force-deflection curve

imancivil · Post by **imancivil** » Sat Nov 29, 2008 7:50 am

Hi all,

I want to use unidirectional element with nonlinear generalized force-deflection capability that can be used in any analysis. The element is defined by a generalized force-deflection curve.
How can I define an optional force-deflection curve?

Thanks.

susan · Post by **susan** » Sat Nov 29, 2008 9:21 am

Dear iman,

You raise an interesting question. i have the same question about this. Although I know in ANSYS it is possible to define a specific force-deflection curve for elements, but in opensees i don't know.

Can anyone help us?

Thanks!

silvia · Post by **silvia** » Sat Nov 29, 2008 4:22 pm

why not use the truss element where you define the section response via the uniaxial section?

imancivil · Post by **imancivil** » Sat Nov 29, 2008 10:47 pm

Daer silvia & susan,

thanks a lot for your consideration. i think i could not mention my purpose clearly.
i have the force-deflection (F-D) curve for the a specific element:

D=-100mm at F=-250 KN
D=-60mm at F=-360 KN
D=-36mm at F=-460 KN
D=-24mm at F=-550 KN
D=-16mm at F=-800 KN
D=-8mm at F=-1100 KN
D=-5mm at F=-2140 KN
D=0mm at F=0 KN
D=0.458mm at F=2525.76 KN
D=2mm at F=2525.76 KN

(F<0 are compression forces and F>0 are tension forces)

how can i apply this behavior to element?

thnx

silvia · Post by **silvia** » Sun Nov 30, 2008 9:38 am

use the hysteretic material for the section, defining A=1, the section stiffness becomes the force-deformation behavior, right?
otherwise, use a zero-length element.....

imancivil · Post by **imancivil** » Sun Nov 30, 2008 10:41 am

Dear silvia,

Thanks for your help.

esi_opensees · Post by **esi_opensees** » Tue Dec 02, 2008 5:44 am

Dear silvia,

would you please tell me why A=1? the area may be greater,equal or less than 1.

silvia · Post by **silvia** » Tue Dec 02, 2008 6:29 am

to make the stress equal to the force....
i may be wrong...

imancivil · Post by **imancivil** » Tue Dec 02, 2008 8:23 am

i agree with silvia; because first we define the properties analysis (section, material,…) for a single element and capture the force-deflection curve; we repeat this step for all the types of elements; then in the next step we apply the data which obtained from the curve on the whole of structure. A=1 causes the stress = force, right?

esi_opensees · Post by **esi_opensees** » Tue Dec 02, 2008 8:34 am

Dear silvia&iman

According to your notions when we applying the behavior of material (Hysteretic material) for entire of structure the value of area is independent (each value is correct). isn’t it?

silvia · Post by **silvia** » Tue Dec 02, 2008 8:44 am

you've got to work throught the modeling with someone in person with pen and paper in front of you.

esi_opensees · Post by **esi_opensees** » Tue Dec 02, 2008 9:30 am

you ridicule me?

i only told my opinions...

silvia · Post by **silvia** » Tue Dec 02, 2008 9:33 am

no, it is really difficult to work through this via this forum.
i was making the recommendation i give everyone who is trying to figure out how to define a model.

esi_opensees · Post by **esi_opensees** » Tue Dec 02, 2008 10:04 am

thanks, you are very kind.

now, would you plz tell me the imancivil's opinion is true or false?

tnx.

silvia · Post by **silvia** » Tue Dec 02, 2008 10:40 am

for uniaxial response, yes, where stress=force/area