Seismic Analysis & Design

7/30/2019 Seismic Analysis & Design

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Seismic Analysis &

Design of10 Story RC Building

(Modal Response Spectra Analysis)

Using ETABS(Metric Units)ACECOMS, AIT


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Table of Content

Objective 5

Problem 5

Step by Step 11

1. Open Existing Model and Unlock Model 11

2. Delete Existing Seismic Static Load Case 14

3. Define Response Spectrum Function 15

4. Specify Response Spectrum Cases 17

5. Run Analysis 21

6. View Modal Analysis Results 24

7. View Results for Response Spectral Analysis 27

8. Run Concrete Frame Design and View Results 36

9.

Run Shear Wall Design and View Results 42


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ETABS Tutorial Example ACECOMS, AIT

Seismic Analysis & Design of 10 Story RC Building (Modal Response Spectra) 5/52

ObjectiveTo demonstrate and practice step-by-step on modal

response spectra analysis and design of 10 story RCbuilding.

ProblemCarry out modal response spectra analysis, anddesign of 10 story RC building as shown in followingdetails based on IBC2000.

3D View


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6/52 Seismic Analysis & Design of 10 Story RC Building (Modal Response Spectra)

Plan View (Unit in m)

BASE STORY 7

STORY 8 STORY 10

6.0

0m

6.0

0m

6.0

0m

2.00 2.00 2.00

2.0

02.0

02.0

0

6.00 m 6.00 m 6.00 m

6.0

0m

6.0

0m

6.0

0m

2.00 2.00 2.00

2.0

02.0

02.0

0

6.00 m 6.00 m 6.00 m


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Elevation View

Material Properties for Concrete (Unit in kg and cm)


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Section Properties

Member Dimension

Beam (width x Height) 30 x 60 cm

Column 50 x 50 cm

Slab Thickness = 15 cm

Shear wall Thickness = 20 cm

Story Height Data

Story Height

Typical Story 3.00 m

Story at base of building 4.00 m

Static Load Cases

LoadName

Load Type Details Value

Self Weight of Structural MembersCalculate automatically using Self

Weight Multiplier in ETABS-

Uniform Load on Slabs:(Finishing + Partition Load) 0.20 t/m2

DEAD Dead Load

Uniform Load on Beams:(Wall Load) 0.50 t/m

LIVEReducibleLive Load

Uniform Load on Slabs:(Use Tributary Area: UBC97)

0.25t/m2


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Modal Response Spectra Parameters (IBC2000)

Parameter Values NoteDamping 0.05 For RC building

Modal Combination SRSS

Directional Combination SRSS

Site Class ETable 1615.1.1

(Soft Clay)

Response Accelerationfor Short Period (Ss)

0.45

Response Accelerationfor 1 Second (S1)

0.18

Site Coefficient ofResponse Acceleration

for Short Period (Fa)

1.86 Table 1615.1.2 (1)

Site Coefficient ofResponse Acceleration

for 1 Second (Fv)3.26 Table 1615.1.2 (2)

Maximum ResponseAcceleration

for Short Period (SMS)0.84

SMS = Fa xSS(Equation 16-16)

Design ResponseAcceleration

for 1 Second (SM1)0.59

SM1 = Fv xS1(Equation 16-17)

Design ResponseAcceleration

for Short Period (SDS)

0.56SDS = (2/3) xSMS(Equation 16-18)

Maximum ResponseAcceleration

for 1 Second (SD1)0.39

SD1 = (2/3) xSM1(Equation 16-18)


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Wind Load Cases (UBC97)

Load CaseParameter

WINDX WINDY

Wind Direction X Y

Wind Speed 90 mph

Exposure Type B (Suburban area)

Importance Factor 1 (Building normal importance)


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Step by Step

1. Open Existing Model and Unlock Model

Step 1-1: Open Existing Model

Start up screen of ETABS, click on Open button or go to File >> Open and findfile from previous example.


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Step 1-2: Save As to New File

Go to File >> Save As and specify new file name.


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Step 1-3: Unlock Model

Click on Unlock Model button

lick on OK to confirm to unlock the model and delete all analysis results

Note: ETABS has locked the model automatically from previous. Model has to beunlocked first before do any modification by clicking on Unlock Model

button . ETABS will delete all analysis and design results after unlock.


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2. Delete Existing Seismic Static Load Case

Step 2-1: Delete Existing Seismic Static Load Case

Go to Define >> Static Load Case, select EQXA and click on Delete Load

Repeat this step to delete EQXB, EQYA and EQYB


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3. Define Response Spectrum Function

Step 3-1: Add New Response Spectrum Function

Go to Define >> Response Spectrum Function and select Add IBC2000Spectrum from drop-down menu.


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Step 3-2: Enter Response Spectrum Function for IBC2000

Specify response spectrum function for IBC2000 as shown in figure below


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4. Specify Response Spectrum Cases

Step 4-1: Add New Response Spectrum Case

Go to Define >> Response Spectrum Cases and click on Add New Spectrum


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Step 4-2: Specify Response Spectrum Case Data for EQX

Enter response spectrum case data as shown in figure below

Note: ETABS will treat response spectrum case as unfactored seismic load (E) inACI load combination for RC frame and shear wall design but responsespectrum load from IBC2000 is factored load then Scale Factor inresponse spectrum case should be divided by load factor (1.4) to changefrom factored load to unfactored load.


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Step 4-3: Add and Specify Response Spectrum Case for EQY

Repeat Step 4-1 and Step 4-2 for response spectrum case (EQY)


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Step 4-4: Deactivate Special Seismic Load Effect

Go to Define >> Special Seismic Load Effect and select Do Not Include SpecialSeismic Design Data


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5. Run Analysis

Step 5-1: Set Dynamic Analysis Parameters

Go toAnalyze >> Set Analysis Opt ions , select Dynamic Analysis, click on SetDynamic Parameters and specify dynamic analysis parameters as shown in figurebelow


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Step 5-2: Start Analysis

Go toAnalyze >> Run Analysis or click on Run Analysis button to startanalysis. ETABS will display deformed shape of model when analysis complete.

Note: ETABS will lock the model automatically from undesired changes. Model

will be unlocked by clicking on Unlock Model button . ETABS will deleteall analysis and design results after unlock.


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Step 5-3: Check Error from Analysis Run Record

Go to File >> Last Analysis Run Log and scroll down to check error message.


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6. View Modal Analysis Results

Step 6-1: Display Mode Shape in 3D View

Select 3D view window, go to Display >> Show Mode Shape or click on Show

Mode Shape button and select desired mode.

To view deformed shape in animation, click on Start Animation.

Note: Time Period of current mode shows at top of 3D window


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Step 6-2: Display Modal Displacement at Particu lar node

Right click on desired node to display modal displacement at current mode shape


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Step 6-3: View Modal Analysis in Tabular Form

Go to Display >> Set Output Table Mode and select items as shown in figurebelow

Select building modal information from drop-down menu

Note: This table can be copied to MS Excel by using Edit >> Copy menu in thiswindow (Not main menu).


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7. View Results for Response Spectral Analysis

Step 7-1: View Analysis Result Diagrams of Frame Elements (Beam orColumn)

Select Plan View by clicking on it, go to Display >> Show MemberForces/Stress Diagram >> Frame/ Pier/Spandrel Forces and select responsespectral analysis (EQX or EQY) from Load and Component


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Note: Sign Convention for Frame Element


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Step 7-2: View Analysis Result Diagram at Particular Frame Element

Right click on desired beam to display particular analysis result diagram

Note: To see analysis results in particular location, move mouse cursor over thisdiagram and see value at bottom of the window


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Step 7-3: Change View to Elevation View at Elevator Location

Click on Set Elevation View button and select elevation view at elevator location


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Step 7-4: View Analysis Result Diagrams of Shear Wall (Pier)

Right click on desired shear wall panel to view particular diagram

Note: Same as frame element, move mouse cursor over this diagram and seevalue at bottom of this window to check analysis results in particular location


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Step 7-5: View Analysis Result Contour in Shear Wall Panels (Elevation View)

Change Plan View to Elevation View by clicking on Set Elevation View buttonand selecting desired elevation for elevator location, go to Display >> Show

Member Forces/Stress Diagram >> Shell Stresses/Forces, select responsespectral analysis (EQX or EQY) from Load and Component. Right click ondesired wall panel to view particular analysis result.

Note: Analysis results at particular location will display at the bottom of windowwhen move mouse cursor over this diagram.


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Note: Sign Convention for Shell Element


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Step 7-6: View Analysis Result Contour in Slab Panels (Plan View)

Change to Plan View by clicking on Set Plan View button and selectingdesired floor, go to Display >> Show Member Forces/Stress Diagram >> Shell

Stresses/Forces and select Load and Component. Same as shear wall panel,right click on desired wall panel to view particular analysis result.


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Step 7-7: View Analysis Results in Tabular Form

Go to Display >> Show Output table Mode, select desired items and click onSelect Loads to specify load case/combination.

Select analysis results from drop-down menu at top-right of screen

Note: This table can be copied to MS Excel by using Edit >> Copy menu in thiswindow (Not main menu).


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8. Run Concrete Frame Design and View Results

Step 8-1: Select Design Code

Go to Options >> Preference >> Concrete Frame Design and select ACI 318-99from Design Code


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Step 8-2: View Load Combination for Concrete Frame Design

Go to Design >> Concrete Frame Design >> Select Design Combo to view loadcombination for concrete frame design. Load combinations have been defined as

selected code from previous step. Select desired load combination from DesignCombos column and click on Show to view load combination parameters (loadfactors and details)

Note: ETABS will define load combination automatically based on selected designfrom previous step.


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Step 8-3: Start Concrete Frame Design

Go to Design >> Concrete Frame Design >> Start Design/Check of Structure


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Step 8-4: Display Longitudinal Reinforc ing for Concrete Frame Design

Select kg-cm, go to Design >> Concrete Frame Design >> Display Design Info,click on Design Output and select Longitudinal Reinforcing from first drop-down

menu.


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Step 8-5: Display Shear Reinforcing for Concrete Frame Design

Go to Design >> Concrete Frame Design >> Display Design Info, click onDesign Output and select Shear Reinforcing from first drop-down menu.


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Step 8-6: Display Concrete Frame Design in Details

To see concrete frame design in details, right mouse click on desired element. Thehighlighted row is the critical location along the element length (maximum requiredreinforcement). More details can be displayed by clicking on button below. ClickOK to close this dialogue.


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9. Run Shear Wall Design and View Results

Typical Shear Wall Design Procedure

Following is a typical shear wall design process that might occur for anew building. Note that the sequence of steps you may take in anyparticular design may vary from this but the basic process will beessentially the same.

1. After create the building model Use the Options menu > Preferences >Shear Wall Design command to review the shear wall designpreferences and revise them if necessary. Note that there are defaultvalues provided for all shear wall design preferences so it is not actuallynecessary for you to define any preferences unless you want to change

some of the default preference values.

2. Run the building analysis using theAnalyze menu > Run Analys iscommand.

3. Assign the wall pier and wall spandrel labels. Use theAssign menu >Frame/Line > Pier Label, theAssign menu > Shell /Area > Pier Label,theAssign menu > Frame/Line > Spandrel Label, and theAssignmenu > Shell/Area > Spandrel Label commands to do this.

Note that the labels can be assigned before or after the analysis is run.

4. Assign shear wall overwrites, if needed, using the Design menu > ShearWall Design > View/Revise Pier Overwrites and the Design menu >Shear Wall Design > View/Revise Spandrel Overwri tes commands.Note that you must select piers or spandrels first before using thesecommands. Also note that there are default values provided for all pierand spandrel design overwrites so it is not actually necessary for you todefine any overwrites unless you want to change some of the defaultoverwrite values.

Note that the overwrites can be assigned before or after the analysis isrun.

Important note about selecting piers and spandrels: You can select apier or spandrel simply by selecting any line or area object that is part ofthe pier or spandrel.


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5. If you want to use any design load combinations other than the defaultones created by ETABS for your shear wall design then click the Designmenu > Shear Wall Design > Select Design Combo command. Notethat you must have already created your own design combos by clicking

the Define menu > Load Combinations command.

6. Click the Design menu > Shear Wall Design > Start Design/Check ofStructure command to run the shear wall design.

7. Review the shear wall design results. To do this you might do one of thefollowing:

a. Click the Design menu > Shear Wall Design > Display DesignInfo command to display design information on the model.

b. Right click on a pier or spandrel while the design results aredisplayed on it to enter the interactive wall design mode. Notethat while you are in this mode you can revise overwrites andimmediately see the new design results.

If you are not currently displaying design results you can click theDesign menu > Shear Wall Design > Interactive Wall Designcommand and then right click a pier or spandrel to enter the interactivedesign mode for that element.

1. Use the File menu > Print Tables > Shear Wall Design command toprint shear wall design data. If you select a few piers or spandrels beforeusing this command then data is printed only for the selected elements.

2. If desired, revise the wall pier and/or spandrel overwrites, rerun the shearwall design, and review the results again. Repeat this step as manytimes as needed.

3. If desired, create wall pier check sections with user-defined (actual)reinforcing specified for the wall piers using the Section Designer utility.Use the Design menu > Shear Wall Design > Define Pier Sections for

Checking command to define the sections in Section Designer. Be sureto indicate that the reinforcing is to be checked. Use the Design menu >Shear Wall Design > Ass ign Pier Sections for Checking command toassign these sections to the piers. Rerun the design and verify that theactual flexural reinforcing provided is adequate.


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4. Assign these check sections to the piers, change the pier mode fromDesign to Check, and rerun the design. Verify that the actual flexuralreinforcing provided is adequate.

5. If necessary, revise the geometry or reinforcing and rerun the design.6. Print or display selected shear wall design results if desired.

Note that shear wall design is performed as an iterative process. Youcan change your wall design dimensions and reinforcing during thedesign process without rerunning the analysis. However, you alwayswant to be sure that your final design is based on analysis properties(wall dimensions) that are consistent with your design (actual) walldimensions.

3per rigid zone

Rigid

Beam

Column

A: Shear Wall wi th Line Loads B: Fin ite Element Model

C: Define Beams & Columns D: Beam-Column Model


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Step 9-1: Change view to Elevation View

Click on Set Elevation View button , select elevation at elevator location and use

Rubber Band Zoom button to zoom shear wall view.


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Step 9-2: Select Design Code for Shear Wall Design

Go to Options >> Preference >> Shear Wall Design and select parameters asshown in figure below.


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Step 9-3: View Load Combination for Shear Wall Design

Go to Design >> Shear Wall Design >> Select Design Combo to view loadcombination for shear wall design. Load combinations have been defined as

selected code from previous step. Select desired load combination from DesignCombos column and click on Show to view load combination parameters (loadfactors and details)

Note: ETABS will define load combination automatically based on selected designfrom previous step.


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Step 9-4: Start Shear Wall Design

Go to Design >> Shear Wall Design >> Start Design/Check of Structure


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Step 9-5: Display Pier Design Information for Shear Wall Design

Go to Design >> Shear Wall Design >> Display Design Info , click on DesignOutput and select Pier Longitudinal Reinforcing.

Note: Longitudinal reinforcing area displayed in above figure is for all 3 shear wallpanels because all of them have been assigned in same pier label (P1) fromprevious example


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Step 9-6: Display Pier Design Details for Shear Wall Design

To see pier design in details, right mouse click on desired pier panel.


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Reinforcement Location for Pier


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Note: Typical Detailing of Shear Wall

Seismic Analysis & Design

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