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Loads on structures:
- -. .- Dynamic (e.g. earthquake)
- Linear (constant stiffness)- Nonlinear (variable stiffness)
Structural Analysis Approaches:-(least accurate; least complex)
-- Nonlinear static (pushover)- Nonlinear d namic time histor
(most accurate; most complex)
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Pushover analysis: pp y ng a orce str ut onorce str ut on to t e structure n an
incremental fashion while monitoring theu vv
base shear (V b) versus control nodecontrol node displacement N .
compromise the simplicity of linear static approachesu y y .
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1- Nonlinearity sources:
- -(consider or not: codes)
-(too many materials behavior models)
2- Nonlinearity modeling:
- Concentrated - Distributed
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Plastic hinge properties:
- -
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Plastic hinge properties:- using codes tabulated properties
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-- a single concentrated force at the top
-
- in ro ortion to the standard code rocedure:
/ x x x x xF w h w h V - in proportion to the product of story masses and
predominant mode shape of the elastic model of thestructure
/ x x x x xF w w V
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4- Control node:- For common buildings, the control node could beselected as roof (top) story node
- Pushover analysis is stopped when the structure reaches:re-defined dis lacement
or
ultimate capacity
-application of lateral loads
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-The global response of the structure and individual
light of the specific performance goals of the system
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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 . 0 .
0 . 3 4 5
Select lateral load pattern:
1 0 0 0
3 4 5 x
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2- Lateral Load Case
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3- Define Push Load Case
1 2
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4- Assign Plastic Hinges
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4- Assign Plastic Hinges
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5- Run
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6- Results OutputDisplay displacement:
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7- Checking Hinges Status
At 0.5 ft roof dis lacement: the erformance levelof the system is Collapse Prevention (CP)