When close to three dozen anchor rods snapped on the nearly completed new San Francisco-Oakland Bay Bridge this spring, it was just the latest in a series of controversies that have dogged the $6.4 billion project since the start.
If the bridge were a person, you would say it had been born under a bad sign. Early on, critics declared the “signature” self-supported suspension portion of the span would be seismically unsafe because it isn’t anchored to Yerba Buena Island—the deck is supported solely by a massive central tower. Then came the revelations that Chinese-made steel deck sections were riddled with microscopic cracks, and that welds inside the bridge’s skyway span section were improperly executed.
And in 2011, two Caltrans employees were sacked for a variety of offenses, including fudging tests on the new bridge.
Caltrans remains stalwart in its support for the bridge. In a statement released after the fractured bolts were discovered, state toll bridge manager Tony Anziano defended the steel used for the devices, maintained the problems seem restricted to a “small batch of rods,” and declared there is no evidence of problems elsewhere on the span.
Still, a consensus seems to be growing among engineers—especially UC engineers—that the new bridge has some very fundamental and worrisome flaws. “It just makes me deeply sad,” said Berkeley civil and environmental engineering professor Abolhassan Astaneh-Asl of the bridge’s cascading problems. Astaneh-Asl was among the first to opine that the self-supported suspension span was seismically deficient. He was criticized in turn by bridge boosters, who claimed he was irate because a design he had submitted had been spurned.
But Astaneh-Asl insists sour grapes had nothing to do with it. “When you’re an engineer, you have an obligation to comment on any project that could endanger public safety,” he says.
And now the broken anchor rods have Caltrans and Bay Area Toll Authority officials casting about for explanations, and engineers pondering a fix. The high-strength steel rods, measuring 3 inches in diameter and 9 to 24 feet long, connect large seismic safety units known as shear keys to the bridge’s deck and support beams. To perform their proper function, the rods must be tightened by bolts after installation. Of the 96 tightened to date, 32 have broken.
Many experts blame the broken bolts on “hydrogen brittleness”: When hydrogen invades steel, it can make it friable and prone to failure under stress. Although Thomas Devine, professor of materials science and engineering, agrees that a problem exists, he said that conclusions on possible remedies are premature—and dangerous.
There are two possibilities for the rod failures, he says: hydrogen embrittlement, or stress corrosion cracking. The culprit is determined by a battery of stress tests of the material.
For now, the evidence is insufficient to decide whether hydrogen in the steel is due to fabrication or environmental factors—and that’s critical, says Devine, because remedial strategies differ significantly for each case. “What’s needed at this point is a complete autopsy, if you will, on every bolt that fractured. Only then can we determine a truly effective solution.”
But even when, or if, the anchor rod problem is remedied, the basic issue of the span’s design remains. Bob Bea, a Berkeley emeritus professor of civil and environmental engineering, believes that the span is fundamentally not “robust” in the engineering sense.
“For an example of a robust structure, look at the Golden Gate Bridge,” says Bea, who has an international reputation in large project risk assessment. “It was designed for stability, for defect tolerance. With the new Bay Bridge, you see a greater concern for elegance, for that signature quality, rather than for robustness. It’s a touchy design—basically, the span is held up by compression, similar to when you pick up a group of books by pushing at the ends. When everything goes perfectly, it’s fine. But when things don’t go perfectly, it’s ‘We have a problem, Houston.’”
Obviously, things haven’t gone perfectly for the new bridge. Bea, a certified welder as well as a world-renowned risk assessment engineer, also is concerned with the integrity of the welds. The welders, however, bear no responsibility for the problem. Their work, says Bea, has been exemplary.
“It’s a perversity in engineering, but most engineers have never built anything,” he explains. On the Bay Bridge, he says, engineers didn’t consider the dimensions of the spaces where welding was required. “[The bridge workers] had to make heroic welds,” he says. “Basically, what they were doing was similar to trying to install a big water heater in a tiny closet. It’s extremely difficult to make good welds under those conditions.”
Caltrans vows the new bridge will stand for 150 years. Astaneh-Asl’s evaluation is at the other end of the spectrum: He thinks one stiff quake could bring down the span. Bea isn’t placing any bets, although he does feel that opportunities were wasted when the design was chosen.
“Everyone was in the sandbox, bickering, bickering,” he said. “Finally, it got to the point… well, you know what they say about the camel being a horse designed by committee? It was like that.”