Spanning the pristine Los Penasquitos Creek and Lagoon, immediately adjacent to the ocean, is the North Torrey Pines Road Bridge replacement. The bridge replaces the structurally deficient and functionally obsolete bridge located on the old Pacific Coast Highway across the outlet of Los Penasquitos Creek.

The new bridge is a haunched, 3-span, cast-in-place, prestressed box girder with an overall length of 340’. The superstructure depth varies from 13’ at the bents to an ultra-thin 3.5’ at mid-span and at the abutments. The structure has a width of 69’-2” which accommodates two traffic lanes, shoulders, a median, and a sidewalk along one side. The bridge was designed to be constructed in two stages so that vehicular, pedestrian and bicycle traffic be maintained throughout construction. The attention to architecture and details for this unique structure were conceived to respect the combination of the spectacular site and high visibility of the bridge.

The graceful convex curvature of the box girder fascia merges the functions of the exterior girder and deck overhang, providing a smooth monolithic appearance. For pedestrians passing beneath the bridge, this form creates a Gothic arch shape between the left and right structures that very subtly references the adjacent bridge over the railway to the north; a goal established through community outreach. The one-of-a-kind hand railing along the edge of the walkway is a reminder to engineers of the infinite number of possible design variations that can provide interest while maintaining safety. The deeply haunched superstructure goes well beyond customary proportions resulting in an extremely thin superstructure at mid-span and a nearly arch-like profile. Special structural details were required for the exterior box girder webs and near the columns where the box girder soffit becomes nearly vertical.

The bridge structure itself is a prime example for engineers of the unique forms that are possible with modern construction materials and techniques. It reminds engineers that adherence to standard solutions is not requisite. The construction of the bridge required overcoming the challenges of building a bridge over water, and a constant threat of wave storm surges, during the 3rd rainiest year on record. Measures such as rip-rap and sheet pile retaining walls were implemented to protect the bridge falsework during construction from wave, tidal, and stream flow forces. Temporary sheet pile retaining walls allowed most of the bridge to be constructed in the dry with only a short span over the inlet.

The harsh marine environment required some unusual design measures. For instance, all bar reinforcement was epoxy coated to provide an extended design life of the structure. Concrete was densified through the use of high proportions of fly ash, thereby reducing chloride penetration into the concrete. The anodized aluminum finish on the railings was specified as marine grade. Working in close coordination with City staff, decision makers and stakeholders, the design team developed a project that met or exceeded all project needs to the extreme satisfaction of the owner and client, by providing the community and region with an architecturally significant landmark and a structurally and functionally safe bridge.

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