Report Draft

STRUCTURAL ANALYSIS AND DESIGN REPORT Of Residential Building

February, 2019

TABLE OF CONTENTS 1.

INTRODUCTION 1.1 1.2 1.3

2.

DETAILED PARAMETERS OF THE BUILDING 2.1 2.2 2.3 2.4 2.5

3.

5 5 5 5 5 5 6 6 6 6 7

THREE DIMENSIONAL VIEWS 8 PROPERTIES AND SECTIONS OF STRUCTURAL ELEMENTS....................................................................................9 BASE REACTIONS 9 DRIFT IN THE BUILDING 10

STRESS ANALYSIS AND DESIGN OF ELEMENTS 12 5.1 5.2 5.3 5.4 5.5

6.

DEAD LOADS (DL) LIVE LOADS (LL) EARTHQUAKE LOADS (EL) LOAD COMBINATIONS

4 4 4

MODELLING AND ANALYSIS OF THE STRUCTURE....................................................................................8 4.1 4.2 4.3 4.4

5.

GENERAL PARAMETERS OF THE BUILDING STRUCTURAL PARAMETERS OF THE BUILDING MATERIAL PROPERTIES ANALYSIS AND DESIGN BASIS DESIGN METHODOLOGY

LOADING 3.1 3.2 3.3 3.4

4.

ABOUT THIS REPORT ABOUT THE STRUCTURE ANALYSIS PROCEDURE

4

ANALYSIS OF THE BUILDING MEMBER STRENGTHS ELEMENT FORCES / STRESSES AND THEIR DESIGN FOUNDATION DESIGN DESIGN OF SLAB

Conclusions and Recommendations

12 12 14 18 20 22

TABLE OF FIGURES Figure 4-1: 3D view of model of the Building Figure 4-2: Deformed shape in EQX 10 Figure 4-3: Deformed shape in EQY 11 Figure 5-1: Comp stress due to DL+LL+EQX load combination Figure 5-2: Comp. stress due to DL+LL+EQY load combination Figure 5-3: Tensile forces due to 0.7DL+EQx 16 Figure 5-4 Tensile stresses on cross walls due to 0.7DL+EQy Figure 5-6: Shear stress on wall due to EQy (DL+LL+EQY) combination Figure 5-7: Shear stress on wall due to EQX (DL+LL+EQX) combination Figure 5-8: Load per meter at plinth level in the building under service. Figure 5-9: Load per meter with earthquake loading.

8

14 15 16 17 17 18 19

TABLE OF TABLES Table 4-1: Properties of Masonry 9 Table 4-2: Sections of Structural Elements 9 Table 4-3: Seismic Enhancing Elements 9 Table 4-4: Base Reaction 9 Table 5-1: Capacity calculation of Horizontal bands.............................................................................12

Structural Design Report

1.

INTRODUCTION

1.1 About this Report This report comprises planning, architectural design and structural design of a Masonry Residential buildings composed of brick masonry in cement mortar. This report includes different parameters for the analysis and design of presented structure. The design results are shown in a convenient tabular format. The principal aim of the structural design is to build a structure, which is safe so as to possess adequate strength, stiffness and stability during the action of all possible loads in its life span. Accordingly, the structural design data are presented in the report.

1.2 About the Structure The structure which is analysed and designed is one and a half storey brick masonry building with solid RCC roof slab on its top. The structure has been strengthened with different vertical and horizontal RC bands so as to improve the seismic performance of the structure.

1.3 Analysis procedure The structure has been modelled and analysed with computer software “SAP2000 ver.14”. The software has very good analysis and design capability which are verified in the verification problems included in the package. It is a Finite Element Method (FEM) based software and requires modelling of the structure by finite-elements. The walls were modelled with shell elements of appropriate property and the building is assumed to be supported at plinth level for the analysis of super-structure. The analysis stresses are used to verify the safety of the provided structural members, including walls. Also, these designs are provided to include the minimum requirements for earthquake resistant measures as per relevant National Nepal Building Codes as well.

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Structural Design Report

2.

DETAILED PARAMETERS OF THE BUILDING

2.1 General Parameters of the Building Building Type No of Storey Height of the building Wall

: Residential Building : one and a half storey : 5.60 m (Including top half storey) : 230 mm

2.2 Structural Parameters of the Building Foundation Type : Continuous Stone wall foundation Walls : Brick Masonry Wall Structural System : Load bearing system Roof : Reinforced concrete roof Soil Type : Soft soil (assumed for using even in soft soil condition) Here, the value of Soil bearing Capacity of soil taken for soft soil conditions i.e. 100KN/m 2

2.3 Material Properties Cement Mortar Brick

: Ordinary Portland cement (OPC) : Cement-Sand mortar (1:6) : Class-A bricks (Min Compressive Strength 5MPa)

2.4 Analysis and Design Basis The building is analysed and designed following the standard codes and norms. National Nepal building code has been used to the extent, available and related IS codes are used, where NBC permits the use. Different codes used for the structural analysis and design are: i. ii. iii. iv.

NBC109:1994 [Load Bearing Masonry] NBC105:1994 [Nepal National Building Code: Seismic Design of Buildings in Nepal] IS1905:1987 [Code of practice for structural use of unreinforced masonry]. IS875:1987 [Code of practice for design loads (other than earthquake) for buildings and structures]

2.5 Design Methodology At first, architectural drawings are prepared considering different functional, geometrical and engineering aspects. Then the building modelled in FEM-based software (SAP2000, version 14) for detailed structural analysis including all material properties, loads and its combination. The analysis results like direct stresses, bending stresses, shear stresses, tension, etc. are determined and checked against the limiting value of the material as per codal provision. The drawings are suitably adjusted to bring the building to safe level as per codal requirements. PAGE: 6

Structural Design Report

3.

LOADING

For the analysis of the building, all the loadings (dead loads and live loads) are calculated based on different parts of IS875:1987. Earthquake load is calculated based on NBC105:1994.

3.1 Dead Loads (DL) These are the permanent load which is not supposed to change during the structure’s design life. The dead loads included in the design are: a. Unit-weight of materials: i. Brick Masonry: 21 KN/m3 including mortar ii. Cement Plaster: 20.5 KN/m3 iii. RCC: 25 KN/m3 b. Roof dead load i. Floor Finish: 1.0 KN/m2 ii. Parapet wall (100mm thick): 2.0KN/m

3.2 Live Loads (LL) These are the loads that may vary its intensity and/or position during design life. Live loads for roofs are calculated as per the functional requirement as specified in IS875 code. As this is one storey building, there are no floors. a. Live loads on roof i. Accessible roof: 1.5KN/m2 ii. Inaccessible roof: 0.75KN/m2

3.3 Earthquake Loads (EL) Earthquake load has been calculated based on NBC105. Basically, horizontal seismic forces shall be considered for the structures that depend on different parameters. Different parameters for generating earthquake loads are: As per NBC105:1994 a. Seismic Zone Factor (Z) : 1.0 b. Importance Factor (I) : 1 (for Residential buildings) c. Str. Performance factor (K) : 4 (for masonry with added ductile bands, as per NBC105) d. Soil type : Soft Soil e. Height of building : 5.60 m f. Length of building : 12.425m g. Width of building : 9.15 m h. Fundamental Time period : 0.143 sec for D = 12.425 m 0.166 sec for D = 9.15 m i. Basic Seismic Coeff. (C) : 0.08 j.

Hor. Seismic Coefficient (Cd)

:

= 0.32

Thus, horizontal seismic coefficient of 32% is used for calculation of earthquake load and applied to the structure with linear vertical distribution as per NBC105:1994. This has been defined in the FEM program as follows: PAGE: 7

Structural Design Report

3.4 Load Combinations Different load combinations are generated as per NBC105:1994 for super-structure design. Wind loads are calculated and used only for the roof truss analysis and design and presented on roof-design section. Total nine load combinations are used for stress analysis of the structure as follows: a. DL+LL b. DL + LL +- EL (total 4-combinatinons for +ve and –ve EL in x & y direction) c. 0.7DL +- EL (total 4-combinatinons for +ve and –ve EL in x & y direction) where: DL = Dead Loads LL = Live Loads EL = Earthquake load

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Structural Design Report

4.

MODELLING AND ANALYSIS OF THE STRUCTURE

The structure is modelled in SAP2000 version14. Shell elements are used to model walls. Roof loads are applied to the walls using slab elements, and parapet wall loads are manually calculated and applied to corresponding walls as applicable. Major RC bands are modelled with frame elements. Different data for modelling are presented in the following sections.

4.1 Three Dimensional Views The three-dimensional view of FEM model of the structure is as shown in Figure Modelling and Analysis of the Structure-1. The major structural member is load-bearing wall, supported by different seismic enhancing elements like RC bands, and vertical rebars. For the masonry wall modelling, a threedimensional four-node shell element having 24 DOFs with 6 DOFs at each node were used while line/frame element having 12 DOFs with 6 DOFs at each node were used to model the bands

Figure Modelling and Analysis of the Structure-1: 3D view of model of the Building

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Structural Design Report

4.2 Properties and Sections of Structural Elements The main structural element is Brick load bearing walls. The thickness of wall is 230mm as shown in plan. The basic compressive strength of masonry (with crushing strength not less than 7.5Mpa) in 1:6 mortar (M2) is taken as 0.59 MPa as per IS1905:1987. Table Modelling and Analysis of the Structure-1: Properties of Masonry Sn. Description Value Remarks 1. Brick 5 Mpa Safe value based on observation 2. Mortar 1:6 Cement:Sand M2 type 3. Basic comp. stress of masonry 0.44 MPa As per IS1905:1987 3. Compressive Strength 1.76 Mpa 4 times basic compressive strength 4. Elasticity of wall (E=550*fm) 968 Mpa Reference FEMA Table Modelling and Analysis of the Structure-2: Sections of Structural Elements Sn. Material Thickness Remarks 1. Brick Wall 230 mm Brick masonry 2. Beam 230mm*325mm Reinforced Concrete 3. Roof Slab 100mm Reinforced Concrete 4. Column 230mm*230mm Reinforced Concrete Table Modelling and Analysis of the Structure-3: Seismic Enhancing Elements RCC flushed bands are provided in the jambs of all the openings. Although walls are designed to be safe without these bands, they maintain the integrity of the wall and increases the ductility of the structure.

4.3 Base Reactions The total horizontal forces applied on the building on earthquake loading is tabulated below. The horizontal forces on each X and Y directions are same as these are calculated are based on seismic coefficient method for low rise building having very low time-periods. Table Modelling and Analysis of the Structure-4: Base Reaction Sn. Load Case FX (KN) FY (KN)

FZ (KN)

1

EQX

-554.357

0

0

2

EQY

0

-554.357

0

3

Seismic Weight

-

-

1732.364

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Structural Design Report

Here, earthquake load has been applied in accordance with earthquake load calculation. These horizontal forces are distributed to each structural member based on their individual seismic masses and experience lateral forces in addition to vertical dead and live forces.

4.4 Drift in the Building Any functional building shall have limited deformation on design earthquake in addition to sufficient strength against failure. This is important to maintain the serviceability of building even after the earthquake. The drift ratio of up to 0.4% is allowed for the building structures. The maximum displacement on each floor and the corresponding drifts are shown in figures below.

Figure Modelling and Analysis of the Structure-2: Deformed shape in EQX

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Structural Design Report

Figure Modelling and Analysis of the Structure-3: Deformed shape in EQY Permissible Deflection = 0.004*2800 mm = 11.2 mm Deflection in X-direction= 2.89mm Deflection in Y-direction= 2.17mm Hence, the deflection of structure is within permissible limit.

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Structural Design Report

5.

STRESS ANALYSIS AND DESIGN OF ELEMENTS

5.1 Analysis of the Building The structural system of this building is load bearing. Brick masonry walls are used as main wall system which are strengthened with horizontal RC bands at plinth, sill, and lintel levels. Additionally, horizontal RC stitch bands at corners and junctions, RC vertical bands on the line of jamb of openings and vertical reinforcement with steel rebar’s at corners and junctions of walls are provided, that improves the ductility and strength of the masonry. The stress levels at different critical locations of the masonry walls and stresses on bands are calculated to determine their sufficiency. The forces and stresses as determined from the FEM analysis is presented in the following sections.

5.2 Member strengths The capacity of each elements of the masonry system, like walls bands and steel sections are determined to check against the actual stresses coming on the member. This way, they can be checked against their adequacy and specifications. Bands and rebar’s are specified at critical locations which are given in detail drawings. Table Stress Analysis and Design of Elements-5: Capacity calculation of Horizontal bands Calculation of strength of bands With fy415 bars Bandage Options B1 Width of band 230 Band thickness 75 Grade of Wire Dia. of wire No. of wires Cover Spacing of wire Total area of wires

415 8 2.00 25.00 172.0 100.53

Allowable Tensile strength of wires

230

Allowable compressive strength of wires

190

Allowable comp. stress in conc Increase in allowable stress in EQ combination Total allowable tensile force Total allowable compressive force

7 0.25 28.9 99.34

Bending in 230mm wall PAGE: 13

Structural Design Report Wall Thickness Band thickness Overall depth Effective Depth Considering maximum stress in bar equals to allowable stress in bar, Lever arm MOR Shear

230 75 230 205.00

Allowable shear stress in masonry Maximum horizontal force (Shear) resisted by band

0.1 32.01

180.00 5.2

Even though, the primary function of masonry elements is to sustain vertical gravity load, structural masonry elements are required to withstand combined shear, flexure and compressive stresses under earthquake or wind load combinations consisting of lateral as well as vertical loads. In these studies, the shear stress, tensile stress and compression stress for working stress load combination for earthquake loading are checked with their respective permissible stress. Even masonry structures are commonly practiced in Nepal, there are lack of experimental mechanical properties of masonry and guidelines and codes for masonry structures. For this study, the permissible strength for masonry are calculated with reference to IS1905:1897. Compressive Stress of Masonry Since the Brick masonry are strong in compression strength, the analysis were conducted for inplane compressive stress due to earthquake loading and compressive stress due to one of critical loading combinations were verified with permissible stress. Permissible Compressive Stress: Compressive strength of masonry units = 5 N/mm 2 Mortar type M2 (1:6 Cement-sand) Basic compressive strength of wall (fb) = 0.44 N/mm2 (from table 8, IS 1905:1987) Permissible compressive stress (fc) = fb X Ks X Ka X Kp Slenderness ration (most common) = h/t or l/t = 2890/230 = 12.56 Stress reduction factor (Ks) =0.83 for above slenderness ratio Area reduction factor (Ka) = 0.7+1.5 A, A being the area of section in m 2 Area reduction factor (Ka), takes into consideration smallness of the sectional area of the elements and is applicable when sectional area of the element is less than 0.2 m 2. But minimum area is 0.35m2 for smallest area. i.e. Sectional Area (A) > 0.2 m 2 Thus, Ka = 1 Shape modification ratio (Kp) = 1.0 (for H/W approx. 0.61 table 10 IS 1905:1987) Hence, permissible compressive stress in Masonry (f c) =0.44*0.83*1*1 =0.3652 N/mm2

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Structural Design Report

Though different walls have different values of slenderness and hence, stress reduction factor, for this report, critical value is selected and used for all walls for the checking. Compressive stress checks due to earthquake load for different walls are given in following sections. Permissible Tensile Stress: As a general rule, design of masonry shall be based on the assumption that masonry is not capable of taking any tension. For this case, tensile stresses are taken by vertical bands and their sufficiency are checked. Tensile stress checks due to earthquake load for different walls are given below in following sections. Permissible Shear Stress: Brick masonry are not much strong in shear strength due to lateral loading. Diagonal cracks were developed due to shear forces. Hence shear stress due to in-plane lateral forces (earthquake loading) was verified for one of the critical load combination with permissible stress. Shear Capacity of masonry is taken as: 0.1+Fd/6 (where Fd=Compressive stress due to dead load). Shear stress checks due to earthquake load for different walls are given in following sections.

5.3 Element Forces / Stresses and their design The forces and stresses in each elements of the building are presented below. The stress diagrams are presented below: Compressive Stresses: As illustrated in the stress diagram for different grids of walls, the maximum compressive stress (minimum stress) on wall is 0.347 MPa which is below the compressive stress limit of 0.3652 MPa of the considered masonry system. Compressive Stress S22 demand in load bearing brick masonry due to site specific earthquake loading is well within permissible value except in very small locations of stress concentration at corners.

Figure Stress Analysis and Design of Elements-4: Comp stress due to DL+LL+EQX load combination PAGE: 15

Structural Design Report

Figure Stress Analysis and Design of Elements-5: Comp. stress due to DL+LL+EQY load combination Tensile Stresses: As illustrated in Figure 5-3, maximum tension on the wall is about 64 KN/m in width of 230mm equivalent to tensile load of 7.36 KN near window opening Band. Hence 2-8mm fe415 bars with capacity of 23KN is sufficient at the jambs of opening. Here, 2-10 mm bars with capacity of 35.88KN is provided at the jambs of opening which is sufficient enough to resist all the tensions limiting the tensile cracks on masonry near opening. In addition to vertical bars at the jambs of opening, two 50x50x2mm thick hollow posts are provided at corners and T-junction in order to provide tensile strength at corners and T-junctions which is sufficient to provide required tensile strength which is very less as compared to side of openings.

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Structural Design Report

Figure Stress Analysis and Design of Elements-6: Tensile forces due to 0.7DL+EQx

Figure Stress Analysis and Design of Elements-7 Tensile stresses on cross walls due to 0.7DL+EQy

PAGE: 17

Structural Design Report Shear Stresses: Shear stresses on different walls and piers are illustrated in the following figures. These stresses are less than the least limiting value of 0.1 MPa for masonry in most of the places. The vertical stress near sill level is 0.24 MPa, thus making the allowable shear of (0.1+0.24/6)= 0.14 MPa. Moreover, the exceeded shear stresses are counter acted upon by the horizontal and vertical bands provided that enhances the shear capacity of the wall. Here as the shear stress has not exceeded the limiting value of masonry, the building is safe in shearing as well.

Figure Stress Analysis and Design of Elements-8: Shear stress on wall due to EQy (DL+LL+EQY) combination

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Structural Design Report

Figure Stress Analysis and Design of Elements-9: Shear stress on wall due to EQX (DL+LL+EQX) combination

5.4 Foundation Design The design of foundation depends on the maximum force on the structure footing during service and during extreme cases of load combination.

Figure Stress Analysis and Design of Elements-10: Load per meter at plinth level in the building under service. PAGE: 19

Structural Design Report The analysis shows the the maximum pressure under service condition is about 70 KN/m. Adding 20% more stress for self-weight of foundation, a total of 84 KN/m load as acting from foundation. Thus, footing depth is provided based on minimum requirement of NBC of 900mm.

Figure Stress Analysis and Design of Elements-11: Load per meter with earthquake loading. Under earthquake, the vertical load increased to 115KN/m with a total of 138KN/m at base. Since, bearing capacity can be increased by 25% in earthquake combination, the foundation with SBC of 100 KN/m2 (125 in earthquake combination) will be safe for the structure. Hence, the foundation width is sufficient for service load as well as seismic loading condition.

Load Combination DL+LL Load per m 70 extra 20% 84 SBC, KN/m2 100 Width of footing Required, m 0.84 Width of footing Provided, m 1.2

Load Combination DL+LL+EQx 115 138 125

Load Combination DL+LL+EQy 99 KN/m 118.8 KN/m 125 KN/m2

1.104

0.95

m

1.2

1.2

m PAGE: 20

Structural Design Report

5.5 Design of Slab Design of Two Way Slab lx = ly = fck = fy = Dia. Of Bar =

3.35 3.85 20 415 8

ly/lx = Two Way Slab

1.149

Overall depth of Slab (D) = Effective depth (d) =

m m N/mm2 N/mm2 mm

125 106

mm mm

Dead Load of Slab = Floor Finish = Total Dead Load =

3.125 1.00 4.125

KN/m2 KN/m2 KN/m2

Live Load =

1.5

KN/m2

Total Load = Factored Load =

5.625 8.438

KN/m2 KN/m2

Type the Value for Slab Type =

3

Status DEPTH OK

Load Calculation

αxαyαx+ αy+

0.046 0.037 0.034 0.028

MxMy-

4.325 3.504

KNm KNm

Type of Slab Interior Pannels One Short Edge Discontinuous One Long Edge Discontinuous Two Adjacent Edge Discontinuous Two Short Edges Discontinuous Two Long Edges Discontinuous Three Edge Discontinuous (One Long Edge Cont.) Three Edge Discontinuous (One Short Edge Cont.) Four Edge Discontinuous PAGE: 21

Structural Design Report Mx+ My+

3.244 2.651

KNm KNm

Check for Depth Due to Moment d= 39.584 mm Check OK Calculation of Area of Steel Required

AstxAstyAstx+ Asty+

Area Calculated mm2 115.62 101.185 86.21 76.16

Minimum Area of Steel Ast,min 150

Check For Min. Area NOT OK NOT OK NOT OK NOT OK

Area Required mm2 150 150 150 150

Dia. Of bar Used mm 8 8 8 8

Suggestted Spacing mm 335 335 335 335

Provide Spacing mm 150 150 150 150

Type Cantilever Simply Supported Continuous

Value of α 7

mm2

Check for Shear Force Maximum Shear Force = 14.13 KN/m Nominal Shear Stress, Tv = 0.13 N/mm2 Pecent of Steel, p% = 0.135 % Shear Strength of Concrete, Tc = 0.265 N/mm2 k= 1.3 Shear Strength in Slabs, Tc'= 0.344 N/mm2 Check OK Check for Deflection Steel Stresss of Service Loads, fs = Modification Factors α= 26 β= 1 γ=

2

Allowable Value = Actual Value = Check

91.52

N/mm2

20 26

52 28.57

OK

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Structural Design Report

5.6 Design of Beam Typical Design Of Beam Output

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Structural Design Report

6.

CONCLUSIONS AND RECOMMENDATIONS

The residential building to be constructed has been designed by meeting all the architectural and structural requirements as envisaged by National Nepal Building Code and IS standards. The building has been structurally analysed with computer program SAP2000v14 and correspondingly designed. All the tensile, bending, compression and shear stresses on the buildings are well within the permissible limits even under the most adverse combinations of different loads, including Earthquakes as per Nepal Building Code. Strict Control over quality of materials and workmanship is required for expected performance of building in future. Hence, following shall be considered during construction works to obtain expected results. A.

General: a. All works to be carried out in accordance with current best practice, Building Regulations, the project specification and relevant Nepal Building Code (NBC), Indian Standards and Codes of Practice. Materials and components to be appropriate for their intended use. b. The construction-works shall only be carried-out by trained mason with supervision of Engineer. c. During construction, the contractor shall be responsible for maintaining the structure in a stable condition and ensuring no part shall be damaged under construction activities. d. Workmanship and materials are to be in accordance with the relevant current Standards including all amendments and the local statutory authorities, except where varied by the contract document. e. All coarse aggregate used shall be crushed stone aggregate. The nominal size of coarseaggregate for RC bands and splints shall not exceed 12.5mm. f. Clean sand, with minimum silt and free from clay and organic materials shall be used. g. Ordinary Portland cement conforming to IS 269:1976 shall be used for all cement works. h. At least 48 hours’ notice shall be provided for all engineering inspections.

B.

Structural: Cast-In-Situ concrete/micro-concrete shall have minimum 28 days’ compressive cube strength of 20N/mm² for all structural members unless otherwise stated. The concrete compressive strength shall be measured on 150*150*150mm cube at 28 days, for various structural elements. Reinforcing steel shall be TOR having minimum yield strength of 415N/mm². However, TMT rebar with ultimate strain not less than 14.5% can also be used. Cover to main reinforcing steel be in accordance with IS 456:1978 & as specified in the structural drawings. Clear Cover of Concrete shall not be less than that given below: a. Concrete surface at soil = 50mm b. Concrete on PCC, Bricks, STONE, etc = 25mm Unless otherwise specified, all horizontal & vertical construction joints shall be roughened. A minimum of 48 hours’ notice shall be given to the Engineer before applying plaster, concrete/micro concrete is poured, in order that the formwork and/or reinforcement may be inspected.

1. 2. 3. 4. 5. 6. 7.

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Structural Design Report

8. All R.C.C work shall be continuously cured for 14-days. 9. All cement plaster works shall be continuously cured for 7 days. 10. Any damage to surface during erection/construction is to be made good.

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