unexpected drift values in dynamic analysis

[dany]

Hi, I'm conducting nonlinear dynamic analysis on a 3 stories aluminum frame. I modeled a frame embedded at the base and I applied an acceleration time history on the base to 4 nodes (which have all the restrain). When I check the results turns out that the whole frame is moved to a very large. It's as if he got to the four nodes of the same basic drift that depends on time. How can I eliminate this error? Thank you for your kind attention. Kind regards

[ricardomonteiro]

Hi dany,
According to your description, and without further knowledge of the model, it seems to me that the problem can be on the ground motion intensity, which may be very high, or at the restraints level, or even at the type of elements, eventually too slender for the structure's mass, with any of these causing such sort of soft-storey mechanism.
Do you think any of this to be possible?
If you want you can send me the model so I can have a look.
Cheers,
Ricardo

[seismosoft]

Dany,

From your description, it seems to us that you could be mistakenly looking at absolute rather than relative displacements.

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