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Seismic Retrofit Phase 2

Phase 2 (2001-2008)

On May 11, 2001, the District Board of Directors authorized award of the Phase 2 construction contract. Phase 2 began in June 2001 and was completed in July 2008. It was the most complex part of the project in terms of design and construction. Federal, state and regional funds totaling $189 million were authorized to complete this phase.

This phase encompasses structural retrofit of many different types of structures of the south approach: the south approach viaduct, south anchorage housing, Fort Point arch, and south pylons. Retrofit measures developed for each of these structures reflect their individual behavior under seismic ground motions and their interaction at points of interface while accommodating their already-in-place historic configuration.

Without closing the Golden Gate Bridge to traffic, the steel support towers and bottom lateral bracing of the south approach viaduct will be entirely replaced, and seismic isolation bearings and joints will be installed at the roadway level. The west wall of the south anchorage housing will be replaced and massive internal shear walls constructed. Five million pounds of external and internal steel plating will be added to south pylon walls. The historic architectural appearance of the external surfaces of the pylons will remain unchanged with the addition of a new external concrete cover on top of the new plating.

The Fort Point arch will be retrofitted with new arch bearings and energy dissipation devices, and isolation joints will be installed. Steel members throughout the entire arch will undergo extensive strengthening.

Not only were immense challenges presented in the design and engineering of this phase of retrofit construction, but the construction site itself presents very unique project limitations. The construction site is located in a very compact area bound on the west by the Pacific Ocean and on the east by very steep slopes. Severe weather including strong wind and high waves are nearly constant. Access consists of two narrow roads that must be shared with thousands of tourists visiting the Golden Gate Bridge and the Historic Fort Point Site located directly below the Fort Point arch structure of the Bridge. Construction on the arch is limited to four days per week to allow limited visitation to the Site. The small construction staging areas available near the work site further restrict the logistics of the construction operations.

In 2005, the Golden Gate Bridge Seismic Retrofit Design and Construction Project, Phase 2, was recognized as the Special Earthquake Engineering Project of the Year by the San Francisco Section of ASCE. In 2006, the Golden Gate Bridge Seismic Retrofit Design and Construction Project was named as one of the top nine Seismic Retrofit Projects of the 20th Century by Applied Technology Council and Engineering News Record as part of their “Celebrating 100 Years of Seismic Structural Engineering and Construction” in the United States.

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