A Simplified Method for Estimating Target Displacement of Pile-Supported Wharf under Response Spectrum Seismic Loading

A single wharf segment tends to behave as a simple 1-DOF structure under transverse component of seismic excitation. Main complexities arise from the significant torsional behavior under longitudinal component of seismic excitation. The objective of seismic analysis is to estimate target displacement at critical piles under transverse and longitudinal components of seismic excitation applied simultaneously. This demand can be done by using Multi-mode Spectral Method (MSM) which is a standard one used in most seismic codes. This paper presents a simplified method, called Equivalent Single mode Spectral Method (ESSM). This method determines target displacement by multiplying the displacement induced by transverse component of seismic excitation and a factor, called Displacement Amplification Factor (F_a), which accounts for torsional components of response and multi-directional effects of seismic excitation. The proposed equations of F_a were from a parametric study using 2520 wharf examples with different conditions of soil and structure. In this parametric study, pile-soil interaction was represented by the Winkler spring model, nonlinear force-deformation response of springs was determined based on Matlock's p-y model for soft clay under cyclic loading and MSM was used as a main tool for seismic analysis. The study showed very good fits between displacements resulted from ESSM and that resulted from MSM.