Incremental dynamic analysis

04-Unexpected behaviour/errors
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iamvishal1
Posts: 19
Joined: 11 Oct 2017, 09:50

Incremental dynamic analysis

Post by iamvishal1 »

Sir,
I am doing incremental dynamic analysis of G+10 story building, but when analysis completed the results shows displacement and other results but when I do G+4 building and same ground motion used but here for G+10 and for G+4 same displacement results are shown for any structure maximum displacement show in software is same why it's happening please give me your guidance. What procedure should I follow for that.
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seismosoft
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Joined: 06 Jul 2007, 04:55

Re: Incremental dynamic analysis

Post by seismosoft »

What do you mean G+10 story building & G+4 building? Further, it is not very clear from your post what exactly is the problem. If it is that the results come out the same for the two models, this is not possible. If the buildings are different, there is no way that the results are the same. Can it be that you changed the structural mode with the same filename, but then you did not run the analysis?

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huffte
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Location: Cookeville, Tennessee, USA
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Re: Incremental dynamic analysis

Post by huffte »

I wonder if your ground motion might have a large residual drift at the end of the record? In which case, if said drift is much larger than the local structural displacements, the results would show up as practically a rigid body translation of the entire structure. I would suggest loading your accelerogram into SeismoSignal or SeismoSpect and looking at the double-integrated ground displacement history to see if there is indeed a large residual drift. If so, you should baseline correct and/or filter the record (both may be accomplished with SeismoSignal or SeismoSpect) prior to using it for structural analysis (or discard the record altogether and make certain you use properly processed ground motion records). If not, then you can rule out this possibility. But it would be a good place to start I think. Best of luck, iamvishal1.
Tim Huff
iamvishal1
Posts: 19
Joined: 11 Oct 2017, 09:50

Re: Incremental dynamic analysis

Post by iamvishal1 »

The ground motion used for analysis are scaled in Seismomatch . Should I use sismosignal to filter ground motion and then scale it in Seismomatch or it sismosignal scale the ground motion.
huffte
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Location: Cookeville, Tennessee, USA
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Re: Incremental dynamic analysis

Post by huffte »

The main issue is to use realistic ground motion records. And you have to decide what loading you are trying to represent with your accelerogram. Since you have used SeismoMatch, I assume you have a target response spectrum. This is good. You should be able to tell from your SeismoMatch run whether or not the issue with your model is the accelerogram. Is there a large displacement at the end of the double-integrated displacement history? If yes, then that is at least part of the problem. If not, then the accelerogram drift is not the problem. SeismoMatch is very good at providing accelerograms with no residual drift.
Tim Huff
iamvishal1
Posts: 19
Joined: 11 Oct 2017, 09:50

Re: Incremental dynamic analysis

Post by iamvishal1 »

I use ground motion and scale them in Seismomatch using with Target response spectrum. But the issue was the displacement at every story same it didn't change.In seismosignal all selected ground motions Baseline correction and filter them and then The scaling off all ground motion with the target response spectrum Is this correct? For Ground motion load to apply in Seismostrut .
admin
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Joined: 06 Jul 2007, 10:25

Re: Incremental dynamic analysis

Post by admin »

Hi iamvishal1,
Make sure that you are also using the correct scaling factor in the Applied Loading module, e.g. if the accelerogram is in g and the project units are in m, then the scaling factor should be 9.81. If instead the units are in mm the scaling factor should be 9810.
Also make sure that you are applying acceleration loads at the base of the building only. Create a dynamic analysis model with the Wizard or the Building Modeller to see how all these are applied.
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