Dear STKO team
I'm working in eigen analysis, but when I match the results with ETABS, the MODAL PARTICIPATION MASS RATIOS is different.
what will be the problem?
The difference is shown in the photo attached.
EIGEN ANALYSIS
EIGEN ANALYSIS
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marafini.f
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Re: EIGEN ANALYSIS
Dear allano89,
as I mentioned in the other comment, you need to check the units you are using. OpenSees as STKO is unit-less, so you need to be consistent in your model. Kg for mass, makes sense if you are using N-m, but it seems to me you are using kN-m, so your masses should be expressed in tons.
I suggest you look in this other thread on ETABS and STKO comparison of Modal analysis:
viewtopic.php?f=40&t=1719
I noticed that your structures differ also in terms of period, so maybe you should check the stiffness of your elements too.
Also, you should check that the finite element formulation of what you are using in ETABS corresponds with the assumptions of the forceBeamColumn, plus the comparability of tthe way the material nonlinearity is modelled in STKO with fiber sections.
I hope this could help.
Let us know how it goes.
Enjoy your modelling
Francesca
as I mentioned in the other comment, you need to check the units you are using. OpenSees as STKO is unit-less, so you need to be consistent in your model. Kg for mass, makes sense if you are using N-m, but it seems to me you are using kN-m, so your masses should be expressed in tons.
I suggest you look in this other thread on ETABS and STKO comparison of Modal analysis:
viewtopic.php?f=40&t=1719
I noticed that your structures differ also in terms of period, so maybe you should check the stiffness of your elements too.
Also, you should check that the finite element formulation of what you are using in ETABS corresponds with the assumptions of the forceBeamColumn, plus the comparability of tthe way the material nonlinearity is modelled in STKO with fiber sections.
I hope this could help.
Let us know how it goes.
Enjoy your modelling
Francesca