STress-strain or Von Mises in stell portal frame

chen · Post by **chen** » Tue Apr 12, 2005 8:34 am

Hellow
I am a student who is using your software to solve portals frames.
The material is steel and we will work in elastic analysis.
I have several questions :
Can I obtain the value of stress in the elements or on the extremity
of the elements ? And can I have them in a ouput file ?
Are there an other way to obtain the value of Von Mises. ?
May you answer because I tried but I can find how ?

silvia · Post by **silvia** » Tue Apr 12, 2005 12:45 pm

yes you can. you use recorders, which you can find in the manual:

http://opensees.berkeley.edu/OpenSees/m ... sermanual/

also have a look at the last part of the manual, under Defining Output within the How-To chapter,

and have a look at the getting started manual

Once you have done all this, let us know what else you may need.

chen · Post by **chen** » Wed Apr 13, 2005 1:56 am

Thanks Silvia, I did but
When I do the model with elastic beam elements it works but i just can't recorder the forces in nodes, And then I use non linear beam colum elements to obtain stress and strain that's means Von Mises,but:

What number of integration point I have to put? I put 8 and it works but was luck...
And when I try to recorder the stress the sofware give a Debug Error!
I give you the files What's missing?

6DOF PORTALFRAME
wipe
model basic -ndm 3 -ndf 6

set L1 5000
set L2 5000

node 1 0 0 0
node 2 0 $L1 0
node 3 $L2 $L1 0

fix 1 1 1 1 1 1 1
fix 3 1 1 1 1 1 1

set E 7100.478
set A 5956.4596
set J 148697059
set Iz 74375333.68
set Iy 74375333.68
set G 4615.3107
set v 0.3

geomTransf Linear 1 0 0 1

element elasticBeamColumn 1 1 2 $A $E $G $J $Iy $Iz 1
element elasticBeamColumn 2 2 3 $A $E $G $J $Iy $Iz 1

set W1XPOS -0.04625252

pattern Plain 1 Linear {
eleLoad -ele 1 -type -beamUniform $W1XPOS 0
}

constraints Transformation
numberer RCM
algorithm Linear
integrator LoadControl 1
analysis Static

recorder Element -file forces.out -time -ele all force
analyze 1
print

6DOF PORTALFRAME NON LINEAR...

wipe
model basic -ndm 3 -ndf 6

set L1 5000
set L2 5000

node 1 0 0 0
node 2 0 $L1 0
node 3 $L2 $L1 0

fix 1 1 1 1 1 1 1
fix 3 1 1 1 1 1 1

set E 7100.478
set A 5956.4596
set J 148697059
set Iz 74375333.68
set Iy 74375333.68
set G 4615.3107
set v 0.3

geomTransf Linear 1 0 0 1

section Elastic 1 $E $A $Iz $Iy $G $J

element nonlinearBeamColumn 1 1 2 8 1 1
element nonlinearBeamColumn 2 2 3 8 1 1

set W1XPOS -0.04625252

pattern Plain 1 Linear {
eleLoad -ele 1 -type -beamUniform $W1XPOS 0
}

constraints Transformation
numberer RCM
algorithm Linear
integrator LoadControl 1
analysis Static

recorder Element -file forcesnonlin.out -time -ele all force
recorder Element -file seccion.out -ele 1 section 1 fiber 0 0 stressStrain;
analyze 1
print

silvia · Post by **silvia** » Wed Apr 13, 2005 9:06 am

okey,
i don't get an error, but i don't get the strains either with case 2.
Here two problems with your input:
1. you are not specifying a system-of-equations solver, with the system command-- a default is chosen for you, though so you are okey.

2. you are using an elastic section and are asking for fiber recorders -- you don't have fibers in your section. that is why you are not getting any stresses or strains. For this type of section you can ask for force, deformation or stiffness, but not for fiber strains.

You are doing a good job in using variables, though, I like that myself!!!

If you are interested in strains, you can back calculate them from the curvature distribution on the section, since it is elastic, otherwise define a fiber section with elastic materials

hope this helps.

chen · Post by **chen** » Mon Apr 18, 2005 7:30 am

Hi silvia ,Thanks But the the section that I have is pipe with radius 320 and thickness 6.
I am looking for the values of stress along the neutral fiber in the diferents points of the beam, Because I really want to obtain the value of the equivalent contraint of Von Mises like :

Jxx = Fx/Sx + z My/Iy + y Mz/Iz
Jxy = Fxy/Sy + z Mx/J
Jxy = Fxy/Sz + y Mx/J

J²v = J²xx + 3(J²xy +J²xy)

How I can define the section to obtain J²v in the extremities of the beam ?
If I can’t is there an alternative way ?
The better than I can obtain is the forces in the extremities and the do by mysef the calculs to get J²v?
thanks
Thanks for your help

silvia · Post by **silvia** » Mon Apr 18, 2005 8:40 am

if you use an elastic section, you may have to calculate such values yourself, in the post-processing. otherwise, use a fiber section with fiber recorders at those points of interest.