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Using SAP2000 Software Package in

Earthquake Engineering (Part II: Pushover)

Sameframebut

differentloading

QD=4.5kips/ft

QD=10.5kips/ft

QD=10.5kips/ft

Loads on structures:

- Static (e.g. self-weight)- Dynamic (e.g. earthquake)

Structures response:-- Nonlinear (variable stiffness)

Structural Analysis Approaches:

- Linear static (ELF)

(least accurate; least complex)

- Linear dynamic (response spectra)- Nonlinear static (pushover)

- Nonlinear dynamic (time history)

(most accurate; most complex)

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Pushover analysis:

Applying a force distributionforce distribution to the structure in an

incremental fashion while monitoring theoccurrence of nonlinear behaviornonlinear behavior and plotting the

base shear (Vb) versus control nodecontrol node displacement

(uN).

compromise the simplicity of linear static approaches

and accuracy of nonlinear dynamic methods.

1- Nonlinearity sources:

- Geometrical (P-Delta effects)(consider or not: codes)

- Material

2- Nonlinearity modeling:

- Concentrated - Distributed

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Plastic hinge properties:

- running section analysis and coming up with M- curves

Plastic hinge properties:- using codes tabulated properties

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3- Lateral load pattern:

- a single concentrated force at the top(good for one-story buildings)

- in proportion to the standard code procedure:

/x x x x xF w h w h V

-

predominant mode shape of the elastic model of the

structure

/x x x x xF w w V

4- Control node:- For common buildings, the control node could be

selected as roof (top) story node

- Pushover analysis is stopped when the structure reaches:

pre-defined displacement

or

ultimate capacity

5- Gravity loads should be applied prior to the

application of lateral loads

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6- Check at performance point :

The global response of the structure and individualcomponent deformations are compared to limits in

g o e spec c per ormance goa s o e sys em

Using SAP2000 for Pushover Analysis

We will use the same frame (elastic beams), justmodify dead loads:

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1- Run Modal Analysis

( 1 )

1 . 0

0 . 7 5 9

0 . 3 4 5

1 0 0 0

Select lateral load pattern:

7 5 9

3 4 5

xF k i p s

2- Lateral Load Case

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3- Modify Dead Load Case

3- Define Push Load Case

1

2

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3- Define Push Load Case

1 2

4- Assign Plastic Hinges

Select column elements:

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4- Assign Plastic Hinges

4- Assign Plastic Hinges

Select beam elements:

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5- Run

6- Results Output

Display displacement:

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6- Results Output

Display pushover curve:

7- Checking Hinges Status

Looking for 0.5 ft roof displacement:

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7- Checking Hinges Status

At 0.5 ft roof displacement: the performance levelof the system is Collapse Prevention (CP)