Spring element with decreasing stiffness

[dcizmar]

I am trying to find a way to model a spring which will behave in the way such that when strain is zero, the force in the spring is maximal.
As the strain is increasing, the force should drop (for example linear). I really don't have an idea how to model this.

[vesna]

You can do this by using Hysteretic material: http://opensees.berkeley.edu/wiki/index ... c_Material.

With this material you can define three points for each direction and construct the material you want.

[dcizmar]

vesna wrote:
> You can do this by using Hysteretic material:
> http://opensees.berkeley.edu/wiki/index ... c_Material.
>
> With this material you can define three points for each direction and
> construct the material you want.

Dear Vesna, thanks for quick replay. I tried numerous tests and so far had no success.
Let me clarify my problem. I would like to model a spring which will behave in this matter:
when force is Pmax the relative deformation is 0, as deformation is increasing the force should decrease as well.
The problem in Hyteretic mat. is that it can not be defined (as I see it) like (Pmax,0) for first point (0,6*Pmax, ey) for second etc.

[vesna]

Would it work for you if you add a point (0,0) at the beginning so you have points in this order: (0,0), (Pmax,0), (0,6*Pmax, ey)?