A troubled bridge over water

Bridges Article November 16, 2007
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On Aug. 1, 2007, a few moments past 6 p.m., a nondescript bridge carrying eight lanes of the U.S. Interstate System over the Mississippi River became a local disaster—a national tragedy. In four seconds the busiest bridge in Minneapolis, typically carrying 140,000 vehicles a day, went from a main commuter artery clogged with rush-hour traffic to a tragic heap of steel and concrete.

First, the 456-ft-long center span and all the vehicles, passengers and construction crews trapped on its road deck disappeared from sight behind a cloud of concrete dust. Hundreds of tons of superstructure made a 108-ft free fall into the river valley. Suspended in midair for a split second, the doomed bridge’s two back spans collapsed, one falling straight back and pancaking on the north side of the river, as the other back span swung sideways and crashed on the southern riverbank.

“I thought I was dead. Honestly, I honestly did. I thought it was over,” Peter Siddon, a mortgage broker traveling toward home in the northbound lanes, told the Minneapolis Star Tribune. “I saw this rolling of the bridge. It kept collapsing, down, down, down, until it got to me.”

When the dust cleared, less than half of the 1,900-ft-long bridge was standing. In the wreckage were 110 vehicles, 17 of them in the river. Within minutes, images of the disaster were beamed around the nation. At the scene it was chaos, pandemonium and a rush to rescue survivors. Fire, smoke and dust signaled to the Twin Cities where eight lanes of superhighway lay in a twisted heap.

The previously anonymous bridge, officially known as bridge No. 9340, became the leading news story around the world. In China, Ji Chunsen, a structural engineer, said, “We couldn’t believe a bridge in America fell to pieces. We didn’t think that would ever happen there. We assumed all of the bridges there were strong.”

Later it would be revealed that 185 people were on the deck of the bridge at the moment of collapse—72% of them injured, many critically. Even worse, 13 were dead.

 

Joining helping hands

At first, commuters, joggers and survivors worked alongside professional emergency personnel. Some survivors needed to be extracted from their vehicles and others pulled from the water. Crowding adjacent bridges, buildings and riverbanks, people were looking for a view and answers.

“Unbelievable! You’ll never cross a bridge again without thinking about this,” Audrey Glassman, who left her work shift at a nearby restaurant to see the rescue operation, told the Star Tribune. The media immediately began setting up broadcast locations. An ever-growing mob of onlookers threatened the work of rescue and retrieval personnel.

At 6:45 p.m. the police began yelling at onlookers to get off the remains of the damaged bridge in fear of further collapse. Clearing an unusually large area around the disaster zone, officials began restoring order as well as creating sanctity for the dead whose bodies were trapped in the river under the fallen bridge. It would be two weeks before some of them would be recovered.

The emergency response was overwhelming, with 50 agencies responding. The first to arrive were the Minneapolis police. It took them just three minutes to get to the disaster zone. Sixty seconds later, the Minneapolis Fire Department arrived. Hennepin County’s Sheriff’s Department’s search and rescue operations were at work within seven minutes. Ten hospitals would eventually receive patients.

In a post-9/11 world, Americans wondered if the destruction was an act of terrorism. The Department of Homeland Security made a statement within hours of the tragedy that the bridge’s destruction did not appear to be such an act. Still, teams from the department’s Federal Bureau of Investigation (FBI) made their way to the disaster zone. The Red Cross served 33,000 meals to the hundreds of first responders, retrieval personnel and investigators in the first 10 days of the crisis.

Emergency road crews worked around the clock in order to create a make-shift interstate system out of Rte. 280, a road running parallel to the incapacitated I-35W. The four-lane divided highway, normally filled with traffic lights, local access points and parking lot entrances, was woefully short of the superior design of an eight-lane superhighway. Within hours of the collapse, crews had covered traffic lights with plastic wrap and blocked points of access and egress with jersey barriers, making the route a crude limited-access highway.

 

A show of force

The National Transportation Safety Board (NTSB), based in Washington, D.C., immediately launched a team of 19 investigators and support staff to Minneapolis. This NTSB team was three times larger than usual. The agency does not respond to every accident. Of most importance are accidents that may trigger national impact on public policy and professional practice. Clearly this disaster qualified. In the end, every NTSB highway engineer and metallurgical specialist was drawn into Bridge No. 9340’s investigation. For an elite organization of just over 3,000 employees, this was a show of force. Clear to all those on the ground, and as is standard in a national transportation tragedy, the NTSB was in control of the disaster site and in charge of the investigation.

Within hours of the bridge’s collapse, the disaster zone looked like part crime scene, part aviation disaster. NTSB inspectors, working behind taped-off areas, were crawling through the wreckage making notes, taking photographs and surveying the scene as recovery crews and divers working next to them continued searching for the missing. In the following days, NTSB agents marked the location of wrecked vehicles with spray paint. Each vehicle was tagged with a number followed by a letter: A for vehicles that had been on the south back span, B for vehicles on the main span and C for vehicles on the north back span. In hopes of finding other clues to the structure’s demise, the NTSB investigators interviewed witnesses, construction workers who had been resurfacing the deck, a kayaker on the river and motorists who had been trapped in the debris and consulted two videos that captured the horror.

The NTSB and FBI investigators began making measurements to produce a computer animation of how the bridge fell. To be sure they captured evidence they would need over the ensuing year-long investigation, the NTSB deployed a helicopter equipped with ultra-powerful photographic equipment to take high-resolution images capable of picking up hairline cracks in the decrepit structural steel.

 

More of the same

The failure of Bridge No. 9340 triggered a political chain reaction across the U.S. Fueled by the media frenzy, bridge hysteria gripped the nation. Every governor and his transportation leaders were on the defensive answering tough questions: How many bridges did their state have similar in design to Bridge No. 9340? Could the state’s highway department claim that their structurally deficient bridges were safe? How were they going to pay for needed repairs without raising taxes, or was a tax hike needed? When The New York Times broke a story shortly after the collapse that flawed gusset plates holding Bridge No. 9340’s key structural support beams together might have caused the accident, the president’s cabinet member for transportation, Mary Peters, issued a national alert requesting all state DOTs to check their inventory and inspect all bridges that were built with similar gusset plates.

One Federal Highway Administration (FHWA) report summed up the effect that Bridge No. 9340’s tragic failure has had in Washington, D.C., “The collapse has had ripple effects in Congress, in the U.S. DOT and in the country that go beyond the immediate tragic impacts.”

“More than 4 billion vehicles cross bridges in the United States every day and, like all man-made structures, bridges deteriorate,” testified Andrew Herrmann, a board member of the American Society of Civil Engineers (ASCE). Sharpening his point during his U.S. Senate hearing held three weeks after the bridge disaster, Herrmann went on to explain that urban bridges, like Bridge No. 9340, are deteriorating at an even more alarming rate, stating, “one in three (31.2% or 43,189) were classified as structurally deficient or functionally obsolete, much higher than the national average (of all bridges—urban and rural).” Not surprising considering the dramatically higher volumes of traffic urban bridges are carrying.

While testifying to U.S. senators and representatives, six state highway officials stated, “Shortfalls in the federal funding are causing maintenance and repairs of the nation’s bridges inventory to lag.” In other words, funding shortfalls mean more dangerous bridges.

The inspector general of the U.S. Department of Transportation, Calvin Scovel, was more to the point when testifying to the Senate Committee on Environment and Public Works that performing and paying for badly needed bridge inspections will be a difficult task for FHWA and its 52 divisional offices. Detailing his agency’s role, Scovel reported he would be conducting an audit of the FHWA bridge inspection program as well as making certain that the FHWA Bridge Program Manual is properly amended and distributed. As far as payments from the federal government to the states, he warned, “We will assess FHWA’s management and tracking of such funding, to the extent to which states effectively and efficiently use these funds to repair or replace structurally deficient bridges and whether states are using bridge funds for other purposes.” In other words, forewarned is forearmed: DOTs had best not be using bridge inspection funds for road-widening projects.

Potential causes for Bridge No. 9340’s failure are numerous. “Water, salt, stress and corrosion make a bridge structurally deficient,” explained a federal highway document on the bridge disaster that was prepared for Congress. Almost certainly the NTSB final report, due out in 2008, will cite many factors that caused the deadly failure. The most talked about are: over-stressed steel support structures—specifically large gussets; other structural support beam problems that may have gone undetected because of their obscure locations; decay caused by everything from road salt to corrosive acids found in bird guano; the devastating effects of expansion of the bridge’s steel deck brought on by extreme temperatures during Minnesota’s cold winters and hot summers; overloading, especially given the weak condition of the over-stressed structure; and the effects of an estimated 287 tons of construction equipment that were on the bridge at the time it collapsed.

Additionally, the impact of four decades of heavy truck traffic will be closely examined. The Associated Press reported, “According to one government study, one 40-ton truck does as much damage to the road as 9,600 cars.” Or, as one bridge inspection professional explained about the bridge disaster, “It’s a truck problem; cars have nothing to do with this collapse.”

Regardless of the cause(s), had the bridge’s flawed conditions been detected earlier, disaster would most likely have been averted. Therefore, the most significant outcome of the NTSB report may be its critical assessment of Bridge No. 9340’s failed inspection program. Bridge inspection procedures around the world are sure to be affected by the findings in Minneapolis.

 

Senses and sensors

For Peter Vanderezee, CEO of LifeSpan Technologies, a structural monitoring business, learning about the I-35W collapse was like recalling where he was when he first heard about the Kennedy assassination. “I had just finished dinner. I sat down on the couch, turned on the TV and it hit me right between the eyes. I couldn’t believe it. I sat there glued to the tube, mesmerized by the images, and wondering if it could have been prevented.”

Two human senses, sight and sound, are the most important determinants in deciding the safety of the nation’s bridges. For much of the motoring public, it is hard to believe that bridge inspectors smacking a $10 hammer against steel and concrete while listening for the sounds a defective support structure may release are all that stand between them and a potential disaster like the I-35W collapse.

Vanderezee believed state DOTs across the country should already be using the high-tech electronic bridge monitoring devices and systems that his firm affixes to superstructures. “Using the same old visual inspection techniques, why should we expect different results this time? And given this tragic experience, one has to wonder why America continues to rely solely on an inspection protocol that the FHWA acknowledges has significant limitations.

“Consider this,” he hypothesized. “If all 756-plus steel-deck truss bridges in the U.S. just ordered to be reinspected by the FHWA had structural monitoring systems installed tomorrow, the total cost of all installed systems would be less than half the funding that was allocated for the “Bridge to Nowhere” in Alaska several years ago. Clearly you can’t just spend your way to safer bridges, but we need to be using more definitive assessment technology. Visual inspections just aren’t good enough for structurally deficient bridges. It’s not that visual inspections should be thrown out, but they need to be recognized for their limitations and used with better technology when warranted.”

Making his point, Vanderezee considered a “what-if” scenario. “Had sensors been used in Minneapolis, where temperature variations are extreme, Mn/DOT may have been able to objectively evaluate the degradation long before the bridge’s condition reached a critical point. On bridges of this type, extreme temperature fluctuations like the ones this bridge experienced before its collapse can have devastating effects. In our experience, as much as 80% of the stress inflicted on this bridge may have been the result of temperature fluctuations, which can damage members of the support structure which often escape notice during visual inspections.”

Vanderezee believed that a bridge like the original I-35W bridge, all 1,900 linear ft of it, could have been outfitted with between 12 and 40 electronic sensors—that’s all. These sensors, a controller, an Internet display of data and a four-year service contract that would arrange for certified engineers to monitor and decipher using a finite-element analysis of vital information available to Mn/DOT would cost approximately $200,000, less than .03% of the total cost for replacement.”

Weeks after the bridge disaster in neighboring Minneapolis, Gov. Jim Doyle of Wisconsin decided that electronic sensors make sense. The governor ordered that 15 bridges in his state that are similar in design to Bridge No. 9340 be outfitted with sensors so that highway officials will have better information about their conditions. Today, in Europe and Asia, new bridges are being outfitted with sensors.

“Along the Pacific Rim and in Europe, they value their infrastructure,” quipped Vanderezee. “They see roads and bridges as delivering economic prosperity and a higher quality of life. Unfortunately, we don’t think about our bridges that way.”

 

To the highest bidder

On Sept. 20, 2007, the Star Tribune led with a banner headline story: “Despite submitting the most expensive price-tag and acknowledging that it would take longer than others to do the job, a Colorado company . . . won an intense competition to build the new Interstate 35W bridge in Minneapolis. A team of companies led by Flatiron Construction, the ninth-largest transportation contractor in the country, won a four-way competition with a $233.8 million bid to replace the bridge.” Flatiron’s bid not only requests more months to build than any other contractor, but is nearly $57 million more than the least-costly bid.

The opening of the price proposals on Sept. 19 took place in a packed room outfitted with electronic scoreboards showing each contestant’s points toward winning the coveted contract. The Flatiron team walked away with the spoils of victory with a high technical score of 91.47. The other bidding contractors received remarkably low scores, with the next highest bidder earning a dismal 67.88. Points, not dollars, mattered most in this competition.

  The effects of losing a multimillion-dollar trophy project—one that the world will be watching—almost guarantees objections are going to surface, especially when there is so much public money involved and so many arguments about the process. Final costs will likely go beyond the awarded $233.8 million as incentives are high: $200,000 for each day of an early completion or up to $20 million for finishing 100 days early, plus an additional $7 million for finishing all work by the proposed completion date as a “no-excuse” bonus for on-time completion. Conversely, liquidated damages also are high at $200,000 per day up to a maximum of $27 million for 100 days of delay, at which point the liquidated damages plunge to $3,500 per day.

The losing contractors, each walking away with the consolation gifts of $500,000, a statutorily prescribed stipend for defraying the costs of bidding on the work, protested the contract award, claiming that the process was rushed and important discussions about design were confused. The three low bidders submitted steel bridge designs because, as one contractor put it, “Steel bridges are less expensive and faster to construct. It takes a lot more time to construct out of concrete.”

  Flatiron’s proposed concrete structure, the other contractors claim, will take longer to build and cost the taxpayers more in the end. Other contractors now say they would have submitted a concrete span had they known aesthetics were going to be weighed so heavily.

“It was a surprise to us that the competition could be won by technical score points and that there was such a wide disparity between Flatiron and the other proposers,” lamented Todd Goderstad, vice president of Ames Construction, whose company, in joint venture with Lunda Construction, submitted the second-lowest price of $178,489,561.

Mn/DOT, however, was clear with what it and the public wanted in a new bridge.

“We believe in the design-build process in Minnesota—in fact, we love design-build. We’ve been very successful in previous competitions here,” asserted Goderstad. “Unfortunately, this selection illustrates that it is possible that neither the lowest bid nor the shortest completion time were important factors in the replacement of this bridge. Look at the scoring scheme—out of a possible 100 points, a proposer could earn 20 for aesthetics, 15 for public relations and another 15 for enhancements. That’s half the total assessment before costs and time of completion were even considered. Even with the current deficit in transportation funding in Minnesota, the point scheme allowed for an award that was $57 million over the lowest bidder.”

Minnesota’s Lt. Gov. Carol Molnau, who pulls double duty as the state’s transportation commissioner, showed no signs of concern about the bid letting. Going a step further, she praised her staff over the process, saying, “Let me tell you, we have the best of the best right here.”

In the rush to rebuild, a lively public debate is being played out in Minnesota’s media, which will probably carry on beyond the new bridge’s ribbon cutting. Regardless of the questions surrounding the bid process in the Twin Cities, it is time for the nation as a whole to begin rebuilding its bridges as well as its belief in its built environment.

SIDEBAR

Initially, the cause seemed like it fell from the sky. Could pigeon dung really be a culprit of the I-35W collapse in Minneapolis? Most experts say probably not, but birds continue to be a health hazard around bridge sites.

“I have seen that pigeon feces does corrode metal and building parts,” Bruce Donoho, founder of Bird-B-Gone, told ROADS & BRIDGES. “When the story is finally analyzed, it would take many, many, many years and a combination of things to actually have the pigeon feces be the cause. There was probably a situation where it added to it, but pigeon feces alone is not going to bring down a bridge.

“I look at it more of a health issue,” he continued. “If anybody is going underneath that bridge to inspect it or maintain it they are going to come in contact with pigeon feces.

“The problem with those feces is they usually become very dry, and if you disturb them they will become airborne. It can be a problem with people coming in contact with that. [Feces] can cause at least 36 known diseases.”

Donoho said he receives many calls from state departments of transportation (DOT), but it usually is because pigeons have become a nuisance to workers and pedestrians walking under the bridge.

With bridge inspections expected to increase in the coming years, those at the DOT level need to be aware of the hazards they are leading their workers into.

Bird netting installed underneath bridges is recommended.

“Another bird that causes problems on bridges is swallows,” said Donoho. “In the spring they come in and inundate a bridge when they build their mud nests.”

About the author: 
McNichol is a freelance writer based in Boston.
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