Comparative analysis of the shear response of RC beams strengthened with externally applied and near-surface mounted timber plates

Abstract

This research experimentally and numerically investigates the feasibility of using low-cost timber plates to enhance the shear behavior of reinforced concrete (RC) beams. Seven simply supported beams with a shear span-to-depth ratio (a/d) of 1.8 were tested under three-point bending, including one control specimen and six strengthened beams. Two strengthening techniques, externally bonded (EB) and near-surface mounted (NSM), were examined using three attachment methods: epoxy only, 10 mm diameter anchor bolts only, and a combination of both. A 3D finite element model (FEM) was developed in ABAQUS V2017 to evaluate the influence of increasing the a/d ratio from 1.8 to 3.1 on the ultimate load, stiffness, and toughness of the strengthened beams. results showed that timber plates, regardless of the strengthening technique, effectively restricted the propagation of the main shear crack and diverted it into multiple secondary cracks. Externally bonded specimens achieved higher ultimate loads than NSM specimens due to the absence of groove-induced reductions in the concrete section. The use of anchor bolts, either alone or in combination with epoxy, prevented debonding and produced the highest ultimate loads, reaching 91 kN and 92 kN, respectively, representing increases of 21.3 % and 22.7 % over the control beam. Both attachment methods also exhibited stiffness improvements of 10.8 % compared to the control beam. Numerical analysis indicated that increasing the a/d ratio from 1.8 to 3.1 led to reductions in stiffness of 43 %-47 %, ultimate load of 18 %-30 %, and toughness of 7 %-30 %. • The shear behavior of RC beams strengthened with timber plates was investigated. • Two strengthening techniques were considered: external strengthening and NSM technique. • Three different attaching methods were used: epoxy alone, anchor bolts alone, or a combination of both. • A Finite element model was developed to examine the effect of the shear span-to-depth ratio. • Using anchor bolts alone or in combination with epoxy exhibited the highest ultimate load.