Strengthening of glued-laminated timber beams using externally bonded fiber reinforced polymer sheets and near surface mounted reinforcement

This study examines the use of externally bonded fiber reinforced polymer (FRP) sheets and near-surface mounted (NSM) reinforcement to improve the flexural strength of glued-laminated (glulam) timber beams. Distributed fiber optic sensors (DFOS) were used to evaluate the distribution of strains over the length and depth of the beams as well as for quantification of the maximum strains in the reinforcing materials. The influence of FRP fiber type (glass or carbon), number of FRP layers, FRP anchorage detailing, and NSM bar type on flexural stiffness, strength, and ductility was assessed. NSM materials for flexural strengthening included both steel and titanium rebar which is a novel solution that, similar to FRP, is light-weight and corrosion-resistant. The results showed that the use of externally bonded FRP sheets on the tension side can promote a compression failure, avoiding brittle tension failure or FRP debonding and result in improvements in stiffness and strength of up to 160 % and 156 %, respectively when compared to the control. The addition of NSM reinforcement in the compression region was found to result in further increases in the beam flexural stiffness and strength by up to 248 % and 230 %, respectively when compared to the control. The distribution of strain and maximum strain achieved in the wood, FRP, and NSM reinforcement are discussed in the paper.