Tutorial 1. Flat Slab

SSSDDDSSS

Contents

Summary 1 Working Environment Setting 3 Enter Material and Section Properties 4 Import a CAD DXF File 8 Define Elastic Support Conditions 9 Enter Column Support Conditions 13 Generate Area Objects 14 Assign Members 17 Enter Wall Support Conditions 21 Enter Punching Check Sizes 22 Enter Loading Data 23 Set Static Load Cases 23

Enter Floor Loads 24

Perform Structural Analysis 28 Verify and Review Analysis Results 30

Load Combinations 30

Verify Reactions 31

Check Reaction Table 32

Verify Deformations 33

Verify Member Forces 34

Check Mesh Line Output 37

Design 39 Enter Design Parameters 39

Shear Check Result 40

Design Floor Slab 42

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Tutorial 1. Flat Slab

MIDAS/SDS Version 3.1.0 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. Set a unit system. 2. Enter material and section properties. 3. Import a CAD DXF file. 4. Define support type. 5. Generate area objects. 6. Assign members. 7. Enter elastic support conditions. 8. Enter static loads. 9. Check and review analysis results. 10. Design

Analysis Model

Unit: mm

<Figure 1> Plan

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▣ Model Description

Analysis Model Flat Slab for office use

Story Height 4.0 m (both above and below the slab)

Support Condition Column Support, Wall Support 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

Use Finish Slab Total

Live Load

Office 1.00 4.70 5.70 2.40 Corridor 1.00 4.70 5.70 3.93

▣ Applied Codes

• Building Code Requirements for Structural Concrete and Commentary (ACI318-02, 2002)

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Working Environment Setting

Unit System

Double click the MIDAS/SDS icon to execute SDS.exe. Open a new file and set a unit system.

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.

<Figure 2> Unit System Assignment

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Enter Material and Section Properties

Before generating a model, enter the material properties of the elements, which will be used as structural members.

1. Main Menu> Model> Properties> Material 2. 3. Name> Slab 4. Type> Concrete 5. Concrete>Standard> ASTM(RC) 6. DB> Grade C4000 7. Apply 8. Confirm the generated material data. Assign the material data for Drop Panel and

Wall similarly (Refer to Figure 3).

<Figure 3> Enter material properties

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Enter the section dimensions of a wall beam, which is an equivalent beam substituted for a core wall.

1. Properties> Section 2. 3. Name> Wall 4. Solid Rectangle> User (on) 5. H> 8000 ; B> 200 6. Check the auto-calculated stiffness data at the bottom of the dialog box (Refer to

Figure 4-①). 7.

<Figure 4> Enter section properties

①

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Enter the thickness data of the floor slab.

1. Properties> Thickness 2. 3. ID> 1 4. Name> Slab 5. Thickness> In-plane & Out-of-plane> 200 6.

<Figure 5> Enter slab thickness data

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Enter the thickness data of the drop panel.

1. ID> 2 2. Name> Drop 3. Thickness> In-plane & Out-of-plane> 350 4. 5.

<Figure 6> Enter drop panel thickness data

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Import a CAD DXF File

To generate a Flat Slab, import a DXF file, which will be the basis for generating slabs, drop panels and core walls.

1. Main Menu> File> Import> AutoCAD DXF File 2. > Flat Slab.dxf 3. Option> Insertion Position> 0, 0 ; Rotate Angle> 0 4.

<Figure 7> CAD DXF File Import

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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. Main Menu> Model> Boundaries> Column Support Type 2. 3. Name> C 4. Support Type> Solid Rectangle 5. Mesh and Link at Column Boundary (on) 6. Material> 7. Standard> ASTM(RC) ; DB> Grade C4000 8. 9. Material> Modulus of Elasticity> 25.1255 ; Poisson’s Ratio> 0.2 10. Thickness> Above> Depth(D)> 700 ; Width(B)> 700 ; Height(H)> 4000 11. 12. Bending Stiffness Scale Factor> 4.0 13. > Check the auto-calculated stiffness data. 14.

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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.

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 2 E IH

α ⋅⋅ .

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 8EIH

. Therefore, α

is taken as 4.

A

H

H E, I

E, I

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<Figure 8> Define Column Support Types

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Define Wall Support Types for the core walls.

1. Supports > Wall 2. 3. Name> Wall 4. Support Type> Thickness 5. Material> 6. Standard> ASTM(RC) ; DB> Grade C4000 7. 8. Material> Modulus of Elasticity> 25.1255 ; Poisson’s Ratio> 0.2 9. Thickness> Above> Thickness(T)> 200 ; Height(H)> 4000 10. 11. Bending Stiffness Scale Factor> 4.0 12. > Check the auto-calculated stiffness data. 13. 14.

<Figure 9> Define a Wall Support Type

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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.

<Figure 10> Assign column supports

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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 ).

<Figure 11> Create area objects for slab

1 2

3Office

Corridor Office

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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).

<Figure 12> Create area objects for drop panels

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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).

<Figure 13> Create area objects for openings

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Assign Members Assign wall beams to the line objects corresponding to the core walls.

1. Main Menu> Model> Member> Beam 2. Zoom Window> Magnify the core at the lower left (Figure 14- 1 ). 3. Select Single> Select the line objects corresponding to the core walls. 4. Type> Wall Beam 5. Material Name> 2:Wall 6. Section Name> 1:Wall 7. 8. Zoom Fit> Zoom Window> Magnify the core at the upper right (Figure 14-

2 ). 9. In a similar manner, assign the Wall Beams.

<Figure 14> Assign Wall Beam Members

2

1

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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.

<Figure 15> Assign Slab Members

①

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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.

<Figure 16> Assign Drop Panel Members

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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.

<Figure 17> Assign Opening Members

①

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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.

<Figure 18> Enter Wall Supports

Drag

Drop

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Enter Punching Check Sizes Enter the column sizes required for punching shear check after performing analysis.

1. Main Menu> Model> Boundaries> Punching Check Size 2. Select Identity> Select Type> Column Support Type 3. Select list> C> 4. Punching Check Size> Column Information> Punching Shape> Rectangle 5. Depth> 700 ; Width> 700 6. Column Position> Inner 7. 8. Select Identity> 9.

< Figure 19> Enter Punching Check Sizes

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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. Main Menu> Model> Static Loads> Static Load Cases 2. Name> DL 3. Type> Dead Load 4. 5. Name> LL 6. Type> Live Load 7. 8.

<Figure 20> Enter static load cases

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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.

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. Status Bar> Length Unit> m 2. Main Menu> Model> Static Loads> Area Load Type 3. 4. Name> Office 5. Load Case> 1> DL ; Area Load> -1 ; Weight (on) 6. Load Case> 2> LL ; Area Load> -2.4 7. 8. Name> Corridor 9. Load Case> 1> DL ; Area Load> -1 ; Weight (on) 10. Load Case> 2> LL ; Area Load> -3.83 11. 12.

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<Figure 21> Define Area Load Types

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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.)

<Figure 22> Check the entry of Office area load

1 Offic

3Office

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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

<Figure 23> Check the entry of Corridor area load

2Corridor

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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.

<Figure 24> Check the layout of auto-generated mesh lines

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Assign analysis options.

1. Main Menu> Analysis> Analysis Options 2. Static Analysis Method> Sparse Gaussian 3. 4. Perform Analysis

<Figure 25> Analysis Options dialog box

<Figure 26> Perform structural analysis

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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.

1. Main Menu> Results> Combinations 2. 3. Select Default Load Combination dialog box> Design Code> ACI318-02 4. 5.

<Figure 27> Generate load combinations

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Verify Reactions Verify reactions due to dead load. The point in Red signifies the maximum reaction.

1. Main Menu> Results> Reactions> Reaction Forces/Moments 2. Load Cases/Combinations> ST:DL 3. Components> FZ> Global 4. Type of Display> Legend (on) 5.

<Figure 28> Reactions at supports

Maximum Reaction

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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.

<Figure 29> Reaction table

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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. Status Bar> mm 2. Main Menu> Result> Deformation> Displacement Contour 3. Load Cases/Combinations> ST:DL 4. Components> DZ 5. Type of Display> Contour, Deform, Legend> 6. Iso View 7. Dynamic Rotate (Check the deformed shape.) 8. Dynamic Rotate (toggle off)> Top View

<Figure 30> Displacement contour

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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

<Figure 31> Inactivate column mesh

①

Pnt1 Pnt1

Pnt2 Pnt2

Cut-Line#1 Cut-Line#2

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7. Main Menu> Result> Forces> Slab Forces/Moments 8. Load Cases/Combinations> CB:gLCB2 9. Slab Force Options> Avg. Nodal ; Avg. Nodal Active Only (on) 10. Components> Myy 11. Type of Display> Contour, Legend 12. Type of Display> Cutting Diagram (on) 13. Status Bar> m 14. Click two points by referring to Figure 31 and to generate Cut-Line#1. 15. Generate Cut-Line#2 by referring to Figure 31. 16. Options> Normal 17. Close the Slab Cutting Line Diagram dialog box. 18.

<Figure 32> Slab moments

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19. Components> Vyy 20. Type of Display> Contour, Legend 21. Type of Display> Cutting Diagram (on) 22.

<Figure 33> Slab shear forces

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Check Mesh Line Output Display BMD, SFD and Deformed Shape along the selected mesh line.

1. Main Menu> Result> Mesh Line Output 2. Load Cases/Combinations> CB:gLCB2 3. X Mesh Line (On) 4. Node on Mesh Line> Select a point on the line ①. 5. Mesh Line Output Option> Average (4 Slabs) 6.

<Figure 34> X Mesh Line Output

①

②

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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.

<Figure 35> Y Mesh Line Output

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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.

<Figure 36> Select a Design Code

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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. Shear Check Result 2. Load Combinations> ALL COMBINATION 3. Check Options> Punching Shear> Stress> Avg. by Side 4. Type of Display> Legend, Values 5. Status Bar> Force Unit> N, Length Unit> mm 6. 7.

<Figure 37> Punching Shear Check Result

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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. Check Options> Punching Shear (off) 2. One-Way Shear (on) 3. Pick points Pnt1 and Pnt2 (Figure 36-①)> 4. Status Bar> Force Unit> kN, Length Unit> cm 5. Component> Vyy 6. 7.

<Figure 38> One-Way Shear Check Result

Pnt1 Pnt2

①

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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> > Absolute (on)> Lines> 850, 1250, 1650 4. y-Grid Lines> > Absolute (on)> Lines> 0, 2000 5.

<Figure 39> Generate Grid Lines

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<Figure 40> Generated Grid Lines

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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.

<Figure 41> Rebar Size and Spacing assignment

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In order to design bottom bars, check the positive moments over the column and middle strips.

1. Main Menu> Design> Slab Design Result 2. Load Combinations> gLCB2 3. Slab Design Result> Avg. Nodal, Bottom, Element, Y-Dir. (Myy) 4. Type of Display> Contour, Legend 5. Rebar (on) 6. Cutting Line Result (on) 7. Name> Column Strip-Positive 8. Pick two points Pnt1 and Pnt2 as Figure 38.> 9. Name> Middle Strip-Positive 10. Pick two points Pnt1 and Pnt2 as Figure 39.> 11. Defined Cutting Lines For Check> Column Strip-Positive (On), Middle Strip-

Positive (Off) 12.

<Figure 42> Design bottom bars over the column strip

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13. Defined Cutting Lines For Check> Column Strip-Positive (Off), Middle Strip-Positive (On)

14.

<Figure 43> Design bottom bars over the middle strip

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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.

<Figure 44> Calculation output