Study of the flexural behavior of reinforced concrete beams strengthened by externally bonded fiber reinforced polymeric (FRP) laminates.

Abstract

The objective of this study is to develop a fundamental understanding of the flexural behavior of Reinforced Concrete (RC) beams strengthened using externally bonded Fiber Reinforced Polymeric (FRP) laminates. An experimental program was carried out where reinforced concrete beams were fabricated, strengthened with Carbon Fiber Reinforced Polymeric (CFRP) laminates, and tested. In addition, material characterization and interface bond tests were conducted. Also, an analytical program was carried out to model the full response of beams under bending, using a mechanics approach. The interface between the FRP laminate and concrete was modeled by two different approaches to define the stress distributions at this level. Failure of the concrete cover was modeled using an energy approach. It was found that interfacial bond failure on the concrete side is the most important type of failure of reinforced concrete beams strengthened by externally bonded FRP laminates. The interfacial bond strength is adversely affected by environmental conditions, such as freeze-thaw cycles. The proposed analytical model, based on equilibrium and strain compatibility, was able to accurately predict failure modes, such as concrete compression crushing and FRP tensile rupture. It was observed that a uniform shear flow assumption is acceptable as an approximate model interfacial bond failure. The predicted magnitude of the stresses at the interface epoxy level is significantly reduced when the material nonlinearity is taken into account. The onset of the interfacial failure is limited by an upper and a lower bound. The strength of the adhesive layer to withstand a biaxial state of stresses (tension, shear) represents the upper bound. This failure does not seem to occur for the current materials used. The strength of the concrete under biaxial state of stresses (tension, shear) represents the lower bound. The methodology proposed in this study, which takes into consideration fracture energy and bonded area of FRP laminate, leads to a reasonable prediction of the occurrence of concrete cover failure, or tooth failure.