The historic Golden Gate Bridge, built in the 1930s, serves as both a major commuter artery in and out of San Francisco and an aesthetic engineering masterpiece in the Bay Area. On October 17, 1989, the Loma Prieta earthquake served as a reminder that the San Francisco Bay region remains vulnerable to seismic activity. Although the Golden Gate Bridge suffered no apparent damage from the earthquake, Loma Prieta became a catalyst for an extensive seismic retrofit to bring the bridge up to today's design standards.
As part of the ongoing seismic retrofit program for the Golden Gate Bridge, the owner and operator of the bridge, the Golden Gate Bridge Highway & Transportation District, contracted with HDR to develop final Plans, Specifications & Estimates (PS&E) for the Phase IIIA Project. The project was advertised in April of 2005. The current Seismic Retrofit Phase IIIA Project addresses the seismic vulnerabilities and rehabilitation of the existing North Anchorage Housing and North Pylon structures.
The North Anchorage Housing is a reinforced concrete structure approximately 350 feet long, 130 feet wide, and between 60 and 110 feet tall. It encloses and protects the main suspension cables and their anchorage assemblies. The roof of the North Anchorage Housing structure serves as the roadway deck connecting the Suspension Bridge Side Span to the North Approach Viaduct. The North Anchorage Housing also incorporates the North Pylon of the Suspension Span, which supports the end of the stiffening trusses and houses the main cable tie-downs. HDR's scope of work includes seismic retrofit of both the structures, and replacement of the existing North Anchorage Housing roadway deck under traffic. The retrofit will render the bridge sufficient to meet current seismic safety standards, and allow it to maintain its function after a major earthquake. Emergency access to the bridge immediately following the earthquake is critical, and loss of function would have a serious impact on the economic foundation of the region.
Adherent to today's seismic safety standards, HDR's final design included engineering changes to the structures that simultaneously preserve the historic and aesthetic integrity of the bridge. All of HDR's work for this project meets the requirements of the Golden Gate Bridge Highway & Transportation District, Caltrans and the Federal Highway Administration.