Seismosoft | Earthquake Engineering Solutions

Hi
1-In IDA analysis , in post processor module, there is a difference between "relative displacement" with respect to a node support and one obtained by subtracting two absolute displacements of those nodes.why?Is this correct?
2-When a node support moves about 10 meters ,why the structure doesnt collapse?

Hi iliya56. When a support node moves about 10 meters, it is likely that you have applied an accelerogram which needs to be baseline adjusted/corrected. If you load your accelerogram into SeismoSpect or SeismoSignal and observe the integrated velocity and displacement histories, you will probably see a large residual displacement. SeismoSpect or SeismoSignal may then be used to correct the accelerogram.

Since stresses in the structure are dependent upon displacements relative to the supports, then the structure does not necessarily fail under the erroneous and problematic drift in ground displacement. Note that in some instances, permanent ground displacements have ben observed in earthquakes, but 10 meters sounds like an uncorrected accelerogram to me.