Bay Bridge designer warned Caltrans in 2010 of weld weakness Engineer warned Caltrans in 2010 of possible vulnerability after quake

A worker uses a lift to reach the underside of the eastern span of the Bay Bridge this month. The bridge is designated as a structure that can carry emergency traffic within a day of a major earthquake, but welds are raising questions about its reliability. less A worker uses a lift to reach the underside of the eastern span of the Bay Bridge this month. The bridge is designated as a structure that can carry emergency traffic within a day of a major earthquake, but ... more Photo: Michael Short, Special To The Chronicle Photo: Michael Short, Special To The Chronicle Image 1 of / 22 Caption Close Bay Bridge designer warned Caltrans in 2010 of weld weakness 1 / 22 Back to Gallery

The lead designer of the new Bay Bridge eastern span warned Caltrans in 2010 that welds used to hold ill-fitting steel road-deck sections together were vulnerable to damage in a major earthquake, documents obtained by The Chronicle show.

Marwan Nader of San Francisco engineering firm T.Y. Lin International said the nonstandard welded connections that Caltrans ultimately accepted on the project would probably suffer only limited, "local damage."

But several experts interviewed by The Chronicle said Caltrans' decision to accept the defective joints could undermine a key feature of the $6.4 billion span - its ability to be open to traffic soon after a quake.

The Bay Bridge is designated as a "lifeline" structure - guaranteed to carry emergency traffic within a day of a major earthquake. If the welded connections holding the road-deck steel sections together are severely damaged, that's unlikely to happen, experts said.

"This span is not robust to begin with," said Bob Bea, a UC Berkeley professor emeritus in civil engineering. "We can't predict exactly how the bridge could fail, but with this issue there is a high likelihood of trouble in its ability to serve as a lifeline structure."

Crucial meeting

Nader issued his warning on Oct. 15, 2010, in a meeting with bridge contractors, outside consultants, top Caltrans officials and three engineers on the bridge project's seismic peer review panel, according to minutes of the meeting obtained by The Chronicle.

The welded connections link giant steel sections - almost 90 feet wide and 18 feet high - that were fabricated by Zhenhua Heavy Industries Co. in Shanghai. The problem for Caltrans and the bridge builders was that when they arrived in the Bay Area in 2010 and were put in place on the suspension portion of the span near Yerba Buena Island, the sections didn't quite fit together correctly.

The sections appeared to line up properly when they were laid on the factory slab in China. Once they arrived and were bolted together for use on the span, however, they no longer fit together the same way.

'Simple mistake'

Ted Hall, a consultant working on the bridge project, said the fabricators had made a "very simple mistake" - they used one method to put the steel sections together on the ground in China, but that method did not replicate how they would behave when suspended on a bridge.

Hundreds of the Chinese fabricator's welds on the steel structure were cracked and had to be repaired, problems that were detailed in a recent report for a state Senate committee. In this instance, however, the welds that had to be used to bind the steel deck structures were made on-site at the Bay Bridge by the lead U.S. contractor.

The issue was not the welds themselves, but the role they had to play in linking misaligned steel sections on the span.

Bending rules

To allow the welded connections, the lead contractor, American Bridge/Fluor Enterprises, needed Caltrans to exempt it from the agency's own standards and the American Welding Society's code for bridges. Both specify that the vertical gap between two pieces of steel on a bridge can be no more than an eighth of an inch.

Many of the Bay Bridge joints on the steel sections were off by as much as three times the acceptable level. But American Bridge/Fluor Enterprises was facing pressure to finish the long-delayed eastern span, as was Caltrans. In early 2011, the agency agreed to the nonstandard connections.

As a result of that decision, the bridge decks have several connections that have extra stress on them, which could lead to significant damage to the road deck in an earthquake, some experts said.

Bea, the professor emeritus at Berkeley, likened an extended welded connection to a dent in an aluminum can.

"When you think of a beer can between two large hands, if you have a small dent in the beer can, it will collapse very easily," Bea said. "It's how we impress a lady in a bar - but it's no way to build a bridge."

'Local damage'

In his 2010 briefing, Nader noted that the steel decks are topped with 2 inches of asphalt, which helps distribute the loading and stress caused by constant traffic.

But with the added force of a quake, he said, the connections between the steel structures could be damaged.

The quake stresses "will be well above yield, and it is anticipated that local damage may occur at these locations," Nader said, citing a study T.Y. Lin International had performed, according to minutes of the meeting.

Nader was not available to comment about the issue, bridge officials said.

'I'll accept that'

Caltrans' chief engineer on the project, Brian Maroney, responded at the 2010 meeting that some damage was "inevitable and manageable" in a major quake, but that it wouldn't have long-term effects on the bridge's ability to carry traffic. It could result in some lanes being shut down for inspection or repairs, he said.

In an interview, Maroney said he recognized that the welded connections could be damaged in a quake.

"We can bend the steel, or yield it - I call that damage. It is damage," Maroney said. "But will it not allow a truck to go over it? Will it mean a bridge will not perform for the community? No. So I'll accept that."

Maroney said he had consulted the peer review panel and other Caltrans engineers before making the call. "That kind of damage is minor compared to what is the standard in earthquakes," he said.

Need to improvise

Martin Pohl, a retired Caltrans steel expert, said the welded connections that Caltrans accepted are more prone to damage in an earthquake. But on a huge infrastructure project, he added, engineers have to be willing to improvise.

"Sometimes you have to make an assessment of whether you think it is a big deal," he said. "If it's local, it is not catastrophic to the entire bridge - sometimes you are forced to accept things that do not meet the specification."

A welding consultant hired by the Metropolitan Transportation Commission to audit the project, Alan Cavendish-Tribe, said bridge builder American Bridge/Fluor Enterprises should have been more vigilant when the deck sections were being fabricated. But he said in an interview that "what we now have, in terms of the finished deck, is satisfactory."

Joseph Nicoletti, a former member of the peer panel who was part of the discussions in 2010, said he too believes the deck will hold up in a quake.

"Anytime you have yield, you are going to have damage," but such damage is likely to be inconsequential, he said.

"If we were concerned, we would have spoken up at the time. We had no ax to grind either way."

Asked about Nader's warning, he said, "That's his opinion - he has to cover his bottom."

'Beauty of steel'

John Fisher, another member of the peer panel, agreed that the weld connections could be damaged in a quake but said it was "not a serious issue."

He said the panel heard what Nader had to say about likely quake damage, but "we disagreed with that."

"The beauty of steel," Fisher said, is that it is "able to absorb a lot of energy. It is going to yield, but I don't consider that to be catastrophic."

But Don Rager, an independent consultant who was involved in assessing other welds on the bridge - and who has long served on the American Welding Society's bridge welding standards board - said Nader's warning should be taken seriously.

He agreed that welded connections between misaligned steel plates could be stretched and twisted in a major quake, and that a significant aftershock could tax them to the breaking point.

"I won't argue with what Marwan said," Rager said. "His word is as good as they come."

No hard questions

Abolhassan Astaneh, a UC Berkeley structural engineering professor and frequent critic of the bridge, said his review of the 2010 meeting notes and other documents provided by The Chronicle led him to conclude that Caltrans and its consultants hadn't looked closely enough at Nader's warning.

No one asked Nader at the meeting to describe the forces that led him to issue his warning, Astaneh said.

"They did not ask Marwan what kind of damage he was talking about," Astaneh said. "Because that damage could mean a fracture throughout the deck, and this bridge cannot tolerate that kind of fracture."

He noted that the bridge builders had kept steel backing bars - normally used only temporarily to keep molten metal from falling through during welding - in place at the welded connections. The bars are angled to account for height differences between the deck sections.

"It's a mess," Astaneh said.

Such backup bars being left in place on Southern California structures contributed to cracks and failures during the Northridge earthquake in 1994, Astaneh said.

Bea said the weld-connection issue is a sign that the bridge was built to the edge of safety margins.

"All of these decisions lead to an erosion of your margin of quality, a factor of safety," Bea said. "If you are close to a cliff, you don't want to keep on walking until you fall off. With the self-anchored span, there is not much margin before you reach the edge."