Bay Bridge tower rod is fractured, Caltrans says

SAN FRANCISCO, CA - MAY 18: Workers overlook the base of the Oakland-San Francisco Bay Bridge on May 18, 2015 in San Francisco, California. After nearly 12 years of construction and an estimated price tag of $6.4 billion, steel supporting the new eastern span of the Bay Bridge continues to be plagued with problems with a recent discovery that one of the steel rods anchoring the Self-Anchored Suspension (SAS) tower has failed an integrity test and is believed to have broken due to corrosion. (Photo by Justin Sullivan/Getty Images) less SAN FRANCISCO, CA - MAY 18: Workers overlook the base of the Oakland-San Francisco Bay Bridge on May 18, 2015 in San Francisco, California. After nearly 12 years of construction and an estimated price tag of ... more Photo: Justin Sullivan / Getty Images Photo: Justin Sullivan / Getty Images Image 1 of / 65 Caption Close Bay Bridge tower rod is fractured, Caltrans says 1 / 65 Back to Gallery

One of the steel rods that anchor the Bay Bridge eastern span’s tower fractured after being exposed to water for several years, Caltrans said Wednesday, in what could be a warning sign for hundreds of similar rods intended to protect the bridge in an earthquake.

A Caltrans official said the failure of the rod might be a “one-off,” and said there was no evidence that the more than 400 other steel rods at the base of the tower were damaged. Several outside experts, however, said photos of the broken rod indicate the presence of corrosion that could also infect hundreds of 25-foot-long rods that sat in water after they were tensioned in 2010.

Some experts said the rod appears to have suffered the same type of damage that led to the 2013 failure of 32 similar rods on the new span’s seismic-stability structures. That failure cost toll-payers $45 million for an engineering work-around and studies of other bolts and rods on the bridge.

Caltrans’ lead bridge engineer on the eastern span project, Brian Maroney, displayed the failed end of the 3-inch-thick tower rod Wednesday at a news conference in Oakland. He said Caltrans didn’t know why the rod had broken and stressed that any conclusion about what caused the failure was “speculative.”

Maroney said Caltrans will await a laboratory analysis of the rod, which was extracted from the base of the 525-foot-tall tower Tuesday night.

One of hundreds of rods

The rod was one of 424 installed to strengthen the $6.4 billion bridge against a mega-earthquake. Suspicion had centered on the rod after ultrasonic tests conducted in April showed that it was shorter than the rods that were installed elsewhere at the base of the span.

Many of those rods also stewed for long periods in water that flooded into their sleeves. At first the problem was freshwater that got in because of a botched grouting and sealing job. But in the past couple of months, water with elevated levels of chloride has accumulated in some of the sleeves — raising fears that salt water from the bay is infiltrating the concrete-and-steel foundation.

Salt water is more corrosive than freshwater, but both can damage the type of hardened steel that make up the tower rods.

Several corrosion experts who examined photographs of the rod that Caltrans displayed said the surface was strikingly similar to the rods that failed on the bridge in March 2013. Like the tower rods, those fasteners were made of galvanized, high-strength steel that is especially susceptible to hydrogen embrittlement, or water-borne corrosion.

“It shows the environment that creates hydrogen embrittlement is at that site,” said Russ Kane, a corrosion expert in Texas who has studied hydrogen-induced failures on oil-drilling platforms and military aircraft.

Series of problems

“This makes you wonder whether they really have found the true extent of this problem,” Kane said. “It seems like every time they look at a new place, they find something there.”

Maroney, however, said he was hopeful that no other rods have been damaged. He said mechanical pulling tests done so far show that all the remaining rods are holding fast.

He said the rod that fractured “appears to be a one-off.”

Lisa Fulton, a corrosion expert and metallurgical engineer in Berkeley, said the rod surface had all the trademarks of hydrogen embrittlement.

“The fractured rod shows textbook features of hydrogen cracking,” she said. The fracture has flat, smooth areas and distinctively different rough areas, she said.

An attack from hydrogen creates a smooth surface where the damage starts, Fulton said. The rod fails when cracking is severe enough to trigger a failure under load.

Yun Chung, a retired Bechtel engineer and specialist in high-strength steel fasteners, said rust was evident on the face of the fracture, showing that the rod had been exposed to water for some time.

“This is real clear evidence of hydrogen embrittlement fracture,” he said. “Given the condition of the susceptibility of the material, (the remaining rods) are all subject to hydrogen embrittlement over time.”

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