Problem with considering torsional modes in opensees

[e.izadi]

Dear Silvia
I have modeled a 3D reinforced concrete multistory generic frame using linearBeamColumn and NonlinearBeamColumn element, Lumped masses including translational and rotational in center of mass as following, I tried to verify the model using Etabs2000 or Sap2000 and finally I found that my model in OpenSees does not consider torsional modes and any change in the amount of rotational mass inertia has no effect on the modal analysis of structure!!! However my model is completely accurate about translational modes. I would appreciate it if you attend the matter.
Sincerely yours.
Esmaeel

#Structural Nodes:
for {set i 0} {$i<[expr $nos+1]} {incr i 1} {
set z [expr $hos*$i]
for {set j 0} {$j<[expr $Ny+1]} {incr j 1} {
set y [expr $j*$Ly]
for {set k 0} {$k<[expr $Nx+1]} {incr k 1} {
set x [expr $k*$Lx]
set tag [expr $k+($Nx+1)*$j+100*$i+1]
node $tag $x $y $z
}
}
}

#Master Joint Nodes:

for {set i 0} {$i<[expr $nos+1]} {incr i 1} {
set z [expr $hos*$i]
node [expr 50+100*$i] [expr $Nx*$Lx*(0.5+$Ecx)] [expr $Ny*$Ly*(0.5+$Ecy)] $z
}

#-------------------------------------Nodes Constraint:------------------------------------
fixZ 0 1 1 1 1 1 1
for {set i 1} {$i<[expr $nos+1]} {incr i 1} {
fix [expr 50+100*$i] 0 0 1 1 1 0
}

#----------------------------------------Lump Masses---------------------------------------
set mt 126
set mr [expr 30.75*$mt]
for {set i 1} {$i<[expr $nos+1]} {incr i 1} {
mass [expr 50+100*$i] $mt $mt 0 0 0 $mr
}

#--------------------------------------Rigid Diaphragms------------------------------------
for {set i 1} {$i<[expr $nos+1]} {incr i 1} {
for {set j 1} {$j<[expr ($Nx+1)*($Ny+1)+1]} {incr j 1} {
rigidDiaphragm 3 [expr 50+100*$i] [expr 100*$i+$j]
}
}
#-----------------------------------------------------------------------------------------------

[vesna]

I see that you are using RC nonlinear beam-column elements and assigning a rigid diaphragm constraints to it. This may cause the problems.

What happens if you only use linear elements?

[e.izadi]

Dear Vesna
Thank you so much for your attention
Regarding your question, I think you misunderstand my means, I didnt use both element simultaneously in my own models, you know, I have modeled it two times in different models. One time using LinearBeamColumn and another time using NonlinearBeamColumn element. I also checked it by means of some simple example. Unfortunately it doesnt work correctly in conjunction with considering torsional modes while the models are completely accurate about translational modes when I use linear element!!
Sincerely yours

[vesna]

Did you define mass in the same way for both models (SAP and OpenSees). How do you see if there are torsional modes when using OpneSees?

[e.izadi]

Thank you Vesna
I modeled it in opensees using linearBeamColumn element, lumped mass in C.M including Translational and rotational, In the same way I modeled it by Etabs2000 accurately. Opensees modal analysis result :

T(1)=0.93584601404567---------Second.

T(2)=0.8495619882890081---------Second.

T(3)=0.270608589586379---------Second.

T(4)=0.25203284969267997---------Second.

T(5)=0.1331896664777591---------Second.

T(6)=0.1286790457285547---------Second.


Modal analysis result of Etabs2000 is:

Mode Period UX UY UZ SumUX SumUY SumUZ RX RY RZ SumRX SumRY SumRZ
1 0.941825 0.0000 80.9428 0.0000 0.0000 80.9428 0.0000 99.6858 0.0000 0.0000 99.6858 0.0000 0.0000
2 0.856489 81.9124 0.0000 0.0000 81.9124 80.9428 0.0000 0.0000 99.6898 0.0000 99.6858 99.6898 0.0000
3 0.634797 0.0000 0.0000 0.0000 81.9124 80.9428 0.0000 0.0000 0.0000 81.9582 99.6858 99.6898 81.9582
4 0.272721 0.0000 12.3279 0.0000 81.9124 93.2707 0.0000 0.0003 0.0000 0.0000 99.6861 99.6898 81.9582
5 0.254392 11.8072 0.0000 0.0000 93.7197 93.2707 0.0000 0.0000 0.0125 0.0000 99.6861 99.7023 81.9582
6 0.189157 0.0000 0.0000 0.0000 93.7197 93.2707 0.0000 0.0000 0.0000 11.7337 99.6861 99.7023 93.6918

And Then I omitted torsional modes in Etabs2000 by changing C.M restraint and the result is:

Mode Period UX UY UZ SumUX SumUY SumUZ RX RY RZ SumRX SumRY SumRZ
1 0.941825 0.0000 80.9428 0.0000 0.0000 80.9428 0.0000 99.6858 0.0000 29.1394 99.6858 0.0000 29.1394
2 0.856489 81.9124 0.0000 0.0000 81.9124 80.9428 0.0000 0.0000 99.6898 52.4239 99.6858 99.6898 81.5633
3 0.272721 0.0000 12.3279 0.0000 81.9124 93.2707 0.0000 0.0003 0.0000 4.4380 99.6861 99.6898 86.0014
4 0.254392 11.8072 0.0000 0.0000 93.7197 93.2707 0.0000 0.0000 0.0125 7.5566 99.6861 99.7023 93.5580
5 0.134728 0.0000 5.0540 0.0000 93.7197 98.3246 0.0000 0.2937 0.0000 1.8194 99.9798 99.7023 95.3775
6 0.130295 4.7444 0.0000 0.0000 98.4641 98.3246 0.0000 0.0000 0.2838 3.0364 99.9798 99.9861 98.4139

As you can see when I omitted torsional modes in Etabs2000, Opensees and Etabs have likely same result!!!!! Please notice mode nomber 3 and 6 which are torsional mode. I have also checked it using Sap2000 and the result is completely similar to Etabs results.

Even I checked modeshapes in opensees using following commands:

#------------------------------------------------------------------------------------------
recorder display "Mode Shape 1" 50 250 500 500 -wipe
prp 20 0 0;
vup 0 0 1;
vpn 1 0 0;
viewWindow -10 10 -10 10
display -1 2 15
#-----------------------------------------------------------------------------------------
recorder display "Mode Shape 3" 700 250 500 500 -wipe
prp 20 0 0;
vup 0 0 1;
vpn 1 0 0;
viewWindow -10 10 -10 10
display -3 2 15
#----------------------------------------------------------------------------------------

[vesna]

From what you sad it looks to me that you are not applying the same constraints to your models in OpenSees and Etabs. You sad that by changing C.M restraint in Etabs you have got the same results as with OpneSees. Why don't you apply the same restraints to both models?

[2015James]

i think that the rotational inertia assigned to the node is too small. you can change the mass [expr 50+100*$i] $mt $mt 0 0 0 $mr to mass [expr 50+100*$i] $mt $mt 0 0 0 100*$mr, then see if the modal periods change or not.
the mass matrix used in opensees is lumped mass matrix, i do not know what mass matrix is used in Etabs2000. Mybe is does matters.

[gandalf]

I have a similar problem. Although the building has strength and stiffness eccentricity, no torsional modes are produced by the modal analysis
(or any torsional response during nonlinear dynamic analysis). Has anyone faced and solved a problem like this before? Thank you
(if anyone has any idea and wants to discuss I can give more info on the model etc)

[benkhalil]

I ALSO HAVE SAME PROBLEM.I NEED KNOW HOW CAN I MODELING BY OPENSEES WITH TORSIONAL EFFECTS. I FINED NAVIGATOR 2.5 . IS IT CAN DO THIS WORK......THANKS