Seismosoft | Earthquake Engineering Solutions

Hi every body
I have a steel frame with infrmFBH. i want to perform IDA ( Drift_max Vs Sa(T)--> spectral acceleration in fundamental period, following of this performance, I want to extract Sa(T) in collapse point. but the IDA curve doesn't have zero-slope and i don't really know what point is collapse point in this curve?
actually, the slope of curve are increasing instead of declining.[V]
thanks a lot

Hi Afakhimi,

With slip, you mean the slope of the curve?

SeismoSoft Suppoty

yes slope. sorry
he is my friend and working on same project.

quote:Originally posted by seismosoft

Hi Afakhimi,

With slip, you mean the slope of the curve?

SeismoSoft Suppoty

yes, i am perplexed for this problem

Hi afakhimi,

There may be many reasons for an IDA envelope curve not to feature a post-peak softening slope (the same may happen when running pushover analysis).

For instance, if your axial load level is relatively modest and your steel material features an ever-increasing hardening, then it may well happen that P-Delta effects will not kick-in and the structure will continue to "harden".

What one needs to do in such cases is to correct any modelling deficiencies (e.g. introduce a fracture strain for the steel, correct the axial load definition, etc) and/or define appropriate failure/collapse criteria (e.g. maximum interstorey drift, maximum chord rotation, etc) which will indicate when collapse occurs (independently of if the analysis continued to run or not).

Rui