Caltrans tests cast doubt on Bay Bridge rods But screening by Caltrans couldn't predict brittleness

Workers continue the construction of the new eastern section of the Bay Bridge, as CalTrans conducts a boat tour of the impacted areas of new eastern section of the Bay Bridge on Wednesday Mar. 27, 2013, in Oakland, Ca. Inspections earlier this month found that 30 large bolts on the new eastern span of the Bay Bridge have fractured. less Workers continue the construction of the new eastern section of the Bay Bridge, as CalTrans conducts a boat tour of the impacted areas of new eastern section of the Bay Bridge on Wednesday Mar. 27, 2013, in ... more Photo: Michael Macor, The Chronicle Photo: Michael Macor, The Chronicle Image 1 of / 9 Caption Close Caltrans tests cast doubt on Bay Bridge rods 1 / 9 Back to Gallery

Caltrans' pre-installation tests on the large steel rods that failed last month on the Bay Bridge project raised doubts about their ability to stretch during an earthquake, but engineers OKd using them without knowing how brittle they could become, a top official acknowledged Monday.

Last week, Caltrans officials acknowledged the snapping of one-third of the threaded steel rods used to bolt down two massive steel boxes - known as shear keys - below the new bridge deck.

The problem now is that the failed rods, which are up to 17 feet long, can't be replaced easily as there is no longer room to put in new ones because the bridge's roadbed has already been installed. Engineers will have to fashion a fix.

Caltrans toll bridge program manager Tony Anziano said the cost of that fix - creating two metal collars around the steel boxes to allow room for new rods to be inserted - will be about $1 million.

He said the work should not delay the planned Labor Day opening of the new bridge. "We're not seeing a delay at this point," he aid.

As engineers work out a fix, Anziano said, Caltrans is conducting a complete review of the fabrication and supply process for the bolts, shipped by Dyson Corp of Painesville, Ohio. Dyson did not forge the steel, but threaded the rods and oversaw the manufacturing process.

He said Monday Caltrans subjected 14 segments of the 96 rods to tests, both for their ductility - the ability to stretch without breaking - and hardness. Dyson tested another 14 segments.

"They cut it up and basically put it under pressure," Anziano said.

The tests conducted by Caltrans were incapable of revealing the suspected problem: that hydrogen, a contaminant, had been introduced as bubbles during the manufacturing process, making the rods brittle.

Testing the rods

While nine of the 14 samples met industry-established ductility requirements, five were slightly below those standards. He said there is no standard for hydrogen embrittlement, and the tests were too short - a matter of minutes - for the rods to fail.

Caltrans reviewed the five lower-ductile rods and, based on the total circumstances, its engineers were "OK with it," Anziano said.

All the rods met or slightly exceeded hardness standards. In the field, however, 33 of the 96 rods failed.

He said Caltrans officials suspect they know how the rods - which were heat treated after being forged to guard against any hydrogen contamination at the steel mill - had later become contaminated when galvanized in molten zinc.

He said the rods were not bathed in acid before galvanization, when they could easily become contaminated. They were sand-blasted instead, he said, lowering the contamination risk.

Once they were shipped in 2008, he said, Caltrans did what quality control tests it could on them.

"In the case of the larger rods, it was determined there was no need to test for hydrogen," he said, saying it was assumed to have been eliminated in processing. "It got in there somehow."

Caltrans has since extracted three of the rods and sent one of them to a private lab for testing and analysis.

Future failure?

Yun Chung, a retired materials engineer for Bechtel Corp., said he is worried that even bolts that did not fail within days could still break in the future.

"What concerns me is hydrogen embrittlement has a delayed failure mechanism - it doesn't happen all of a sudden," Chung said. "The time to failure after the bolt is tightened is a function of many factors, including the hardness and the stress level. It's difficult to say when the failure could occur."

Chung said field testing for embrittlement is possible. "There is a test of hydrogen embrittlement - but it takes a different type of specimen and it has to be placed under a static load, where you raise the stress and hold it there for long periods of time."