How to model a spring?

[Rodgers]

Hi, I was wondering how spring can be modeled in OpenSees.

What I need is to simulate Winkler's foundation under PCC slab.

After looking and playing around, I found a way to accomplish this using the ZeroLength element in OpenSees. Basically I add a shadow node that has the same coordinates as the node I want to attach the spring to. Fix the shadow node and add a zerolength element with the shadow node as node I and the target node as node J.

This seems to get the job done, but there is a little hassle: shadow nodes can't be shared by different target nodes because otherwise some element won't have "zero length". So I will end up with one shadow node for each place I want to attach the spring.

This is not too bad, but I am just wandering if there is a way to avoid the need to have a shadow node. I am about to cut down the ZeroLength element code to get such an element.

Any comments?

[silvia]

i think the shadow node is the way to go.