International Concrete Abstracts Portal

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.

This paper summarizes the seismic aspects of the recently updated ACI 543 Committee document on design, manufacture, and installation of concrete piles. Although re-approved in 2005, the original Committee document was last updated in 2000. As part of the latest update, an entire Chapter on seismic design and detailing was prepared. The current state of practice regarding seismic ground motion determination and seismic soil–structure interaction was reviewed so as to be incorporated into the Committee document. In addition to summarizing the key seismic aspects of the Committee document, the paper will highlight the changes from previous versions.

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.

Pile-supported marginal wharves have geometrical characteristics that make them prone to torsional response when subjected to earthquake induced inertial forces. Because of expected early system non-linear response due to the soil-structure interaction, lateral displacement demands on the piles cannot readily be estimated from conventional elastic modal response spectrum analyses and modal combination techniques. These displacement demands may be obtained using non-linear time-history analysis. Nevertheless, modeling the non-linear response of the wharf is still impractical in many design offices. For this reason, simple approximate methods that can estimate the critical pile displacement demand as the spectral displacement corresponding to a predominant translational (transverse) mode natural period of the wharf multiplied by a Displacement Magnification Factor (DMF) is adequate for design purposes. This paper revisits the earlier work of Benzoni and Priestley (2003) and computes, through non-linear time-history analysis, DMFs of short, long and linked segment wharves. Furthermore, the paper also reports shear key forces observed in the non-linear analyses of linked segment wharves. Finally, equations are proposed for calculating the DMFs and to estimate the forces for the design of shear keys.