A Bridge Too Weak?

A UC Berkeley professor believes the unique new Bay Bridge design is fatally flawed

If only Abolhassan Astaneh were a flake he could be dismissed. But as an internationally recognized authority on the design of steel structures, the UC Berkeley engineering professor and his jeremiads against one of the most expensive public works projects in Caltrans history aren't so easily ignored.

It isn't just that he considers the state's plans to replace the east span of the Bay Bridge — with its colossal $2.9 billion price tag — to be a boondoggle. Although that might seem reason enough to apply the brakes to a project enormously over budget and years behind schedule, especially considering that California is nearly broke, Astaneh's chief concern has little to do with dollars and cents.

Instead, the principal expert to whom Caltrans turned for advice on how to bolster Bay Area toll bridges after the 1989 Loma Prieta earthquake believes that the “signature” segment of the planned new eastern crossing between Yerba Buena Island and Oakland — a “self-anchored” span suspended from a single, 525-foot-tall tower — could be a catastrophe waiting to happen.

Neither he nor anyone else denies that the existing east portion, opened in 1936 and exposed as unsafe after part of the upper deck collapsed during the deadly 1989 quake, is long overdue for replacement or major retrofitting. But Astaneh argues that the novel design of the suspension section of the bridge — to be the longest of its kind in the world and comprising roughly 14 percent of the entire new east span — is inherently unsafe in an earthquake, sandwiched as it is between the San Andreas and Hayward faults.

While careful not to appear unconcerned about Astaneh, Caltrans officials reject his view. “We appreciate what Professor Astaneh has to say, but we don't share the same level of concern [about seismic vulnerability],” says Caltrans Chief Deputy Director Dan McElhinney, who is overseeing the new bridge project. “A good many engineers and others have looked at the design and have determined that the bridge will be safe.”

Astaneh has spent the last six years telling anyone who will listen that a major quake with an epicenter near the bridge could cause the 1,850-foot-long suspension segment of the planned 1.5-mile crossing to crumble into the bay like a giant Erector set. After years of delay, work on the rest of the eastern bridge, a long causeway officially referred to as a “skyway” but derided by critics as a “freeway on stilts,” began in 2002. In the last year, huge cranes hauled in to drive pilings deep into the bay's muddy bottom have become a familiar part of the landscape.

Even with the skyway construction under way, the project remains problematic. Caltrans is rudderless after Jeff Morales, an appointee of former Gov. Gray Davis and a driving force behind the bridge project, resigned as director earlier this month after three years on the job to make way for someone of Gov. Arnold Schwarzenegger's choosing.

Amid little fanfare, Caltrans in January once again pushed back the opening of bids on construction of the suspension span's tower and cables until late May. Caltrans now says it will be 2010 — or 21 years after the Loma Prieta quake served notice about the vulnerability of the existing bridge — before the new one is complete. Only three years ago officials were saying it would be ready by 2006 or 2007. Since then costs have soared, more than doubling original estimates. Citing the enormous challenge associated with building the one-of-a-kind suspension span, key contractors continue to balk at Caltrans' construction timetable, making Astaneh's design critique appear to be more relevant than ever.

But the professor's misgivings about the span's seismic characteristics are only part of the bad news from someone whose advice about steel bridges has long been in high demand and who was part of the research team called upon to help pinpoint the cause of the World Trade Center collapse after the Sept. 11, 2001, terrorist attacks. He insists the new bridge, too, is vulnerable to a potential terrorist bombing.

Astaneh says that a limited analysis based on computer modeling suggests that even a relatively small car bomb at the right spot could cause the entire suspension span to collapse, something that experts say is next to impossible with the Golden Gate Bridge or either of the Bay Bridge's existing spans. He says Caltrans should get independent security consultants to conduct extensive blast resistance tests, which he believes the agency has neglected to do, and determine once and for all whether the bridge will be capable of absorbing the explosion of a terrorist bomb. “It is ironic,” says Astaneh, “that after all these years and so much money the new bridge in my view will be more, not less, vulnerable than the span we now have.”

Caltrans' McElhinney says the matter “has been looked at by a variety of federal agencies.” Caltrans, he says, is “doing all that we can to provide a structure that considers possible attacks on the bridge,” including creating plans for the U.S. Coast Guard and the California Highway Patrol to monitor the span. He declines to specify what sort of blast tests may have been conducted or by whom. But Herb Rothman, the New York-based principal design engineer of the suspension segment, is less circumspect when asked if the design has been examined for vulnerability to a car bomb.

“We didn't design for blast,” he says.

There is little disagreement about one thing: Building the curved suspension span is a huge challenge, requiring engineering methods never before attempted in a seismic zone.

With a typical straight-decked suspension structure, such as the Golden Gate Bridge, towers are erected first, the main cables are hung between them, and the deck is attached to the cables. That process is reversed with a self-anchored suspension bridge. Because the suspension cables are anchored in the deck, rather than in the ground at either end of the bridge, the deck must be placed high above the water on a temporary edifice known as “falsework.” Then the cables attaching it to the tower are connected. [page]

This means building two bridges — one temporary and the other permanent. Seismic issues aside, the method required to construct such a bridge makes it enormously costly compared to other design alternatives. That is why two engineers with international stature, who served on an advisory panel entrusted with recommending a winner among several competing designs deemed less aesthetic, opposed the self-anchored concept.

“[It] is simply not an efficient and rational structure,” says Manabu Ito, a professor emeritus at Tokyo University who is among Japan's most renowned structural engineers. Ito was part of the 36-member advisory panel assembled by the Metropolitan Transportation Commission in 1997 to help decide what kind of bridge to build after political winds prompted a shift in Caltrans' original aim of merely retrofitting the existing east span.

Critics complained that the competition was hardly that at all, and describe the MTC's deliberations as rife with conflicts of interest, noting that several of the advisory panelists were connected to contractors whose designs they were responsible for judging.

Besides Ito, another notable dissenter was T.Y. Lin, a professor emeritus at UC Berkeley whose pioneering work in prestressed concrete had a profound influence on modern structural design. After the MTC's 1998 final approval of the self-anchored suspension span, Lin denigrated the choice as a “monument to engineering stupidity” and predicted that if built, the bridge would become a “laughingstock.”

Lin, who died recently, said little publicly about the new bridge after those blistering remarks. His critique might have attracted more attention had he not been in the awkward position of having promoted his own design for the east span while a member of the MTC advisory group. In the end, the winning concept was submitted by a consortium that included the company Lin founded half a century ago and later sold, T.Y. Lin International of San Francisco.

Several people close to Lin during the 16 months that the advisory committee held its hearings say the legendary engineer harbored some of the same safety concerns about the self-anchored design that Astaneh expresses. “There's no question that he had misgivings about it,” says Steve C. Thompson, a Mill Valley architect who also served on the panel.

R. Gary Black, a UC Berkeley professor of architecture (who, partnering with Astaneh, promoted his own bridge design for a time), agrees. “I talked to T.Y. extensively during that time, and he had two issues with [the chosen] design. One was cost. He just thought it was a needless waste to build a bridge that way. And the other was potential safety. He hadn't done the kind of work that Professor Astaneh had done, but he felt it didn't really make sense to build [that type of bridge] in a seismic zone.”

Unlike regular suspension bridges, where the main cables are connected to large concrete anchor blocks firmly buried in solid ground, the self-anchored bridge's cables will be hooked directly to the deck. The cables will run from beneath the deck on one side, up to the tower and down to beneath the deck on the other side, before looping back up and over the tower in the opposite direction.

“Think of a tower holding up a tray,” Astaneh says. “Instead of being anchored in the ground, as is traditionally the case, the bridge is essentially holding itself up. That means if there is a sufficient rupture, all or part of the span could unravel.”

An aspect of the design that Astaneh finds particularly troublesome is the tonguelike connector joints linking the suspension portion of the bridge with the skyway. A quake powerful enough to cause the earth beneath the bridge to shift, a phenomenon known as permanent displacement, could make the suspension span and skyway break apart, he says.

In the Loma Prieta quake, connector joints were the culprit when ground motion triggered a partial collapse of the existing bridge. Land beneath the span moved about 12 inches, snapping bolts that held segments of the bridge together. The result: A 50-foot-long section of the upper roadway collapsed at one end and fell onto the lower roadway at the ninth pier from the East Bay shore.

Given the steel truss design of the existing span at the break point, even if the lower deck had given way the worst that would have happened is that the bridge would have been severed at Pier E-9, like a gap in a row of teeth, says Astaneh. “But with a self-anchored suspension span, permanent displacement could cause a completely different story,” he says. “Because the suspension cables are anchored into the deck, should the deck give way and lose compression, there's nothing to hold the cables. The entire [suspension] span could unravel.”

Herb Rothman, the bridge's chief design engineer, discounts that scenario. “This bridge will be very well suited to a high seismic area,” says Rothman, 79, whose professional credits include having been project engineer during construction of New York's Verrazano-Narrows Bridge in the 1960s. “As far as we're concerned, the bridge has ideal earthquake characteristics, and meets all the standards that the state mandated for it.”

Although a few smaller self-anchoring spans using two towers have been built in the last 20 years, including one in Japan and another in South Korea, the Bay Bridge crossing will be by far the world's longest self-anchored structure borne by a single tower. As a result, Astaneh notes, there are no seismic performance data available for this type of bridge. “If they build this bridge and the Hayward fault ruptures, there is a high probability that the resulting earthquake would severely damage the bridge, and possibly cause a partial or catastrophic failure of the main span,” he says.

Astaneh shared his concerns with MTC officials before the advisory panel approved the design in 1998. He did so again in 1999 after then-San Francisco Mayor Willie Brown, with help from the Navy, succeeded in delaying final state and federal approvals following a brouhaha over the span's alignment across Yerba Buena Island property owned by the Navy. (The federal land has since been turned over to the city of San Francisco.) Alarmed that little was happening to replace the unsafe existing bridge more than a decade after the Loma Prieta quake, the Clinton administration intervened in 2000 to help settle the dispute. [page]

After hearing a lengthy presentation from Astaneh in 1999, Brown held a news conference the next day to announce his opposition to the single-tower design, saying he was convinced it was unsafe. Although critics accused him of posturing, suggesting that Brown's agenda was to torpedo any design that might interfere with plans by politically connected friends to develop part of Yerba Buena Island, the mayor never recanted his safety concerns.

With a boost from Brown, Astaneh was dispatched to Washington, D.C., where he gained an audience with Clinton administration staffers including a high-level assistant to then-Transportation Secretary Rodney Slater. With Brown and the Navy resisting the self-anchored design on one side, and Caltrans, the MTC, and Gov. Davis pushing for the bridge project to move forward on the other, the U.S. Army Corps of Engineers was called in to study the issue.

Although the Army engineers gave their seal of approval to the bridge design, a voluminous Corps report issued in October 2000 can hardly be classified as a ringing endorsement. About the best the engineers could say about the seismic concerns Astaneh had raised was that “the design team is moving along a path to design a bridge that meets the seismic performance criteria” established by the MTC.

The Army Corps concluded that the bridge was not designed for a “maximum credible earthquake,” or MCE, along either of the two nearby fault lines. An MCE denotes the most severe ground motion considered possible at a given location. Scientists say the San Andreas fault, which runs beneath the peninsula on which San Francisco rests, is capable of producing an MCE of 8.0 on the Richter scale, and that the Hayward fault, which passes beneath the Oakland hills within five miles of the bridge, could produce a 7.25 shaker. By comparison, the Loma Prieta quake, which, among other things, collapsed the Cypress Freeway in West Oakland, killing 42 people, and killed another person on the Bay Bridge, measured 7.1. But its epicenter was 60 miles south of the bridge; experts say damage to the span would have been worse had the epicenter been closer.

Caltrans and the new Bay Bridge's designers say their plan incorporates the highest seismic safeguards. But they based their calculations on a different model, called the “safety evaluation earthquake.” SEE places more emphasis on the probability of a major quake occurring during the bridge's anticipated 150-year life span.

The Army engineers didn't take a position on which is the better approach. Neither did they pass judgment on the self-anchored bridge's seismic characteristics compared to other designs.

“On a scale of A to F weighing seismic safety reliability and cost efficiency, where A is the best system and F is unacceptable, how would you rate the standard anchored suspension bridge and the proposed self-anchored, asymmetric single tower, pile-supported East Span replacement?” reads a question posed in an appendix to the Army Corps report. The engineers' response: “The rating requested in this question is outside the current scope of work.”

The MTC board voted 11-1 in favor of the self-anchored design recommended by its advisory panel. Then-Oakland Mayor Elihu Harris was the lone dissenter, at the time citing cost and aesthetics as his primary objections. His successor, Jerry Brown, took a similar position. Looking back, Harris now says, “I think [the MTC] was too eager to get on with it. And it was too dismissive of Astaneh.”

Although his expertise remains highly sought-after by others, Astaneh says he has paid a price as the bridge's chief naysayer.

After he spoke out, Caltrans halted payments on a $500,000 grant to the university's engineering department for work being done under Astaneh's supervision. “Caltrans is not good at tolerating dissent,” he says. Caltrans denies any retaliation, saying budget cuts forced it to scale back spending for academic research.

Inevitably, Astaneh's stance has been labeled as sour grapes by some who note that a competing bridge design that he and R. Gary Black submitted was among those that the MTC panel rejected. The suggestion draws a chuckle from the professor. “Oh, come on,” he says. “More than 275,000 people a day cross that bridge. We're talking about people's lives.” As for his design, he insists, “We were very proud of it, but from my perspective it was as much an exercise for my students as anything. I never expected that it would be chosen, and I certainly wasn't heartbroken over it when it wasn't.”

Even now, he says, if the governor or someone else were to ask, he would recommend scrapping the self-anchored span and finding another way to link Yerba Buena Island and the East Bay, even if it meant merely extending the skyway. But he isn't on a crusade.

“My friends and my wife have said, 'Why not just be quiet about the bridge?' But it's very simple. If, God forbid, a tragedy should occur on that span someday, I don't want anyone to say I didn't do enough to speak up.”

Tags: , , , ,

Related Stories