I am trying to do static seismic load generation as per IBC code and I am getting the warning messages below. What does these mean and how can I get rid of these ?
**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.
These are standard warning messages that are printed by the software in the analysis output file whenever it finds that there are static seismic load generation commands in the file and those are not followed by PERFORM ANALYSIS and CHAGE commands. These warnings are generated irrespective of whether MEMBER TENSION/COMPRESSION/REPEAT LOAD/MEMBER SELECTION has actually been used in the file or not. Another thing to note here is that although the warning message mentions UBC/IBC, it is applicable to seismic load generation as per any of the seismic codes supported by STAAD.Pro.
When the PERFORM ANALYSIS and CHANGE command is used after a static seismic case, the software actually saves the generated seismic loads and later reuses these data when required for example in REPEAT LOADS or in re ANALYSIS. Else it generates the data but does not save it for further use. Hence when you have conditions like MEMBER TENSION/COMPRESSION/REPEAT LOAD/MEMBER SELECTION, you should follow up each static seismic load case by a PERFORM ANALYSIS and CHANGE.
If none of the conditions mentioned in the warning above exists in your model, you may leave out the PERFORM ANALYSIS and CHANGE but in that case you would keep getting the warnings. You can of course ignore the warnings in that case but as a matter of good practice, it is better to have the PERFORM ANALYSIS and CHANGE added after every static seismic case, as shown next.
LOAD 1 LOADTYPE Seismic-H TITLE SESIMIC IN X DIR
IBC LOAD X 1
LOAD 2 LOADTYPE Seismic-H TITLE SEISMIC IN Z DIR
IBC LOAD Z 1