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General Description
Section 1
1-78
any PDELTA, NONLINEAR, dynamic, or TENSION/
COMPRESSION member cases. The multi-linear spring command
will initiate an iterative analysis which continues to convergence.
1.18.2.5 Tension / Compression Only Analysis
When some members or support springs are linear but carry only
tension (or only compression), then this analysis may be used. This
analysis is automatically selected if any member or spring has been
given the tension or compression only characteristic. This analysis is
an iterative analysis which continues to convergence. Any member/
spring that fails its criteria will be inactive (omitted) on the next
iteration. Iteration continues until all such members have the proper
load direction or are inactive (default iteration limit is 10).
This is a simple method that may not work in some cases because
members are removed on interim iterations that are needed for
stability. If instability messages appear on the 2
nd
and subsequent
iterations that did not appear on the first cycle, then do not use the
solution. If this occurs on cases where only springs are the
tension/compression entities, then use multi-linear spring analysis.
There may not be any Multi-linear springs, NONLINEAR, or
dynamic cases.
1.18.2.6 Non Linear Cable/Truss Analysis
(available in limited form)
When all of the members, elements and support springs are linear
except for cable and/or preloaded truss members, then this analysis
type may be used. This analysis is based on applying the load in
steps with equilibrium iterations to convergence at each step. The
step sizes start small and gradually increase (145 steps is the
default). Iteration continues at each step until the change in
deformations is small before proceeding to the next step. If not
converged, then the solution is stopped. The user can then change
analysis parameters or modify the structure and rerun.
See sections
5.30, 5.37,
1.11