In the United States, approximately 25 percent of the nearly 600,000 bridges are considered to be structurally deficient or functionally obsolete, as reported by the U.S. Department of Transportation (DOT). According to the American Society of Civil Engineers’ (ASCE) 2009 Report Card for America’s Infrastructure, bridges were given a grade of C with no improvement since the last report in 2005. A $17 billion annual investment is needed to substantially improve current bridge conditions. Currently, only $10.5 billion is spent annually on the construction and maintenance of bridges.
For over 20 years, FRP composite products used in new bridge construction and rehabilitation has provided bridge engineers and owners with innovative and cost effective solutions. In several instances, composites preserve historic landmarks while ensuring a structure’s structural integrity. In new construction, features such as lightweight, corrosion resistance, and prefabrication have contributed to the goals of accelerated bridge construction by reducing assembly and installation time resulting in lower costs for deploying FRP composites technology. In rehabilitation, features such as speed and minimal disruption to the structure while in service have provided bridge owners with solutions for extending the service life of bridge structures. The technology continues to evolve with better products and solutions for many new applications.
The Broadway Bridge in Portland, Ore., has been carrying cars, trucks, buses, bicyclists and pedestrians across the Willamette River for over ninety years. Opened on April 22, 1913, it is one of only three Rall-type bascule bridges still operating in the U.S., and according to Multnomah County, the bridge owner, it is by far the largest. This historic bridge has average daily traffic of 33,000 vehicles per day. Not surprisingly, in February 2003, as the bridge approached its 90th Anniversary, the Multnomah County Bridge Section, which manages and maintains the Broadway and five other Willamette River bridges in Portland, embarked on a major renovation project aimed at upgrading the structure to assure its continued service well into the 21st century.
While the Rall-type opening mechanism is unusual, it poses the same requirements for its double-leaf movable span as most other bascule bridges. The deck must be light enough to allow opening of the bridge using reasonably sized counterweights, lift motors and gear sets, while providing the strength required supporting modern vehicle loads. At that time, the Multnomah County planners wanted to replace the steel grating with a new decking that offered light weight, a solid surface with good traction in wet, snowy or icy conditions and quiet ride, and low maintenance requirements. The contractor installed the full 11,790 square feet of decking (32 FRP composite panels measuring approximately 46 feet x 8 feet each).