Seismosoft | Earthquake Engineering Solutions

Dear all,

I am running an IDA analysis to find response of a shear wall of 4 stories.

By a pushover analysis previously i found the yield moment of this wall was only 400 kN.m .

However in the IDA, the wall is taking moments well ahead of its yield point. It takes moments of 1000kn.m at the maximum displacement point.

How is this possible . Can some one explain this behavior?
I used the exact same file for both analysis just changing the type of analysis from IDA to static pushover.

Dear imish,

Have you searched the Help System for "dynamic analysis static capacity"? If you do (it's always a good idea to do so), you will find the following, at the 'Member action effects' page':

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4. In principle, the internal forces developed by frame elements during dynamic analysis should not exceed their static capacity, derived through a pushover analysis or hand-calculations. However, some factors may actually lead to differences:
i) if cyclic strain hardening of the rebars takes place, then this may lead to differences particularly for what concerns comparisons with hand-calculations (where strain hardening is normally not accounted for).
ii) if the the elements feature distributed mass, then their bending moment diagram developed during dynamic analysis will differ from its static analysis counterpart, and hence the shear forces cannot really be compared. (however, moments still can)
iii) if equivalent viscous damping is introduced, then the structure/elements may deform less, hence elongate less, developing higher axial load, and thus higher moment capacity.
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Hopefully, the above will assist you in continuing with your (certainly wise) analyses checks.

Seismosoft Support