Zero-Length Elements to modle a damper

[wangjingze0720]

I want to use the Zero-Length Elements to modle a damper. K= 6.8098e6,
C= 3.24e5.But I do not know if my program is right,any one can help me?
uniaxialMaterial Elastic 1 6.8098e6;
uniaxialMaterial Viscous 2 3.24e5 1;
uniaxialMaterial Parallel 3 3 5;
element zeroLength 1 $iNode $jNode -mat 3 -dir 1;

[wangjingze0720]

if my program is wrong,please tell me how to modify it.

[vesna]

Most of the users use one of the following two ways to model dampers:
1. truss element and viscous material.
2. force-based beam-column element and Maxwell material (here is an example: http://opensees.berkeley.edu/wiki/index ... l_Material)

[wangjingze0720]

I thingk I can use zhe frist two ways to model dampers(truss element and viscous material).
I can use the viscous material to define the C= 3.24e5,BUT how can I define the K= 6.8098e6?
I know K=EA/L, but the E(elastic modulus) has not be deifined.
I think the stiffness can be defined by the Truss Element. please tell me how to define the K= 6.8098e6 ?

#uniaxialMaterial Viscous $matTag $C $alpha
uniaxialMaterial Viscous 1004 3.24e5 1;

#element truss $eleTag $iNode $jNode $A $matTag
element truss 3 2 3 1 1004；
if I define the dampers like this, what is the elastic modulus of the viscous material? E=3.24e5 when alpha
set to be 1?

[vesna]

For what you are trying to do the second way would work better. Look at the example: http://opensees.berkeley.edu/wiki/index ... l_Material

[wangjingze0720]

But I think force-based beam-column element and Maxwell material to model the damper is not appropriate
for the length of damper is nearly to be 0 and the damper has not a section.
Ineed to know is it right to use the the Zero-Length Elements to modle a damper like this:
uniaxialMaterial Elastic 1 6.8098e6;
uniaxialMaterial Viscous 2 3.24e5 1;
uniaxialMaterial Parallel 3 3 5;
element zeroLength 1 $iNode $jNode -mat 3 -dir 1;

I thingk the Parallel Material in the program is the same as a Maxwell material . And the Zero-Length Elements need not define the length and section.

[wangjingze0720]

I used the Zero-Length Elements to modle a damper.
BUT I found the acceleration in ends of damper ($iNode $jNode )was too large.
so I the there may be something wrong with the damper which was modled by the Zero-Length Elements.
And I do not thingk force-based beam-column element and Maxwell material is appropriate for my damper.

[vesna]

In Maxwell material elastic spring and viscous material are connected in series, but in your case they are connected in parallel. If you believe that what you are doing is right you can stick to it.

Also make sure to define the stiffness of the elastic spring as force/displacement not as stress/strain.