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STAAD Commands and Input Instructions
Section 5
5-368
5.38 Change Specification
Purpose
This command is used to reset the stiffness matrix. Typically, this
command is used when multiple analyses are required in the same
run.
General format:
CHA
NGE
This command indicates that input, which will change the stiffness
matrix, will follow. This command should only be used when an
analysis has already been performed. The CHANGE command
does or requires the following:
a) sets the stiffness matrix to zero,
b) makes members active if they had been made inactive by a
previous INACTIVE command, and
c) allows the re-specification of the supports with another
SUPPORT command that causes the old supports to be
ignored. The SUPPORT specification must be such that the
number of joint directions that are free to move (DOF or
"releases") before the CHANGE must be greater than or equal
to the number of "releases" after the CHANGE.
d) Also, the supports must be specified in the same order before
and after the CHANGE command. To accomplish this when
some cases have more supports than others do, you can enter
unrestrained joints into the SUPPORT command list using
FIXED BUT FX FY FZ MX MY MZ. It is best to put every
joint that will be supported in any case into every SUPPORT
list.
e) CHANGE, if used, should be after PERFORM ANALYSIS
and before the next set of SUPPORT, LOADS.
f) Only active cases are processed after the CHANGE command.