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Extended Question: When I get negative stiffness(i.e Diagonal<0), and P-Delta analysis does not converge, does this indicate instability and buckling?
Answer: Convergence problems may correlate with P-Delta behavior. Inadequate member capacity and insufficient structural support may lead to instability and buckling. Excessivley Excessively large stiffness values may also disrupt convergence by causing numerical problems which adversely affect computation.
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It may be best to troubleshoot the model without P-Delta until you are confident that behavior is appropriate. If problems persist with geometric nonlinearitynon-linearity, it may be helpful to run, after the P-Delta load case, a modal 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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