Hello
I am trying to model fluid viscous damper using "truss element" and "viscous material'.
I found that the crosssectional area of truss element makes effect on the capacity of viscous damper.
I think the capacity of fluid viscous dampers should be determined by only the damping coefficient and power factor.
Could you tell me how the crossectional area of truss element makes effect on the capacity of the modeled viscous damper?
Thank you.
With viscous material you define stress-strain relationship of your material. This material is then assigned to section of your truss element that has area of $A. The force in the truss element is calculated as stress*$A, and displacement of the element as strain*(length of the element). As you change the length of your element and the cross-sectional area of your element the stiffness of your element is changing and thus the capacity of the viscous damper.
As I know, pure viscous material has no stiffness. Therefore, it should not change as the changing of the length and area of element.
Stress-strain relationship of pure viscous material can be defined by the viscous coefficient and the rate of strain to time.
Please tell me if I am making any mistakes on the concept of viscous material...
Thank you.
You are right about the material, but after you assign it to an element with a specific length and cross-sectional area you will add some stiffness to your system.
vesna wrote:
> You are right about the material, but after you assign it to an element
> with a specific length and cross-sectional area you will add some stiffness
> to your system.
Dear Vesna
This makes me somewhat confused... then what should be the cross-sectional area of element if I want to define the viscous damper only with the dashpot model (that has only the viscousity)? I tried the analysis with zero cross-sectional area and found that the viscous dampers could not make any effect to the behavior of the structure.
Hi vesna
I think zero length element has the same effect with the truss element if we put the length and cross sectional area of the truss element as 1.0.
And the capacity of viscous material is proportional to the area or length of the truss element.
Anyway, I found the way to define the fluid viscous damper in a building structure with OpenSees.
I appreciate for your help.
Thank you.
Can you share with us the way you found to define the fluid viscous material? Don't you use the viscous material with the truss element? And Vesna if you don't define elastic modulus I don't think you add stiffness to the structure.
