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STAAD Commands and Input Instructions
Section 5
5-302
parameter is entered on any spectrum case it will be used for all
spectrum cases.
ZPA f7 = For use with MIS option only. Defaults to 33 Hz if not
entered. Value is printed but not used if MIS f6 is entered.
SOIL TYPE f8 = the types of soil. f8 is 1 for rocky or hard soil, 2
for medium soil and 3 for soft soil sites. Depending upon time
period, types of soil and damping, average response acceleration
coefficient, Sa/g is calculated.
Notes:
1. The design base shear V
B
(calculated from the Response Spectrum
method) is compared with the base shear V
b
(calculated by
empirical formula for the fundamental time period). If V
B
is less
than V
b
, all of the response quantities are multiplied by V
b
/V
B
as
per Clause 7.8.2. To have STAAD compute the empirical base
shear V
b
, please enter the data described in Section 5.31.2.5
and place that data before the first load case in the STAAD
input. STAAD does not calculate the fundamental frequency of the
structure needed for the empirical base shear V
b
calculation; so
you must enter either the ST parameter or the PX and PZ
parameters in the Section 5.31.2.5 DEFINE 1893 LOAD data.
2. The following interpolation formula is adopted for interpolation
between damping values as given in Table 3.
Interpolation and/or extrapolation of ground response acceleration
for a particular mode has been made for determining the spectrum
ordinates corresponding to the modal damping value for use in
Response Spectrum analysis. The relationship that shall be used
for this purpose is defined by :
Sa =
ξ
ξ
B
Ae +
−