Use of Glass-Fiber-Reinforced Polymer Tendons for Stress-Laminating Timber Bridge Decks

Researchers at the University of Maine led an effort in the mid-1990s to develop and use glass-fiber-reinforced polymer (GFRP) tendons, instead of the commonly used steel-threaded bars, for stress-laminating timber bridge decks. The GFRP tendons are 12.7 mm (0.5 in.) in diameter and consist of seven-wire strands similar in construction to steel prestressing strands. Because the modulus of elasticity of the GFRP tendons is approximately 1/9 that of steel, they are not as susceptible to loss of prestress as steel bars and may not have to be restressed during the life of deck. In 1997, researchers obtained funding to design, construct, and monitor a stress-laminated timber bridge located in Milbridge, Maine, utilizing the new GFRP tendons. The bridge was constructed from preservative treated No. 2 and better eastern hemlock laminations and is 4.88 m (16 ft) long, 7.75 m (25 ft, 6 in.) wide, and 350 mm (14 in.) deep. Based on 4.25 years of field monitoring the tendon forces and moisture content, the GFRP tendons have maintained an adequate prestress level without having to be restressed.