Plink goes the pendulum arm as it smashes into a 3-inch section of steel. The sound is high-pitched, which tells any metallurgist with a good ear that the piece is brittle. The arm is the business end of a Charpy impact tester—it swings into a thing and, on impact, measures how much energy it took to break that thing. In this case, the thing is steel from a new bridge connecting two cities in one of the most seismically active places on the planet. And the steel broke. The flat, glittery inner surfaces show that in its short time holding together the new Bay Bridge, the steel corroded.
This relatively low-tech method is among a battery of tests that materials scientists are using to determine why several anchor rods securing the newest portion of the San Francisco Bay Bridge, the region’s busiest, failed their earthquake inspections. The first alarms sounded in 2013, when seismic tests found 32 faulty rods. They’d been sitting in a large pool of water, corroding. Many were pried out of the concrete for testing, and the failures prompted a broader investigation that turned up four more compromised rods. The bridge’s engineers want to pry them out and ship them to labs in Illinois and Alabama that will bang, pull, beat, and twist out the cause of their failure.
The Bay Bridge doesn’t just span San Francisco Bay—it practically connects two active fault lines. To the west, cutting up through the city of San Francisco, is the infamous San Andreas, source of the bridge-busting, building-buckling, World Series-stopping 1989 Loma Prieta temblor1. To the east, running through the East Bay, lies the Hayward Fault. It hasn’t shaken seriously since 1868, but seismologists suspect it has a one in three chance of producing a 6.8 magnitude earthquake by 2036. And it cuts right under UC Berkeley’s football stadium. […]