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STAAD Commands and Input Instructions
Section 5
5-200
ST f
5
= Optional value for type of structure (=1 for RC
frame building, 2 for Steel frame building, 3 for all
other buildings). If this parameter is mentioned the
program will calculate natural period as per Clause 7.6
of IS:1893(Part 1)-2002.
DM f
6
= Damping ratio to obtain multiplying factor for
calculating S
a
/g for different damping. If no damping
is specified 5% damping (default value 0.05) will be
considered corresponding to which multiplying factor
is 1.0. Refer Table 3 of IS: 1893(Part 1)-2002.
PX f
7
= Optional period of structure (in sec) in X direction.
If this is defined this value will be used to calculate
S
a
/g for generation of seismic load along X direction.
PZ f
8
= Optional period of structure (in sec) in Z or Y
direction. If this is defined this value will be used to
calculate S
a
/g for generation of seismic load along Z or
Y direction.
DT f
9
= Depth of foundation below ground level. It should be
defined in current unit. If the depth of foundation is 30
m or below, the value of
A
h
is taken as half the value
obtained. If the foundation is placed between the
ground level and 30 m depth, this value is linearly
interpolated between
A
h
and 0.5A
h
.
Notes
By default STAAD calculates natural periods of the structure in
both horizontal directions respectively which are used in
calculation for base shear. If, however, PX and PZ are mentioned
the program will consider these values for calculation of average
response acceleration coefficient. If instead of PX and PZ values
ST is mentioned the program will calculate natural period
depending upon the empirical expression given in IS: 1893 (Part
1)-2002.
Example
See section 5.32.12 under Generation of IS:1893 Seismic Load.