P-delta + Modal Spetral Analysis
P-delta + Modal Spetral Analysis
(OP)
Is there an option in SAP2000 to take into account the p-delta effect when you are working with load combinations which have a Response Spectrum load case?
I know that it makes no sense to combine p-delta with a response spectrum result because it loose the sign. But how can I have this amplification into account?
Currently I'm scaling up the drifts and forces by the ASCE 7-05 Section 12.8.7 coefficient. Is there another way? Regards,
Sebastian
I know that it makes no sense to combine p-delta with a response spectrum result because it loose the sign. But how can I have this amplification into account?
Currently I'm scaling up the drifts and forces by the ASCE 7-05 Section 12.8.7 coefficient. Is there another way? Regards,
Sebastian





RE: P-delta + Modal Spetral Analysis
As you already pointed out, there isn't a reasonable way to include response spectrum (RS) results in a P-delta case. You could define nonlinear P-delta load cases which include static earthquake loads, but not RS loads. Alternatively, a direct integration time history analysis for seismic loads could consider P-delta
I don't have it in front of me at this moment, but doesn't 12.8.7 refer to amplification of static results?
RE: P-delta + Modal Spetral Analysis
in my opinion it doesn't say that this amplification is only valid for static results.
According with ASCE 7.05 Section 12.8.7: "Where the stability coefficient (teta) is greater than 0.10 but less than or equal to the incremental factor related to P-delta effects on displacements and member forces shall be determined by rational analysis. Alternatively, it is permitted to multiply displacements and member forces by l.O/(l - teta)."
Regarding you answer, according with ASCE I need to take p-delta effect into account if teta is > 0.10. The "stressed" modal cases could amplify the forces but I think that it isn't the same. Thanks, regards.
Sebastian