Civil Engineering/pushover analysis
my name is mudakkir ahmed, presently doing my masters dissertation work in the topic, pushover analysis of 3d asymmetric rcc buildings ....please enlighten me with the following queries..
1.when im performing modal pushover analysis in etabs 2013 as well as etabs 9th version in the 3rd mode shape the software is not displaying the performance point (it says N/A) also the base shear and displacements obtained in the 3rd mode are very less.what should i do to achieve performance point in mode 3(rotation mode)?
2.The 3rd mode under consideration is a rotational mode shape.there is a option in etabs 2013 which says monitored displacement while defining the pushover load cases ...the displacement automatically is changed to radians which means etabs 2013 identifies the 3rd rotational mode...am i right in defining the rotational pushover load case...if yes then why is the performance point not obtained ?
suggest an alternative method or solution to achieve performance point in the 3rd mode shape...
note:the building is a 10 storey rcc l-shaped 4x6 bay building in x and y-direction.
ANSWER: Dear Ahmed
May I know what you want to catch doing a 3rd mode push over analysis?
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I want to evaluate performance point for three directions(x,y,z) and want to conclude that structure is most critical and showing least performance in 3rd mode (z-direction)by by using performance point.
In my opinion a mode cant have a real performance point. you can estimate a dummy performance point using displacement spectrum with related modal period of vibration. You must apply a loading pattern according to the 3rd mode of vibration.
Please let me know your further idea.