Golden Gate Bridge officials are preparing to launch the final and largest phase of a decades-long project to make the 85-year-old structure withstand stronger earthquakes.
The Golden Gate Bridge, Highway and Transportation District plans to select a construction contractor later this year to begin preliminary work on the estimated $880 million final phase. The project will upgrade the main span and the towers and allow the bridge to withstand a magnitude 8.3 quake, which would be comparable to the destructive 1906 San Francisco earthquake.
“For us, we really are going through one of the most important undertakings on this bridge,” said district engineer Ewa Bauer-Furbush. “That’s the project for us.”
The seismic retrofit project, which was launched in 1997, was prompted by the Loma Prieta earthquake in 1989. The 15-second, 6.9-magnitude quake caused major damage to bridges and highways, including the collapse of the top deck of the Bay Bridge and the Cypress Street viaduct in Oakland. The Golden Gate Bridge had no observable damage but was located about 60 miles north of the quake’s epicenter.
A vulnerability study conducted by the bridge district after the Loma Prieta earthquake found that a magnitude 7.0 quake with an epicenter near the bridge could cause major damage to the span. A magnitude 8.0 temblor would create a substantial risk of collapse at the two viaducts on the San Francisco and Marin entry points as well as at the Fort Point Arch.
About $260 million in seismic upgrades were completed at these vulnerable sections of the bridge from 2001 to 2014. District staff said the bridge no longer faces the risk of collapse at these sections, but the main suspension bridge still faces the risk of significant damage.
The final phase will install 38 devices to absorb quake energy that would otherwise flow into the bridge, Bauer-Furbush said. Special joints will be added to the sides of each tower and near the pylons at each edge of the main span that allow for three-dimensional movement.
Construction crews will also strengthen structures themselves, including the road deck and the bases of the tower, to minimize the input of seismic energy and thereby reduce damage, Bauer-Furbush said.
The bridge district expects the project will not result in full traffic closures, but some lanes might be closed.
Bauer-Furbush said three contractors have submitted applications for the project in response to a request sent out in May. The district’s board is expected to select a contractor and begin a yearlong process to work through each step of the construction to set prices, timelines and other details.
“At every step of the way we will know what goes into the construction price and to verify what we’re getting pricing from the contractor that is the acceptable market value,” Bauer-Furbush said. “We also will hire an independent construction cost estimator.”
“If everything goes as planned, then we will issue notice to proceed with the preconstruction services in January 2024,” Bauer-Furbush said. “By the end of next year or the beginning of 2025, we hope we can award a construction contract.”
The final retrofit project still has a substantial funding gap that must be closed before its planned 2025 construction start. About $451 million of the $880 million has been raised, with the majority of that funding coming from the $1.1 trillion federal infrastructure legislation of 2021.
The price is about $1.4 million higher than originally estimated and could increase further in the next year.
“The economy has a lot of risks in terms of prices of commodities and labor,” Bauer-Furbush said. “We still think this is the order of magnitude we will be dealing with.”
The district aims to close the funding gap through state funds.
The Metropolitan Transportation Commission is the nine-county Bay Area’s top transportation planning and financing agency. The commission oversees funding for seven state-owned bridges in the region, but not the Golden Gate because it is funded by its own special district. The commission does not have funds earmarked for the seismic retrofit project.
“Nonetheless, we believe that this is an important regional priority and have for a long time,” commission spokesman John Goodwin said. “Over the years we have advocated for the Golden Gate Bridge seismic retrofit program through its various phases to receive federal dollars.”
More information about the seismic retrofit project can be found at shorturl.at/pwxH1.