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Overview
Download & View Tutorial - Flat Slab as PDF for free.
Summary In this example, we will construct a Flat Slab model and perform analysis and design. We will generate a Flat Slab model by importing a DXF file.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Set a unit system. Enter material and section properties. Import a CAD DXF file. Define support type. Generate area objects. Assign members. Enter elastic support conditions. Enter static loads. Check and review analysis results. Design
Analysis Model Unit: mm
Plan
1
Tutorial 1
▣ Model Description Analysis Model
Flat Slab for office use 4.0 m (both above and below the slab) Column Support, Wall Support
Story Height Support Condition Slab Size
56.4 m×20 m
▣ Structural Materials Concrete
ASTM, Grade C4000
Reinforcing Bar
Grade 60
▣ Section Data (㎜) Slab
Thickness = 200
Drop Panel
Thickness = 350
Column
700×700 (rectangular shape)
Core Wall
Thickness = 200
▣ Applied Load 1) Floor Load (kN/㎡) Dead Load Finish
Slab
Total
Live Load
Office
1.00
4.70
5.70
2.40
Corridor
1.00
4.70
5.70
3.93
Use
▣ Applied Codes •
2
Building Code Requirements for Structural Concrete and Commentary (ACI318-02, 2002)
Flat Slab
Working Environment Setting Unit System Double click the MIDAS/SDS icon system.
to execute SDS.exe. Open a new file and set a unit
1. New 2. Save> Select a folder.> File Name> Flat Slab 3. 4. Main Menu> Tools> Unit System 5. Length> mm ; Force (Mass)> kN 6.
Unit System Assignment
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Tutorial 1
Enter Material and Section Properties Before generating a model, enter the material properties of the elements, which will be used as structural members. 1. 2. 3. 4. 5. 6. 7. 8.
Main Menu> Model> Properties> Material Name> Slab Type> Concrete Concrete>Standard> ASTM(RC) DB> Grade C4000 Apply Confirm the generated material data. Assign the material data for Drop Panel and Wall similarly (Refer to Figure 3).
Enter material properties
4
Flat Slab
Enter the section dimensions of a wall beam, which is an equivalent beam substituted for a core wall.
1. 2. 3. 4. 5. 6.
Properties> Section Name> Wall Solid Rectangle> User (on) H> 8000 ; B> 200 Check the auto-calculated stiffness data at the bottom of the dialog box (Refer to Figure 4-①).
Define Elastic Support Conditions Define boundary conditions. MIDAS/SDS automatically calculates the elastic support stiffness of columns or walls supporting a floor slab by using the main dimensions such as section sizes, story heights, etc and the material properties such as modulus of elasticity. First, we define the elastic support stiffness of column supports, which will be assigned by using the Column Supports.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
Main Menu> Model> Boundaries> Column Support Type Name> C Support Type> Solid Rectangle Mesh and Link at Column Boundary (on) Material> Standard> ASTM(RC) ; DB> Grade C4000 Material> Modulus of Elasticity> 25.1255 ; Poisson’s Ratio> 0.2 Thickness> Above> Depth(D)> 700 ; Width(B)> 700 ; Height(H)> 4000 Bending Stiffness Scale Factor> 4.0 > Check the auto-calculated stiffness data.
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Tutorial 1
Tip The program will automatically calculate the rotational stiffness of column support based on the Bending Stiffness Scale Factor entered here. The boundary conditions of the model used for the determination of the bending stiffness factor for the columns, α, are shown below.
E, I
H
A E, I
H
Let the columns above and below have the same story height, H, modulus of elasticity, E and moment of inertia, I. Then the rotational stiffness of column support equals 2α ⋅
E⋅I . H
Where, E: Modulus of elasticity of the columns I: Moment of inertia of the columns H: Story height of the columns α: Bending stiffness factor for the columns Rotational stiffness of column support at A is found to be is taken as 4.
10
8EI . Therefore, α H
Flat Slab
Define Column Support Types
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Tutorial 1
Define Wall Support Types for the core walls. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
Enter Column Support Conditions Assign column support conditions.
1. Point Object Snap (on), Line Object Snap (on) 2. Main Menu> Model> Boundaries> Column Supports 3. Column Support Type> C 4. Select Single> Select the point objects to enter column supports. 5. 6.
Assign column supports
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Tutorial 1
Generate Area Objects Create area objects at the locations of slab, drop panels and openings by referring to Figure 1 (plan). First generate three area objects for slab. The slab needs to be divided into three area objects in order to enter different area loads for different floor uses.
1. Main Menu> Model> Objects> Create 2. Object Type> Area 3. Rectangle> Pick the upper left corner and the lower right corner of the bright green rectangle (See Figure 11- 1 ). 4. Polygon> Pick each corner of the red polygon (See Figure 11- 2 ). 5. Polygon> Pick each corner of the turquoise polygon (See Figure 11- 3 ).
1
2
Office
3 Corridor
Office
Create area objects for slab
14
Flat Slab
Based on the DXF underdrawing, generate area objects at the locations of drop panels.
6. Main Menu> Model> Objects> Create 7. Object Type> Area 8. Rectangle> Pick the upper left and lower right corners of each drop panel (See Figure 12).
Create area objects for drop panels
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Tutorial 1
Generate area objects at the locations of openings by referring to the DXF underdrawing.
9. Object Type> Area 10. Rectangle> Create area objects at the opening locations (Openings are shown enclosed by blue lines in Figure 13).
Create area objects for openings
16
Flat Slab
Assign Members Assign wall beams to the line objects corresponding to the core walls.
1. 2. 3. 4. 5. 6. 7. 8.
Main Menu> Model> Member> Beam Zoom Window> Magnify the core at the lower left (Figure 14- 1 ). Select Single> Select the line objects corresponding to the core walls. Type> Wall Beam Material Name> 2:Wall Section Name> 1:Wall
Zoom Fit> Zoom Window> Magnify the core at the upper right (Figure 142 ). 9. In a similar manner, assign the Wall Beams.
2
1
Assign Wall Beam Members 17
Tutorial 1
Assign Slab Members.
1. Zoom Fit 2. Member> Slab (Refer to Figure 15-①). 3. Select Single> Select three area objects corresponding to the slab (Refer to Figure 11- 1 , 2 and 3 ). 4. Option> Add/Replace 5. Type> Slab 6. Material> 1: Slab 7. Thickness> 1: Slab 8.
①
Assign Slab Members
18
Flat Slab
Assign Drop Panel members.
9. Member> Slab 10. Select Single> Select area objects corresponding to the drop panels (Refer to Figure 16). 11. Option> Add/Replace 12. Type> Drop Panel 13. Material> 2: Drop 14. Thickness> 2: Drop 15.
Assign Drop Panel Members
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Tutorial 1
Assign Opening Members to the openings.
16. Member> Opening (Refer to Figure 17-①). 17. Select Single> Select area objects corresponding to the openings (Refer to Figure 17). 18. Option> Add/Replace 19. 20.
①
Assign Opening Members
20
Flat Slab
Enter Wall Support Conditions We have already assigned column supports. Assigning wall supports corresponding to the core walls is now remaining. Assign the previously defined Wall Support Type to the core wall locations by Drag & Drop.
1. Works Tree> Section> 1:Wall> Line objects assigned “1:Wall” section will be selected. 2. Works Tree> Boundaries> Wall> Drag & Drop into the Model Window.
Drag
Drop
Enter Wall Supports
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Tutorial 1
Enter Punching Check Sizes Enter the column sizes required for punching shear check after performing analysis.
Enter Loading Data Now that the entry of geometric shape, stiffness and boundary conditions of the floor slab was completed, we will enter the loads next.
Set Static Load Cases Enter static load cases prior to entering loads.
1. 2. 3. 4. 5. 6. 7. 8.
Main Menu> Model> Static Loads> Static Load Cases Name> DL Type> Dead Load Name> LL Type> Live Load
Enter static load cases
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Tutorial 1
Enter Floor Loads In MIDAS/SDS, line loads and area loads can be assigned to objects using defined load types, or loaded by directly entering loading values for each load case.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Status Bar> Length Unit> m Main Menu> Model> Static Loads> Area Load Type Name> Office Load Case> 1> DL ; Area Load> -1 ; Weight (on) Load Case> 2> LL ; Area Load> -2.4 Name> Corridor Load Case> 1> DL ; Area Load> -1 ; Weight (on) Load Case> 2> LL ; Area Load> -3.83
Tip If the Weight option is checked, the self-weight of the area object will be automatically included in the dead load. This will automatically update the self-weight of the area object according to the change of the slab thickness.
24
Flat Slab
Define Area Load Types
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Tutorial 1
Assign the defined area load type of Office to the office area objects.
1. Main Menu> Model> Static Loads> Area Load 2. Load Type> Office 3. Select Single> Select area objects 1 and 3 (See Figure 22). 4. 5. Iso View 6. Dynamic Rotate (Check the entry of floor loads.)
3 Office 1 Offic
Check the entry of Office area load
26
Flat Slab
Assign the area load type of Corridor to the corridor area object.
7. Dynamic Rotate (toggle off)> Top View 8. Load Type> Corridor 9. Select Single> Select an area object 2 (Figure 23). 10. 11. Iso View 12. Dynamic Rotate (Check the entry of floor loads.) 13. 14. Dynamic Rotate (toggle off)> Top View
2 Corridor
Check the entry of Corridor area load
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Tutorial 1
Perform Structural Analysis The data entry process for performing floor slab analysis is completed thus far. Specify the maximum size of elements to be auto-generated, and then perform structural analysis. Mesh lines auto-generated in MIDAS/SDS do not exceed the Maximum Mesh Line Dimension defined by the user and always pass through point objects. Therefore, we may add point objects at the locations where we wish to generate mesh lines. MIDAS/SDS has been formulated with an up-to-date (Multi-frontal) Sparse Gaussian Solver, which improves accuracy of analysis results and remarkably reduces analysis time. The (Multi-frontal) Sparse Gaussian Solver will be applied to the analysis of this example. 1. Main Menu> Model> Model Control Data> Maximum Mesh Line Dimension> 0.5 2. 3. Display> Object> Mesh Line (on) 4.
Verify and Review Analysis Results Load Combinations Generate load combinations for member design by linearly combining the load cases, which were used for the structural analysis. Selecting a design standard will automatically generate load combinations as per the standard.
Verify Reactions Verify reactions due to dead load. The point in Red signifies the maximum reaction.
1. 2. 3. 4. 5.
Main Menu> Results> Reactions> Reaction Forces/Moments Load Cases/Combinations> ST:DL Components> FZ> Global Type of Display> Legend (on)
Maximum Reaction
Reactions at supports
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Tutorial 1
Check Reaction Table Check reactions in a table format. With the result table, the summation of reactions due to load cases or load combinations can be checked.
1. Main Menu> Results> Result Tables> Reaction 2. Active Dialog> DL(ST), LL(ST) 3.
Reaction table
32
Flat Slab
Verify Deformations Verify the deflections of the floor slab due to service load cases. Note that cracking of slab and long term (creep and shrinkage) effects are not reflected here.
1. 2. 3. 4. 5. 6. 7. 8.
Status Bar> mm Main Menu> Result> Deformation> Displacement Contour Load Cases/Combinations> ST:DL Components> DZ Type of Display> Contour, Deform, Legend> Iso View Dynamic Rotate (Check the deformed shape.) Dynamic Rotate (toggle off)> Top View
Displacement contour
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Tutorial 1
Verify Member Forces Verify the member forces of the Slab for the factored load combinations.
1. Display> Boundary> Punching Check Size (on)> 2. Inactivate the column mesh (in order to exclude columns in the calculation of average internal nodal forces). 3. Magnify each column to select the mesh inside columns (See Figure 31-①). 4. Inactivate (See Figure 31) 5. Select Works Tree> Member> Beams> Walls 6. Right click and select Inactive
① Pnt2
Pnt2
Pnt1
Pnt1
Cut-Line#1
Cut-Line#2
Inactivate column mesh
34
Flat Slab
7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
Main Menu> Result> Forces> Slab Forces/Moments Load Cases/Combinations> CB:gLCB2 Slab Force Options> Avg. Nodal ; Avg. Nodal Active Only (on) Components> Myy Type of Display> Contour, Legend Type of Display> Cutting Diagram (on) Status Bar> m Click two points by referring to Figure 31 and to generate Cut-Line#1. Generate Cut-Line#2 by referring to Figure 31. Options> Normal Close the Slab Cutting Line Diagram dialog box.
Slab moments
35
Tutorial 1
19. Components> Vyy 20. Type of Display> Contour, Legend 21. Type of Display> Cutting Diagram (on) 22.
Slab shear forces
36
Flat Slab
Check Mesh Line Output Display BMD, SFD and Deformed Shape along the selected mesh line.
1. 2. 3. 4. 5. 6.
Main Menu> Result> Mesh Line Output Load Cases/Combinations> CB:gLCB2 X Mesh Line (On) Node on Mesh Line> Select a point on the line ①. Mesh Line Output Option> Average (4 Slabs)
①
②
X Mesh Line Output 37
Tutorial 1
7. Y Mesh Line (On) 8. Node on Mesh Line> Select a point on the line ②. 9. Mesh Line Output Option> Average (4 Slabs) 10.
Y Mesh Line Output
38
Flat Slab
Design SDS design capabilities include Calculation of reinforcement for floor slabs/foundation mats Check for two-way shear at column/pile locations and concentrated loading points of a slab/foundation mat Check for one-way shear at critical sections specified by the user In this example, we will check the reinforcing bars by automatic calculation, and perform two-way shear check and one-way shear check for the slab. Also, an overall reinforcing design output will be produced.
Enter Design Parameters Select a design code for design.
1. Main Menu> Design> Design Code 2. Design Code> ACI318-02 3. Design Reduction Factor> For Flexure> 0.9 ; For Shear> 0.75 4.
Select a Design Code
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Tutorial 1
Shear Check Result Check punching shear and produce the punching shear check results. Punching check by Stress will reflect the shear stress resulting from the unbalanced moments. 1. 2. 3. 4. 5. 6. 7.
Shear Check Result Load Combinations> ALL COMBINATION Check Options> Punching Shear> Stress> Avg. by Side Type of Display> Legend, Values Status Bar> Force Unit> N, Length Unit> mm
Punching Shear Check Result 40
Flat Slab Check one-way shear at the effective depth from the drop-panel face. The shear check results over the column strip will be produced. 1. 2. 3. 4. 5. 6. 7.
Check Options> Punching Shear (off) One-Way Shear (on) Pick points Pnt1 and Pnt2 (Figure 36-①)> Status Bar> Force Unit> kN, Length Unit> cm Component> Vyy
①
Pnt1
Pnt2
One-Way Shear Check Result 41
Tutorial 1
Design Floor Slab Moments vary across the slab panel. For the reinforcement design, consider the average moments over the column and middle strips. Generate Line Grid at certain column and middle strip locations. 1. Line Grid> 2. Grid Name> G1 3. x-Grid Lines> 4. y-Grid Lines> 5.
Specify the materials and sizes of reinforcing bars and the bar spacing for reinforcing design. 1. Enter the material data and design code in Main Menu> Tools> Preferences> Property & Design. 2. Main Menu> Design> Design Criteria for Rebars 3. For Slab Design> Rebar> #4 4. Spacing> @100, @125, @150, @175, @200, @225, @250, @300, @350 5.
Rebar Size and Spacing assignment
44
Flat Slab
In order to design bottom bars, check the positive moments over the column and middle strips. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Main Menu> Design> Slab Design Result Load Combinations> gLCB2 Slab Design Result> Avg. Nodal, Bottom, Element, Y-Dir. (Myy) Type of Display> Contour, Legend Rebar (on) Cutting Line Result (on) Name> Column Strip-Positive Pick two points Pnt1 and Pnt2 as Figure 38.> Name> Middle Strip-Positive Pick two points Pnt1 and Pnt2 as Figure 39.> Defined Cutting Lines For Check> Column Strip-Positive (On), Middle StripPositive (Off)
12.
Design bottom bars over the column strip
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Tutorial 1
13. Defined Cutting Lines For Check> Column Strip-Positive (Off), Middle StripPositive (On) 14.
Design bottom bars over the middle strip
46
Flat Slab Click to produce automatic design results. Summary calculations will display the calculation process for the current bar placement. From the design results only maximum/minimum values will be displayed. The results by Cutting Line Result will be also displayed.
