Bay Bridge has more problems...

Fears of failure grow for rods on Bay Bridge eastern span

By Jaxon Van Derbeken

New documents raise questions about the integrity of the steel rods that hold together the Bay Bridge eastern span and point to potentially widespread problems that experts warn could lead to premature failure.

An engineer who studied tiny cracks found in flooded rods at the base of the bridge’s tower — a problem Caltrans has downplayed — discovered similar cracks in rods elsewhere on the $6.4 billion span. That cracking, experts say, could make the rods far more vulnerable to failure than the agency has acknowledged.

Separately, Caltrans now concedes that it did not inspect the new bridge’s 2,000-plus rods when they were delivered to ensure their threads met industry specifications, and has since discovered that some if not all of them fall short. It’s a problem that experts warn could weaken the rods down the line, and may have damaged some already.

Caltrans is studying the implications of the discoveries, both of which first surfaced in the tower.

Caltrans discovered the micro-cracks after water flooded many of the 400-plus sleeves that hold the tower rods, including one that failed. Although Caltrans dismissed the tiny cracks as unlikely to cause further problems, experts outside the agency cautioned that such cracks could be the harbinger of embrittlement — the process by which hydrogen invades the steel and causes it to corrode.

In a newly released report, an independent engineer revealed that micro-cracks were also found in three rods elsewhere on the bridge, far from the tower and its floodwaters — on seismic-stability structures where 32 of the fasteners failed from embrittlement in 2013.

‘Some risk’

The rods were removed during a $20 million testing program that Caltrans launched after that mass failure to determine whether the bridge’s rods could be counted on. The agency concluded that the span’s fasteners were sound, although the three test rods failed prematurely.

The engineer’s report, Caltrans disclosed last week to The Chronicle, revealed that micro-cracks had been found on three failed rods, which he said could have implications for the tower rods.

“There is some risk that the cracks would grow enough to cause problems,” wrote Stephen Christoffersen, an engineer for URS Corp. who prepared his report for the Metropolitan Transportation Commission.

Christoffersen suggested lowering the tension on the tower rods to ease the stress on them, and said that if they can be kept dry, they should be fine. His report did not address what, if anything, should be done about rods elsewhere on the bridge, and he did not respond to requests for comment.

‘Going to fail’

Caltrans concluded that the rods’ current tension levels are well within a safety margin that engineers established after the $20 million testing program was completed. The agency’s chief engineer on the project, Brian Maroney, said he doesn’t think micro-cracking is an issue, but concedes that Christoffersen’s findings warrant more tests.

“I have no evidence that they are significant. Steve Christoffersen suggests they are,” Maroney said. “If there is any concern, let’s take the opinion, let’s go to the lab and do some tests.”

Outside experts said Caltrans has cause for concern — and not just at the tower.

“If they have these cracks, they are going to fail over time,” said Patrick Pizzo, a metallurgical engineering professor emeritus at San Jose State University. “They are all susceptible to failure.”

He added, “They did $20 million worth of work and (Christoffersen) finally realizes that now you have cracks and they can grow. They stumbled into a problem ... and now it’s going to cost them.”

Russell Kane, a corrosion expert who has advised the military and oil industry on hydrogen embrittlement, said the discovery of micro-cracking away from the tower means the rods are more vulnerable than Caltrans’ test results suggest.

“The safety factors they have been talking about that they believe they had, before cracking would start, are gone,” Kane said. “Now they don’t have the fudge in this factor that they thought they had.”

Bad rod threads

Earlier this month, the three-member panel that oversees the eastern-span project authorized $685,000 for more testing to gauge the risk from the cracks in the tower. The board also decided to spend $250,000 for inspections and tests on another tower problem — the poor quality of threads on the rods.

The threaded ends are where nuts secure the 25-foot-long pieces of steel to the tower and its foundation. Engineers have discovered stripped threads on three rods in the tower.

Maroney said the threads did not comply with industry specifications and were too small to lock properly with the nuts. “They are not what we want,” he said.

“This is really, really important to know a lot about,” he said. “This is arguably the most important thing to know about.”

The Materials Engineering and Testing Services branch of Caltrans admitted in a report to bridge officials in April that no one checked the bridge rods’ quality during production at Vulcan Threaded Products in Alabama or after they were shipped to California in 2007. Caltrans accepted them anyway, in violation of the agency’s rules.

“It looks like we didn’t do the quality assurance we were supposed to do,” Maroney said.

“They never should have been accepted this way,” said Mason Walters, a bridge engineer in San Francisco who reviewed the Caltrans documents for The Chronicle.

Test results

Maroney said that despite the problems, most of the tower rod threads held up during recent tests in which engineers used jacks to pull on them for several minutes. Those results give him comfort that they will hold fast in an earthquake. Outside experts aren’t so sure.

“A one-time test is only good for the time of the test — it doesn’t predict the deterioration in strength over time,” said Bernard Cuzzillo, a Berkeley mechanical engineer who specializes in failure analysis.

It turns out that, like the micro-cracks, the problem of thread quality is not limited to the tower.

In July, Caltrans engineers did a survey of the rod quality on the span and found that all 20 fasteners tested — 12 of them away from the tower — had thread problems. None satisfied tolerances set by the American National Standards Institute to assure durability.

Some threads were too big, some were too small and some were not cut to the correct angle, the engineers found.

Substandard connections can cause tearing damage if threads are too big. If too small, they can concentrate stress on what is left of the rod threads, causing damage that can make them prone to attack from hydrogen.
No guarantee

Experts say that the higher the stress put on the rod, the more likely it is to snap.

“This thread problem means that Caltrans doesn’t know what the actual stresses are, and so can’t guarantee their structural integrity,” Pizzo said.

“It’s a very shoddy job all the way around,” said David Williams, a consultant in Oakland who specializes in earthquake engineering for bridges and marine foundations.

Williams, who worked on the BART Transbay Tube retrofit, said rod specifications are sacrosanct.

“Clearly there was no quality assurance on anything,” he said. “The whole thing is mind-boggling.”

Experts pointed to both problems — micro-cracking and thread quality — as threats to the span over the long haul.
“They are parallel paths for failure,” Cuzzillo said. “They could work together or separately. If one doesn’t get you, the other will.”

But Maroney said the rods have done well on many tests and are made of resilient steel, capable of overcoming any flaws in the threads.

Bay Bridge problems

Cable: Bridge maintenance experts urged Caltrans to retrofit the span’s main cable to protect it from corrosion, and the project’s chief designer warned that leaks raised the threat of corrosion in the cable’s two anchorages.

Tower rods: Water has flooded most of the 400-plus rod sleeves in the tower foundation. One rod has failed, and others developed tiny cracks. Caltrans says the rods aren’t in danger.

Deck concerns: Several of the 14 giant steel boxes that form the two bridge decks did not fit together neatly during construction. The bridge’s chief designer acknowledged that some joints are likely to suffer “local damage” in a big earthquake.

Leaks: Water has been leaking into the hollow bridge structure since at least 2012. Caltrans says there has been no damage, but outside experts say there are indications of rust and corrosion.