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h2. Why does P-Delta analysis not converge for certain load cases?

*Extended Question:* Does the inability to converge indicate instability and buckling, or should I change certain analysis parameters?

*AnswerANSWER:* Convergence problems may correlate with [P-Delta|kb:P-Delta effect] behavior. Inadequate member capacity and insufficient structural support may lead to instability and [buckling|kb:Buckling]. Excessivley large stiffness values may also disrupt convergence by causing [numerical problems|kb:Numerical problems] which adversely affect computation.

When a model fails under P-Delta effect, increase the size and/or quantity of columns and bracing to improve lateral capacity and avoid buckling. As an alternative, you may also refine the factors and/or loads applied during analysis.

It may be best to troubleshoot the model without P-Delta effect until you are confident that behavior is appropriate. If problems persist with geometric nonlinearity, it may be helpful to run, after the P-Delta [load case|kb:Load case], a [modal|kb:Modal analysis] analysis which uses Stiffness At The End Of This Stage. Modal analysis may then reveal the source and location of instability.

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*Related Incident:*
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