Design analysis and experimental behavior of precast concrete double-tee girders prestressed with carbon-fiber-reinforced polymer strands

This paper deals with the design philosophy and the flexural performance under service loads of the precast, prestressed concrete girders constituting the deck of a recently constructed pedestrian bridge. This simple structure combines innovative materials and novel composite manufacturing technologies to ensure that degradation due to steel corrosion does not undermine the longevity of the bridge. The two girders, cast in the shape of double tees with shortened flange overhangs, were prestressed with 0.6 in. (15 mm) diameter, seven-wire carbon-fiber-reinforced polymer (CFRP) tendons and reinforced with basalt-fiber-reinforced polymer bars. Despite the complexity inherent in its tensioning, CFRP strand has already been used for other prestressed or post-tensioned applications, but never before in large diameters for the fabrication of structural elements with thin cross sections. The selected percentage of the guaranteed capacity of the CFRP tendons applied at jacking was, for the first time, higher than the 65% limit imposed by ACI 440.4R-04 guidelines.

A load test was performed at the precasting yard with concentrated loads corresponding to service conditions, with the tested girder remaining uncracked. The strains measured in the reinforcement and the detected deflections of the girder showed agreement with the analytical predictions. CFRP prestressing technology can be used successfully in thin-walled concrete sections beyond the limits suggested by current guidelines and without significant technological drawbacks.