TR.26.4 Modal Damping Information
To define unique modal damping ratios for every mode. STAAD.Pro allows you to specify modal damping either directly or by using Rayleigh damping (the algebraic combination of mass-proportional damping and stiffness-proportional damping). This will be used in a dynamic analysis when MDAMP has been specified.
Damping may be entered:
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by specifying that the program EVALUATE each mode’s damping based on the frequency of the mode and the minimum and maximum damping entered here. The formula used to evaluate the damping is given in Evaluate Damping.
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by specifying that the program CALCULATE each mode’s damping based on the frequency of the mode and the mass factor, ALPHA, and the stiffness factor, BETA. The formula used to calculate the damping is given in Calculate Damping.
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explicitly for some or all modes (EXPLICIT).
The damping entered will be used in time history load cases and in response spectrum load cases that use the CQC or ASCE4 methods and/or Spectra vs. Period curves versus damping.
General Format
DEFINE DAMPING INFORMATION
{ EVALUATE dmin (dmax) | CALCULATE ALPHA c1 BETA c2 (MAX dmax MIN dmin) | EXPLICIT d1 (d2 d3 d4 … dn ) }
END
Where:
| Parameter | Description |
|---|---|
| dmin | the minimum damping ratio to be used in the evaluate damping formula |
| dmax | the optional maximum damping ratio to be used in the evaluate damping formula |
| ALPHA c1 | the mass-proportional damping coefficient, α, used in the cacluate damping formula |
| BETA c2 | the stiffness-proportional damping coefficient, β, used in the cacluate damping formula |
| MAX dmax, MIN dmin | optional minimum and maximum damping ratios, respectively, sed in the calculate damping formula |
| d1 d2 … dn | the damping ratios for each mode given in the explicit method |