Interface Behavior in Fiber-Reinforced Polymer-Strengthened Beams Subjected to Transverse Loads: Maximum Transferred Force

Experimental results of externally bonded strengthened beams, available to date in the literature, have shown the existence of some types of brittle failures that involve the premature laminate debonding before reaching the design load. Since the design procedure to obtain the laminate area to strengthen a reinforced concrete element should avoid these premature failures, there is a need to understand the mechanism of the debonding process in order to prevent it. This paper studies the evolution of the debonding process through the propagation of an interfacial crack by using nonlinear fracture mechanics assuming a bilinear constitutive law for the interface. The transference of stresses between the laminate and the concrete through the interface is first analyzed in a simple case of a pure shear specimen. Later on, this formulation is extended to a general case of a beam subjected to transverse loads. As shown in the analysis performed, the transferred force between both adherents should be limited to a maximum value to prevent laminate debonding. This theoretical maximum transferred force has been obtained for each case studied and will be the basis for the development of a future design proposal.