Midas Civil Buckling P-Delta and Geometric Nonlinearity
Definition
Midas Civil buckling, P-Delta, and geometric nonlinearity are the stability-related procedures that account for axial-force-dependent stiffness, displaced geometry, and critical load factors.
How It Works
The analysis reference separates linear buckling from nonlinear geometric effects. Buckling analysis is an eigenvalue-style procedure for critical load factors and buckling shapes. P-Delta analysis captures second-order force effects from axial loads acting through lateral displacements. More general geometric nonlinearity requires incremental equilibrium iterations because stiffness depends on the current configuration.
Solver Development Notes
Buckling requires a linear stiffness matrix, an initial-stress or geometric stiffness matrix, and an eigenvalue solver.
P-Delta should be treated as a second-order equilibrium correction, not as a postprocessing scale factor.
Geometric nonlinearity requires clear choices for tangent update, load stepping, convergence criteria, and force recovery.
Verification should include columns, frames, and bridge-pier examples where first-order and second-order responses diverge.
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