ANALYSIS AND DESIGN OF RC BUILDINGS USING SAP-

2000

Ratnesh KumarResearch Scholar

Department of Earthquake EngineeringIndian Institute of Technology Roorkee

“COMPUTER IS A DUMB MACHINE”

Is it true ? Present generation computers!!!!!

we must know two thingsThe language which it can understand properly

The expected outcome of command which can be validated

Correct input in proper format will only fetch a correct solution

MODELINGInputs

Material properties, Equilibrium and Compatibility Equations, Energy and Work Principals, Incompatible Elements, Boundary Conditions, Analysis Methods, Design Principal and Philosophy

Information about building and site conditionNumber of frames with spacing of columns

Longitudinal direction

Transverse direction

Number of stories and type of diaphragm

Usage of building

Soil condition, Seismicity condition, Wind

LOAD CALCULATION

Dead Load IS 875-1978 (Part-1)

Imposed Load (Live) IS 875-1978 (Part-2)

Earthquake IS 1893-2002 (Part-1)

Wind load, Snow load and other loads should be

calculated based on relevant codal provisions

Flow diagram for dead load calculation

Flow diagram for live load calculation

Flow diagram for Wind load calculation

Flow diagram for earthquake load calculation

Flow diagram for equivalent static earthquake load calculation

Flow diagram for earthquake response spectrum calculation

Linear and nonlinear analysis methods

LOAD COMBINATION

1.5 (DL + IL)

1.2 (DL + IL ± EL)

1.5 ( DL ± EL)

0.9 DL ± 1.5 EL

Earthquake is not likely to occur simultaneously with wind or maximum flood or maximum sea waves

while designing structure earthquake should not be combined with wind, maximum flood or maximum sea waves

Simplified Nonlinear Analysis

Salient PointsDetermination of capacities beyond elastic limit

Pushover procedure is used to determine capacity

Capacity spectrum method and Displacement coefficient method are used to determine performance point (ATC 40)

Performance point – The point of intersection of capacity spectrum and demand spectrum

Creation of structures computer model

Classification of model elements as primary or secondary

Application of lateral storey force

Adjustment of lateral force so that some element is stressed within 10% of its member strength

Revise the model using zero stiffness for the yielding element

Apply new incremental load to revised model

Add increment of lateral load and corresponding increment of roof displacement to the previous total

to give a accumulated value

Is anelement

(or group of elements) has reached significant level of

strength degradation

No

Yes

Plot the capacity curve

Is structure has become

unstable

NoModel structure

excluding yieldedmember

Superimpose capacity curve to get global capacity curve

yes

STEP BY STEP PROCEDURE

Plan of Building

Elevation of Building

STEP 1

Click The icon shown to open SAP 2000

STEP 2

Window as shown here will open Click OK

Change units in the drop down box shown,

to KN, m, C

STEP 3

Go to File New Model

Window as shown here will

openClick to

Grid Only

STEP 4 Window as shown here will open. Input no of grid lines in X direction as 5, Y direction as 4 and Z direction as 16Also input Grid Spacing in X direction as 7.5, Y direction as 7.5 and in Z direction as 3.Note: If grid spacing is varying in any direction, it can be changed using edit grid button.After finishing it click OK. The grid model of building will be ready. Save the model in a folder.

STEP 5 Go to drop down menu Define Materials… a dialogue

box Define Material will open. Define CONC (For concrete). Define various parameters in boxes. Here M 30

and Fe 415 have been considered.Go to drop down menu Define Frame Sections… a

dialogue box Frame Properties will open. Click second drop down box of “Choose Property Type to Add”

Add Rectangular Add New property Rectangular Section. Give some section name for Beam, define

parameters in boxes, and also define Concrete Reinforcement. Similarly same things will be done for Columns. To use cracked section, click Set Modifier to

change stiffness of members to account for cracked section, click OK.

STEP 6Click Draw button, click to

draw Frame/ Cable/Tendon. A dialogue

box will open, click on Section to find

appropriate section.Draw section on GUI by

clicking on nodes.In this problem draw only ground floor beams and

columns.Note: View can be

changed by designer at any time while drawing

sections.

STEP 7After drawing sections again go to drop down menu Define Load Cases… a dialogue box Define Loads will open as shown. It can be observed that a load named Dead is already defined with a self weight multiplier 1, this case is for lself weight of members drawn in previous steps. User should not remove or change this load case. Define other load cases as Slab dead, Live_1 (for less than or equal to 3 kN/m2), Live_2 (for more than 3 kN/m2), Live roof, Partitions, Equivalent static EQ_X, Equivalent static EQ_Y, Wind and so on.Note: User should use self weight multiplier as 0 for all the defined cases. Response spectrum for earthquake should not be defined here.

STEP 7

To distribute various loads on slab to beams, yield line

pattern of loading should be used. In Present problem, slab

panel is square so the load will be distributed on triangular

pattern.

Slab Load (Hatched area):

SLAB_DEAD

25(Density) X 0.15(Thickness) X 3.75(Height of triangle)

=14.0625 kN/m

LIVE_2kN

3.75(Height of triangle) X 2 (Intensity of loading) = 7.5 kN/m

LIVE_ROOF

3.75(Height of triangle) X 2 (Intensity of loading) = 7.5 kN/m

STEP 8

Select members on which same loads are to be applied. Go to drop down menu Assign Frame/Cables/Tendon Loads Distributed a dialogue box Frame Distributed load will open. Change load case name to SLAB_DEAD, Assign Trapezoidal Load

STEP 9

To define all members in model, replicate command can be used. This command will replicate all members including loads.Go to drop down menu Edit Replicate a dialogue box replicate will open. Define Increments in dz 3 and Increment Data as 14. Click OK, Building model will be generated. Check for loads replication option in Modify/Show Replicate Options…

On beams at roof level remove Live load by assigning 0 intensity and replacing the existing load. Assign ROOF _ Live over these beams

STEP 10

To assign support, select all the nodes at bottom most grid line either by clicking or by windowing. Go to drop down menu Assign Joint Restraints a dialogue box Joint Restraints will open. Make all DOF’s fixed. Click OK

STEP 11To incorporate rigid floor action, select all the nodes at first floor level either by clicking or by windowing. Go to drop down menu Assign Joint Constraints a dialogue box Assign/Define Joint Constraints will open. Click Diaphragm in box Choose type of constraints. Click to Add New Constraints. A dialogue box will open as shown

Make constraint axis as Z Axis, and assign a different diaphragm constraints to different selected Z level

STEP 12 Go to drop down menu Define Functions Response Spectrum a dialogue box Define Response Spectrum will open

Choose Function Type to Add Spectrum from File Add New Function, a dialogue box shown will open. Browse previously defined response spectrum file

(A file in notepad should be defined prior to this command, containing Period Vs Acceleration in two columns).

After loading this file, convert it to user defined.

STEP 13Go to drop down menu Define Analysis Cases a dialogue box Analysis Cases will open. Click to Add new Case, Another dialogue box will open, as shown Analysis Case Type Response Spectrum. Define A name (eg. Res_X)

Use Load Name U1, Function as defined previously and scale factor (ZIg/2R). Similarly define another case in Y direction with load name U2

STEP 14

Go to drop down menu Define Mass Source, A dialogue box will open, Define Mass source from LOADS

Use factor 1 for all the load cases of Dead load and appropriate factor for Live load based on codal provisions. Do not consider Roof Live Load.

STEP 14Go to drop down menu Analyze Run Analysis, A dialogue box will open as shown, Click Run Now

STEP 15

After finishing the analysis, go to Display Show TablesDetermine base reactions for different load cases and compare it with manually computed results. Also check modal information.Determine base reactions in RES_X and RES_Y cases correspondingly in X and Y directions, this will give base shear (VB) in X and Y direction. Determine the correction

The numerator is calculated as per IS 1893 (Part 1): 2002. Multiply the obtained

with previously determined (ZIg/2R) factor in response spectrum cases and modify it. Again follow step 14. Check base reactions in RES_X and RES_Y cases correspondingly in X and Y directions.

VB

VB

STEP 16

Go to drop down menu Option Preferences Concrete Frame Design, A dialogue box will open Value to Indian IS 456-2000

STEP 17

Go to drop down menu Define Combination, A dialogue box will open, Click to Add New Combo

Define combinations with appropriate scale factor as per codal provisions

STEP 18

Go to drop down menu Design Concrete Frame Design Select Design Combo, A dialogue box will

open, select all the combination defined in previous step.

Go to drop down menu Design Concrete Frame Design Start Design/Check of Structure. The

building will be designed for severe most combination for each member

STEP 19Go to drop down menu Select Frame Sections, A dialogue box will open, select all the Beams, and unlock the model

STEP 20

Go to drop down menu Assign Frame/Cable/Tendon Hinges, A dialogue box will open

Click Add again, A dialogue box will open as shown, Define Auto Hinge Type From Tables in FEMA 356 Select a Fema 356 Table Table 6-7 (Concrete Beam –Flexure) Item i. Click Ok, Again a dialogue box will open

Define parameters as shown in this figure. Click Ok, again previous dialogue box will open as shown below, Change Relative Distance to 1, Add, Do the same thing as done for relative Distance 0

STEP 20 Go to drop down menu Select Frame Sections, A dialogue box will

open, select all the Columns.Go to drop down menu Assign Frame/Cable/Tendon Hinges, A

dialogue box will open as in previous case, repeat the same as in previous step but use Select a Fema 356 Table Table 6-8 (Concrete

Column –Flexure) Item i. Input values

STEP 21 Go to drop down menu Define Analysis Cases a dialogue box Analysis Cases will open. Click to Add new Case, Another dialogue box will open, Nonlinear Analysis Case Type Static

Define a name (Push_Gravity_X), and apply loads and define other parameters

STEP 22

Go to drop down menu Define Analysis Cases a dialogue box Analysis Cases will open. Click to Add new

Case, Another dialogue box will open, Nonlinear Analysis Case Type Static, define mode proportional load case. Continue from state at End of Nonlinear States

Push_Gravity_XDefine a name (Push_ X), and apply loads and define

other parameters

Similarly define the push gravity and mode proportional analysis in Y direction.

Repeat the cases for negative direction.Use scale factor as -1.

Repeat step 14. This will conclude nonlinear analysis