Seismosoft | Earthquake Engineering Solutions

Dear Seismosoft Support Service,

I am modelling a simple 3 storey frame in Seismostruct V.7.0.3 for dynamic time history analysis. Although the supports are fixed (x+y+z+rx+ry+rz), they are having great lateral displacement values. Moreover,the top displacement and base displacements are the same, thus the relative displacements are very small. Is it possible?

It sounds as if you have a large residual drift in your acceleration history loading. I would suggest you load the acceleration history into SeismoSignal or SeismoSpect, check for the residual drift, and apply a baseline correction without filtering if need be. Either of the above programs can handle the baseline correction. You would then load the corrected acceleration history into SeismoStruct to replace the original one. This is where I would begin anyway. Best of luck, meser1905.

Dear huffte,

Thanks for your response. But that doesn't solve my problem. I have changed the accereleration history also with many other records. But the problem still remains. In every step of record, the fixed supports move. I tried many things but still need help.

Well, certainly the fixed nodes do move since the ground moves. So it seems the large displacement you speak of is not a residual support displacement at the end of the analysis. For some reason, your structural elements are very, very stiff if you are getting no relative displacements. I would double-check units and input parameters like E, dimensions, link property units, multiplier for acceleration loading, etc.

meser1905,

As huffte noted already, if you apply an accelerogram at your support nodes, these will inevitably move. If you wish them to stay still, then simply refrain from imposing any dynamic loading on them (though, at this point of course, there would be no point in running a dynamic analysis).

Best,

Rui

Hi

I am facing this problem. What's the use of applying ground motions if the FIxed node is also moving? is this a bug?

No it is not a bug. This is how dynamic loads are applied to the supports in dynamic analysis in all structural analysis packages.
If you do not want to have residual displacements, apply baseline correction to your accelerograms.
Seismosoft Support

I'm facing this very dilemma. Would you recommend leaving the residual displacements as is?

What you are interested in is the drift between the different levels of your model, not the total deformation of the record that you are applying. If you do not want to have residual displacements, apply baseline correction to your accelerograms.
Seismosoft Support