Flexural Behavior and Design Of Post-Tensioned Beams With Prestressing CFRP System

Post-tensioning technique has been widely used in the construction and strengthening of prestressed highway bridge girders. It provides structural integrity, control of cracks, deflection and camber, thinner structural members, and profiled tendons. The high ductility, elastic modulus, and strength of prestressing steel strand helped the concrete prestressing techniques to become widespread. However, steel has one main deficiency, which is corrosion. The unbonded tendons are exposed and vulnerable to atmospheric conditions. Even for the bonded case, there is no guarantee that the cables are protected from corrosion agents, especially the grout is not prestressed and is susceptible to cracking. For the last three decades, using prestressing Carbon Fiber Reinforced Polymer (CFRP) tendons in concrete bridge beams has been an active research area. It has proven to be an excellent alternative to steel strands in prestressed concrete bridge applications, especially in aggressive environments where corrosion resistance is essential.

This dissertation investigates the flexural behavior and design of post-tensioned beams with prestressing CFRP systems through comprehensive experimental, computational, and analytical investigations. The experimental program includes design, construction, testing, and analysis of five full-scale post-tensioned AASHTO type-I composite girders under flexural monotonic and fatigue loading. The computational study includes calibration of a Finite Element (FE) model based on experimental tests conducted in this research and from literature. A parametric study was conducted on the FE models to investigate the effect of different parameters that have not been included in the experimental program and provide data points for the analytical investigation. Three different studies were conducted in the analytical program to: 1) investigate the accuracy of different approaches for estimating the force in unbonded prestressing tendon at the ultimate, 2) propose a minimum auxiliary bonded unstressed reinforcement for unbonded post-tensioned beams, and 3) calibrate a strength reduction factor for flexural strength of unbonded CFRP post-tensioned beams.