Ominous new cracks found on Bay Bridge rods
Tiny cracks found on some of the rods on the new Bay Bridge tower potentially endanger the rest of the more than 400 remaining fasteners that secure the tower to the foundation in an earthquake, Caltrans officials said Tuesday.
They also acknowledged that one of four high-strength tower anchor rods they have examined apparently snapped after it was exposed to water and became brittle. That was the same headache that cost the agency $45 million to fix in 2013 when 32 rods used on seismic stabilizers failed after being left stewing in water.
Brian Maroney, Caltrans’ chief engineer on the bridge project, said the microscopic cracks found on at least two rods lead him to believe the problem could be widespread, and that the rods could be repaired or even replaced if necessary. Nearly all the rods have been exposed to water and about a quarter of them have sleeves that routinely flood with several inches of bay water within days of being drained.
“As an engineer, if I have these micro-cracks I have to assume they exist in every rod,” Maroney said.
Tests on a third rod, a fastener removed after it failed to hold during a test, showed it had failed with a “fast brittle fracture,” Maroney told a three-member bridge oversight panel at its meeting in Oakland.
Experts say the only way such a high-strength rod could fail after becoming brittle was from exposure to hydrogen in the water.
Lisa Fulton, a Berkeley-based engineer and corrosion expert who has studied the problem on the bridge project, said the latest discovery "means that there doesn't have to be a lot of force on those rods for them to break.
"That could indicate that we don't need an earthquake for them to snap, that they are unreliable in the service loads that they are under now," she said. “The micro cracking is a sure sign of hydrogen attack. It's a portent of catastrophe.”
Yun Chung, a retired Bechtel engineer and a specialist in bolts, said he studied the failed rod and believes it cracked due to hydrogen exposure before it failed.
"There is no other cracking mechanism that is operating on the Bay Bridge," he said, adding that other rods could suffer similar failure.
Under questioning from Steve Heminger, executive director of the Metropolitan Transportation Commission and head of the three-member oversight panel, Maroney said the brittle fracture of the tower foundation rod was similar to the fracturing of 32 anchor rods at the eastern end of the self-anchored suspension span.
Hydrogen embrittlement was deemed the cause for those failures. The problem was discovered in March 2013, just months before the scheduled opening of the new bridge.
Patrick Pizzo, a metallurgical failure expert and retired San Jose State University professor, said the results are ominous. He scoffed at Caltrans statements that all but a handful of the bolts passed pull tests to determine their strength. It can take years for water to cause hydrogen embrittlement in steel, he said.
“That's one failed rod already in two years,” he said. “But what about tomorrow? What about 10 years? Fifty years? How many would be left in 150 years?”
Maroney told the committee the rods could be replaced, repaired or modified. The rods definitely need to be cleaned, dried and protected. Replacement would be possible, he said, but costly.
Other approaches include removing the grout surrounding the rods and replacing it with a type of grease that would force out water. Reducing the tension on the rods also could alleviate the problem of micro-cracking, he said.
Members of the committee, clearly frustrated at the continuing flow of bad news, declined to approve new expenditures for cleaning and protecting the rods, saying they wanted to wait for recommendations from a panel of experts that’s looking into the problem. The panel is expected to suggest further testing to determine the extent and severity of the problem.
