Seismosoft | Earthquake Engineering Solutions

Hi,
I'm trying to run a RAS analysis on an unreinforced masonry building, but the result I got was very strange. I tried several spectra on two models, and both gave me extremely small displacements that are less than 3 mm.
What I did is the following:
- Under RAS parameters tab, Add standard to the Loading combinations;
- Under RAS parameters tab, Add a spectrum as Given accelerograms, one example I used was ChiChi.dat;
- After I ran the analysis, I reviewed structural displacement under Global Response Parameters tab for all the 4 combination outputs, both x-axis and y-axis, and all the nodes.
Doing this, the maximum displacement I got so far is 2.5mm, which is obviously wrong since it does not match the results from pushover and time-history.
I must have missed something important. Could you please help me with what I did wrong with RSA? Really appreciate that.
Best Regards,
Aslinn

Aslinn, are you getting displacements from the "Deformed Shape Viewer" or from the "Global Response Parameters" table? At least on my computer, on which I am running SeismoStruct 2020 Release 1 Build 1, the numbers on the plot are off by the factor specified in the response spectrum definition compared to the numbers in the table, which appear to be correct. I may need to adjust some setting to get the plot correct, but I am not sure. Hope this helps. Best of luck in your work.

Note that the response in RSA is linear elastic, contrary to the response in nonlinear dynamic analysis and pushover analysis. This could also explain the discrepancies
Seismosft Support

huffte wrote: 08 May 2020, 14:59 Aslinn, are you getting displacements from the "Deformed Shape Viewer" or from the "Global Response Parameters" table? At least on my computer, on which I am running SeismoStruct 2020 Release 1 Build 1, the numbers on the plot are off by the factor specified in the response spectrum definition compared to the numbers in the table, which appear to be correct. I may need to adjust some setting to get the plot correct, but I am not sure. Hope this helps. Best of luck in your work.

Hi,
Thank you for your reply. I'm using SeismoStruct 2020 Release 1 as well. It seems to me that the numbers under 'Deformed Shape Viewer' and 'Global Response Parameters' are the same, but after I multiply them by the factor, 9.81, the numbers are more reasonable. Is this what we should expect?
Best Regards,
Aslinn

Probably this is a coincidence. A more reasonable estimate is the (nonlinear displ)=(q-factor)*(linear displ), however this is also a big approximation.
You should not mix and compare linear and nonlinear deformations directly.
Seismosoft Support
PS: This discussion is beyond the scope of this support forum. You should better make this discussion with your supervisor.