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The Minnesota Daily, Stacy Bengs/AP
Vehicles scattered along the broken remains of Minnesota’s Interstate 35W bridge after
it collapsed on August 1, 2007 (AP)

Lack of Calculations Blamed for Minneapolis Bridge Collapse

November 14, 2008 05:10 PM
by Anne Szustek
The National Transportation Safety Board is releasing a report Friday on the role of an oversight in the design of the gusset plates in the Aug. 1, 2007, collapse of the Interstate-35W bridge in Minneapolis.

New National Engineering Review Standards Likely

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NTSB investigators concluded that the root cause of the Minneapolis bridge crash was a lack of calculations to determine the thickness of the bridge's gusset plates; the plates were a half inch rather than the 1 inch needed to sustain the bridge's weight and torsion.

On August 1, 2007, adjacent to downtown Minneapolis, a 40-year-old overpass of I-35W collapsed during evening rush hour over the Mississippi River, killing 13 people and injuring some 145 others.

The numerical error is partly blamed on a now-deceased civil engineer who was working for Sverdrup & Parcel (S&P), the firm hired by the government during the 1960s to design the I-35W overpass. Jacobs Engineering acquired S&P some 10 years ago.

Federal transportation officials examined more than 10,000 pages of Jacobs Engineering documents, which showed no calculations for the I-35W bridge's gusset plates, leading analysts to deduce that the necessary computations were never actually made.

"We're looking back 45 years and inferring an error of omission based on a lack of documentation. It's a fair inference," NTSB Director of Research and Engineering Vern Ellingstad was quoted as saying by the Minneapolis-St. Paul Star Tribune.

On top of the gusset design glitch, the NTSB concluded that inadequate oversight by the Federal Highway Administration (FHWA) and the Minnesota Department of Transportation (MnDOT) also played a role in the bridge's demise.

"While the design firm did not check its own work, neither did MnDOT and the FHWA," Joseph Epperson, a structural analyst with the NTSB, told the Star Tribune.

This information will likely be used in both formulation of new review policy on governmental infrastructural, as well as in the numerous lawsuits filed by the families of those who perished or sustained injuries in the bridge collapse.

After the dust cleared, the nation focused greater attention on the state of bridges. Finger pointing ensued: in regards to both structural deficiencies as well as perceived failure on the part of governmental oversight bodies.

The tragedy rocked the Twin Cities metropolitan area and was the subject of constant coverage. State and federal bodies pushed through for a new bridge to be rebuilt across the key commuter artery, which passes just to the northeast of downtown Minneapolis and west of much of the University of Minnesota campus.

A new bridge over I-35W opened around dawn on Sept. 18 this year. Led by members of agencies that responded during the bridge’s Aug. 1, 2007, crash, drivers and passengers snapped pictures of the reopening in the pre-dawn twilight and waved to one another.

The new I-35W bridge, unlike its predecessor, is built with concrete, rather than steel. Its structure also is “redundant,” meaning that if one section of the bridge gives way, the other will not go down with it.

Designed by Florida firm Figg Engineering Group, the “smart bridge” has 323 data-collecting sensors measuring torsion, weight load and temperature changes—important in a climate that vacillates between sub-zero cold and triple-digit heat. Other sensors and cameras are to detect traffic flow and entry into unauthorized areas, as well as activate a de-icing system when weather conditions necessitate.

According to the Associated Press, the Minn. Department of Transportation fast-tracked the I-35W bridge rebuilding project, which was valued at $245 million. Contractors had the bridge ready in 11 months—far ahead of the Christmas Eve deadline. It was also completed on budget, which translates into the maximum bonus possible for the contractors, estimated at some $27 million.

Goverment fast-tracking and a streamlined construction scheduled pushed through the Minneapolis bridge reconstruction project. But other infrastructural works in Minnesota and across the nation have lagged, causing Pa. Gov. Ed Rendell to say at a June 28 press conference, “We need federal intervention, and federal intervention at a big level.”

The conference was held in north Philadelphia near the site of the March collapse of a pillar supporting an overpass of Interstate Highway 95, forcing three days of detours and emergency repairs.

“Bridging the Gap,” a report by the American Association of State Highway and Transportation Officials unveiled at the conference, revealed that 152,000 out of the country’s 600,000 bridges—about one in four—are structurally deficient. It will take an estimated $140 billion to repair the bridges to safety standards.

On July 24, the House of Representatives voted 367-55 to pass the National Bridge Reconstruction and Inspection Act, a bill that would allocate an extra $1 billion to repair structurally unsound bridges. The bill would also require that states certify that all interstate highway overpasses in their jurisdiction are safe before funds can be spent on other transportation infrastructures.

Most bridges in the United States are meant to last 50 years without needing any improvements. Most highway overpasses, constructed as part of the interstate highway system, are nearing the half-century mark.

Video: Footage of the I-35W bridge collapse

Background: The Minneapolis bridge collapse

Related Topic: ‘Army Corps Admits to Knowing Little of Levees’

Reference: Government infrastructure spending

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