Flexural behavior of precast concrete box beams post-tensioned with unbonded, carbon-fiber-composite cables

A common problem in prestressed concrete box-beam bridges is the corrosion of steel reinforcement due to seepage of moisture and chemicals through longitudinal cracks in the deck slab between adjacent beams. Replacing conventional steel reinforcement with non-corroding fiber-reinforced-polymer (FRP) reinforcement eliminates the corrosion potential in the concrete member. This paper presents the flexural behavior of box-beam bridge systems that are reinforced with prestressed carbon-fiber-composite cables. Three box-beam bridge models were designed, constructed, instrumented, and tested to failure. The three bridge models had the same cross section and dimensions. Each bridge model was formed by aligning two precast, prestressed concrete box beams adjacent to each other, filling the gap between the beams with concrete grout, applying deck slab. Each bridge model was reinforced with 14 bottom pretensioned strands, 14 top nonprestressed strands, and 8 bottom nonprestressed strands. Two of the bridge models contained 12 unbonded longitudinal strands, which were post-tensioned for only one of the models. The third bridge model did not contain any unbonded longitudinal strands. Generally, the model that included unbonded longitudinal post-tensioning demonstrated improved flexural behavior and minimized deflections.