North Torrey Pines Bridge Seismic Retrofit: Part II, Structural Analysis and Design

The historic North Torrey Pines Road Bridge in Del Mar, California, is a 15-span precast concrete tee-girder structure built in 1933. The bridge has been classified as structurally and seismically deficient and functionally obsolete, with a sufficiency rating of 19 out of 100. Through the Caltrans Retrofit and FHWA Rehabilitation Program, the structure was to be rehabilitated or replaced for improved sufficiency and to satisfy seismic life safety. The combination of complex site geology, its deteriorated state, structural irregularities, site constraints, and the requirement to preserve its historic designation presented a challenging task. The solution was a performance-based methodology, more complex than typically applied in California, which led to a unique multifaceted retrofit and rehabilitation approach. Design and analysis included detailed inelastic static analysis, secant spectral methods, and nonlinear time-history analysis with multi-support excitation. The resulting solution included ground remediation, substructure strengthening, stiffness decoupling, a replacement superstructure, and new abutments on deep foundations.