Analysis of interfacial stresses on narrow beams strengthened by FRP straps with a side anchorage system

Interfacial stress concentrations at fiber-reinforced polymer (FRP) ends can easily cause premature debonding failure of FRP-strengthened beams. To solve this problem in narrow beams, a hybrid strengthening method was proposed in our previous study, but the theoretical stress analysis was lacking due to the complexity at the anchorage zone. In this study, the interfacial stresses of the hybrid strengthened beam were initially analyzed by decomposing it into a purely bonded beam under three different effects, including the load on the beam, the tensile force at the end of the FRP strap released from anchor plates and a pair of eccentric forces induced by the side anchorage system towards the midspan. By summing the special solutions of the three cases, the expressions for the total interfacial stresses of a hybrid strengthened beam were determined. Moreover, a formula for the shear stiffness of the side anchorage system was proposed, in which the side plate and the bolt were compared to a deep cantilever beam and an elastic foundation beam, respectively. Finally, a finite element model was developed to verify the applicability of the proposed theoretical model. The theoretical and simulated results were in satisfactory agreement for a hybrid strengthened beam.