The Bay Bridge, Nearing Age 90, Gets a Physical

For most of the past year, Caltrans contractors have conducted a far-from-routine physical on an 89-year-old patient: the monumental western span of the San Francisco-Oakland Bay Bridge.

In a process completed in September, engineers opened up the massive main cables that support the bridge’s double-deck roadway between Yerba Buena Island and San Francisco’s Rincon Hill to check on conditions inside. The results from that exam are due by early next year.

The last time crews looked inside the cables was in 2003, during a major seismic upgrade project. The Metropolitan Transportation Commission said this year’s checkup was the first systematic investigation of the 25-inch diameter cables since the Bay Bridge was completed in 1936.

To Bart Ney, the chief spokesperson for the Caltrans office that covers the Bay Area, the Bay Bridge is one of the engineering wonders of the world. During a late-night visit to the bridge earlier this year, he recited some of the features that make the bridge unique.

“You’re standing on a very special bridge,” Ney said, during a stop on the upper deck. He pointed out that the western side of the bridge is actually two spans, each of which ties into a humongous center anchorage that, he noted, “has more concrete in it than the Empire State Building.”

Beginning last fall, ironworkers and engineers moved along the main cables, removing the outer housing at select locations to expose the tightly packed bundles of galvanized steel wire inside.

“What we’re doing out here is we’re taking a look at the main cables that actually hold the deck up that you drive on,” Ney said. “And so, at 10 different locations, we’re going inside the cable, we’re opening it up, and we’re testing the steel inside of it.”

Each cable consists of more than 17,000 wires that were spun into place, bound together, tightly compressed and painted with a special protective paste before the outer housing was installed.

At each of the 10 testing locations, workers used hammers and mallets to drive large wedges into the tightly packed bundle of wires. Engineers gave the wire a visual inspection, snipped out short sections for laboratory testing and then spliced those cut strands back together. The inspection also studied how air moves through the interior of the cables — a concern given the bridge’s constant exposure to humidity and salt.

Caltrans and the Bay Area Toll Authority, the regional agency that oversees the Bay Area’s state-owned bridges, will use that information to decide whether to install a dehumidifying system to help protect the cables.

As part of this project, crews also replaced a half dozen of the vertical suspender ropes that help support the western spans’ road decks. Ney said the ropes to be replaced were identified by engineers with Caltrans’ structural maintenance inspection team as part of an evaluation conducted every two years.