T.Y. Lin International (TYLI) was selected by the California Department of Transportation to upgrade the historic Laurel Street Overcrossing in San Diego, California, to current earthquake safety standards. The overcrossing, also known as the Cabrillo Bridge, carries vehicles, pedestrians, and bicyclists and is a vital link across State Route 163 and Cabrillo Canyon into Balboa Park, one of the San Diego’s main visitor destinations.
The 769-foot-long Laurel Street Overcrossing was built in 1915 and is a reinforced concrete cantilevered hollow arch structure with a maximum height of 129 feet. Retrofitting for seismic strength and rehabilitation was required due to corroded steel and unsound concrete. Resembling a Roman aqueduct, the bridge is listed on the National Register of Historic Places, which made preservation of its historic character a controlling design criterion.
TYLI’s scope of work included performing detailed inspections; determining the scope and cost of necessary rehabilitation work; developing the seismic retrofit strategy; preparing final plans, specifications, and estimate (PS&E), and providing support during construction for both the rehabilitation and seismic retrofit. Retrofit measures included locking the midspan expansion joints through longitudinal post-tensioning of the superstructure, improving the transverse seismic behavior. TYLI developed several construction stages to facilitate these post-tensioning operations. The piers were strengthened by adding vertically post-tensioned shear walls, which extend from the foundation into the superstructure and provide sufficient shear and displacement capacity for the design seismic event.
Rehabilitation measures consisted of repairing unsound concrete throughout the structure; correcting the deck drainage system; repairing the deck internal catwalk system; installing permanent access features, such as doors, ladders, and platforms; and upgrading electrical components to current code requirements.
- TYLI developed an innovative seismic retrofit strategy using both response-spectrum and non-linear time history analyses.
- The historic character of the bridge was preserved by concealing all retrofitting within the internal framework.
- For seismic stability, the superstructure uses external post-tensioning similar to that used in precast segmental bridges.
- Pedestrian access was maintained on the bridge at all times during construction.
- Bridge closure to traffic was successfully limited to a short, four-month window.
- New exterior concrete was colored and textured to match the existing structure.
- New exterior lighting in the canyon illuminates the bridge arches at night.