I am currently breaking down my model components and making sure they are correct. I have modeled a simple column with a fixed base in both opensees and SAP2000 and get completely different results. Is there something wrong with my model? My SAP calculations gives me a period of 0.38276 sec and my Opensees seems a little long at 1.1777 sec
# clear clache
wipe all
# basic 2D model with 3 degrees of freedom
model basic ndm 2 ndf 3;
# make files to store data
file mkdir Data;
file mkdir Model;
source Wsection.tcl; # wsection
node 101 0 0
node 301 0 312;
fix 101 1 1 1;
mass 301 0.34083 1e9 1e9;
uniaxialMaterial Steel01 1 55 29000 .03;
puts "material defined"
geomTransf PDelta 1;
puts "pdelta defined"
#Element Properties
#W14x257
set d 16.38
set bf 15.995
set tf 1.89
set tw 1.175
set nfdw 16
set nftw 16
set nfbf 16
set nftf 16
Wsection 1 1 $d $bf $tf $tw $nfdw $nftw $nfbf $nftf
puts "wsection"
#Defining exterior column Iyy
element forceBeamColumn 1 101 301 5 1 1
puts "elements"
set numModes 1
# record eigenvectors
#
for { set k 1 } { $k <= $numModes } { incr k } {
recorder Node file [format "modes/mode%i.out" $k] nodeRange 1 6 dof 1 2 3 "eigen $k"
}
# perform eigen analysis
#
set lambda [eigen $numModes];
# calculate frequencies and periods of the structure
#
set omega {}
set f {}
set T {}
set pi 3.141593
foreach lam $lambda {
lappend omega [expr sqrt($lam)]
lappend f [expr sqrt($lam)/(2*$pi)]
lappend T [expr (2*$pi)/sqrt($lam)]
}
puts "periods are $T"
# write the output file cosisting of periods
#
set period "modes/Periods.txt"
set Periods [open $period "w"]
foreach t $T {
puts $Periods " $t"
}
close $Periods
# create display for mode shapes
#
# $windowTitle $xLoc $yLoc $xPixels $yPixels
recorder display "Mode Shape 1" 10 10 500 500 wipe
prp 312 312 1; # projection reference point (prp); defines the center of projection (viewer eye)
vup 0 1 0; # viewup vector (vup)
vpn 0 0 1; # viewplane normal (vpn)
viewWindow 200 200 200 200; # coordiantes of the window relative to prp
display 1 5 20; # the 1st arg. is the tag for display mode (ex. 1 is for the first mode shape)
# the 2nd arg. is magnification factor for nodes, the 3rd arg. is magnif. factor of deformed shape
Thanks in advance
Eigen Analysis
Moderators: silvia, selimgunay, Moderators

 Posts: 93
 Joined: Mon Apr 14, 2008 10:53 pm
Re: Eigen Analysis
most probably the mass source in two programs are different. please apply sigma (pAL/2) to your nodal mass in opensees.
Re: Eigen Analysis
I'm sorry is sigma a command in opensees? I am not quite sure what you mean. Thanks for your help!