Damping Ratio

[Gholamreza]

Hello Everyone,
I modeled a 9story structure and I'd like to have specific damping ration for the first mode. I can calculate the critical damping (Cc=2mw), and we know damping ratio = (Damping-coefficient/Critical-Damping). Any idea how I can specify damping coefficient ? should I use Rayleigh command to specify the damping coefficient ? Thanks

[Prafullamalla]

If I am not wrong you are searching for this..

# set damping based on first eigen mode
set pi [expr acos(-1.0)];
set freq [expr [eigen 1]**0.5]
set period [expr 2*$pi/$freq]
puts $period
set damp 0.02;
rayleigh [expr 2*$damp*$freq] 0. 0. 0.

[Gholamreza]

That exactly what I needed. Thank you