Direct integration vs Modal history in SAP2000
Direct integration vs Modal history in SAP2000
(OP)
Hi all.
I am analyzing my bridge model using non-linear direct integration and modal FNA analysis but the results from both tests are different. Modal FNA analysis give smaller result vs. direct integration.
I did try using displacement and acceleration time history for direct integration and those results are the same, but the modal FNA analysis is about 0.5 of the DI result. Is this supposed to be the case? I know that the numerical solutions used are different.
Also, I am considering multi-support excitation, but I think it's not computed properly using modal FNA analysis. I'm asking because bridge model with pile and soil springs take a very long time, say 24 hrs, to compute.
Thanks all.
I am analyzing my bridge model using non-linear direct integration and modal FNA analysis but the results from both tests are different. Modal FNA analysis give smaller result vs. direct integration.
I did try using displacement and acceleration time history for direct integration and those results are the same, but the modal FNA analysis is about 0.5 of the DI result. Is this supposed to be the case? I know that the numerical solutions used are different.
Also, I am considering multi-support excitation, but I think it's not computed properly using modal FNA analysis. I'm asking because bridge model with pile and soil springs take a very long time, say 24 hrs, to compute.
Thanks all.





RE: Direct integration vs Modal history in SAP2000
Google "CSI FNA time history" and you'll find a number of technical write-ups
RE: Direct integration vs Modal history in SAP2000
For the first case, i did not specify any NL links. The 2nd case (bridge-pile) now considers NL links. I will try your suggestions.