Originally built in 1933, the North Torrey Pines Road Bridge was deemed structurally and seismically deficient in 1990. To bring the historic structure up to current seismic standards, the project team had to deal with structural irregularities, varying soil conditions and a tight sight—all while keeping the bridge open during construction.
The nonlinear retrofit plan involved isolating the superstructure from the existing columns and prestressing the entire bridge for continuity. This allowed contractors to keep the classic facade of the bridge intact while providing a seismically stable design. At the same time, the entire superstructure was removed and replaced with precast girders to architecturally match the existing structure.
To stabilize the soil during the retrofit, the project team injected 700 cu yd of grout into 533 holes in the ground ranging from 1 ft to 3 ft deep. Additional support was gained by installing deep foundation abutments, along with shear reinforcement, retrofitting on the columns and the addition of below-grade bent shear walls.
Corrosion of the structure was limited by a cathodic protection system of mesh and anodes installed below ground, within the bents.
To keep the bridge open during construction and avoid interruptions to the traveling public and the railroad, work was staged and the roadway was widened with temporary structures that alternated in each direction to carry auto and bicycle traffic.
Falsework construction provided an interesting hurdle, according to the project team. Designated an historic site in the National Register of Historic Places, the bridge’s varying superstructure depth and parabolic shape required careful planning to work around. This prompted the contractor to use “tables” at each pier to spread the high load during concrete pouring.
North Torrey Pines Bridge Retrofit and Replacement
Owner City of Del Mar
Lead Design Firm and Structural Engineer Kleinfelder
Contractor Flatiron Construction Corp,
Civil Engineer Project Design Consultants