Performance Based Seismic Retrofit Design of Brooklyn Basin Wharf-Paper

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Brooklyn Basin’s planned 10-acre Shoreline Park will occupy a historic 1,200-foot wharf built in the 1930s on timber and concrete piles. Because the site contains soft Young Bay Mud beneath a shoreline rock dike, earthquake-induced lateral spreading could impose substantial kinematic loads on the piles, in addition to shaking-related inertial loads.<br /><br />Inspectors assessed all 2,519 piles using ASCE Manual of Practice 130. They rated 279 as severely damaged and 187 as having major damage, primarily from seawater exposure and reinforcing-steel corrosion in the tidal and splash zones. Repairs use fiber-reinforced polymer (FRP) jackets filled with high-strength grout; piles with more than 20% section loss also receive new reinforcing cages.<br /><br />The wharf’s seismic retrofit was designed to meet California Building Code Chapter 31F Level 2 Life Safety requirements. Site-specific ground motions and nonlinear, three-dimensional pushover analyses were used to evaluate both inertial and kinematic effects, including their prescribed combination. The analysis also modeled the interaction between the soil, piles, and a potential sliding wedge of the rock dike and underlying mud, accounting for the stabilizing “pinning” forces of the piles.<br /><br />Key measures include 36-inch-diameter steel pipe piles along the landside, additional closely spaced piles where needed to stabilize the slope, a reinforced-concrete deck overlay, and replacement of the deteriorated timber apron with concrete piles and deck. The new piles reduce demands on the existing structure and help limit lateral spreading. Analyses showed the retrofitted wharf meets the required performance criteria, with supplementary piles used where needed to limit ground displacement.

Keywords

Brooklyn Basin

Shoreline Park

wharf retrofit

seismic analysis

lateral spreading

Young Bay Mud

pile corrosion

FRP jackets

California Building Code

ground motion modeling