Design Approach for CFRP Prestressed Concrete Bridge Beams,

Abstract

This paper presents a design approach for carbon fiber-reinforced polymer (CFRP) concrete bridge beams prestressed using bonded pretensioning and unbonded post-tensioning tendons arranged in multiple vertically distributed layers along with non-prestressing CFRP rods. Design equations to determine the flexural capacity and to compute the stresses and strains in concrete and tendons are provided. In addition, based on parabolic stress-strain relation for concrete and linear stress-strain relation for tendons, a computer program was developed to compute the overall response of the beam such as deflections, strains, cracking loads, and post-tensioning forces. The design equations and the accuracy of the nonlinear computer program were validated by comparing the analytical results with experimental results from a full-scale double-T (DT) test beam. The difference in the analytical and experimental values of the ultimate moment capacity of the DT-test beam is negligible, whereas the corresponding difference in the ultimate forces in unbonded externally draped post-tensioning strands is approxi- mately 4.1%. A detailed parametric study was conducted to examine the effect of the reinforcement ratio and the level of pre- stressing forces on the deflections and ultimate load-carrying capacity of the full-scale DT-beam. It is observed that the reinforce- ment ratio and the level of prestressing have significant effect on the moment-carrying capacity and ultimate load deflection of the beam. The combination of bonded and unbonded prestressing levels (0.3 to 0.6) can significantly increase the ultimate moment capacity of an over-reinforced beam.