The Golden Gate Bridge, Highway and Transportation District is preparing to launch the final and largest phase of a decades-long project to make the 85-year-old structure withstand stronger earthquakes.
The agency is set 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.
“For us, we really are going through one of the most important undertakings on this bridge,” said district engineer Ewa Bauer-Furbush to The Mercury News. “That’s the project for us.”
This seismic retrofit project, which began in 1997, was prompted by the 1989, 6.9 magnitude earthquake that caused major damage to roads and bridges in surrounding areas.
Though the Golden Gate bridges was located 60 miles from the quake's epicenter, a later vulnerability study found that a 7.0 quake near the bridge could cause major damage to the span. Anything above that magnitude could contain potential for an all out collapse.
About $260 million in seismic upgrades were completed 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 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.
The bridge district expects the project will not see full traffic closures, but some lanes might be closed.
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 Bipartisan Infrastructure Investment and Jobs Act.
The full strategic plan for construction can be found here.
Source: The Mercury News