Non-linear analysis of concrete beams prestressed and post-tensioned with carbon fiber reinforced polymer (CFRP) bars.

The deterioration of concrete bridges has been a major concern for structural engineers especially with regard to deterioration caused by the corrosion of steel reinforcement. One of the promising avenues to overcome this problem is to take advantage of the non corrosive characteristic of the Fiber Reinforced Polymer (FRP) bars in reinforcing and/or prestressing concrete bridges. In addition FRP bars have high specific strength, i.e., strength to weight ratio, when compared to conventional steel. Using FRP bars in a combined system of internal prestressing and external post-tensioning provides a potential solution to increase the service life of concrete bridges. However, due to the difference in the mechanical properties between FRP tendons and steel, the flexural behavior of beams prestressed and post-tensioned with internally bonded and externally unbonded carbon fiber reinforced polymer (CFRP) tendons is different when compared with the behavior of beams prestressed with conventional steel bars and/or tendons. Also, as these beams can be post-tensioned with unbonded tendons the deflection of the whole system becomes a controlling parameter in the analysis. An analytical model has been developed to examine the behavior of beams prestressed and post-tensioned with CFRP tendons. First, finite element analysis has been carried out to calibrate the tension stiffening characteristic of concrete in order to take into consideration the difference in the bond behavior between CFRP tendons and steel for beams prestressed with bonded tendons. The calibrated tension stiffening is used in the analytical model for the proper modeling of the cross-section curvatures and deflection calculations. Three analytical approaches that account for the tension stiffening of concrete in indirect approaches were also applied to examine the change in the post-tensioning force and were compared with the analytical model. These approaches use the ACI 440.4R-04 committee recommendation, ISIS equation and CEIB-FIP code approach to evaluate the effective moment of inertia used in beam deflection. Furthermore, results from two experimental programs were used to validate the proposed analysis. The first experimental program tested a full scale Double-Tee beam (DT-beam) prestressed and post-tensioned with CFRP tendons, and was conducted at Construction Technology Laboratories, Skokie, Illinois. This beam is a replica of the beams used in the superstructure of the Bridge Street Bridge constructed over the Rouge River in Southfield, Michigan, USA. The second experimental program was conducted at Lawrence Technological University, Southfield, Michigan, USA for box beams prestressed with internally bonded and externally unbonded CFRP tendons to examine the behavior of these beams.Dept. of Civil and Environmental Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2006 .A23. Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3963. Thesis (Ph.D.)--University of Windsor (Canada), 2006