Design Considerations for the Kinematic Loading of Piles

Abstract

Performance-based seismic design provisions for pile-supported piers and wharves highlight the need to evaluate the combined effects of inertial loading, largely associated with the dynamic response of the structure, and kinematic loading resulting from permanent, seismically-induced deformation of the foundation soils. Inertial and kinematic loads on piles are routinely evaluated in an uncoupled manner with the combined load estimated by summation of the peak loads, or a fraction of the peak loads, resulting from the two, independent solutions. This approach requires considerable judgment as both modes of seismic loading involve highly nonlinear soil-foundation-structure interaction (SFSI) therefore superposition of the independent solutions is not strictly appropriate. The evaluation of seismic performance is further complicated when considering the phasing of these non-synchronous load situations. This paper focuses on the results of an investigation of the seismic performance of pile-supported wharves to long-duration ground motions. Dynamic SFSI was evaluated using a 2-D nonlinear geomechanical model that was first calibrated using data from field case histories, physical modeling, and pile load test data prior to application for a terminal wharf at the Port of Los Angeles. The modeling supplements field case histories and physical modeling results, which highlight the need to consider the time- and location-dependent nature of the inertial and kinematic loads on piles, the pattern of accumulated cyclic shear strain in the foundation soils, and soil-pile interaction in rockfill dikes and wave armor layers. Primary geotechnical considerations are summarized with recommendations for practical analysis of pile performance.