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Section 5
5-301
TOR indicates that the torsional moment (in the horizontal
plane) arising due to eccentricity between the centre of mass and
centre of rigidity needs to be considered. If TOR is entered on any
one spectrum case it will be used for all spectrum cases.
X Y Z f1, f2, f3 are the factors for the input spectrum to be
applied in X, Y, & Z directions. These must be entered as the
product of
R
IZ
*
2
. Any one or all directions can be input.
Directions not provided will default to zero.
ACC indicates Acceleration spectra will be entered.
SCALE f4 = Scale factor by which design horizontal acceleration
spectrum will be multiplied. This factor signifies that the
structures and foundations, at which level base shear will be
calculated, are placed below the ground level. Default value is 1.0.
DAMP , MDAMP and CDAMP. Select source of damping input.
f5 = Damping ratio for all modes. Default value is 0.05 (5%
damping if 0 or blank entered).
DAMP indicates to use the f5 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 is the composite damping of the structure calculated for
each mode. One must specify damping for different materials
under CONSTANT specification.
MIS f6 = Use Missing Mass method. The static effect of the
masses not represented in the modes is included. The spectral
acceleration for this missing mass mode is the f6 value entered in
length/sec
2
(this value is not multiplied by SCALE). If f6 is zero,
then the spectral acceleration at the ZPA f7 frequency is used. If
f7 is zero or not entered, the spectral acceleration at 33Hz (Zero
Period Acceleration, ZPA) is used. The results of this calculation
are SRSSed with the modal combination results. If the MIS