It's been almost a month now since the brand new eastern span of the Bay Bridge officially opened for traffic — 24 years and nearly $US6.4 billion since 1989's Loma Prieta earthquake collapsed a section of the original.
Now they stand side-by-side, but not for (too) long; a "construction and demolition" plan is underway to completely raze and clear away the old, seismically out-of-date structure, while concurrently building a new onramp from Yerba Buena Island and completing the bike path from there to Oakland.
Commuters anticipating a sudden now-you-see-it, now-you-don't disappearing act of the redundant span will likely be disappointed — the effort is projected to take a solid two years to complete. A massive dose of dynamite certainly would have been the quickest and most dramatic strategy, and not unprecedented; back in 1984, the state transportation department blew up Menlo Park's Dumbarton Bridge to the shock and awe of gathered tourists and local lookieloos. But Bill Howe, Senior Engineer on the current Yerba Buena Island Transition Structure 2 project, notes that the "uncertain nature" of explosives makes it too risky for this kind of complicated procedure.
Which is to say nothing of the environmental impact of laying waste by explosion. While demo crews were required to collect Dumbarton's wayward parts from the salt water expanse, Howe's team hopes to keep falling debris to an absolute bare minimum. "We're committed to ensuring that the amount of materials that drop into the Bay is zero," he says. The old eastern span is also home to one of the largest cormorant colonies on the west coast and the estuary itself is home to more shore birds and water fowl than any other in the state; they've become accustomed to the consistent construction over the past decade, and efforts have been made to ensure the delicate handling of their habitat.
The cantilever will be systematically dismantled in the reverse order from which it was built, starting with the top level, which used to carry cars headed from Oakland towards SF. During this time, the lower deck will function as a path to haul the various component parts back to dry land in Oakland.
TEKLA, a 3D building information software, will allow the group to "model the bridge member by member," Howe says. "We can assign material properties and moments of inertia," which can then be updated to reflect real-time changes to the evolving schedule and developments. Ultimately, the only remains will be nestled three feet below the existing mudline.
So what's to become of all the leftover debris? According to Howe, it becomes the property of the contractor. Possible final resting places include being recycled for urban use in Oakland, or shipped through a CA-based vendor to China.
One local entrepreneur hopes to keep the pieces stateside for an architectural salvage proposal he's dubbed the Bay Bridge House. David Grieshaber recently launched a competition to come up with a plan for a sustainable abode and multi-use space composed of cast-offs from the historic span — a kind of cousin to SsD Architecture's 2006 prototype Big Dig House, which repurposed discarded concrete and steel from Boston's epic urban reconstruction. Whether Grieshaber will manage to make it happen remains to be seen, but if nothing else it seems he's got time. The scale of the job means that for bystanders, the best way to understand the scope is time-lapse once everything is through. "I think it will largely look like paint drying or grass growing," Howe says of the in-progress views.