<![CDATA[Accurate representation of pile-soil interaction is essential for performance-based assessment of pile-supported wharves because lateral resistance, effective fixity, and plastic-hinge development depend strongly on surrounding soil conditions. This study compares a conventional virtual-fixity-point (VFP) idealization with a calibrated soil-structure interaction (SSI) model for a bulk carrier wharf in Gresik, Indonesia. Three models were evaluated: the existing wharf with VFP supports, the same structure with distributed SSI springs, and an optimized SSI model with reduced steel-pipe-pile diameters. The 20 m-wide platform was modeled in SAP2000 under operational, berthing, mooring, environmental, and seismic loads. Lateral springs were derived from LPILE p-y analyses, assigned at 1 m depth intervals, and validated using pile-deflection profiles under a 100 kN lateral load. Linear analysis evaluated demand-capacity ratios and serviceability displacements, while nonlinear pushover analysis used fiber hinges and strain-based criteria. Relative to the VFP model, the SSI model reduced earthquake DCR from 0.648 to 0.548 and seismic displacement from 76.92 to 43.17 mm, while increasing performance-point base shear by 27%. The optimized model reached a DCR of 0.770, and maximum pile strains remained within 19.2–21.0% of the Minimal Damage limit, confirming safer and more efficient structural optimization for comparable pile-supported marine infrastructure in seismic regions]]>
