Question
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h2. How are tension-only members |
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modeled during response-spectrum analysis? |
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Answer
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:
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*Answer:* [Tension-only|kb:Tension and compression limits tips] and compression-only behavior are nonlinear effects which should be evaluated using nonlinear [time-history|kb:Time-history analysis] analysis because [response-spectrum|kb:Response-spectrum analysis] analysis (RSA) is a linear method which does not consider nonlinear assignments during formulation. [Links|kb:Link] and all other nonlinear properties do not affect RSA. RSA uses effective stiffness and effective damping, and is based on the stiffness used for the corresponding [modal|kb:Modal analysis] 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:
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!Modal_load_case.png|align=center,border=0!
{center-text}Figure 1 - Stiffness{center-text}
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Nonlinear [time-history|kb:Time-history analysis] analysis should be run to consider complete nonlinear behavior.
h1. See Also
* [Tension and compression limits|kb:Tension and compression limits tips] article
* [Tension-only elements in ETABS|etabs:Tension-only elements in ETABS] article |