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STAAD Commands and Input Instructions
Section 5
5-352
5.37.1.4 Steady Ground Motion Loading
This set of commands may be used to specify steady ground motion
loading on the structure, the ground motion frequency, the modal
damping, and the phase relationship of ground motions in each of the
global directions.
General format:
⎧ DAMP f ⎫ ⎧ ABS
2
⎫
STE
ADY GROUND FREQ f
1
⎨ CDAMP ⎬ ⎨ ⎬
⎩ MDAMP ⎭ ⎩ REL ⎭
This command specifies the ground motion frequency and damping.
FREQ. The f
1
value is the steady state frequency (Hz) at which
the ground will oscillate.
DAMP , MDAMP and CDAMP. Select source of damping input.
f
2
= Damping ratio for all modes. Default value is 0.05 (5%
damping if 0 or blank entered).
DAMP indicates to use the f
2
value for all modes.
MDAMP indicates to use the damping entered or computed with
the DEFINE DAMP command if entered, otherwise default value
of 0.05 will be used.
CDAMP indicates to use the composite damping of the structure
calculated for each mode. One must specify damping for different
materials under the CONSTANT specification.
ABSolute or RELative. Ground motion results in output file will
be relative to the ground unless ABSolute is specified. Graphical
results are relative. This option has no effect for the force loading
cases.