seismic analysis tips
seismic analysis tips
(OP)
hi few days ago i have posted one question and wondered about answer. i am worried about either my question was not well posed or otherwise. let me frame my question from other perspective as i am beginner in LSDYNA so can anybody expert if FEM and LSDYNA also give me some tips of seismic analysis in LSDYNA.
Thanking in anticipation
Thanking in anticipation





RE: seismic analysis tips
Presently I am working with ANSYS/LS-Dyna. My problems relates to seismic analysis of steel joints. Like asad93 I am also a beginner with LS-Dyna.
I tried a some standard problems like a SDOF system, a single bay portal and continous column. I applied the seismic loads as acceleration time histories (Using AX DOF) to the ground nodes. The ground nodes are fixed. I am not sure if I am doing it correctly because the results do not make any sense. The resultant accleration at top of the structure should amplify and the structure should act as a filter, i.e., the resultant accleration history at top nodes should have frequency content close to structural natural frequency. But it is not happening, instead I am getting rigid body modes.
Can anybody in the forum throw some light on how to analyse a structure for a seismic ground motion using ANSYS/LSDyna or LS-Dyna.
Thank you all.
RE: seismic analysis tips
i would be grateful to share your experience.
RE: seismic analysis tips
I think the software gives us the absolute displacements. We need to subtract the ground displacements at each time instant to get the relative displacements. But I am still not confident of the analysis. You are right if its an elastic analysis there should be no residual deformation.
Thanks for sharing your experience. looking forward to your reply.
deep
RE: seismic analysis tips
Second check the displacement that results from the defined acceleration time history (integrate the time history twice) I believe the large displacements you are seeing result from the base motion displacement....which is probably what it should be since earthquakes usually don't return to where they started from .........If you want to remove the rigid body displacements you should filter and detrend the input motion...
Ed.R.