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STAAD Commands and Input Instructions
Section 5
5-192
5.31.2.3 Colombian Seismic Load
Purpose
The purpose of this command is to define and generate static
equivalent seismic loads as per Colombian specifications using a
static equivalent approach similar to those outlined by UBC.
Depending on this definition, equivalent lateral loads will be
generated in horizontal direction(s).
Description
See Sections
1.17.2, 5.32.12 and
E
xamples manual
p
roblem no. 14
The seismic load generator can be used to generate lateral loads in
the X & Z directions for Y up or X & Y for Z up. Y up or Z up is
the vertical axis and the direction of gravity loads (See the SET Z
UP command). All vertical coordinates of the floors above the
base must be positive and the vertical axis must be perpendicular
to the floors.
Methodology :
Seismic zone coefficient and parameter values are supplied by the
user through the DEFINE COLOMBIAN LOAD command.
Program calculates the natural period of building T utilizing clause
1628.2.2 of UBC 1994.
Design spectral coefficient (Sa) is calculated utilizing T as,
Sa = Aa I (1.0 + 5.0 T) when, 0 ≤ T ≤ 0.3 sec
= 2.5 Aa I when, 0.3 < T ≤ 0.48 S in sec
= 1.2 Aa S I / T when, 0.48 S < T ≤ 2.4 S in sec
= Aa I / 2 when, 2.4 S < T
where,
Aa = Seismic Risk factor (user input)
S = Soil Site Coefficient (user input)
I = Coefficient of Importance (user input)