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GPS Monitors Bridges09-12-07 | News

GPS Monitors Bridges

The Mercer Slough bridges in Bellevue, Wash. were built over a peat-filled wetland. Lateral movement of the thick peat deposit has damaged the pile-supported structures.

After the Minnesota bridge collapse, municipalities across the country took a closer look at their bridge ratings and their state DOT evaluations. The deck, substructure and superstructure of a bridge are each evaluated. Those ratings go into a ?EUR??,,????'??sufficiency number,?EUR??,,????'?? which rates the bridge from 1 to 100. The sufficiency rating takes into account about 75 factors.

The Fed may provide funding for replacement if a bridge’s sufficiency number is 50 or below. If the number is between 51 and 80, then the state may receive funding for rehabilitation, which requires more major repairs than typical maintenance.

Minnesota has 1,135 road spans rated ?EUR??,,????'??structurally deficient,?EUR??,,????'?? which is 8.7 percent of the state?EUR??,,????'???s 13,008 bridges, 20 feet or longer, that are subject to annual inspections. Another 451 spans are ?EUR??,,????'??functionally obsolete,?EUR??,,????'?? and 65 of those bridges are more than a century old.

The Washington State Department of Transportation (WSDOT) is using the latest in Global Positioning System (GPS) technology to monitor some of its bridge infrastructure. The Mercer Slough bridges were built over a peat-filled wetland. Lateral movement of the thick peat deposit has damaged the pile-supported structures. WSDOT determined it needed accurate, quantitative data.

A customized GPS system from Leica Geosystems is monitoring the Mercer Slough interchange, which has several bridges dating from the 1940s through the 1990s that carry the I-90 mainline and ramps into Bellevue, Wash. The custom GPS is said to deliver ?EUR??,,????'??millimeter level motion detection?EUR??,,????'?? for real-time bridge monitoring.