Flexural Behavior of CFRP-Pretensioned Girders

Highway bridge beams are subjected to aggressive environments, temperature fluctuations, and a large number of loading cycles. The combination of these factors can result in deterioration of highway bridge beams’ serviceability and strength. Beams prestressed with steel are susceptible to corrosion when subjected to environmental exposure. The corrosion of the prestressing steel reduces the beams’ load-carrying capacity and may result in catastrophic failures. Carbon fiber reinforced polymers (CFRP), as an emerging material, have potential to replace prestressing steel and provide corrosion-free prestressed bridge girders. The application of this novel CFRP material in bridges necessitates understanding some of the critical parameters that affect the design and long-term behavior of prestressed concrete bridge beams.

This dissertation comprehensively investigates the use of prestressing CFRP in bridge beams using experimental, computational, and analytical approaches. A review of the existing literature indicated a lack of research on full-scale CFRP prestressed bridge beams, especially ‘I’ shaped beams, which are most commonly used in highways. The majority of reported tests have been conducted on small-scale, rectangular beams with spans and depths of less than 30 feet and less than 20 inches, respectively. As such, these tests are not representative of the behavior that can be expected from full-scale bridge beams. The experimental study includes construction, testing and analysis of eight full-scale composite AASHTO Type-I prestressed concrete beams under flexural monotonic and fatigue loading. Results of the experimental studies showed that the CFRP prestressed beams can exhibit higher strength and similar or lower deformability compared to steel prestressed beams. Further, CFRP prestressed beams’ wide distribution of cracks and deformation at ultimate load provide enough warning before failure. The computational study consisted of Finite Element (FE) model validation and an investigation of the effect of different parameters including level of prestressing, composite behavior, and reinforcement ratio on the behavior of CFRP prestressed beams. The analytical study included an evaluation of prediction models and a reliability analysis. Results from the analytical study showed that the conventional prediction models can be easily implemented to perform flexural analysis of CFRP prestressed beams. Additionally, a reliability analysis was conducted using the Monte-Carlo Simulation (MCS) approach to calibrate the strength reduction factor for CFRP prestressed beams considering the statistical variability of the model parameters and the modelling uncertainty. The reliability study suggested a strength reduction factor of 0.75 for CFRP prestressed beams. Finally, the findings of this study suggest design guidelines for CFRP prestressed beams.