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Section 5
5-333
5.34 Modal Calculation Command
Purpose
This command may be used to obtain a full scale eigensolution to
calculate relevant frequencies and mode shapes. It should not be
entered if this case or any other case is a TIME LOAD or
RESPONSE SPECTRUM case. For Steady State/Harmonic analysis
this command must be included in the load case that defines the
weights and weight moment of inertias for eigensolutions (see
sections 1.18.3 and 5.32).
General Format:
MOD
AL (CALCULATION REQUESTED)
This command is typically used in a load case after all loads are
specified. The loads will be treated as weights and weight moment
of inertias for eigensolutions (see sections 1.18.3 and 5.32). The
user is advised to specify the loads keeping this in mind.
This case will be independently solved statically and dynamically.
Static results using the loads will include joint displacements,
member forces, support reactions, and other outputs computed
from a normal static analysis without any dynamic effects
included.
In addition, the Dynamic results (using loads as masses) will
include Mode Shapes and Frequencies.
See Sections
5.31, 5.32+
1.18.3
Notes
The MODAL CALCULATION command can be included in any of
the primary load cases, but only in one of them.