i've modeled a 6 story RCmoment frame with buckling restrained braces. i've used truss element for yeilding portion and elastic beamcolumn for elastic portion. for connecting chevron brace to the beam i've introduced 4 nodes in the middle point of the beam(nodes are :master node1and slaves are 2,3,4)then i used equaldof command in the following manner ,is this procudure is correct? when i increase the cross sectional area of the brace and runing eigen analysis the period does not change.why?
equalDOF 1 2 1 2 3
equalDOF 1 3 1 2( hing connectin for left brace)
equalDOF 1 4 1 2(hing connectin for right brace) ?
my be you don't release the beam-column joint and your structure has Moment beahve or have a problem in your model
if send your model file to my mail, my I can help you. I should see your modeling to help better .
You can use three beamcolumn elements, as for the elastic portion, elastic element can be adopted, as for the plastic portion, dispBeamColumn element can be used. for example, there are four points 1 2 3 4 for the brace, 1 and 2, 3 and 4 define the elastic beam, 2 and 3 define plastic elment, then you use equalDOF (only translational DOFs) command to connect 1 and 4 with the frame nodes. Then the frame only pass axial force to the brace. This will work out. Good luck!
The change of cross section of the brace element has very little effect in the period of the structure compared to the lTeral stiffness of the structure. If you change the area excessively, you will notice very little change in period. Do you see any change in the period in decimal places?
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