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- Run modal analysis, then check for instabilities while reviewing results (modal shapes, periods, etc.). Instabilities are clearly indicated by animating mode shapes.
Other tips
- To locate disconnected elements, try assigning unit mass to all DOF and running a modal analysis. The modal shapes will identify disconnected elements that cannot support load and prevent convergence in nonlinear analysis.
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NOTE: A variation of this process may be used to troubleshoot convergence problems which occur during time-history analysis. When a certain step fails to converge, run analysis until that step, then run modal analysis using stiffness at that step to check for instabilities. |
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