Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	Analysis Solutions
	Subarea:	Response Spectrum Analysis
	Original Author:	Sye Chakraborty Bentley Technical Support Group

I am currently working on a seismic model which requires a response spectrum input. 
What I am finding is that regardless of the value I specify for damping, the displacements and forces appear the same. Is this right?

The damping factor that one specifies in the input has no effect at all if the combination method is SRSS. For the SRSS scheme, the effect of damping is built into the spectrum values (period vs. acceleration or period vs. displacement) that the user specifies. In other words, if the damping factor is f1, the acceleration that the user should provide ought to be A1 corresponding to period T1. If the damping factor is f2, the acceleration ought to be A2 for the same period T1. In other words, for the SRSS method, the effect of damping has to be reflected on the spectral acceleration or spectral displacement that is being input. The damping coefficient by itself does not have a direct impact on the results. It's effect is indirect.

With the CQC method, it is a different story. Damping will generally have an impact on the results, because, the damping factor is an explicit term in the equation used in CQC.