OAKLAND -- In the most comprehensive examination to date of why bolts broke on the new Bay Bridge, an analysis released Wednesday faults Caltrans for inadequate specifications and insufficient testing of the steel. It will cost as much as $10 million to fix the mistake and could delay the span's Labor Day opening.
State engineers also assured members of the Bay Area Toll Authority that the chosen fix for key seismic stabilizers compromised by the snapped bolts -- a steel saddle and heavy metal strands -- will make the span as safe as the original design.
During the most detailed public briefing since news of the broken bolts surfaced, Steve Heminger, executive director of the Metropolitan Transportation Commission, faced stern questioning and acknowledged the crisis in public confidence over the $6.4 billion bridge. The new span has long been billed as a safer alternative to the existing 1936 bridge where a piece of the deck fell in the 1989 Loma Prieta temblor and a motorist died.
While transportation officials want to move traffic onto the new, safer span as soon as possible, they said they couldn't tell the authority until May 29 if the repair job will be finished in time for a Sept. 3 opening, citing unresolved negotiations with the contractor. And ultimately, he said, it will be up to the governor to sign off.
Fabricated in 2008, the faulty steel bolts met custom Caltrans and industry specifications issued to the bridge contractors. But the material succumbed to a well-known chemical reaction with hydrogen that made them brittle, concluded a three-member team of metallurgists led by Salim Brahimi, a Canadian engineer and chairman of the ASTM International standards board on fasteners.
If the rods had been subjected to a more rigorous test for toughness, or a measure of how well they resist cracking when under stress, "it's likely they would have failed that test and we wouldn't have installed them on the bridge," Heminger conceded.
"The situation was exacerbated by the fact that we installed (the rods) in a place where we couldn't get them out," said Heminger, who also leads the Toll Bridge Program Oversight Committee. "That should have cautioned folks at the time, 'Gee, maybe we should test them before we put them in.' That is one of the lessons we've learned."
Among other steps the agencies are taking to reassure themselves and motorists of the new span's seismic integrity:
The bridge repair calls for installing a steel saddle on top of two shear keys -- which contain the broken rods -- positioned directly above the columns and below the bridge deck in the pier east of the main span tower. Shear keys help control sway during an earthquake.
The saddle will cradle 430 steel rope strands made of steel twice as strong as the 96 anchor bolts, explained veteran Caltrans bridge engineer Brian Maroney following the meeting. The ends of the strands will be anchored on the outside of the pier cap and covered with reinforced concrete.
The clamping force will match that of the original anchor rods, confirmed Marwan Nader, T.Y. Lin vice president and lead design engineer.
While the three agencies overseeing the bridge construction are understandably focused on how to make the shear keys operable so the bridge can be safe, others continue to ask who was responsible for choosing a type of galvanized steel known for its hydrogen susceptibility.
If the fabricator or one of the contractors were to blame, Caltrans could seek reimbursement for the cost of delay and repairs. However, Heminger said the manufacturers followed Caltrans' custom specifications. Absent a private culprit, the costs will fall squarely on tollpayers' shoulders.
"There was no discussion today about how these bolts were selected in the first place," authority member and San Francisco Supervisor David Campos said during a stern line of questioning.
High-strength rods of this material and grade can be successfully galvanized with proper testing and specifications, the engineers also wrote in the report. But neither Caltrans Director Malcolm Dougherty or Heminger appeared to know how Caltrans and T.Y. Lin bridge designers selected the type and grade of steel used for 2,306 fasteners on the self-anchored suspension span.
Many of the design decisions were made before 2004, and the men said their staffers are looking for the written documentation and minutes.
ASTM International, formerly American Standards Testing and Materials, warns of hydrogen assault on galvanized high-strength steel, and Caltrans' own bridge design manual prohibits its use on bridges except for special applications.
But deviations from standard specifications are commonplace, Maroney told the authority, adding that there are hundreds of other examples on this bridge alone. Many requirements don't apply as written to individual projects and engineers routinely issue special provisions that vary from the standards in numerous areas, he said.
The much-anticipated metallurgical forensics analysis found that the batch of galvanized rods fabricated in 2008 by Dyson Corp. in Ohio per Caltrans' specifications was particularly vulnerable to fracturing caused when hydrogen atoms squeeze into the spaces in steel's molecular crystalline structure and weaken its strength, according to the analysis released Wednesday.
Tests showed the surface on the large rods -- 3 inches in diameter and 17 to 24 feet long -- was too hard. The harder the steel, the higher its susceptibility to hydrogen.
The report points to galvanizing as the likely source of the hydrogen that led to the fractures. When the bolts came under tension, the trapped element started moving within the steel and triggered the cracks.
Given that the rods broke within a week after contractors tightened them down in early March, the engineers said the source of the hydrogen was probably not the water that pooled in the casings while the rods sat on the bridge for five years.
Contact Lisa Vorderbrueggen at 925-945-4773; follow her at Twitter.com/lvorderbrueggen.
2008: Dyson Corp. in Ohio fabricates 96 steel anchor rods of 3 inches in diameter and 17 to 24 feet long for use in the large pier east of the main tower in the replacement self-anchored suspension span of the Bay Bridge.
March 1, 2013: American Bridge Fluor Joint Venture, the bridge contractor, begins tightening down on the rods, which connect shear keys to the pier's two columns. Sandwiched between the bridge deck and the columns, the shear keys help control sway during an earthquake.
March 8-15, 2013: The contractor and Caltrans inspectors find 32 busted bolts and opt to loosen the nuts on all 96 rods including 192 in adjacent shear keys and bearings.
March 27, 2013: Caltrans briefs members of the Bay Area Toll Authority about the bolts after the news hits the media.
May 8, 2013: Caltrans, California Transportation Commission and Bay Area Toll Authority unveil repair plan, which involves anchoring the shear keys to the pier cap with high-strength steel cables at a cost of up to $10 million. It's unknown if the bridge will open as scheduled Sept. 3; the agencies are negotiating with the contractor.
Source: Staff research