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Section 5
5-187
5.31.2.2 UBC 1994 or 1985 Load Definition
Purpose
This set of commands may be used to define the parameters for
generation of UBC-type equivalent static lateral loads for seismic
analysis. 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.
Total lateral seismic force or base shear is automatically calculated
by STAAD using the appropriate UBC equation(s).
V = ZIC
W (per UBC 1994) (1)
See Sections
1.17.2, 5.32.12
and
E
xamples manual
p
roblem no. 14
Rw
V = ZIKCSW (per UBC 1985) (2)
Note:
1) All symbols and notations are per UBC
2) Base shear V may be calculated by STAAD using either the
1994 procedure (equation 1) or the 1985 procedure (equation
2). The user should use the appropriate "ubc-spec" (see
General Format below) to instruct the program accordingly.
STAAD utilizes the following procedure to generate the lateral
seismic loads.
1. User provides seismic zone co-efficient and desired "ubc-spec"
(1985 or 1994) through the DEFINE UBC LOAD command.