Evaluating the Seismic Capacity of a Newly Designed Wharf at the Port of Oakland

This paper presents the findings of a seismic capacity study of the recently designed Berth 59 wharf at the Port of Oakland (the Port), California. The study was conducted to evaluate whether or not the wharf would collapse in a 2500 year San Francisco Bay Area seismic event. The wharf had been designed in accordance with the Port's seismic design requirements and criteria explained below. The Port's wharf design criteria require designing for strain limits for the forces resulting from three seismic levels. The three levels are events having 50, 20, and 10 percent probability of exceedance in 50 years. The return periods for these events are approximately 75 years (Level I), 225 years (Level II), and 500 years (Level III), respectively. The wharves are expected to suffer no or little damage and remain fully functional during and immediately after a Level I event. The wharves are not expected to collapse during a Level III event. The design criteria are derived from an acceptable risk approach such as is shown in the American Society of Civil Engineers (ASCE), Technical Council on Lifeline Earthquake Engineering (TCLEE) Monograph No. 12, Seismic Guidelines for Ports. "Acceptable Damage" increases as the probability of risk decreases. The original design considered three return periods, 75, 225, and 500 years. The "Acceptable Damage" increased as the return period increased. The criteria were consistent with the acceptable risk approach. This evaluation looked at a much higher return period and allowed greater damage. The seismic capacity study was accomplished by performing nonlinear pushover analysis and a soil structure analysis to evaluate the effect of slope displacements. In the pushover analysis, the magnitude of static lateral force is increased until the wharf is no longer stable. Ground motions for various earthquake levels were developed using probabilistic seismic hazards analyses (PSHA). The probabilistic analyses were conducted for three return periods (500, 1000, and 2500 years), which are equal or higher than the Level III event. In addition to the inertial forces and displacements calculated using pushover analysis, the performance of the Berth 59 piling was also evaluated for slope movement (kinematic soil-structure interaction (SSI) effects). The soil deformations were computed using FLAC (nonlinear finite difference program) as well as pseudostatic slope stability analysis combined with Newmark-type sliding block analysis. It was determined that the wharf at Berth 59 is not expected to collapse due to events with return periods of 2500 years.