3D Channel Section

[FedericoIori]

Hi,

i'm trying to model an one story x-braced frame. The braces are single channel section ( UPN 180), and i want to model them with ForceBeamColumn elements. The model still doesn't work properly ( i'll look further into it before asking ), but i noticed that when i run the static pushover analysis if i use w section for the braces ( the formulation used in SCBF example) at least the analysis runs for a while before failing, instead with the code i made to model channel section the analysis doesn't run at all (being more specific, the error message is : "failed to get compatible element forces & deformation", for every element of the braces).

This is the code i made, based on the W section code i found in the SCBF example:

############################################################################################
# USection3D.tcl
#
# This routine creates a fiber section and aggregates torsion to it.
#
# Variables
# secID = section ID number
# matID = material ID number
# matTorsion = torsion material ID number
# d = nominal depth
# bf = flange width
# tf = flange thickness
# tw = web thickness
# zs = centre of gravity distance from external web border
# nfdw = number of fibers along web depth
# nftw = number of fibers along web thickness
# nfbf = number of fibers along flange width
# nftf = number of fibers along flange thickness
# E = modulus of elasticity
# J = Torsional constant (can be found in steel manual)
############################################################################################

############################################################################################

proc USection3D { secID matID matTorsion d bf tf tw zs nfdw nftw nfbf nftf E J} {
set dw [expr $d-2*$tf]
set y1 [expr -$d/2]
set y2 [expr -$dw/2]
set y3 [expr $dw/2]
set y4 [expr $d/2]

set z1 [expr -$zs]
set z2 [expr $bf-$zs]
set z3 [expr -$zs+$tw]

set secTag [expr $secID + 4000]

section fiberSec $secTag {
# nfIJ nfJK yI zI yJ zJ yK zK yL zL
patch quadr $matID $nfbf $nftf $y1 $z1 $y1 $z2 $y2 $z1 $y2 $z2
patch quadr $matID $nftw $nfdw $y2 $z1 $y2 $z3 $y3 $z1 $y3 $z3
patch quadr $matID $nfbf $nftf $y3 $z1 $y3 $z2 $y4 $z1 $y4 $z2

}

# assign torsional Stiffness (for 3D Model)
set nu 0.3; # Poisson ratio for steel
set G [expr $E/2.0/(1+$nu)]; # shear modulus
set GJ [expr $G*$J]; # torsional stiffness
uniaxialMaterial Elastic $matTorsion $GJ; # define elastic torsional stiffness
section Aggregator $secID $matTorsion T -section $secTag; # combine section properties
}

Can someone tell me if the problem is here or should i look elsewhere?

Thanks in advance, and sorry for my terrible english.

Federico Iori.

[FedericoIori]

I found out which was the mistake: one point in the patch definition was not written in the correct order. Now everything works fine!

[vesna]

I ma glad you solved the problem.