Damper Modeling

[dunzo123]

I am comparing the dynamic response of a structure (steel special moment resisting frame) w/o a damper and w/ a damper. The damper goes diagonally from one node to another in the bays of the frame. The method in which I have modeled the damper appears to be incorrect as the results are the same for both the frame w/ the damper and w/o the damper. Could you please take a look at how I have modeled the damper as diagonal truss elements in a frame? Any assisstance is greatly appreciated.


# uniaxialMaterial Viscous $matID_damper $C $alpha

uniaxialMaterial Viscous 3 23.3 1;

# section Uniaxial $DamperSecTag $matID_damper $string;

section Uniaxial 6 3 P;


element truss 16 1 6 6; # damper diagonally oriented from node 1 to 6

[lightegg]

try a smaller alpha

[fmk]

don't add it to a section and then add it to the truss .. just create a truss material with the viscous material as the material.

[lightegg]

Thanks! As you say, we define truss directly with viscous material. but how to define the material area?

[fmk]

the area is a variable supplied as part of the command for the truss .. have a look at the manual.

[code]
element truss $eleTag $iNode $jNode $A $matTag
[/code]

[lightegg]

Sorry，what I want to say is we define section area depend on what, my english is poor. Thanks for your reply!

[fmk]

set the area = 1, and determine the material properties for the damping you want based on following:

strain = (disp(2)-disp(1))/L
strainRate = (vel(2)-vel(1))/L
material->setStrain(strain, strainRate)

resistingForce = material->getStress()*A;
dampTangent = material->getDamp()*A;
tangent = material->getTangent()*A;

i.e. watch out for divison by L.

[lightegg]

That's a great help!
If I put viscous material in a truss element, dose L equal the truss length?
And what is L stand for if I use a zerolength element with viscous material?

[fmk]

the zero length element has zero length (L in what i posted would just be 1) .. and yes for truss L is length.

[lightegg]

Thanks!