US sees flaw in Zakim Bridge
Says 6 warped steel plates may pose safety concerns, but the state disagrees
Six steel plates that hold in place support cables of the Leonard P. Zakim Bunker Hill Bridge show signs of warping, and the state needs to quickly determine whether they present a hazard to tens of thousands of people who cross the bridge daily, according to a federal inspector general's report obtained by the Globe.
The report labeled the deformed plates an "immediate or dangerous condition" and said they could be a sign that the plates are overstressed.
But a top state official said last night that an investigation by his agency had already determined that the plates became warped when they were originally welded and thus do not reflect excessive stress or pose a safety risk.
"It is not a safety issue, but rather a defect associated with the installation," said Bernard Cohen, the state transportation secretary and chairman of the Massachusetts Turnpike Authority, which maintains the bridge over the Charles River.
However, the warping was not seen in the state's 2005 inspection of the bridge or during quality checks before the span opened in 2003, according to the federal report. The report said a construction flaw should have been identified in those earlier inspections, suggesting that the warping might have occurred later.
Cohen said he could not immediately explain why the defects had not been identified earlier.
Officials from the US Department of Transportation's inspector general's office identified the slightly bent anchor plates among five major potential safety concerns in the 7.5 miles of bridges and tunnels that are part of the $15 billion Big Dig project.
In the aftermath of a fatal tunnel ceiling collapse in July 2006, Governor Mitt Romney commissioned a "stem to stern" safety review of the Big Dig, but the inspector general conducted an audit of the review and concluded that it understated the risks because its initial findings were compiled so quickly.
In addition to the concerns about the Zakim Bridge, the investigators urged the state to immediately assess whether a fire involving two or more trucks inside the Ted Williams Tunnel could generate enough heat to cause ceiling bolts to fall out. The ceiling bolts are secured by epoxy, the same material that failed in the Interstate 90 connector tunnel ceiling collapse. Though the Williams ceiling is much lighter and has a more durable design than the connector ceiling, epoxy is known to melt at high heat.
Cohen said the fire safety concern was valid, but he said it relates equally to tunnels across the country. The Ted Williams Tunnel, which opened in 1995, was designed to withstand the heat of a single truck fire as federal regulations required, he said. If the federal government wants a more conservative design, Cohen said, it should apply to tunnels nationwide.
The Zakim Bridge's elegant cables are secured to the bridge's steel girders by dozens of anchor plates. The failure of many of these plates could compromise the bridge's structural integrity and "lead to progressive bridge failure," the inspector general's office said in the 26-page report. The report said the absence of any mention of deformed plates in the most recent inspection report "underscored the need to fully assess the safety risk in a timely manner."
The inspector general's staff briefed members of Congress earlier this month on the report's findings. "They weren't concerned enough to shut the bridge down; at the same time, they wanted to keep a close eye on it," said US Representative Michael E. Capuano, a Somerville Democrat and a member of the House Transportation Committee who attended the briefing.
"I asked them if people should stop driving over it, and they said, 'Don't worry about it,' " he said.
Cohen said Governor Deval Patrick became concerned almost as soon as he took office about the safety of the Zakim Bridge and other sections of the Big Dig identified in the original stem-to-stern review. Cohen hired the engineering firm of Wiss, Janney, Elstner Associates, the same firm that performed the original review, to follow up and act on the issues raised in the initial phase.
In March, the Federal Highway Administration sent a letter to the Patrick administration warning that it was making insufficient progress on addressing concerns raised in the stem-to-stern review, according to the report.
"We agreed that additional immediate attention needed to be paid to the warped anchor plates, which is why we put our consultant on it right away," Cohen said. He said the outside engineers determined that high heat from the welding process had deformed the six plates when they were installed and that nothing further had happened to the plates since their installation. As a result, Cohen said, he concluded that the warped plates were not a symptom of stress.
In general, the federal investigators concluded that the stem-to-stern review of the Big Dig was done in a professional manner by Wiss, Janney, but pointed out that the engineers had to compile their initial results in just 90 days, resulting in some safety issues not being thoroughly addressed and given high enough priority.
The inspector general brought in the Army Corps of Engineers to conduct technical analysis of the Big Dig's safety, and they found that Wiss, Janney had underestimated several other potential safety hazards. They said Big Dig officials have not done enough to estimate the impact of an earthquake on tunnel ceilings. In addition, they called for more studies on the effects of fires in the tunnels generally.
Finally, the safety reviewers said they remain concerned that the Ted Williams Tunnel ceiling is suspended by epoxy bolts. While acknowledging that the bolts and epoxy are different from the ones that failed in the connector tunnel accident, they said they were "still concerned about the long-term reliability" of the bolts. In particular, they said that a fire involving two trucks could generate much more heat than a single vehicle, potentially melting the epoxy and causing a collapse.
But Capuano said the public should take all of these findings in stride, saying that they represent potential dangers rather than immediate threats.
"This is not the final report," he added.
Cohen said he welcomed the federal inspectors' review, but wished they had taken fuller account of the state's efforts since the stem-to-stern report was released last November.
That $5.7 million safety review found that the Big Dig was fundamentally safe, but identified an array of specific concerns such as decaying ceilings in both the Callahan and Sumner tunnels that connect downtown to Logan International Airport.
Cohen said the state has followed up aggressively, and his spokesman said initial repairs have begun in the Sumner tunnel ceiling.