Question
How
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are tension-only members
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modeled during response-spectrum analysis?
Answer
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Response spectrum analysis is a linear type of analysis for which effective stiffness and effective damping are used. Nonlinear properties (such as those defined for nonlinear links and other nonlinear elements like cables) are ignored for response spectrum analysis. The response spectrum analysis is based on the stiffness used for the related modal analysis case - it can be either stiffness for zero initial conditions or stiffness at the end of nonlinear case:
If you need to consider complete nonlinear behavior, it would be necessary to run nonlinear time history analysis.: Tension-only and compression-only behavior are nonlinear effects which should be evaluated using nonlinear time-history analysis. Response-spectrum analysis (RSA) is a linear method which does not consider nonlinear assignments during formulation. Links represent another nonlinear assignment which does not affect RSA. RSA uses effective stiffness and effective damping according to the stiffness used in the corresponding modal analysis case. Stiffness may be based on zero initial conditions or that at the end of the nonlinear case. These options are shown in Figure 1:
Figure 1 - Stiffness
Nonlinear time-history analysis should be run to consider complete nonlinear behavior.
See Also
- Tension and compression limits article
- Tension-only elements in ETABS article