method is

seismic motion is set using the design seis-

called fault analysis).

mic motion II for the trench type earth-

However, presently

the data necessary for analysis and the

quake.

analytical method are not sufficiently es-

(4) When it

has been concluded that the exis-

Therefore, the design seismic

tence of any active fault is unknown, the

motion is set by using the design seismic

design seismic motion is set using the

motion I decided based on the observation

above-mentioned design seismic motion I,

records of Hyogoken-Nanbu Earthquake,

from the viewpoint of obtaining conserva-

one of the recent largest inland type earth-

tive results for design, since it cannot be

quakes, or by fault analysis.

concluded that there is no active fault.

tablished.

Investigation of active fault near the design site (B)

Positive

Negative

No Design seismic motion II (E)

Design seismic motion I (D) Yes

Selection of seismic zone coefficient (G)

Selection of seismic zone coefficient (G)

Corrected design seismic motion II

Corrected design seismic motion I

Design seismic motion ill (F)

Decision of design seismic motion

* 1) If the design seismic motion III is smaller than the corrected design seismic motion II, the corrected design seismic motion II is used as the design seismic motion. Fig. 6.2.1

Design Seismic Motion Setting Flow

6-5 @Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Fig. 6.2.2

Earthquake-Resistant Design Flow for High Pressure Gas Pipelines against Seismic Motions of Level 2

Design Seismic Motion I or II (set based on earthquake observation records)

Design Seismic Motion III (set by fault analysis)

.Natural Period of Ground of Surface Layer

4.H :EVsjOH j :T=-=-, V s = - - ' - - -

.Ma:cimum Velocity in the Ground of

v, H H ; Thickness of ground of surface layer (m)

ied depth of gas pipeline): v

V s ; Shear wave velocity in the ground of surface layer (m/s)

Maximum ground displacement: Uh

I r Elastic wave survey xC""", Sand L Clay Estimate from N value -.:::::::::: Sand Clay

Surface Layer at Design Site (at bur-

0.7 E . 0.6 0.7 E • 0.85 0.7 E • 6NO.2! 07 E12 • NO·078

.Apparent Wavelength of Seismic Motion :L=V·T V;Apparent propagation velocity of seismic motion

(2.5,800)

V (rn/s)

.Apparent Horizontal Propagation Velocity of Wave: V a. Apparent propagation hodograph

(0.15, 100)

b. Calculation of simple phase velocity c. Detailed analysis (Haske] matrix method, etc.)

T (s)

To calculate according to any of a, band c.

.Ground Displacement of Surface Layer 1tZ

.Ground Strain

. T· Sv : cos-

aa

V (cm/s)

(0.1, 8.0)

v ; Seismic zone

f ~7,50) (0.7, 100)

(0.1, 4.0)

coefficient z ; Buried depth of pipeline (m) Sv; Standard response velocity (cm/s)

T (s)

.

.Ground Strain of Uniform Ground :

E Gl=2 1t X

UhlL

•

Ground

Strain

of Irregular

Shallow

Ground: EG2= IE G12+ EG/ E G3: Ground strain caused by irregular shallow ground

(* *)

@Seismicisolation 6-6 @Seismicisolation

No

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Design of Straight Pipe

Ground strain due to (*) or (**)

January, 2000

Design of Bend and Tee

Ground displacement due to (*) or (**)

E G

.Strain Transfer Coefficient

Uh

.Displacement Transfer Coefficient a * = q* • aa q* ; Coefficient considering sliding

between pipe and ground Relative displacement between pipe q. Coefficient considering sliding between

and ground : 6. = (1- a *) .

pipe and ground

Al =

~

KI E'A

~

; Ground spring constant in axial direction of pipe

• Strain of Pipe caused by earthquake E p = a • E G (a • E G < E y)

=

.Strain of Bend or Tee during Earthquake

(ex • E G ~ e y) E y; Yield strain of pipe material :

Ep

Uh

In the case of irregular shallow ground, the value at or near the place where the bend or tee is installed is used.

E B,T= f3

EG

E B,T=

B,T •

6. (f3 B,T~ 1.27 E y)

C· f3B,T ·6.(f3 B ,T > L

27 E

y)

f3 B,T ; Coefficient of conversion C ; Plastic state correction factor

.Allowable Strain : Allowable strain of straight pipe, bend and tee 3%

No

Examination of Design Modification

@Seismicisolation @Seismicisolation 6-7

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

[B] Investigation ofActive Fault

January, 2000

(Description)

For investigation of any active fault, the

(1) The conclusion as to whether the existence

information concerning the position, prob-

of any active fault is "positive", "negative" or

ability, activity; etc. of any inland active fault

"unknown" can be made in reference to Ta-

likely to produce large seismic motions to the

ble 6.2.

planned pipeline is collected from existing

Table 6.2.2

existence of any active fault is "positive",

documents.

"nezative" or "unknown" ....

(Description) (1) For any inland active fault, basically, the

Conclusion "Positive"

active faults belonging to probabilities I and II of "Active Faults in Japan (New Edition)" are investigated for comprehensive evaluation also in reference to the active fault list

"Negative"

stated in "Investigation and Observation Plan for Foundations Relating to Earthquakes",

Criterion for concluding that the

the earthquakes assumed in the

regional disaster prevention plan and other findings in the latest investigation and re-

"Unknown"

search results. (2) If any active fault found as a result of active fault investigation is found not to be imminent in activity and not to act during the service life of the pipeline,

it can be ex-

cluded from the investigation. [C] Judgment as to the Existence of Active

Fault

Criterion · It is judged that "The existence of any active fault likely to produce large seismic motions is positive." Fig. 6.2.3 shows the relation between the distance from an active fault and the magnitude of an earthquake. · It is judged that "The existence of any active fault likely to produce large seismic motions is negative." Fig. 6.2.3 shows the relation between the distance from an active fault and the magnitude of an earthauake. · It is not confirmed that there is no active fault in a plain covered with a thick sedimentary layer. ·A complicated earth structure is formed with boundaries of three plates gathering underground, as in the metrooolitan area.

(2) The boundary line of Fig. 6.2.3 is obtained by calculating the weak ground conditions with a ground surface velocity of 64 cmls as the boundary on the conservative side.

If

Whether the existence of any active fault

the shortest distance from the active fault

likely to give large seismic motions to the

concerned to the planned pipeline and the

planned pipeline is "positive", "negative" or

magnitude of the earthquake likely to be

"unknown" is concluded by taking the fol-

caused by the active fault exist on the left

lowing into consideration:

side of the boundary line,

(1) Distance of the planned pipeline from the

face velocity caused at the planned pipeline

the ground sur-

when the active fault aets is larger than 64

active fault (2) Magnitude of earthquake estimated from the length ofthe active fault

cm/s.

If they exist on the right, the ground

surface velocity is smaller than 64 em/s. The surface ground velocity of 64 cm/s was obtained by converting 50 cm/s, which is the

@Seismicisolation 6-8 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

response velocity of design seismic motion II

January, 2000

(Description)

caused by the trench type earthquake speci-

(1) The design seismic motion I was decided by

fied in "Design seismic motion II", into the

obtaining the velocity response spectrum on

ground surface velocity (50 x 4J 7[

= 64,

4J 7[:

the seismic base rock (engineering under-

coefficient for converting the response of

ground base rock) based on 16 observed

single-degree-of-freedom system into the re-

waves of two horizontal components at the

sponse of continuum).

hypocenter region and nearby (within 10 km from the active fault) eight sites of the

8

I I I I I II II

I

I

L

"Positive' I

I

I I I I

I

the non-excess probability.

[E] Design Seismic Motion II _.

~ .

I

o

I

Th~ _d~Sign seismic motion II is shown in

l!'lg.

(j.~.5. 300

.

~s

I

J0

20

30

40 .7-;50)

The shortest distance from an active fault, d (km)

0

Fig. 6.2.3 Criterion for concluding whether the existence of any active fault likely to produce large seismic motions is positive or negative

V (O.l.U

3 0.1

(3) As an example of the methods for estimating

Fig. 6.2.5

proposes the following formula:

M : Magnitude of an earthquake specified

The design seismic motion I is shown in

~

"'r

c~'e _ Co >

(1) The design seismic motion II was set at one

V

Earthquake-resistant

design

Course,

tion (December 1996) . Earthquake-resistant design (draft), Design

3Or--+-74--+++f+H--+-+-+-I v

Standard and Description of Railway Structures, Etc. (November 1998) [F] Design Seismic Motion III

~er; ~

Velocity response spectrum of as-

Highway Bridge Specifications and Descrip-

II II

c-, a>

'.0

ence to the two spectra.

[D] Design Seismic Motion I

B

2.D

half of the design seismic motion I, in refer-

by Meteorological Agency

-.;

J.O

(Description)

L: Length ofthe active fault

c -

0.:5

sumed trench type earthquake

LoglOL = a.6M - 2.9

o>

0.2

Natural period of ground of surface layer T (5)

the magnitude of an earthquake, Matsuda

Fig. 6.2.4.

considering

I

I

I

5

I

Hyogoken-Nanbu Earthquake,

11111 11111 11111 1111I

I I I

I I

'Negative" .

I I

VI

,I

I

I

1.-1"

I

6

,

I I

{O.1.I.Q

I

The design seismic motion III is calculated

,

I 0..3

I

I 1.0

1.0

5.0

Natural period of ground of surface layer T (5)

Fig. 6.2.4 Velocity response spectrum of assumed inland type earthquake

by fault analysis. (Description) (1) If the seismic motion calculated by fault

@Seismicisolation 6-9 @Seismicisolation

I

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

analysis is smaller than the corrected design

January, 2000

(Description) Fig. 6.2.6 shows the zone classification map

seismic motion II caused by the trench type earthquake at the planned pipeline, the cor-

for the seismic zone coefficient.

rected design seismic motion II is used as

(3) Ground Displacement and Ground Strain of Surface Layer

the design seismic motion.

[A] Natural Period of Ground of Surface Layer

[G] Seismic Zone Coefficient (1) The zone classification is the same as the classification specified in the Recommended

Practices

for

The basic natural period of ground of surface layer is obtained from the following formula:

4- H

Earthquake-

T=~

Pipelines (Japan Gas Association, March 1982).

where

Vs

Resistant Design of High Pressure Gas

T: Natural period of ground of surface layer(s) H: Thickness of ground of surface layer n ~

(2) The seismic zone coefficient is the value stated in Table 6.2.3 for each zone. Table 6 2 3 Seismic Zone Coefficient Zone Classification

Seismic Zone Coefficient

Special A Zone

1.0

A Zone

0.8

B or C Zone

0.7

(=

.

(m)

j=l

Vs : Shear wave velocity in the ground of surface layer (rn/s)

[

_

Vs; Shear wave velocity of

n

"" Vs - H

f;::

j

j

~:

j-th layer (mJs) Thickness of j-th layer

H

Special A Zone

m o .

§

Fig. 6.2.6

-_.

LH j)

AZone

BZone CZone

Zone Classification for Seismic Zone Coefficient

@Seismicisolation @Seismicisolation 6-10

(m)

J

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

of Section 6.2.3 (2) [D]

[B] Apparent Wavelength of Seismic Motion

The apparent wavelength of seismic mo-

T: Natural period of ground of surface layer(s)

tion in the direction along the ground surface is obtained from the following formula:

z : Buried depth of pipeline (m) H: Thickness of ground of surface layer (m)

L= V' T

where L : Apparent wavelength of seismic motion in the direction along the

(2) When design seismic motion II is used, it

is obtained from the following formula:

ground surface (m)

U

V: Apparent propagation velocity of seismic

motion (m/s)

=~. Jr

h

2

T' v· S

VII

(T)' cos (

JrZ )

2H

where SVII(1): Response velocity of design

T: Natural period of ground of surface layer(s)

seismic motion II (cm/s), according to

The apparent propagation velocity of seismic motion is obtained from Fig. 6.2.7.

Fig. 6.2.5 of Section 6.2.3 (2) [E]

3000

II III

! Ii

2000

I,

1000

I I I I 1111

I

i

u,I .

I

!

500

!

,

i. : II

/

I

I

I

! i I!! I . /

I

I

!

!

I

i

i I ! 10

I

! I

I

Viii'!

II

I i

'

; I

/11 I

i III1

: !,:

1=(0.15,1~

,

!

50

I

0.5

0.2

1.0

II

I

,,

2.0

: 5.0

Natural period of ground of surface layer, T (s)

Fig. 6.2.7

Apparent propagation velocity of

(3) When design seismic motion III is used, the ground displacement of the surface layer at the buried position of the pipeline

of Uniform Ground The ground strain of surface layer in the case of uniform ground is obtained as follows: (1) When design seismic motion I is used, it is obtained from the following formula:

seismic motion [C] Ground Displacement of Surface Layer The ground displacement of surface layer

E G1

where

=V

E G1 :

is obtained as follows: obtained from the following formula: h

=~. Jr 2

•

E GIO •

1rZ) cos( 2H

Ground strain of surface layer in the case of uniform ground

(1) When design seismic motion I is used, it is

U

snecified for (1) - ...- - " ,.

[D] Ground Strain of Surface Layer in the Case

I

I

Hrf~ HI'l --- -- -

is directly calculated.

i

I

0.1

i

I

i

200

100

I I !

'rnp ntnpr i'lvmhnli'l - - - - - - - - - - -oJ ----- - - -

T' v· S. (T)' cos ( r I

JrZ )

2H

where U;,: Ground displacement of surface

v: Seismic zone coefficient, according to 6.2.3 (2) [G] E GIO :

Ground strain of surface layer of

design seismic motion I in the case of uniform ground, according to Fig. 6.2.8

layer (em) v: Seismic zone coefficient, according to Sec-

(2) When design seismic motion II is used, it is obtained from the following formula:

tion 6.2.3 (2) [G] SVI(T): Response velocity of design seismic

E Gl

=V

•

E GIlD •

1rZ) cos ( 2H

motion I (cm/s), according to Fig. 6.2.4 where

E GIlD:

Ground strain of surface

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

layer of design seismic motion II in the

Ground

6.2.9

In the case of irregular shallow ground, a

.§ "

ground strain larger than that in the uniform 1.0

,

U)~

,

:::~

.~] " r"

:::o

,.~

- '" -

rJJ '"

(0.1.0.102

-=

~

g

.:l .-

o

~

o:E

\Qj.o:~i

L..-ri !'N..,! I

,

,

0.0 2

,

,

I

,

i

iii

!

i

i

i I i ! ! !!! , Ii i ! i ! t i i !!

I

! ! i i1

I

j

I i

i ! ! !

! i

i

into account for earthquake-resistant design.

[Description

i

I

i

1

!

i

i

I I

!

i

J

Ground Strain of Irregular

(a) The ground strain caused in irregular shallow ground is calculated by superimposing the ground strain of uniform ground on the ground strain caused by inclined seismic

I

! ! ! ! ! 11 _'----'-....o.........I I I 0.01.-1-1---'---'---'---'---'-............._ 0.1 0.2 0.5 1.0 2.0 5.0

base rock.

Natural period of ground of surface layer, T (5)

Fig. 6.2.8

1J

Shallow Ground

,,

, !

!

ground can happen, and this must be taken

, !

I

i

!

I

,

, ,

i ii ,ii !i ! !~ ! i i ..... I i i i i i Ii , I (2..S.1i.16j I I ! i ! !! l i i

i

0.05

-=~

rJJ _.5

, I l1

OJ

'00

i

nVCQr-°.

~~

,

i

'. , ! lA

~

~ ,~ -g ~ c 0.1

,, , ,,

!

0.5 0

:l 0

~ E » .... 0.20

::

(4) Ground Strain ofIrregular Shallow

case of uniform ground, according to Fig.

0; __

.~

January, 2000

Ground strain of surface layer

of design seismic motion I in the case of

where

cG2

=.J

g2 G1

cG3

=n

-0.3 (%)

E

+ c 2G3

G1: Ground strain of uniform ground,

according to 6.2.3 (3) [D] "Ground strain

uniform ground

of surface layer in the case of uniform , .~"'g 0.50 0;

<::

o

s:::

~ ~

c: .-

j

0 20

.

- s:::

.... :l

i

a

,

<:: '"

,,

,

!

~ <:3 D. 05 (0.1.0.05 11

i

i

i

.-s:::..l:

,

OJ

!

,

~

~ .5

rJJ::::

-:: c

i

D. 02

;; .!:!

e "'0 o. 01

CJ

:E

I*"

! ! .(O.7,0~! I'~. I : I I (0.15.0.~ ! i i !,ll] i

0.1

I i

!

0.2

i

i , !

!

,, ,

i

'.J

i

! !

,, , ! i i· i i I i

I i !! ! iI i

I

Ii

i I !i 0.5

i

1.0

! , i

E G3:

low ground Ground strain caused by inclined seismic

i

j

i

i

i

I ,

i

!

,

base rock n: In the case of corrected design seismic

!I i

-~

~.o.~)--+-

,

!

I i

j

i

!

I

I

I

2.0

i

I

,,

motion I: v (seismic zone coefficient, according to Section 6.2.3 (2) [G] )

i

i

In the case of corrected design seismic mo-

iI i

tion II: 0.5 x v 5.0

Natural period of ground of surface layer, T (s)

Fig. 6.2.9

E G2:

!

j

i

o

,

ground" Ground strain caused in irregular shal-

!

i i i !! i

: o ...... ~ 0 1n ~

, i

:l 0

'""' CJ.... .;: .... -

, , , ,

(b) As the ground strain of uniform ground

E ci.

the ground strain of uniform ground at the

Ground strain of surface layer of

position where the surface layer thickness

design seismic motion II in the case of

becomes maximum at the irregular shallow

uniform ground

ground portion or that at the position where

(3) When design seismic motion III is used, the ground strain of the surface layer at the position of the buried pipeline is directly calculated, including the influence of irregular shallow ground.

it becomes minimum, whichever is larger, is adopted. (c) The ground strain of irregular shallow ground is taken into account when the angle of inclined base rock is 5 or more.

@Seismicisolation @Seismicisolation 6-12

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

(5) Confining Force of Ground [AJ Confining Force of Ground in the Axial Direction of Pipe

I

The confining force of ground in the axial

~~

o

direction of a pipe is approximated by bilinear expression using the critical shear stress

'C

/AY/

H o= LSm

cr per unit surface area of the pipe

and the ground spring constant k 1, or obtained by measurement. Critical shear stress:

'C

cr

= 1.5N/cm2

[B] Confining Force of Ground in the

(O.15kgflcm~

Ground spring constant: k,

=6.0N/cm

3

(O.6kgficmS]

Transverse Direction of Pipe The confining force a of ground in the transverse

direction

of

a

prpe

18

approximated by the bilinear expression or

r cr

the straight line using the initial gradient of the bilinear expression, using the maximum confining force

(J

cr of ground per unit pro-

jected area and the yield displacement i5 cr, or obtained by measurement.

Relative Displacement 0

Table 6.2.4 Confining Force of Ground in the Transverse Direction of Pipe by Diameter Diameter (mm)

Maximum Confining Force of Ground

Yield Displacement

k 2 = a crt 6 cr

a cr N'cm" (kgf/crrr')

6 cr cm

Nzcm" (kgf/cm'')

32 (3.2)

3.0

11 (1.1)

(Typical example) 750

Straight line

c C ::l

...o

""

c.e c

a cr

Bilinear expression

co

...

<.2

""c : 0' cr

D (Outer diameter)

Relative displacement O.

6-13 @Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

a

(6) Earthquake-Resistant Design of Straight

=

q. ao

where a: Strain transfer coefficient of the

Pipe

straight pipe (for the strain transfer coeffi-

[A] Strain of Straight Pipe Caused by Earthquake

cient a of the straight pipe, the same for-

The strain of a straight pipe caused by an

mula as used in the Recommended Practices

earthquake is obtained from either of the

for Earthquake-Resistant Design of Gas

following formulae:

Pipelines is used.)

(1) If the strain of the straight pipe is in the

a 0: Strain transfer coefficient of the straight

elastic range, that is, if a .

E

G'::::

s» then

E

pipe without sliding taken into account

(2) If the strain of the straight pipe is in the plastic range, that is, if a •

EG

>

E y'

then ~:

where

E p:

Strain of the straight pipe caused

by earthquake pipe, according to (B) of the following

5.4.1.

L: Apparent wavelength of seismic motion(cm)

section. G: Ground strain, according to

Ey :

rection of the pipe per unit length of pipeline [N/cm2 (kg£'cm~], according to Section

0:: Strain transfer coefficient of the straight

E

Ground spring constant in the axial di-

and

Yield strain of the pipe material

E : Elastic modulus of the pipe [N/cm2 (kgficmZ)], E

= 2100000 kgf/crrr'

A: Sectional area of the pipe (em")

[Description] (1) If the strain of the straight pipe exceeds the buckling limit, the strain of the pipe af-

t : Wall thickness ofthe pipe (em) r G: Sear stress acting on the pipe surface [Nzcm" (kg£'cmZ)]

ter buckling is calculated, for example, using FEM analysis with buckling behavior taken into account.

The buckling limit is the

buckling initiation strain

E buckle

(%) speci-

t cr:

Sliding initiation critical shear stress

when sliding occurs between the pipe

fied in the Recommended Practices for

and the surrounding ground [N/cm2

Earthquake-resistant design of Gas Pipe-

(kgficmZ)]

lines.

q: Sliding reduction coefficient

q ::: 1- cos

where t: Wall thickness of the pipe (em) D m : Average diameter of the pipe (em)

q = arcsin ( ::

[B] Strain Transfer Coefficient

The strain transfer coefficient of a straight pipe is obtained from the following formula:

~ + Q.

rG'::::r

cr

J'

-(; -

q

~ ) sin ;

,

s1

q=l

Q: Correction factor for evaluating q on the

conservative side, 1. 5

@Seismicisolation 6-14 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

(7) Earthquake-Resistant Design of Bend and Tee

Gr

= fJr6-

(2) If the strain of the tee caused by an earth-

A bend or tee may be greatly strained de-

quake is in the full plastic range, that is, if flr6- > 1.27&y' then

pending on the piping conditions, and this must be taken into account for earthquakeresistant design.

&r = 2flr6where

E

r: Strain ofthe tee caused by

[Description 1] Strain of Bend Caused by Earthquake

earthquake {3r: Coefficient of conversion of the tee (Vern),

The strain of a bend caused by an earthquake is obtained from either of the following formu-

according to Description 5. zl: Relative displacement (em), according to

lae or by FEM analysis,

Description 3

(1) If the strain of the bend is in the elastic

range or partially plastic range, that is, if flB6- ~ 1.27&y' then

E

y: Yield strain of the branch pipe adjacent to the tee

[Description 3] Relative Displacement between

&B = flB6-

Pipe and Ground

(2) If the strain of the bend is in the full plastic

range, that is, if flB6- > 1.27&y' then

&B = CBflB6where

EB:

Strain of the bend caused by earth-

and ground is obtained from the following formula: Ll = (1- a*)o U h where Ll: Relative displacement (em)

Uh: Ground displacement of the surface layer

quake {3 B: Coefficient of conversion of the bend

(Vern), according to Description 4.

zl: relative displacement (em), according to

(em) ex * : Coefficient concerning relative displacement between pipe and ground

a*

Description 3 Ey :

The relative displacement between a pipe

Yield strain of the pipe material

GB : Correction factor for the strain ofthe bend

in the full plastic range

=q *

0

ao

ex 0: Strain transfer coefficient of the straight pipe without sliding taken into account q*: Sliding reduction coefficient concerning

GB = 2 (below 600A)

relative displacement

GB =1 (over 600A including 600A) [Description 2] Strain of Tee Caused by

0

Earthquake The strain of a tee caused by an earthquake

rG~rcr

is obtained from either of the following formu-

where

lae or by FEM analysis. (1) If the strain of the tee caused by an earth-

~2) -~ ocos~, q*::;l ( 2-2

q*=sin~ 1+ ~ q=l

~ ~ arCSin(::)

Furthermore,

r G: Shear stress acting on the pipe surface

quake is in the elastic or partially plastic range, that is, if flr6- ~ 1.27&y' then

@Seismicisolation 6-15 @Seismicisolation

[N/cm 2 (kgf/cm 2) ]

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

r or: Sliding initiation critical shear stress

direction of the pipe per unit length [Nzcm" (kg.fi'cm~]

when sliding occurs between the pipe and the surrounding ground [N/cm 2 (kg.fi'cm~]

E: Elastic modulus [N/cm2

[Description 5] Coefficient of Conversion of Tee

[Description 4] Coefficient of Conversion of

The coefficient of conversion of a tee is ob-

Bend The coefficient of conversion of a bend is ob-

tained from the following formula:

tained from the following formula:

fJT

2i B A1 D/(5 + R1~11 + 413115(1 + b2 ) 2

fiB

=

2

1)

4A 2 + LI]A] C

bII

-3

•

_

~? -;;-2

l-LnlCA

2

/ • "\ ~ -.. -;;-3 -~4-Tr)nlCA

{1 + RI~ + TrnRI + (4 -Tr)nR 2 I

b 3 = nR 3-3{Tr A - + Tr] 2 2nAR

2_+!!.-+ { +( RA 2

Tr]

2nAR

+ ( 1-

2

2}

] )b,

2)b,}

bend, obtained from the following formula: 1.95

B- (~~r/3

the following: Subscript 1: Branch pipe side

nAR

(l/cm) iB: Stress index for the bending load of the

i -

where the subscripts for D, A, land 1. express

--2

where [3B: Coefficient of conversion ofthe bend

Subscript 2: Main pipe side [3 T: Coefficient of conversion of the tee (l/cm)

D: Outside diameter (em)

A: Sectional area (crrr')

I: Moment of inertia (ern") L: Apparent wavelength of seismic motion(cm)

or 1.5, whichever is larger

I:

n : Flexibility factor of the bend, obtained from

V~l

11;.: Ground spring constant in the transverse direction of the pipe per unit length

the following formula: 1.65 n=

= 42;2 D]A2~:

10A+5L12 (1+b 2)+10Ab 3 1 + 2R1 + (Jr - 2}nR 2 1

b =

(kgflcm~]

[N/cm 2 (kg:flcm~]

(~~)

E: Elastic modulus [Nzcm" (kgflcm~] (8) Allowable Strain

A: Sectional area of the pipe (crrr)

R: Radius of curvature (em)

The allowable strain of a straight pipe, bend or tee is 3%.

I: Moment of inertia (em") D: Outside diameter of the pipe (cm)

[Description]

L: Apparent wavelength of seismic

(A) Allowable strain on the seismic motion of

Level 2 was determined based on the damage

motion(cm)

-,{If;

caused by the cyclic ground displacement of

A:

the extremely low cycle.

V4t-

11;.: Ground spring constant in the transverse

Regarding the

number of the cyclic ground displacements,

@Seismicisolation @Seismicisolation 6-16

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

by taking the same concept as the Recommended Practice for Earthquake-Resistant Design of High Pressure Gas Pipeline (1982. 3),

the repetition number of times of the

maximum strain was determined to be" equivalent to the fatigue damage which one seismic motion of Level 2 gives to the pipeline.

As it is enough if one seismic motion of

6.3 MEDIUM-AND LOW-PRESSURE GAS PIPELINES 6.3.1 Basic Policy on Earthquake-Resistant Design (1) General Principles

Earthquake-resistant design for mediumand low - pressure pipelines is aimed at achieving greater pipeline flexibility and there-

Level 2 occurs during the design lifetime of

by reducing gas pipe leakage or breakage.

the pipeline, the number of the cyclic ground

(2) Quantitative Flexibility Evaluation

displacements to be considered on the seismic motion of Level 2 are approximately 3 to 5 times.

Method for Pipelines Aseismic strength is judged by calculating the capability of the pipeline to absorb the

Setting the allowable strain in the light of

stipulated ground displacement.

If the value

the fatigue design curve of ASME, the allow-

exceeds the design ground displacement de-

able strain of the base metal is 3% if assumed

termined by ground and other conditions, the

the repeated times of 3 to 5.

pipeline is judged to be earthquake-resistant.

It can be con-

sidered in general that the strain of 3% doesn't impede the operation and it has enough safety margin from the viewpoint of

6.3.2 Earthquake-Resistant Design Procedure The procedure is shown in Fig. 6.3.1.

the experimental data and the performance

Evaluation of earthquake resistance is based

of the steel pipe.

on the following items.

(B) Buckling is allowed because it doesn't lead

to leakage directly.

But in the case that

there is possibility of strain occurrence to cause buckling on a straight pipe, in other words, the case that the occurred strain ex-

CD Selection of burying conditions @ Calculation of design ground displacement @ Calculation of pipeline ground displace-

ment absorption

ceeds the initial buckling strain specified on

@ Selection of ground displacement input

the seismic motion of Levell, 35 . tJDm (t :

@. Selection of standard strain and standard

pipe thickness (em), Dm: average diameter of the pipe (cm), the strain which occurs on the pipeline after buckling should be calculated correctly by the method such as the finite element method (FEJ\.1).

displacement @ Evaluation of earthquake resistance 6.3.3 Design Ground Displacement The design ground displacement for evaluating pipeline flexibility is determined by the following formula. . 1) Horizontal displacement (in axial direction of pipe) : U

= a 1a 2 U O

2) Vertical displacement (perpendicular to

@Seismicisolation 6-17 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Desig-n Ground Displacements Horizontal

U

= a 1a 2 U o

Vertical

V

= 1/ 2U

January, 2000

Canabilitv to Absorb Ground Displacement Designing Pipings

Input Ground Displacement Models

. Straight

. Horizontal

Pipings

Displacement in which

. Pipings with

. Vertical

a 1 = Seismic zone factor

bends, branche

Displacement

etc. a 2 = Factor according to the

I

combination of pipeline type and ground

~

conditions

Allowable Limits . Allowable strain

U o=Standard design ground

(e 0)

displacement

. Allowable displacement (00' eo)

Evaluation of Capability to Absorb Ground Displacement Simple formulas [

. Nume~cal calCulatiOn] . Expenment

,

I -

Evaluation of Flexibilitv

L\u and L\v

I

I

Su » U L\v> V

Fig. 6.3.1 : Flow Diagram of Earthquake-Resistant Design of Medium - and Low - Pressure Pipelines

@Seismicisolation @Seismicisolation 6-18

I

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

pipe axis): V = 1/ 2U In the formula, a] is determined by the

January, 2000

combination (1) Soil layer dating back to the Triassic E;a.

or earlier (hereinafter called "rock layer")

seismic zone factor in Table 6.3.1 of which the division of area is the same as that shown in

(2) Diluvium layer

Fig. 6.3.1 in 6.4 Appenclix 6.4.1. Table 6.3.2 shows that a 2 is a factor repre-

(3) Alluvium layer less than 10m thick or layer in which soft layer is less than 5m

senting the combination of pipeline type and

thick.

* Provided there exists a rock layer or firm

ground condition. Uo is determined as 5.0 (em) in standard

diluvium layer (N) 50, seismic wave veloc-

design ground displacement.

ity of more than 300m/sec.) II. Area formed chiefly by alluvium layer of

The ground condition type in Table 6.3.2 is based on "6.3.4 Definition of Ground Condi-

more than 10m or soft layer of more than

rion."

ill a. Mixture of soil layer equivalent to Condi-

6.3.4 Ground Condition

tion I and a layer equivalent to Condition

Ground conditions are determined the state

IT, or are in which the two types are mixed

of the ground in the general area w here piping

illb. Border are between soil layer and sturdy

is installed and by the piping installation's geographic location.

structure built upon foundation equivalent

I . Area formed by any of the following ground

to Condition IT and other locations where

types or areas where the three are found in

displacement is evidently discontinuous

Table 6.3.1: Seismic Zone Factors (a l )

SA

A

B

1.0

0.8

0.6

C 0.4

Table 6.3.2: Factors according to the combination ofthe kind of pipeline and ground conditions (a 2)

~ Classification of Pipeline Medium pressure A (3 ~ P< 10kgflcmZ) Medium pressure B (1 ~ P< 3kgflcmZ) Low pressure (main) (P< lkgflcmZ) Low pressure (service) (P< Lkgf/crn")

I

II

ill

0.9

1.3

1.8

0.7

1.0

1..4

0.5

0.7

to

0.7

1.0

1.0

@Seismicisolation 6-19 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

F2

6.3.5 Pipeline Capability to Absorb Ground

!1u=---

JiDrAE

Displacement (1) Capability of Straight Piping to Absorb

Fa:

where,

of screwed joint portion

Ground Displacement in Axial Direction (1w)

iii) Piping with mechanical joint

Su

The capability of a straight pipe to absorb ground displacement in the axial direc-

Allowable tensile strength

Where,

= 00 +2 (0 1 +02+·····+0n)

° 0

is the maximum displacement

tion(!::..u) under ground conditions I, IT, and

of joint in the center of ground displacement,

Illa , as shown in Fig. 6.3.2 is a ground dis-

at which leakage or serious damage of joint is

placement that can be absorbed by the pipe at

expected.

51'

°

2 , ••• ,

On represents allow-

a displacement input that focuses on one

able displacement (slipout) in joints adjoining

point on the ground surface.

the joint in the center, calculated taking into

i) A pipeline with continuous restraint force

account the reduction in load due to the ground restraint force between the joints.

from projection in axial direction [a] Reduced elastic modulus model (for poly-

one end in Ground Condition lib to absorb

ethylene pipe, etc.) -

!::..U =

The capability of a straight pipeline fixed at axial ground displacement is ground dis-

2

AE£o [mm]

placement that can be absorbed when the

wr

where, A: Area of cross-section (mnr')

input of ground displacement that concentrates at the border of a structure and ground

D : Pipe diameter

E : Reduced elastic modulus (Nzmnr) r : Restraint force of ground per unit surface of pipe (Nzmm") e 0 : Allowable strain (specified in Section

is added, as shown in Fig. 6.3.4.

(2) Capability of a Straight Piping to Absorb Ground Displacement in Direction Transverse to Axis The capability of straight piping to absorb

6.3.6) [b] Elastoplastic calculation model (welded

ground displacement in the direction transverse to its axis (!1v) in Ground Condition I ,

steel pipe)

IT, or IIJa is ground displacement that the

AE {£} +.11.(£0

2

2

-

ev

) }

Su = - - - - ' - - - - - - - - : . . . . ! . . . .

trDr

piping can absorb when transverse displace- . ment concentrates on one point on the ground,

e v : Yield strain of pipe

as shown in Fig. 6.3.5.

e 0 : Allowable strain of pipe

i) A pipeline with homogeneous rigidity along

E : Elastic modulus (N/mmZ)

its axis (steel pipe with welded joint

}.E : Tangent modulus of pipe

or polyethylene pipe)

ii) Piping showing localized reduction in ten-

sile stress on cross-section (such as steel pipe with screwed joint)

!1v=

2.fie'" D

~4El --£ kD

0

Where, E : Reduced elastic modulus (N/mm~

@Seismicisolation @Seismicisolation 6-20

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

f:,u ~

January, 2000

Ground Displacement

......lJ> Restriction of Soil

--.. --.. --.. --.. -+ --..

I

Pipe

I

Fig. 6.3.2 : Ground Displacement Input for Ground Conditions I, II, and IDa

~

O"v

__-

. . AE

~----=-_

1

Fig. 6.3.3: Bilinear Elastoplastic Model of Steel Material

Ground Displacement

--v> c.... ~

Ground Restraint Force --..-+-+-+--..-+

~

'-:

~~r--;:;U-----:=-----r-------------~

.3

:r.;

I >:?i

Fig. 6.3.4 : Ground Displacement Input on Piping Fixed at One End in Ground Condition IDb

~~-------------r""

-~~-.--.~--- ..-.... -..

--_ ....... - .......... -_ ..... - .. --- .... -_., I,

.............................................. .. ..'I

Fig. 6.3.5: Ground Displacement Input in Transverse Direction Under Ground Condition I, II, or ID a

@Seismicisolation 6-21 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

1 : Moment of inertia of cross-section (mm 4)

the plastic limit and the reduced elastic

k : Reduced coefficient of subgrade reaction

modulus (E) applied when calculating the

(Nzmm") ii) Piping with localized drop in strength

against bending moment (steel pipe with screwed joint) Llv=

.fie

4

Jr

EI

/

~4EI --M kD

material's ability to absorb ground displacement, which depends upon the material, are shown below. 1) Steel pipe: Allowable strain .... £0=3 [%] Reduced elastic modulus

.... E =3.0X 104 [N/mm2J

0

Where, M o : Mome.it atthe location of localized drop in strength (N . mm) E : Elastic modulus (N/mm~

2) Ductile cast-iron pipe : Allowable strain.... £0=2 [%] Reduced elastic modulus

.... E =3.0 X 104 [Nzmm'']

The capability to absorb ground displacement when the pipe is fixed to structure under Ground Condition J:Ifu, as in Fig. 6.3.6, is displacement that the pipe can absorb when

3) Polyethylene pipe : Allowable strain .... £0=20 [%] Reduced elastic modulus

.... E =3.0 X Hf [N/mmZ]

displacement concentrates at the border of

When, however, reduced elastic modulus is

the structure and ground. (3) Capability of 3-D piping to Absorb Ground Displacement (Llu) The capability of 3-D piping system com-

inapplicable for steel or ductile cast-iron pipe, Young's modulus that is within the range of elasticity is applied.

prised oflow - pressure service and internal

Steel pipe: 2.1 x lOS [Nzmm']

pipes under Ground Condition I, Il , or ma

Ductile cast-iron pipe: 1.6 X lOS [N'mnr']

is ground displacement that the piping can

absorb at the displacement shown in Fig.

Coefficient A used to determine the tangent modulus (AE ) used to calculate elasticity of steel pipe is founded upon the following:

6.3.7. The absorption capability of a 3-D piping system buried under Ground Condition Illb and fixed at one end to a structure is ground displacement that can be absorbed when the

--1 =7.1 X 10-3 (2) Allowable Displacement for Mechanical Joints and Expansion Fittings Standard displacement for expansionjoints

ground displacement shown in Fig. 6.3.4 is

such as mechanical and flexible joints for

applied.

connecting pipes in ways other than welding is the official value specified under JIS or

If no nominal

6.3.6 Allowable Strain and Allowable

other equivalent standards.

Displacement (1) Allowable Strain in Pipe Material (£0)

value is found, it is determined as the dis-

and Elastic Modulus (E) The Allowable strain (£0) that is set over

placement that removes airtightness or inflicts serious damage or deformation upon a major part of the joint.

@Seismicisolation @Seismicisolation 6-22

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

................. "..f.

.

V

6.v

Fig. 6.3.6 : Ground Displacement Input in Transverse Direction for Piping Fixed at One End Under Ground Condition ill b

Location of Ground Displacement Input

Pwad

~

<;~l

Residential Land

I I

Gas Meter

Crank Pipe

Main or Service Pipe

Service Pipe

Internal Pipe

a) Location of Ground Displacement Input

Service Pipe Element

Internal Pipe Element

b) Division of Service Pipe and Internal Pipe Elements and Displacement of Each Element Fig. 6.3.7: Ground Displacement Input for Service and Internal Pipe System and Calculation of Ground Displacement Absorption Capability (Sample)

@Seismicisolation 6-23 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

6.4 Appendix

by evaluating fatigue damage m plastic

6.4.1 Earthquake-Resistant Design of

range.

High-Pressure Gas Pipeline

(2) The design method for bends and tees is

(1) Basic Concept of Earthquake-Resistant

very important because seismic forces

Design

concentrate in them, while smaller strains

A Recommended Practice for Earthquake-

in a straight pipelines are due to the slip-

Resistant Design of High-Pressure Gas Pipe-

page between the pipe and the ground.

line is based on greatly improved concepts with

(3) The standard consider the seismic waves

regard. to the evaluation of seismic motions

apparently propagating along the ground

and interaction (slippage) between the ground

surface and the strain in ground with in-

and the gas pipeline.

clined base rock.

Features of the Recom-

mended Practice (Standards) are as follows.

Table 6.4.1 shows the flow diagram of the

(1) The design method consists of strain design.

earthquake resistant design based on the

Strains during. an earthquake are

above concept.

allowed to be in excess of the elastic limit

Fig. 6.4.1 : Seismic Zone Coefficient

@Seismicisolation @Seismicisolation 6-24

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Table 6.4.1 Flow Diagram. of Earthquake-Resistant Design a ions £or elSIDlC Mt

Desrgn ) (2) Natural Period of Surface Layer

(1) Horizontal Seismic Intensity at Base Rock & == 0.15' u i : U, U 1 : Coefficient of Importance

T=--,r;= I';

:rr~

H

~(~') '. Elastic Wave

Others

Survey

LO

0.8

Estimate from N,Value

u, : Seismic Zone Coefficient

(3) Apparent Wavelength of Seismic Motion L== V' T V: Apparent Propagation Velocity of Seismic Motion

. HI

H : Thickness of Surface Layer (m) V s : Shear Wave Velocity in Surface ~

Pipeline Buried under Public Road in UrbanArea VI

4 'H

XC

<

<

Layer V 0.6 0.85

Sand Clay

f--.

(1.0, 800)

~

(m/s)

Sand 62N 0.021 Clay 122N 0.078

T (s)

I ~ (4) Displacement Amplitude of the Surface Layer 2 JrZ cosU =-T'Sv 'K h

oJ<

JrZ

(5) Strain in Ground with Uniform Surface Layer

(0.6, 150)

Sv

E 01

.=

&al

=

2H

2w' U. L 3 • S•• K •• fr'

V

w' • cos-.2H

,j.

(cm/s)

(6) Strain in Ground with Inclined Base Rock

/ , : . 1 ' 25)

c G2

T (s)

=~CG/ +C G / K

c G3 =X'~'

51 : Velocity Response Spectrum per Unit Seismic Intensity at Base Rock (cm/s) z : Depth of Pipeline (m)

tan(J •

V,

wz

cos2H

Z : T<0.3s

Z==405'T Z : T~0.3s X == 122 . (J : Inclination of Base Rock (deg.)

( (7) Design of Straight Pipe ) (7)' Strain Transfer Coefficient a

l

;

q

I

l+(~r At·r.

s:

a

[ (8) Design of Bend and Tee )

Q

(8)' Displacement Transfer Coefficient

a* == q* • a o

q : Coefficient Considering Slippage between

q' : Coefficient Considering Slippage between

Pipe and Ground

J. =

,

~ E'A K,

K1

Pipe and Ground Relative Displacement of Pipe and Ground

Ground Spring Constant in Axial Direction

Do == (1- a*) • Un

1 (7)"

J.

-

L Strain in Straight Pipe

=a Cd = a

Uniform Ground

c"1

Inclined Base Rock

•

(8)" Strain in Bend and Tee

cGJ

= i, . a'

Uniform Ground

5"2

Inclined Base Rock

c V4 -t.

. a'

B=PB • Do 5 r == Pr' • Do

Bend

. cG2

2. Strain in Joint (welded) of Straight Pipe

5

Tee 5 Gl

fJ : Coefficient of Convention

5 G2

i; : Stress Index

(

I

I (9) Allowable Pipe Strain

J

1

(9)' Allowable Strain in Straight Pipe (i) 1.0% or (ii) 35t/Dm ("10) (Buckling Strain Obtained by Actual Measurement with Safety Factor of 1.25 taken into Consideration), Whichever is Smaller

(9)" Allowable Strain in Joint of Straight Pipe, Bend and Tee 1.0%

6-25 @Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

(2) Seismic Motion for Design

H in Equation

(a) Horizontal Seismic Intensity at Base Rock sidered for design is given by Equation

base rock.

Here,

represents the thickness "Vs- shows the shear

wave velocity in the surface layer.

CD

Determi-

nation of the base rock face depends on an N value not less than 50 or a measured shear

······CD CD,

®

of the surface layer.

The horizontal seismic intensity to be con-

In Equation

January, 2000

wave velocity of 300m/sec or more. 0.15 is the basic input at VI

is a coefficient of impor-

tance and v 2 is the seismic zone coefficient

(c) Apparent Wavelength of Seismic Motion Apparent wavelength of seismic motion is given by

show in Figure 6.4.1.

...... @

L= V' T

(b) Natural Period of Surface Layer

V in Equation @ is the apparent propaga-

Equation (2) gives the natural period of the

tion velocity of seismic motion.

surface layer.

Figure 6.4.2

shows the relationship between the natural period and the apparent propagation velocity.

......@.

(1.0,800)

(0.25, 100) 0.1

1.0 Natural Period (8)

5.0

Fig. 6.4.2: Apparent Propagation Velocity of Seismic Motion (0.6, 150)

100 50

(0.1, 25)

1Q

'--_---J_--'-_---'-_.LJ....L..1-.l....L_ _-'-_...l.-_-'--~

0.1

0.5 1.0 Natural Period (8)

5.0

Fig. 6.4.3 : Velocity Response Spectrum per Unit Seismic Intensity

@Seismicisolation @Seismicisolation 6-26

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

i \' : stress index (i v = 2.0)

(d) Displacement Amplitude of Surface Layer Equation @) gives the displacement ampli-

(4) Design of Bend and Tee (a) Strain in a Bend The strains in bends (e B) are given by

tude of the surface layer.

Uh

2 . S; • K = -T oh

•

JC cOS-· .•.... @

1C

January, 2000

®.

Equation

2H

®

cB = flB • .1

where where

S; : velocity response spectrum per unit

.1 : relative displacement between the

seismic intensity

pipe and the 'ground

z: depth of pipeline

fJ B

S, is given by Figure 6.4.3. (e) Strain in Ground with Uniform Surface Layer

:

coefficient of convention for bend

2 ' iB 'A .1 'D ·1(5+R' 2) 'bl l+ 4 ' 2 3
PB = .

3

10 'A+5'L']' l "I

The strain in the ground with a uniform

= 21r'

Uh

/

L

@

b =

The strain in the ground with inclined base

_

n

_ -:;-

.

f _ v~

2

C G3

= cGl + cG3

1-2' n . R 2 2

•

=k :

K

~ tan

r.

e. COS-2H

~=n'R3.23.{'::+ 2

E G3 :

strain in ground occurring by difference in displacements of two points

"'1 2

+(4 -;r) . n . R 2

;r']

2'n'A'R

2+(1

2

;r']

) .

2'n'A'R 2

] 2)''1

n'A'R

b} 2

:

Stress index for bending load on bend

n : Flexibility factor of bend A : Sectional area of pipe

e : inclination of base rock

R : Radius of curvature of bend

k : coefficient related to the natural pe-

I : Moment of inertia D : Outside diameter of pipe

riod of ground surface

L : Apparent wavelength of seismic motions

(3) Design for a Straight Pipe (a) Strain in a Straight Pipe The strain in a straight pipe is given by

= a'

......(J)

cGI

(b) Strain in a Pipe Welded Joint

:

Ground spring constant in the trans-

verse direction to the axis per unit pipe length

The strain in a pipe welded joint is given by Equation @.

E : Young's modulus of pipe The relative displacement between the pipe

......@ where

~'4~ . V4E0 K2

Equation (J). CPl

.,A.'}

where fJ B : Coefficient of convention of bend iB

where

_

- A

12'_ (4 _ it') . n •R 3 • 23

2){2 +;r' n • R • l

\.R.1 1lZ }, •••••• @

n2

}

,(_2 +.::+

2

(l+b:z)+1O·,A·~

n - 1'\

-.t..) -

rock is given by Equation @. cG2

.

"\'\

(l+R 'l)' {2+;r'n'R' l+(4-;r)'n ·R2 • A.

b = (1 + R .

(1) Strain in Ground with Inclined Base Rock

....

1 -t- L. - .I'( - A. -t-

l

surface layer is given by Equation @. cGl

•

and the ground is given by Equation @,

.1 = (1- a*) . U;

@Seismicisolation 6-27 @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

where

q"

branch

a * : displacement transfer coefficient a* = q * . a o

f3 T1

Sine: .1*) - 2; l*co{2; .1*) ~2 {l-( 4~*r} ;J

c

=

January, 2000

+

IT

4

°

A

= 1 + 4 (Y1 I

2

D1T

°

•

A2

+ L • II

Y2 ) 3 ( D:

1 + 2(A.! 1.A.2)3(D 2

(Adopt q* = 1, when slipping judging value

°

(C-l)

°

3

Al ° C

/ D1 ) D1)

/

where iT : Stress index

SJ
' . fJ T2 = IT

(b) Strain in a Tee

°

The strains in tees (c T) are given by Equa-

Y22oD2ToAI (1 2 ) , '2.Al+2oLo12°A.21:T

Note: Subscripts with sectional area A, sec-

tion @ and@.

cn cn

I/

- ,4' -

= f3T! • L1 2 = f32 • L1 j

......@ ,

ond moment of area I, outside diameter D, and

......@

...1.

are: Subscription 1

~j

:

Straight pipe in branch part

relative displacement between the main Subscription 2

pipe and the ground L1 2 : relative displacement between the

Straight pipe in main part

branch pipe and the ground f3n : coefficient of convention for branch

Tee in branch part

Subscription 2T

Tee in main part

(c) Stress Index and Flexibility Factor

when seismic waves input in parallel to main pipe f3 T2 : coefficient of convention for main pipe

Subscription IT

Stress index and flexibility factor of bends and tees are shown in the below table.

when seismic waves input in parallel to Type

Stress Index

The Larger one of Bend

1.95

IB

('/)'"

(Butt weld elbow)

Flexibility

Illustration

Factor

Unit: em

1.65

e;2

n~

R

or 1.5.

)

.

:-1>

-

-

The larger one of Tee (Butt weld tee)

Ir

7

( )2/3

0.67'

+~"

or 2.0

where

r: Mean radius of pipe

t: Wall thickness

D: Outside diameter of pipe

R: Radius of curvature

@Seismicisolation @Seismicisolation 6-28

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

(5) Allowable Strain

Gas Association and officially approved by the

Seismic strains in straight pipeline are uni-

government authorities as safe and reliable

form tensile or compressive strains in the en-

techniques for use in the gas industries.

tire area.

ing the pipelines from inside with polymer

The allowable strain in a straight

pipeline is smaller value of 1 % or the allowable

Lin-

tubes is typical of these techniques.

strain due to buckling given by Equation @.

4

E=- •

3

t --n Dm

......@

Damage susceptibility of pipelines depends on : (1) the distance from the origin of earth-

where E :

6.4.3. Block System of Pipeline Networks

quake (the shorter the distance is, the more

buckling strain

n: 0.11

intense the earthquake ground motion is, in

t: pipe wall thickness (em)

general); and (2) the ground conditions

Dm: mean diameter of pipe (=D-t) (em)

(damage is apt to be concentrated to the areas

The allowable buckling strain is given by 35

with very soft grounds, in general).

Therefore,

(tlDm) (%) using Equation @ with a safety

the degree of concentration of damage varies

factor of 1.25.

greatly from an area to another. To isolate heavily damaged areas from less

Earthquake Countermeasures for Gas

damaged areas, the block system of pipeline

Distribution Systems - the Status Quo

networks are in effect in major gas industries in Japan.

This system is aimed at minimizing

6.4.2. Improvement of Earthquake

the number of suspended customers, as a re-

Resistance of Pipelines

sult, maximizing the efficiency of reetoration

Improving the earthquake resistance of pipelines is essential to : (1) prevent disaster

activities. The block system takes a hierarchical struc-

caused by gas leakage; (2) minimize the sus-

ture; large blocks cover wide areas and the

pension of supply of gas; and (3) minimize the

blocking valves are remotely operated at the

restoration works thus enabling fast restora-

control center; these blocks are divided into

tion of supply of gas to the customers.

medium size networks which are not connected

The Recommended Practices for Earth-

mutually; the medium sized blocks are

quake-Resistant Design of Gas Pipelines de-

equipped with block-valves by which the blocks

scribed in the preceding Chapters are aimed at

can be divided further into small blocks (valves

the improvement of the earthquake resistance

are rperated manually).

of newly constructed pipelines. Retrofitting techniques have been developed and are being applied to the old pipelines. There are several kinds of retrofitting techniques which are recommended by the Japan

6-29 @Seismicisolation @Seismicisolation

@Seismicisolation @Seismicisolation

B?jfIJ61~10~

B5: 933

25,000 971

* THE 1995 HYOGOKEN-NANBU EARTHQUAKE

ijZJJX:8~6~

A4: 306

4,854 45,714

*

ijZJJX:5~5~

B5: 254

6,796

ijZJJX:6~12~

B5:407

5,825

ijZJJX:9~2~

B5: 499

9,500

Ei'&W~B!E~!J-;q 1994~J-A!Jy~±lliEiEi'&~~,*1!r

EARTHQUAKE RESISTANT DESIGN STRUCTURES IN JAPAN 1984 EARTHQUAKE RESISTANT DESIGN STRUCTURES IN JAPAN 1988 EARTHQUAKE RESISTANT DESIGN • STRUCTURES IN JAPAN 1992 EARTHQUAKE RESISTANT DESIGN • January,2000

FOR CIVIL ENGINEERING FOR CIVIL ENGINEERING

*

FOR CIVIL ENGINEERING

*

CODES IN JAPAN

6,000 BBfIJ59~7~

B5:265

BBf1J63~7~

B5: 259

ijZJJX:4~10~

B5:259

7,767

ijZJJX:12~1~

A4: 171

2,700

@Seismicisolation @Seismicisolation

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Published by

Earthquake Engineering Committee Japan Society of Civil Engineers Yotsuya Lrchome Shinjukuku Tokyo, 160-0004 Japan FAX +81-3-5379-2769

E-mail jsce-pubescivil.or.jp

Distributors Maruzen Co.,Ltd. International Division P.O.Box 5050 Tokyo International 100-3191 Japan TEL +81-3-3273-3234 Copyright

FAX +81-3-3278-9256

© JSCE 2000 EARTHQUAKE RESISTANT DESIGN

ISBN4-8106-0266-4 Printed in Japan, Waco Co.,Ltd.

@Seismicisolation @Seismicisolation