IDA problem

[martinmasanes]

Dear all
I'm performing an IDA analysis but got a problem: Even scaling the ground motion to high values, the plot of Drift vs Sa(T1) remains practically linear, so I doen't get an 'infinite drift' to define the collapse.
The pushover curve is fine, it have a yielding point and after it, it have a segment of negative slope, so I think the model has no problems, please help.

[fmk]

what is happening to the roof displacements as you increase the amplitude, i.e. are you hitting the yield points? and can you get infinite drift with the model you are using??

[martinmasanes]

Yes, I'm sure I'm reaching the yield point int the roof displacement I'm not sure if I can answer the seccond question. Now I'm trying changing the geom. transformation from PDelta in beams and columns (Corotational in braces) to all Corotational for a scale grater than Sa=1.5 g. In don't know if I can reach infinite Drift with this parameters (and delta t=0.001 seconds):
constraints Plain
numberer RCM
system UmfPack
test RelativeNormDispIncr 1.0e-4 30
algorithm NewtonLineSearch -type Secant
integrator Newmark 0.5 0.25
analysis Transient

Thanks for your help

[cxqiu]

Hi, it is not easy to figure out the reason since we don't see the modeling information. But I suggest you to try more ground motion records. btw, I guess Sa=1.5g is not so large that it can collapse a structure.