Finite Element Modeling of RC Beams Strengthened with Prestressed NSM-CFRP Strips Subjected to Severe Environmental Conditions

摘要

A nonlinear 3D Finite Element (FE) analysis was performed to predict the post-exposure load-deflection responses of Reinforced Concrete (RC) beams strengthened in flexure using prestressed Near-Surface Mounted (NSM) Carbon Fibre Reinforced Polymer (CFRP) strips. Five RC beams (5.15 m [16.90 ft] long) were modeled including one un-strengthened control beam and four beams strengthened using NSM-CFRP strips prestressed to 0, 20, 40, and 60% of the ultimate CFRP tensile strain. The beams were severely deteriorated due to applying accelerated environmental conditions consisting of 500 freeze-thaw cycles: three cycles per day between +34°C [93°F] to -34°C [-29°F] with fresh water spray for 10 minutes at a rate of 18 L/min [4.8 gallon/min] at temperature +20°C. The accelerated environmental conditions used in this study equivalent to 0.46 year of exposure inside a chamber, corresponds to a minimum lifetime of 12.8 years in Canada. Simultaneously, each beam was subjected to a sustained load equal to 62 kN [13.9 kip] representing 47% of analytical ultimate load of the non-prestressed NSM-CFRP strengthened RC beam. The degradation which occurred in the concrete properties, concrete-epoxy interface, and steel reinforcement was considered in the FE model. Also, debonding at the concrete-epoxy interface was simulated by assigning shear and normal fracture energies and the prestressing was applied to the CFRP strip using an equivalent temperature. The FE model was validated with the experimental test results. However, the experimental and numerical load-deflection curves were comparable up to yielding but after yielding, the predicted curves were not in good agreement with the experimental ones.