Government Technology - March 2008 - (Page DC26)

Emerging Technologies Bridge Detectives Minneapolis bridge collapse spurs monitoring innovations. beams; the gusset plates were only half the thickness they should have been. The NTSB investigation found no evidence that cracking or corrosion played a role in the collapse. However, the tragedy had already drawn muchneeded attention to the problem of corrosion in aging bridges. The Minnesota Department of Transportation (Mn/DOT) knew of some risks beforehand: Prior to the accident, Mn/DOT was so concerned about the bridge’s structural deﬁciencies that ofﬁcials considered replacing it. Other proposed ﬁ xes included bolting steel plates to the bridge to prevent stressed areas from cracking. Mn/DOT ofﬁcials, though, ultimately decided that only more frequent visual inspections were required. Today, U.S. bridges are almost entirely visually inspected, and if corrosion or cracks are spotted, tests using eddy currents, ultrasound or penetrating dyes are often used. However, detecting weak spots visually is an imperfect science. Bridging the Monitoring Gap BY CHANDLER HARRIS | CONTRIBUTING WRITER W HEN THE MINNEAPOLIS Interstate 35W bridge collapsed on Aug. 1, 2007, sending 88 vehicles and hundreds of people into the Mississippi River — 13 were killed and 100 injured — nobody, including state bridge inspectors, foresaw such a catastrophic event. The collapse was a sad reminder of the aging U.S. infrastructure, which needs a $1.6 trillion overhaul over the next ﬁve years, according to the American Society of Civil Engineers. Its report graded the U.S. infrastructure as a D in 2005, down from a D+ in 2001. Bridges earned a cumulative C. U.S. bridges are a pressing concern because stress loads have increased substantially due to a spike in trafﬁc congestion. Since the Minneapolis I-35W bridge was built in 1967, the number of vehicles using the bridge had tripled, according to state documents. Also, truck weight limits have increased nationally, according to the U.S. Department of Transportation (DOT). The I-35W bridge had been diligently inspected since 1993, and it always passed. Although state ofﬁcials knew the bridge needed repairs, they had no idea the bridge was in danger of collapse. In January, the National Transportation Safety Board (NTSB) announced the bridge failed due to a design ﬂaw in the gusset plates that connected steel A new engineering technology, structural health monitoring (SHM), is being developed to address critical infrastructure needs. SHM uses sensors embedded in structures to alert crews of defects in critical structures before catastrophic failures occur. The process uses wireless technology to monitor a structure’s physical properties such as loads, stresses, strains and cracks, as well as changes in chemical and electrical properties related to deterioration — corrosion, fatigue, chlorides and humidity. Experts see wireless sensors as a cheaper, more 26 DIGITAL COMMUNITIES MARCH 08

Table of Contents Feed for the Digital Edition of Government Technology - March 2008

Government Technology - March 2008 Contents Point of View Big Picture The Last Mile On the Scene Four Questions for... Top 25 Doers, Dreamers and Drivers Let's [Not] Get Physical No Data Left Behind Conservation King Community Drug Test Reinventing the System Better Late Than Never Closing the Deal Spectrum Products Personal Computing signal:noise Digital Communities The Expanding Focus of Digital Communities The Digital Imperative Hot Fusion Redefining Municipal Wireless Made in the USA Bridge Detectives The 2008 Agenda

Government Technology - March 2008

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