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STAAD Commands and Input Instructions
Section 5
5-198
5.31.2.5 Definition of Lateral Seismic Load per
Indian IS:1893 (Part 1) – 2002 Code
Purpose
This feature enables one to generate seismic loads per the IS:1893
specifications using a static equivalent approach. Depending on
this definition, equivalent lateral loads will be generated in
horizontal direction(s).
See Sections
1.17.2, 5.32.12 and
E
xamples manual
p
roblem no. 14
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
The design base shear is computed by STAAD in accordance with
the IS: 1893(Part 1)-2002 equation 7.5.3.
V = A
h.
W where, A
h
=
g
Sa
R
IZ
..
2
Note:
All symbols and notations in the above equation are as per
IS: 1893(Part 1)-2002
STAAD utilizes the following procedure to generate the lateral
seismic loads.
1. User provides seismic zone co-efficient and desired "1893(Part
1)-2002 specs" through the DEFINE 1893 LOAD command.
See section
5.32.12
2. Program calculates the structure period (T).
3. Program calculates S
a
/g utilizing T.