Experts urge quick action to protect Bay Bridge cable

The eastern span of the Bay Bridge has been beset by problems with high-strength rods and a lack of access to maintain the structure. An international team of experts is recommending an immediate retrofit to protect the main cable from corrosion. less The eastern span of the Bay Bridge has been beset by problems with high-strength rods and a lack of access to maintain the structure. An international team of experts is recommending an immediate retrofit to ... more Photo: Michael Macor, San Francisco Chronicle Photo: Michael Macor, San Francisco Chronicle Image 1 of / 54 Caption Close Experts urge quick action to protect Bay Bridge cable 1 / 54 Back to Gallery

An international group of bridge maintenance experts is urging the immediate retrofit of the $6.4 billion new eastern span of the Bay Bridge to protect the main cable from corrosion and to allow for inspections of other potentially vulnerable areas on the structure.

In its report to Caltrans and a Bay Bridge oversight committee, the maintenance peer review panel cited concerns ranging from the span’s well-publicized problems with high-strength rods to a lack of maintenance access on the project.

But the integrity of the main cable was a key issue that emerged during a yearlong study by the experts, who included the Golden Gate Bridge’s chief engineer and officials of the Bronx Whitestone Bridge in New York, Hong Kong’s Tsing Ma Bridge and the Forth Road Bridge in Scotland.

Recently, the chief designer of the Bay Bridge project warned Caltrans that rainwater leaks posed a corrosion risk to the two chambers where the cable strands splay out under the road deck. Now, the maintenance panel is sounding the alarm about the main cable itself — a bundle of steel strands that loops over the top of the tower, under the bridge and back over the tower.

Problems elsewhere

The problem, the experts said, is that similar cables on bridges elsewhere have been attacked by corrosion. And the Bay Bridge, because of the way it was built, is particularly difficult to inspect for such damage.

The cable is wrapped with steel and filled with corrosion-fighting paste, and its suspended cables are painted white. But the panel said such “conventional methods” have “not been effective on large numbers of these bridges around the world.”

“Cracks in wires and wire breaks have been found within the cables of a significant number of suspension bridges,” the group said. “It would appear that there is now serious doubt on whether the traditional method of painting to provide protection to the main cables of these bridges is sufficient to provide a service life similar to the full design service life of the bridge.”

One way to protect bridges is to pour a corrosion-fighting grade of oil into the enclosed cable, but that requires a costly opening up of the cable along much of its length, the expert panel said. An alternative is blowing dry air at low pressure inside the cable, a method that is becoming standard for new bridges.

Not too late

Caltrans decided not to install such a system on the eastern span when it was being built, concluding that the approach was untried, the report said. But it’s not too late, and there’s “little doubt” it would be effective, the experts said.

“Unless there are overwhelming difficulties that prevent such a system from being fitted, it should be installed as soon as possible,” the report said.

The group did not give a cost estimate, but outside experts said it would probably be in the tens of millions of dollars. The most likely source of funding would be toll-payer dollars.

Bay Bridge officials can draw on a $68 million pool of maintenance money but must compete for it with seven other state-owned toll bridges.

Steve Heminger, who chairs the Bay Bridge’s oversight committee, said there will be “some conversation about” the dehumidification proposal with Caltrans.

“We asked for advice. We don’t have to take every bit of advice we get,” Heminger said. “We’ll have a conversation with Caltrans, and we’re going to take it from there. The maintenance of this bridge is a 150-year project — it doesn’t all have to get done in year one.”

Caltrans said in a statement: “Corrosion and cracking is what you look for on every bridge, not just the Bay Bridge. We are employing some dehumidification, and if more is warranted we will address that.”

David Williams, a bridge expert who specializes in seismic stability and marine foundations, said the report is sobering.

“They are very subtly saying you need a very significant budget to keep operations, inspections and maintenance going,” Williams said.

‘Challenging’ problems

Even with a cable retrofit, Caltrans faces “very challenging” problems when it comes to inspecting and repairing the bridge because of its unique design, the report said. Many crucial areas are all but inaccessible.

One issue is that the main cable and the smaller supporting cables cross over the heavily traveled roadway, the group noted, posing a risk to employees and motorists alike during any repair work. And there is no way for inspectors to get into the steel-wrapped main cable to check it for corrosion. “That should be addressed,” the panel said.

The ends of the cable are secured inside the deck in twin anchorages at the eastern end of the suspension span instead of being above the bridge surface. Although that was “very innovative,” it imposes “extremely high compressive forces into the deck” that complicate maintenance, the panel found. The risk is “excessive cracking” of the concrete piers that support the span from the bottom.

Another “obvious concern” is the continued cracking threat to the high-strength rods used throughout the span, especially in light of the failure of 32 of the steel fasteners in 2013, the panel said. Hundreds of additional rods in the bridge tower’s foundation could be at risk of corrosion after being swamped by bay water, although Caltrans has downplayed the danger.

Another corrosion danger lies below the road deck, the maintenance experts said. The steel tendons used to hold the skyway together are impossible to check for damage, and the panel warned of examples in other bridges “where corrosion of tendons has gone unnoticed and failures have occurred.”

The panel cited the 1960s-era Hammersmith flyover in London, where salt water and grit corroded the tendons. Officials there found the corrosion in 2011 only after installing an acoustic monitoring system to check for cable breaks, something the maintenance panel urged Caltrans to consider.

In its statement, Caltrans said: “It’s no secret that there are access challenges to this bridge. That won’t stop us from protecting it. We’re open to considering any suggestion in the report.”

‘Lack of consideration’

Overall, the report’s recommendations are “very unusual — but everything about this process is unusual,” said Mason Walters, a San Francisco structural engineer whose firm specializes in seismic design and has retrofitted public buildings and bridges, including the San Diego-Coronado Bridge.

“Many things have gone wrong” with the eastern span, Walters said, “and now the fact that there is a significant maintenance bill, that shows a lack of consideration in the design and construction of this project.”