GOETHALS BRIDGE REPLACEMENT PROJECT - PERFORMANCE-BASED DESIGN OF THE DRILLED SHAFT FOUNDATIONS-Paper

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The Goethals Bridge Replacement Project replaced the aging New York–New Jersey crossing with two parallel bridges, including long approach structures supported by large-diameter reinforced-concrete drilled shafts socketed into bedrock. The shafts, 4.5–9 feet in diameter, use permanent steel casing for construction, corrosion protection, and concrete confinement.<br /><br />The foundation design used a performance-based seismic approach with two earthquake levels: a Functional Evaluation Earthquake (FEE), after which the bridge must remain fully accessible, and a Safety Evaluation Earthquake (SEE), after which emergency access must be maintained and full access restored within months. The design followed AASHTO seismic and general LRFD specifications. Because their reinforcement requirements differ, the more stringent code governed minimum longitudinal reinforcement, while the seismic guide’s less restrictive requirements were used for transverse confinement reinforcement.<br /><br />A nonlinear, three-dimensional finite-element model represented concrete behavior, large displacements, and soil–shaft interaction. Nonlinear horizontal and vertical soil springs were developed from geotechnical data and modeled using LPILE and APILE curves. XTRACT supplied moment–curvature relationships for the shafts and columns. Pushover analyses assessed displacement capacity and potential plastic hinge formation.<br /><br />Results indicated that plastic hinges would form only at force levels well above those expected during seismic loading, and pier displacement capacity exceeded seismic demand in both principal directions. The authors conclude that advanced nonlinear analysis is important for accurately evaluating long, continuous bridge approaches and that finite-element results provided a useful check against conventional pile-analysis methods. They also note that the differing AASHTO provisions can produce substantially different reinforcement demands, and that counting casing toward strength—not only confinement—might yield a more economical design.

Keywords

Goethals Bridge

bridge replacement

seismic design

reinforced concrete drilled shafts

finite element analysis

performance-based design

AASHTO LRFD

soil-structure interaction

pushover analysis

corrosion protection