The Bay Bridge crosses from San Francisco to Oakland and carries about 260,000 cars per day. When it opened in 1936, it was the largest span in the world. After a portion of the East Span collapsed in the Loma Prieta earthquake of 1989, it was determined that the bridge’s lack of seismic resiliency was going to be a problem in California, and the replacement and retrofit efforts began.
Demolishing the Bridge, Protecting the Bay
Once the new bridge was constructed, the old one had to be disassembled. In the past, bridge demolition was fairly straightforward – usually involving sticks of dynamite. The challenge was to develop a demolition method that was both safe and environmentally friendly while remaining efficient. Glosten assisted California Engineering Contractors with the marine aspects of the demolition, reversing the construction process by disassembling sections of the span and demolishing them on land.
A Barge-Based Solution
The method that was developed to demolish the bridge involved lowering 504-foot bridge spans onto barges, and lifting 288-foot bridge spans off the piers and onto barges. The barges would then transport the structures dockside to be demolished and recycled. Glosten selected the barges capable for the job, determined how to safely configure them, designed the span support structure, and analyzed the stability of the barges during loadout, transport, and dismantling. Additionally, the project team determined wind/current conditions, towing configuration and limitations, and mooring design to maintain the vessel position during span lowering. Glosten also provided on-site support for the lift off and/or lowering of bridge spans.
Challenge Complete, Ahead of Schedule
The demolition was completed eight months ahead of schedule. The team succeeded in lowering the 504-foot spans in just one month each, and took down the 288-foot spans at a rate of two spans per month. In the end, a challenging engineering feat was accomplished with respect paid to the safety and environmental concerns set forth in the contract. The Bay Bridge will now be seismically resilient for many years to come.
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