Pile-supported marginal wharves are a critical component of port infrastructure. A primary region of post-earthquake structural damage is the connection between the pile and the wharf deck. Review of prior experimental studies into state-of-the-practice connections indicates these can sustain cyclic deformation demand but at the cost of deterioration in resistance and significant damage. Damage within the connection is difficult to access and its repair is costly. Therefore, there is an interest in reducing the damage under moderate levels of seismic demand while sustaining the capacity under large cyclic drifts. An experimental study was undertaken to investigate mechanisms to limit damage while maximizing strength and deformation capacities of precast piles and their connections. Several structural concepts were investigated including (1) intentional debonding of the headed reinforcing bars, (2) supplemental rotation capacity through the addition of a cotton duck bearing pad above the head of the precast pile and (3) supplemental material to sustain the lateral deformations while minimizing deck damage. The final design incorporated all of these concepts. The results show significantly reduced damage. A design method is proposed to facilitate adoption of the proposed connection design in structural engineering practice. A comparison with other connection designs is made via fragility functions to assess their seismic performance.

This study was conducted to examine the seismic behavior of piers built on prestressed concrete piles founded in dense sand with grouted dowel bar connections. The following key observations were made. (1) The ground motions that caused collapse typically had a displacement pulse or fling in the record. These characteristics were particularly harmful to longer period, more flexible piers. (2) In general connection and in-ground steel demands were low; with few cases experiencing steel strains larger than 0.03. This indicates that sway instability due to P-Δ effects is the most common cause of collapse for piers. (3) A stability index limit of 0.25 provides sufficient protection against dynamic collapse when P-Δ effects are ignored in the analysis for piers supported on prestressed concrete pile, while a stability index limit of 0.1 will protect against significant P-Δ displacement amplification variability when increased analytical accuracy is desired. (4) For typical pile lengths and axial loading the P-Δ sensitive behavior is expected and the stability index limit will likely control the displacement capacities over material strain limits. Finally a simple procedure was proposed to help identify when a pier is potentially at risk from instability due to dowel bar fracture.

The seismic design of pile-supported marine structures such as piers and wharves is largely governed by their unique structural configuration and the special loading conditions associated with the operations that take place on the structure. The operation of heavy equipment and the stacking of heavy loads -usually well in excess of the self-weight of the structure- have significant implications on the seismic analysis and design of this type of structures. This paper reports a series of recommendations for the seismic analysis and design of piers, wharves and platforms supported on prestressed concrete piles, in presence of massive mobile equipment and/or stacked containers. Because of their significance in terms of structural safety and impact on construction costs of container and bulk handling terminals, emphasis is given to the evaluation of the percentage of live load to be considered as a source of seismic mass and a detailed discussion is presented on the need to rationalize the process of combining live loads with dead and earthquake loads as part of the definition of extreme load combinations in the seismic analysis and design of elevated platforms supported on piles. The paper includes a review of the treatment given to these loading aspects by specialized marine infrastructure design codes and offers specific recommendations.

This CD consists of 8 papers that were presented at a technical session sponsored by ACI Committees 357, 423, and 543 at the ACI Convention in Minneapolis, MN, in April 2013. The papers cover key aspects relevant to seismic analysis, design, detailing and experimental testing of precast prestressed concrete piles as substructure elements of marine structures. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-295

Over the past several years, the Ports of Los Angeles (POLA) and Long Beach (POLB) have undertaken numerous engineering studies to improve the seismic design of pile-supported wharf structures. It was concluded that the displacement-based seismic design methodology results in more robust and economical wharf structures. The displacement-based design allows plastic hinges to form at predetermined locations, which can be readily identified and repaired after an earthquake. Both Ports sponsored and funded specialized studies and an experimental program at the University of California at San Diego (UCSD) to confirm seismic design assumptions. Also, port-wide ground motion studies were completed to develop acceleration and displacement response spectra and time-histories for the different levels of earthquakes specific to each Port. Displacement-based seismic design procedures for pile-supported container wharves are included in two separate documents: “The Port of Los Angeles Code for Seismic Design, Upgrade and Repair of Container Wharves” and the “POLB Wharf Design Criteria”. This paper addresses the seismic, structural, geotechnical and soil-structure interaction aspects of these documents and discusses various studies that were undertaken to support the development of the displacement-based seismic design.