I have a reinforced concrete building model where inelastic fiber elements were emploed for the structural elements. I did a pushover analysis where the resulting capacity curve will be used for capacity spectrum method (i.e. nonlinear assessment). There is no need to modify flexural stiffness of the members with regard to cracking, since I use a nonlinear fiber model. But I should also perform an eigenvalue analysis and determine modal properties of the building, which will be used to convert capacity curve into modal coordinates (Sa-Sd). Will the eigenvalue analysis with inelastic fiber sections be a correct representation for the cracked sections? Or should I modify the modulus of elasticity to represent cracked section properties in eigenvalue analysis?

- emreakin offline
**Posts:**11**Joined:**08 Aug 2017, 13:55

In Eigenvalue analysis, the characteristics of the members are all elastic. Hence, indeed you should modify the modulus of elasticity to represent cracked section properties. Note also that all current methodologies for the calculation of the target displacement have formulas that calculate the effective (cracked) period from the elastic (uncracked) one.

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