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When a model fails under P-Delta, increase the size and/or quantity of columns and bracing to improve lateral capacity, and thereby avoid buckling. Walls that have been modeled uising using membrane type area element (never recommended) or shells with unrealistic thickness and or low stiffness modifiers can buckle and cause convergence issues. As an alternative, you may also refine the factors and/or loads applied during analysis.
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Buckling can also occur in horizontal floor elements such as beams and floors, if the floors take in plane loads (i.e have no diaphragm or semi rigid diaphragm) and have insufficient capacity, due to structural properties or small stiffness modifiers. Using rigid diaphragms and checking if the analysis converges can help rule out this as the cause of the problem.
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Additional suggestions which may resolve negative-stiffness errors include:
- Remove auto line constraints. Select all deck/shell objects in the model, then select Assign > Shell Elements > Auto Line Constraint Edge Constraint , check the Do NOT create Edge Constraints, and uncheck the Apply to Full Structure (not just Selection) option. This will remove auto line constraints and possibly resolve instabilities.
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