I am working on a 2D frame to study the response of Base isolated structure. I did modal analysis analytically in MATLAB and tried comparing with modal analysis output of ETABS. The modal time periods obtained is not same. I choose the stiffness of isolator to obtain time period of 2.2s which is closed to ETABS result of 2.4s while I am getting period of 3.4s from MATLAB.
It would be a great help if anyone can figure out the problem. Thank you
Dear Bikesh Kila Shrestha
1 - check the Mass , Stiffness & damping matrices of your structure to be the same as each other in ETABS and MATLAB in your constraint structure ( without base isolation ).
2 - check the Mass , Stiffness & damping matrices of your structure to be the same as each other in ETABS and MATLAB in your isolated structure .
3 - check the mechanical properties of your springs ( link elements ) in ETABS and MATLAB and ensure that damping is applied in true and same direction in both MATLAB & ETABS files .
4 - Finally i guess your MATLAB script of isolated structure is not true .
Hossein Safar Yousefifard For fixed base case, the results are almost same in both ETABS and MATLAB. As of damping, I have not included them both in ETABS and MATLAB as the damping is very low and wouldn't significantly affect the modal analysis.
The link element has only been assigned with its horizontal stiffness (a very simplified modelling).
I also think the MATLAB script for isolated structure might be the problem but that is what I am getting from the literatures I referred. If you can explain a bit on the script, I might be helpful. And thank you for your effort.
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