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STAAD Commands and Input Instructions
Section 5
5-208
5.31.2.7 CFE (Comision Federal De Electricidad)
Seismic Load
Purpose
The purpose of this command is to define and generate static
equivalent seismic loads as per MANUAL DE DISEÑO POR
SISMO - SEISMIC DESIGN HANDBOOK COMISION FEDERAL
DE ELECTRICIDAD - ELECTRIC POWER FEDERAL
COMISSION - October 1993 (Chapters 3.1, 3.2, 3.3 and 3.4)
specifications. Depending on this definition, equivalent lateral
loads will be generated in horizontal direction(s).
Description
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 CFE LOAD command.
Program calculates the natural period of building T utilizing
Raleigh-Quotient method. If time period is provided in the input
file, that is used in stead of calculated period.
c = Seismic coefficient is extracted from table 3.1
a
0
, T
a
, T
b
, and r are obtained form table 3.1
The acceleration a is calculated according to the following:
a= a
0
+ (c-a
0
) x T/T
a
if T<T
a
a= c if T
a
≤ T ≤ T
b
a= c (Tb/T)
r
if T>T
b