unexpected stressStrain response.

[mohsenrock]

Dear Experts,

I have successfully simulated a 2D frame with 2 steel braces and have conducted a pushover analysis. The uniaxial material of the two braces are the same so I do expect the same stress-strain behavior but with opposite signs for both braces. The force-displacement response of the control node is exactly the same as I expected. However, when I plot the stress-strain curve of one of the fibers of one of the sections of the braces, the compressive part is smaller than the tensile part, ie., the stress-strain response of the tensile brace and compressive brace are not equal. Since I have not induced any imperfection, thus buckling is neglected and I should have the same stress-strain for braces, right? (of course with opposite signs)

for the braces I am using
section Fiber $BraceTag {
patch circ $IDSteelB 5 5 0.0 0.0 0.0 [expr $Rb1] 0.0 360.0
}
uniaxialMaterial Steel01 $IDSteelB $FyB $EsB $Bbrace

and also for brace elements

element nonlinearBeamColumn 4 5 6 2 $BraceTag $IDBraceTransf
element nonlinearBeamColumn 5 7 8 2 $BraceTag $IDBraceTransf

Is there anything that I am missing?

[selimgunay]

Did you check the elongation and shortening of the two braces? Their absolute values don't need to be necessarily equal