Uncouple Axial Force and Moment in beams

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geoStru
Posts: 37
Joined: Mon Aug 24, 2020 12:24 pm

Uncouple Axial Force and Moment in beams

Post by geoStru »

Hello everyone,
is it possible to uncouple, for the beams with fiber section, the behaviour between Axial Force and Moment?
In SAP when introduce a Rigid Diaphragm the axial force in beams is 0, but not in OpenSees.
How could I do to obtain the same behaviour for the beams in OpenSees?

I tried to duplicate the nodes and applied the equaldof but it doesn't work. For example
node 121 $X1 $Y1 $Z2
node 1211 $X1 $Y1 $Z2
node 122 $X2 $Y1 $Z2
node 1222 $X2 $Y1 $Z2

equalDOF 121 1211 2 3 4 5 6 (the beam is along the X axis)
equalDOF 122 1222 2 3 4 5 6

element nonlinearBeamColumn 221 1211 1222 $np $BeamXSecTag $IDBeamXTransf;
selimgunay
Posts: 916
Joined: Mon Sep 09, 2013 8:50 pm
Location: University of California, Berkeley

Re: Uncouple Axial Force and Moment in beams

Post by selimgunay »

The most direct way is to compute the moment-curvature externally and assign it to your section instead of the fiber section
geoStru
Posts: 37
Joined: Mon Aug 24, 2020 12:24 pm

Re: Uncouple Axial Force and Moment in beams

Post by geoStru »

selimgunay wrote: Tue Dec 08, 2020 10:23 am The most direct way is to compute the moment-curvature externally and assign it to your section instead of the fiber section
how can I do this?
selimgunay
Posts: 916
Joined: Mon Sep 09, 2013 8:50 pm
Location: University of California, Berkeley

Re: Uncouple Axial Force and Moment in beams

Post by selimgunay »

You can do it using a zerolength section or 1) model a cantilever column, 2) assign a fiber section to it, 3) apply the axial force that you want to compute the moment-curvature for, 4) do a lateral pushover on your column, 5) record the moment-curvature at the bottom integration point
insap
Posts: 1
Joined: Thu Dec 17, 2020 6:09 am
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Re: Uncouple Axial Force and Moment in beams

Post by insap »

selimgunay wrote: Wed Dec 16, 2020 10:34 am You can do it using a zerolength section or 1) model a cantilever column, 2) assign a fiber section to it, 3) apply the axial force that you want to compute the moment-curvature for, 4) do a lateral pushover on your column, 5) record the moment-curvature at the bottom integration point
Thanks.
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