Spring and dashpot

[bassking]

Hello, i'm studiyng the seismic response of a multi span bridge. In my analysis i take great attention to the soil-structures interaction. The simpliest model to study the problem is to substitute the soil under the foundation with a spring and a dashpot. So i have a costant K for the spring and a C for dashpot, can i use zeroLength element for the analysis, maybe using Maxwell material, who take in account stiffness and damping?

[bassking]

Can i assign 2 different zeroLenght element (defining 2 different material -elastic and viscous-) at the same 2 node?

[vesna]

If your spring and a desh-pot are in series you can use maxwell material. If they are in parallel, use elastic and viscose material and connect them in parallel using Parallel material: http://opensees.berkeley.edu/wiki/index ... l_Material. Then, assign this material to one zero-lenght element.

[bassking]

Dear Vesna,
My spring and dashpot work in parallel, so i use Parallel material command. I also made a simple model (linear oscillator) and run 2 different zero lenght or only one with parallel material, the results are the same.

[vesna]

Yes, they should be the same. However, I find it more elegant if one element is used instead of 2.

[partla]

Hi bassking,
I’m trying to model a retaining wall and I want to simulate soil – structure interaction. But I don’t know to use which materials and elements for this problem. There is plenty of options like PYsimple material, Maxwell material, spring and dashpot and etc. Now I want to know how you dealt with this problem in your case. I’ll be happy hearing from you.
Thanks in advance
Amin

[bassking]

Well, it depends of the kind of problem that you are studing: frequency or time domain, stedy state or time history.
There's plenty of text book about the problem, and plenty of symple model to analyse soil-structure interaction model.
I use in particular the Lumped parameter model proposed by Wolf, springs and dashpot that work in parallel (and i use parallel material for that: one elastic and one viscous) and extra masses (but i recommand you to see the teory first).

[partla]

Thanks for your attention,
I’m studying a time domain dynamic analyses with different time histories. You are right I should first study the theory. Which books do you suggest? As I mentioned before my problem is the wall and soil behind it and I want simulate the interaction of wall and soil. Thank you again.

[bassking]

For your problem in particular i don't know what to suggest...
If you are study a time domain analyses i can recommend you the books of Wolf about dynamic soil structure interaction:

Foundation vibrationanalysis using simple physical models

Soil-Structure inetaction analysis in time domain

[partla]

Thank you bassking. I'll study them