Building large objects is often a Herculean task. But what about the demolition of bridges, dams, aircraft carriers, supercomputers, and rocket hangers? Here is some of the points for tearing down the Bay Bridge between San Francisco and Oakland:
Control the Tension
The piers of the cantilever truss aren’t holding the bridge up. They’re holding it down. “This is like a highly strung bow,” says senior bridge engineer Brian Maroney. (A bow made of 50 million pounds of steel.) “You don’t want to just cut the bow because the thing will fly off in all directions.” So crews will first remove the pavement on the upper deck to lighten the bridge’s load and reduce the tension. Next they’ll isolate steel supports, jacking them out of tension until they can be cut without whipping apart. Then they’ll slowly release the jacks.
Cut the Truss Spans
Named for their length in feet, the 504 and 288 truss spans are not under as much tension as the cantilever, so there’s less chance they’ll explode in your face when you cut into them. Still, caution is called for: The 80-year-old steel is not like modern steel; crews must be prepared for differences in strength and hardness.
Cart the Pieces Away
The steel beams are coated with greenish-gray paint, under which is a coat of lead-based stuff. To avoid contaminating the bay, all that metal has to be trucked away and cleaned, after which it will be resold as scrap.
Build a Monument
The massive art-deco column of pier E1, near Yerba Buena Island, may be preserved as a monument to the bridge that served the Bay Area for 77 years. The E2 pier will also likely remain and be converted into an observation platform for the new span.
And then the piers still have to be demolished. Impressive operation all around. It would be interesting to see all of the costs and manpower associated with such demolitions.