Thermoplastic Bridge Performance Monitoring

Overview

On October 1, 2010 a law passed in the State of North Carolina making the discarding of plastic bottles illegal. In keeping with the State mandate, the world’s first thermoplastic composite bridge was designed and erected at Camp Mackall, across Big Muddy Creek.

The bridge replaces an unserviceable wooden structure that had a load rating of 4.2kt (4.7 tons). The new bridge, constructed from approximately 40kt (43 tons) of recycled plastic (approximately 65 percent high density polyethylene plastic from dish washing detergent bottles and 35 percent polypropylene plastic from vehicle bumpers), has a load rating of over 65kt (70 tons), able to withstand the heaviest loads such as the M1A1 Abrams tank. It bends but doesn’t break!

In fact, its structural integrity surpasses that of traditional materials such as steel, wood and cement. It defies catastrophic failure and grows stronger when exposed to environmental elements. Additionally, being constructed of plastic means it resists corrosion, insects, and other environmental effects, so replacement cost is reduced. It is projected to have a minimum 50-year service life.

The photo above shows an M1A1 Abrams tank being driven over the bridge during the dedication ceremony.

The project was sponsored by the Fort Bragg Directorate of Public Works, Department of Defense/Army Corrosion Prevention and Control Program and the Army Installation Technology Transition Program.

What We Did

Engineered Monitoring Solutions (EMS) of Newberg, Oregon, USA was awarded a contract by the US Army Corps of Engineers to install a comprehensive monitoring system for the bridge to profile short-term and long-term performance.

Bridge instrumentation includes (16) surface temperature sensors, (12) laser displacement sensors including temperature and (9) strain transducers including temperature, metrology instrumentation includes temperature, relative humidity, wind speed and direction, rainfall and solar radiation. The displacement sensors and strain transducers monitor key support girders of the bridge.

Two Campbell Scientific based data acquisition systems were deployed, a CR1000 for the metrology instrumentation, a Campbell CR9000 for the bridge instrumentation. The bridge instrumentation is stored in 2 tables, one table records 60 minute averages, the second records data at 100Hz for 16 seconds during passing of vehicles. The CR9000 programming includes logic to detect vehicle passage based on measurements from the instruments.

We were tasked with building the project database including the project views and all automated and manual outputs and hosting the database. Our MultiLogger Suite database software was utilized for the database, our MLWeb software provides Internet access to EMS, the Corps of Engineers and Camp Mackall personnel. All data, including events, may be selected in the project interface and either extracted to a chart or to Excel for further analysis.

A view of the project interface including sample static and event outputs is shown to the right.