problem in nonlinear modeling

[shjelvan]

Hi
I try to use Static pushover analyze for a steel moment frame. My problem is in columns nonlinear modeling. I use dispBeamColumn element and fiber section with steel02 material for columns. (Here is the part of code which builds the fiber section for columns)




#bf: flange width
#tf: flange thickness
#h: section height
#d: web height
#tw: web thickness

proc FiberSecModel {secID bf tf h dw tw} {

# Create the material and section
# Fy in N/cm2
# E in N/cm2

uniaxialMaterial Steel02 $secID 28800 20000000 .01 18 0.925 0.15 0 1 0 1 0;
section Fiber $secID {
patch quad $secID 20 4 [expr -$bf/2] [expr -$h/2] [expr $bf/2] [expr -$h/2] [expr $bf/2] [expr -$dw/2] [expr -$bf/2] [expr -$dw/2]
patch quad $secID 20 4 [expr -$bf/2] [expr $dw/2] [expr $bf/2] [expr $dw/2] [expr $bf/2] [expr $h/2] [expr -$bf/2] [expr $h/2]
patch quad $secID 4 20 [expr -$tw/2] [expr -$dw/2] [expr $tw/2] [expr -$dw/2] [expr $tw/2] [expr $dw/2] [expr -$tw/2] [expr $dw/2]
}
}

i used this section with DispBeamColumn element for columns
But it seems that the code does not work so well and columns stiffness and yield moment (even when there is no axial force) are less than it should be. Does anybody know what’s wrong?!
thank you

[fmk]

probably integer math, divide by 2. and not 2