URGENT : Uniaxial Material Suggestion???

[amber22v]

Hello all,
Can somebody give me some idea that which material to use for my springs (trusses basically)? I want an E value of 0.01 on tension side and E = 10000 on compression side of my force deformation relation.

Right now I have assigned ElasticBilin Material for which I have assigned following properties-

uniaxialMaterial ElasticBilin 1 0.01 0.01 0.000001 -10000 -10000 -0.000001; # defined with $EP1=0.01, $EP2=0.01,
$epsP2 =0.000001, $EN1=-10000,
$EN2=-10000,$epsN2=-0.000001

After assigning this material to truss element(2 nodes: 1 fixed, 1 free ) on application of 50 kips force(on free node in axial direction of truss ), it gives me displacement of 5000 at free node (thats fine ). However, it again gives me -5000 for force -50 kips but in reality it should be -0.005 (-50/10000). I dont understand why its behaving as linearly elastic instead of nonlinearly elastic ( even though the E on the two side of force deformation are different). Can somebody please explain ?? or correct if I am wrong.


Thanks a ton in advance
Amber

[vesna]

Sorry for taking so long to respond to your question. i was out of office until today.

You did not define your material well. It should be like this:
uniaxialMaterial ElasticBilin 1 0.01 0.01 0.000001 10000 10000 -0.000001

Be aware that the unloading curve follows the loading curve exactly. There is no hysteresis loop.

If you need a material with the hysteresis loop and different compression and tension behavior use hysteretic material: http://opensees.berkeley.edu/wiki/index ... c_Material