Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	Analysis Solutions
	Subarea:	Dynamic Analysis
	Original Author:	Phil Riegel, Bentley Technical Support Group

How to account for the damping effects of springs when performing a dynamic analysis

Suppose you have a model containing spring supports, perhaps to represent soil or piles.  When performing a dynamic analysis (for example by applying a time history load or response spectrum load), the program has the ability to consider the damping effect of these springs.  There are two main steps that must be completed in order for this to work properly:

1.  Enter the CDAMP command - If CDAMP is specified then "composite damping" is used, as determined by the values for material damping (and spring damping, if defined).  This means the damping of structural entities (members, plates, solids) is considered according to their material assignment, as well as the damping of spring supports. 

For time history loading CDAMP is included in the time history definition:

For response spectrum loads CDAMP is specified in the load itself:

2.  Enter the SDAMP or SPRING DAMPING command - the actual damping value for the springs can be defined one of two ways. 

The Set SDAMP command can be specified by going to the Miscellaneous Commands menu under the Analysis and Design tab:

The value entered will be applied to all spring supports in the model.

The other way is to enter the SPRING DAMPING command into the STAAD Editor, as described in section TR.26.5 of the STAAD.pro Help documentation:

This command allows you a bit more control than SET SDAMP because you can specify the specific node to be considered and also enter separate damping values for the X, Y, and Z directions.