Damping matrix multi degrees of freedom

[Batzo]

Hi,
In mdof I have those matrices:

I have m and k, how do I find c?

 

[WARose]

Typically with damping, you just assume something.

 

[Batzo]

Ok, i assume 5% damping ratio.
What next?

 

[WARose]

What next?

I don't get the question. What are you trying to do?

 

[Batzo]

I want to calculate "c". I have m and k.
Assuming damping ratio 5%,
What method to use?
What are the equations?
Can u show me the calculation?

 

[JoelTXCive]

Do you have any of the other parameters? Acceleration? What is the displacement?

 

[Batzo]

I have building and forces properties:

But those are not relevant...
I have no displacement / acceleration.

Can I use
c=2*zeta*m*wn ?
I want to use central difference method as in biggs book (1964)

 

[WARose]

I want to calculate "c". I have m and k.
Assuming damping ratio 5%,
What method to use?
What are the equations?
Can u show me the calculation?

You just said you just said you were going to assume damping. But in any case, if you have Tedesco's Structural Dynamics book, see example problems 12.2 through 12.6.

 

[JoshPlumSE]

Typically, you will use a "Rayleigh Damping" assumption where the damping matrix is approximated by modified combinations of the mass and stiffness matrices.

https://www.orcina.com/webhelp/OrcaFlex/Content/html/Rayleighdamping,Guidance.htm

 

[Batzo]

I have tried using rayleigh...
but the matrix in position c(3,3) is not equal to -c(2,3):
From chopra