For the engineering-minded reader, here is an interesting article on the new San Francisco Bay Bridge that is being built (a new Eastern portion that is, between Yerba Buena Island and Oakland).
You may remember that the last one had a section of the upper deck collapse in the 1989 Loma Prieta quake. This one is designed to withstand the greatest lateral displacement expected from a quake in the next 1500 years. And what fascinates me is one of the key features, “sacrificial sections of weaker steel” that will absorb the energy, sparing the rest of the structure. These are 60 foot long sliding steel tubes at the joints, and hinge plates that connect the four shafts that make up the single tower of the suspension bridge portion. I immediately thought of how Indy cars are designed to shed pieces in an accident, to bleed off the energy–this seems to be the same principle. Unlike an Indy Car, though, if the hinge plates are deformed in an earthquake, the bridge will still be operational–they’ll still be strong enough to hold the sections of the tower together, and can be replaced at greater convenience, without shutting down the bridge.
That is so cool.