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.

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.

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 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.

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.