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Section 5
5-195
5.31.2.4 Japanese Seismic Load
Purpose
The purpose of this command is to define and generate static
equivalent seismic loads as per Japanese 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).
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 :
Seismic zone coefficient and parameter values are supplied by the
user through the DEFINE AIJ LOAD command.
Program calculates the natural period of building T utilizing the
following equation
T = h ( 0.02 + 0.01 α)
where,
h = height of building
α = ratio of steel part
Design spectral coefficient ( Rt ) is calculated utilizing T and Tc
as follows
R
t
= 1.0 when T < T
c
= 1 - 0.2 ( T/T
c
- 1)
2
when T
c
≤ T ≤ 2T
c
= 1.6 T
c
/ T when 2T
c
≤ T