Orthotropic Material

[ahmetalperparker]

Hi,
I have a very simple example for quad element and I compared the results with Sap2000. For isotropic elastic material, the results are same. For orthotropic material, the results are different. I think the formulations are same for quad element in both programs. And as a result, the results should be same. Where is the difference coming from?
Here is my example...

####
wipe;
file mkdir Output;
model basic -ndm 2 -ndf 2;
nDMaterial ElasticOrthotropic 1 1000 2000 3000 0.1 0.1 0.1 1000 1000 1000
node 1 0.0 0.0;
node 2 0.0 10.0;
node 3 10.0 10.0;
node 4 10.0 0.0;
element quad 1 1 4 3 2 1.0 PlaneStress 1;
fix 1 1 1;
fix 2 1 1;
pattern Plain 1 "Linear -factor 1.0" {
load 3 0.0 -1000.0 ;
load 4 0.0 -1000.0 ;
}
recorder Node -file Output/Displacements.txt -time -nodeRange 1 4 -dof 1 2 disp;
constraints Transformation
numberer RCM
system BandGeneral
test NormDispIncr 1.0e-6 6
algorithm Newton
integrator LoadControl 1
analysis Static
analyze 1
####

[fmk]

did you try the sap orthotropic material using isotropic properties to check. here is the OpenSees check:

set E 1000.
set v 0.1
set G [expr 0.5*$E/(1+$v)]

foreach matType {"Isotropic" "Orthotropic"} {
wipe;
model basic -ndm 2 -ndf 2;

if {$matType == "Orthotropic"} {
nDMaterial ElasticOrthotropic 1 $E $E $E $v $v $v $G $G $G
} else {
nDMaterial ElasticIsotropic 1 $E $v
}
node 1 0.0 0.0;
node 2 0.0 10.0;
node 3 10.0 10.0;
node 4 10.0 0.0;
element quad 1 1 4 3 2 1.0 PlaneStress 1;
fix 1 1 1;
fix 2 1 1;
pattern Plain 1 "Linear -factor 1.0" {
load 3 0.0 -1000.0 ;
load 4 0.0 -1000.0 ;
}
constraints Transformation
numberer RCM
system BandGeneral
test NormDispIncr 1.0e-6 6
algorithm Newton
integrator LoadControl 1
analysis Static
analyze 1
puts "$matType [nodeDisp 3] [nodeDisp 4]"
}

[ahmetalperparker]

Ok, I found the difference. OpenSees uses lower triangle for compliance matrix for poisson ratios. Calculating by hand the appropriate equivalents of poisson ratios give same results.
Thanks a lot.