Quasi-static p-y hysteresis loop for cyclic lateral response of pile foundations in offshore platforms

Pile foundations of the coastal and offshore structures always have strong nonlinear response due to marine environmental loads. Derived from the specific hyperbolic p-y curve and the soil stiffness degradation with the average shear strain, the quasi-static p-y hysteresis loop is modeling to develop the BNWF approach for analysis of the soil-pile interaction under low cycle number and irregular cyclic loads. The hysteresis loop simulates various important features, such as the soil-pile nonlinearity, the soil degradation, and the soil-pile gap formation. The developed hysteresis loop is consisted of the elastoplastic and drag-gap components, which the elastoplastic component simulates the nonlinear characteristics of soil-pile system and the gap-drag component considers the repeated separation and closure effects of the soil-pile interface. As the quasi-static p-y hysteresis loop subjects to the constant, variable and mixed amplitude displacement loadings, loop patterns can reflect the reasonable soil-pile interaction mechanism correctly, including the soil-pile separation and the soil degradation. The p-y hysteresis loop shape reflects the trend of irregular loads and the soil-pile gap affects the pattern of the hysteresis loop. The developed quasi-static p-y hysteresis loop incorporated in the generalized BNWF method to analyze the soil-pile interaction under the cyclic loads.