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G.17.3.3 Damping Modeling

Damping may be specified by entering values for each mode (either explicitly or calculated), by using a formula based on the first two frequencies, or by using composite modal damping. Composite modal damping permits computing the damping of a mode from the different damping ratios for different materials (steel, concrete, soil). Modes that deform mostly the steel would have steel damping ratio, whereas modes that mostly deform the soil, would have the soil damping ratio. 

Modeling Methods

Damping Method Related STAAD.Pro Command
A single specified value, used by all modes DAMP
Composite damping based on values specified for each material which can include the effect of spring damping, if defined. CDAMP
Modal damping which is explicitly defined for each mode. MDAMP
Modal damping which is calculated for all modes. MDAMP, using either the CALCULATE or EVALUATE method