The failure of Minneapolis' 35-W bridge wasn't due to corrosion. It wasn't an act of terrorism. It was a design flaw, a metal plate too thin to serve as a junction of several girders, according to results of a federal investigation.
The bridge, designed in the 1960s, lasted 40 years. But maintenance and repair jobs added weight to the span, straining its weak spot. The bridge collapsed on Aug. 1, 2007, killing 13 people.
The National Transportation Safety Board's report of this collapse should provide invaluable information to highway departments nationwide. Utah has one bridge of the same design northeast of Tremonton. It crosses the Bear River to an electrical substation but is rarely used and poses little danger, Utah Department of Transportation officials told the Utah Transportation Commission some two weeks after the Minnesota collapse.
That's welcome news. It is also reassuring that the designs of state-owned bridges constructed now include redundancies so an entire span does not fail if one component falters.
However, the investigation of Minnesota's bridge failure spotlights the importance of re-analyzing a bridge's design before embarking on any major modifications or repairs.
Another concern is many bridges nationwide were not designed or built for the loads they carry each day. These issues are often addressed by limiting vehicle weights and traffic loads on these spans, but it's hardly a silver bullet. At some point, states will have to pony up to replace aging spans. According to a report by the American Society of Civil Engineers, it would cost $1.6 trillion to bring the nation's infrastructure to "good" condition.
Compared to many states, Utah's bridges are in relatively good shape. Some 94 percent of Utah's bridges are in good or fair condition, according to UDOT officials. The agency has completed a number of bridge replacement projects in recent years, including the innovative rapid bridge replacement at 4500 South over I-215, completed last fall. The same technology will be used for a number of bridge replacements along I-80, in the heart of the Salt Lake Valley.
Statewide, it would cost some $9 billion to replace all of the state's bridges. Considering the entire state budget could top $12 billion this year, replacing every bridge is a pipe dream. But Minnesota's experience is instructive in that extreme care must be taken to ensure work done in the name of "repair" or "modification" doesn't, instead, compromise a bridge's structural integrity.