Question

Is the "P-delta effect" automatically considered in the SACS Static Analysis with Pile/Soil Interaction? Do we need a specific input card to activate the effect?

Answer

1. Yes, PSI analysis already includes the P-delta effect on the piles. You do not need to activate the P-delta separately using the LCSEL PD when using PSI. Just ensure that your soil curves are properly defined (non-linear), the structure is fully modeled (jacket & pile), and convergence tolerances are set appropriately in PSI.

PSI integrates the full superstructure (jacket) in the stiffness matrix, including geometric stiffness matrices that capture P-delta effects on the jacket from:

• Axial compression (dead loads)
• Lateral loading (wave, current, wind)
• Structural displacements under environmental loads

These second-order effects are automatically included in the PSI solution when the full structure (pile & jacket) is modeled, non-linear soil curves (P-y, T-z, etc.) are used, and an iterative convergence criterion is defined in the PSI input.

The P-delta options on the OPTION line are for the superstructure analysis (jacket and topside). For PSI, there is no need to turn on any option, as PSI performs a nonlinear analysis which, by default, includes the p-delta effect on the piles. The P-delta effect is included in the PSI module’s iterative solution process, both below and above the mudline

IMPORTANT NOTE:

Including the P-delta effect is a necessary condition for the pile analysis results to be accurate. PSI analysis is a nonlinear analysis (and so is the P-delta effect). It is not possible to remove the P-delta effect from a PSI analysis.