Corrosive salty water threatens 120 Bay Bridge anchor rods

Caltrans engineers display a three-inch rod which was found to be broken from the base of the SAS tower of the new Bay Bridge, during a news conference in Oakland, Calif. on Wednesday, May 20, 2015. The rod was removed from the tower and will be sent to a lab for analysis. less Caltrans engineers display a three-inch rod which was found to be broken from the base of the SAS tower of the new Bay Bridge, during a news conference in Oakland, Calif. on Wednesday, May 20, 2015. The rod was ... more Photo: Paul Chinn, The Chronicle Buy photo Photo: Paul Chinn, The Chronicle Image 1 of / 58 Caption Close Corrosive salty water threatens 120 Bay Bridge anchor rods 1 / 58 Back to Gallery

About a quarter of the steel rods that anchor the tower of the new Bay Bridge to its foundation are in sleeves flooded with corrosive salty water — a critical threat that the head of Caltrans said Thursday must be addressed to avoid compromising the span’s integrity.

During an emergency teleconference, a three-member panel charged with overseeing the $6.4 billion project — composed of the heads of Caltrans, the Metropolitan Transportation Commission and the state transportation commission — were told that 120 sleeves encasing high-strength rods designed to keep the tower from being damaged in a major earthquake continually flood with salty water.

The development is worrisome for Caltrans because salt is known to accelerate corrosion, which attacks metal over time and has been linked to numerous disasters, including the ruptured pipeline that spilled more than 100,000 gallons of crude oil along the Santa Barbara coast last month.

Caltrans director Malcolm Dougherty said the bridge’s foundation — as with any marine structure — could never be fully watertight. Still, he said saltwater intrusion is a key issue with the new eastern span, because the foundation structure has “sensitivity to water getting to some components. We need to protect this — we need to come up with a solution.”

Among the most vulnerable components are the more than 400 rods that are held in place by nuts at the base of the foundation, below water level. The galvanized rods have been a persistent concern, with Caltrans acknowledging they were put at greater risk of cracking during processing, suffered damage in shipment, and were put under heightened stress when the tower was pulled back to keep it from leaning toward Oakland.

‘2 strikes right there’

Of the 120 rod sleeves that are penetrated with water, half fill with more than 6 inches of water in a matter of weeks, Caltrans officials said — and many of those well up with a foot of water in a matter of days after being drained. At least one sleeve, the agency said, has been regularly filling with as much as 5 feet of water.

Water samples from the sleeves showed chloride levels about half of that found in sea water, officials said. Chloride, known to accelerate corrosion, appears in very low levels in rainwater and freshwater.

The prospect that San Francisco Bay salt water may be intruding the foundation and getting to the rods, which are susceptible to waterborne hydrogen corrosion failure, is “two strikes right there that we’ve got,” said Steve Heminger, executive director of the Metropolitan Transportation Commission.

So far, three of the rods that secure the bridge’s 525-foot tall tower have failed in the past two years. Bridge officials are now particularly concerned about one of the failed rods — part of a cluster that regularly is flooded on the west part of the foundation near Yerba Buena Island — which could be indicative of more widespread corrosion problems for the bridge.

Common feature in failures

Dougherty pressed for rapid testing of that rod. Independent experts who have reviewed photographs of the fractured end of the rod say it shows clear signs of thread failure — the stripping of the connection with the nut — as well as hydrogen embrittlement, the process that causes high-strength steel to suddenly fail after being exposed to water.

In 2013, 32 rods on the eastern part of the bridge failed suddenly after soaking in water for years. If microscopic examination confirms that embrittlement occurred on the broken rod, it could mean that the balance of the rods on the span are under similar threat.

Caltrans officials said the common feature in all of the failures to date has been a failure of the threads that bind the rods to the nuts at the base of the tower. They have downplayed hydrogen-induced corrosion as a possible factor.

On Thursday, independent experts who reviewed newly released Caltrans photos of the damage to the latest rod said the threat of corrosion is not the only problem the agency needs to assess. They pointed to photos of the rod that appear to show that the nut — which is supposed to hold the rod against a steel plate at its bottom — may have been too weak to do its job.

The nut is still under a steel plate, but the rod shows signs that the nut threads broke off and stayed in the rod, one expert said.

“The photos make clear that there is thread failure in the nut — which raises the question of the condition of the rest of the nuts that are presumably similar,” said Bernard Cuzzillo, a Berkeley mechanical engineer.

Testing rod, assessing risk

Cuzzillo said the rod also suffered damage, but the nut problem was more significant.

“If you take the whole rod and nut system and pull it (until it fails), it should not pull out of the nut, it should be a fracture of the rod,” he said. “It means the threaded joint is significantly weaker than it is supposed to be because it is failing in the wrong spot. It is supposed to be stronger than the weakest link itself.”

In an effort to deal with the risk to the tower foundation and the rods, the bridge panel authorized spending $750,000 to expedite testing of the rod that fractured and pay for a panel of 10 experts — including a marine foundation specialist — to examine the results and assess the risk to the structure.

Caltrans’ chief bridge engineer on the project, Brian Maroney, said Thursday that the cost of testing the foundation and the rods could end up being as much as $10 million.

The project is running about $50 million in the red.

Jaxon Van Derbeken is a San Francisco Chronicle staff writer. E-mail: jvanderbeken@sfchronicle.com Twitter: @jvanderbeken