International Concrete Abstracts Portal

This paper discusses the results of an experimental program carried out at the Englekirk Structural Engineering Center of the University of California in San Diego (UCSD) to provide data for the performance-based seismic design of vertical pile-supported marginal wharves. Strong earthquake-induced inertial lateral loading may cause significant damage to the wharf in two critical locations (i) at the pile-cap connection, and (ii) at the location of the pile maximum bending moment below the ground. Two pile-cap assemblies, representative of the two most critical piles of a marginal wharf and the surrounding quarry-run fill, were built at full-scale and tested under quasi-static reversed cyclic loading to large lateral displacements. The piles in the test units were precast pretensioned and were connected to the deck through grouted dowels and were also embedded in quarry-run fill, as is often the case in these marine structures. The test units displayed a very stable hysteretic response. This paper describes the test specimens, their hysteretic response together with the predicted response, the progression of damage in the test units, and the distribution of the applied lateral force among the two piles. The paper also highlights the most relevant implications for performance-based design of marginal wharves.

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 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.

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.

The structural analysis of prestressed concrete piles is similar to the analysis of reinforced concrete columns in many respects but there are important detail differences. The construction of the M – P (moment-thrust interaction) curve requires consideration of the stress-strain curve for strand and of the substantial initial strains in the steel and concrete. When considering length effects, it will be found that much of the length of a prestressed pile will remain uncracked, which contributes significantly to its stability against buckling.