fixed support error

02-Getting started with the modelling
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meser1905
Posts: 3
Joined: 26 Jun 2015, 10:31

fixed support error

Post by meser1905 »

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?
huffte
Posts: 978
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: fixed support error

Post by huffte »

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.
Tim Huff
meser1905
Posts: 3
Joined: 26 Jun 2015, 10:31

Re: fixed support error

Post by 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.
huffte
Posts: 978
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: fixed support error

Post by huffte »

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.
Tim Huff
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ruipinho
Posts: 165
Joined: 07 Dec 2013, 14:37

Re: fixed support error

Post by ruipinho »

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
mafmoh123
Posts: 3
Joined: 13 Feb 2018, 10:14

Re: fixed support error

Post by mafmoh123 »

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?
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seismosoft
Posts: 1184
Joined: 06 Jul 2007, 04:55

Re: fixed support error

Post by seismosoft »

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
EduardoBur
Posts: 1
Joined: 26 Mar 2018, 10:11

Re: fixed support error

Post by EduardoBur »

I'm facing this very dilemma. Would you recommend leaving the residual displacements as is?
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seismosoft
Posts: 1184
Joined: 06 Jul 2007, 04:55

Re: fixed support error

Post by seismosoft »

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
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