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STAAD Commands and Input Instructions
Section 5
5-164
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a) See Section 5.5 for explanation of the SET NL command.
The number that follows this command is an upper bound
on the total number of primary load cases in the file.
b)
STAAD performs up to 10 iterations automatically,
stopping if converged. If not converged, a warning
message will be in the output. Enter a SET ITERLIM i
command (i>10) before the first load case to increase the
default number of iterations. Since convergence may not
be possible using this procedure, do not set the limit too
high. If not converged, a message will be in the output.
c)
The principle used in the analysis is the following.
•
The program reads the list of springs declared as
SPRING TENSION and/or COMPRESSION.
•
The analysis is performed for the entire structure and
the spring forces are computed.
•
For the springs declared as SPRING TENSION /
COMPRESSION, the program checks the axial force to
determine whether it is tensile or compressive. Positive
displacement is TENSION. If the spring cannot take
that load, the spring is "switched off" from the
structure.
• The analysis is performed again without the switched
off springs.
•
Up to ITERLIM iterations of the above steps are made
for each load case.
•
This method does not always converge and may
become unstable. Check the output for instability
messages. Do not use results if the last iteration was
unstable. You may need to include some support in
each global direction that is not tension (or
compression) only to be stable on every iteration.