Damping for nonductile concrete

[Kate_Rhoades]

Hello,

I have a couple of general questions about damping within STKO. I am currently modeling a 7 story nonductile concrete building. So far, I have been using the Rayleigh damping option provided in the analysis steps, and using the frequencies from the first and 7th modes and 5% damping in the linear model (please see attachment).

Overall, do you have any further recommendations for using Rayleigh damping for concrete buildings for linear and nonlinear models? Should I use more modes to capture the behavior? Are 5% and 2.5% reasonable damping values for linear and nonlinear concrete buildings?

Is modal damping also available in STKO?

Thank you so much!

[STKO Team]

Overall, do you have any further recommendations for using Rayleigh damping for concrete buildings for linear and nonlinear models?

Just I would use Kinit instead of Kcurr for nonlinear model (Kcurr is the tangent stiffness and may contain negative terms when you have softening)

Should I use more modes to capture the behavior?

No if you already capture a good percentage of participating mass

Are 5% and 2.5% reasonable damping values for linear and nonlinear concrete buildings?

Yes they are reasonable.

Is modal damping also available in STKO?

No, but you can use a AnalysisStep->misc_commands->customCommand to insert it via tcl script