Dynamic performance of twin-pile platforms in inclined seabed under combined wind-wave loading

This study develops a hybrid analytical–numerical framework for the dynamic response of twin-pile platforms under combined wind–wave loading on an inclined seabed. A frequency-domain model based on Timoshenko beam theory and the Pasternak two-parameter foundation considers shear deformation, soil continuity, pile–pile interaction, deck loads, and P–Δ effects. The model is validated against ABAQUS finite element simulations, with prediction errors below 10% for displacement and bending moment. Horizontal and sloping seabeds are compared under four representative sea states. Results show that seabed inclination amplifies pile-head displacement, shifts the displacement zero point about 10 m deeper under extreme conditions, and increases peak acceleration by 15–55%. The twin-pile asymmetry is mainly governed by the wave shielding effect, while the slope acts as an amplifying factor. The inclined seabed weakens the stability of the superstructure–pile–soil system: uneven plastic deformation of the surrounding soil causes unstable restoring forces during pile cyclic movement, intensifying negative acceleration fluctuations, especially at the pile top, a critical region of dynamic stress concentration.