Fatigue Behavior of Prestressed Tubular Bridge Deck of Fiber-Reinforced Polymer

An experimental study was undertaken to assess the flexural fatigue performance of a new deck system of fiber-reinforced polymer (FRP) that has been installed on a bridge in Delaware County, Ohio. The deck consists of a series of 4-in. (102-mm) square pultruded FRP tubes with a thickness of 1/4 in. (6.4 mm), laid side by side on existing stringers, perpendicular to the direction of traffic. The tubes are posttensioned up to 20 kips (90 kN) with 0.6-in. (15-mm) diameter seven-wire strands at midpoints between the stringers in the direction of traffic. Four double-span FRP deck specimens with two different tube sizes and three different span lengths were tested in flexural fatigue under AASHTO-prescribed footprint of wheel loads for an HS20 truck. Panel action in the deck system was inadequate for the most part, as only the tubes that were directly under the load carried the majority of the load. Subsequent slippage between these tubes and their adjacent tubes can cause cracking in the asphalt overlay. However, no such crack has been observed on the actual bridge after 1 year in service. Panel action is generally improved at higher prestress levels. Prestressing also offers additional redundancy and reserve strength for the system. While longer span decks fail in bending, shorter span decks generally suffer from local shear failure as a result of stress concentrations at the corner of the tubes under the applied load or at the support. The fatigue problem is less critical for longer span decks and smaller tube sizes.