I know when I input seismic UBC/IBC seismic loads I should type Perform Analysis and Change after each load case.
The problem is, I am using National Building Code of Canada to generate seismic loads in my model and STAAD Pro still gives me the warning:" IF THIS UBC/IBC ANALYSIS HAS TENSION/COMPRESSION OR REPEAT LOAD OR RE-ANALYSIS OR SELECT OPTIMIZE, THEN EACH UBC/IBC CASE SHOULD BE FOLLOWED BY PERFORM ANALYSIS & CHANGE."
I don't have either of those commands in my STAAD model, who can kindly tell me what's wrong in the attached model? Thank you!
Although the warning message mentions UBC/IBC, it is applicable to seismic load generation as per any of the codes including the NBC of Canada. It is a generic warning and is provided whenever the software finds that an automatic seismic load generation has been used, irrespective of whether member tension/compression/REPEAT LOAD/MEMBER SELECTION has been used or not. In your case, since neither of these exist, you may simply ignore the warning. Else you may simply get rid of these warnings by adding the PERFORM ANALYSIS and CHANGE after each seismic case as shown next
LOAD 1 SEISMIC LOAD +X
************************************************************************************
NRC LOAD X 1
PERFORM ANALYSIS
CHANGE
*
LOAD 2 SEISMIC LOAD +Z
NRC LOAD Z 1
Answer Verified By: Jack Xiao
Thank you for your reply.
Before I posted this question, I tried to add PERFORM ANALYSIS & CHANGE after each seismic case in the last model and then the warning has gone. But, in another model (see attached) using NBCC generated seismic loads, even thought I don't have PERFORM ANALYSIS & CHANGE after seismic cases, that IBC/UBC warning does not appear. Does it make sense?
I do get the warning message when I analyze the second file that you attached. Are you not getting the same ?
Sorry, I opened another model which has PERFORM & CHANGE command and I mixed up the two similar models. Thank you very much!