Shear and Flexural Strengthening of Glued-Laminated Timber Beams Using Externally Bonded Fiber-Reinforced Polymer Sheets

This study evaluated the effectiveness of using externally bonded fiber-reinforced polymer (FRP) sheets at increasing the load-carrying capacity of glued-laminated (glulam) timber beams. The investigation examined a range of strengthening configurations, including the use of U-wraps for shear strength enhancement and the combination of U-wraps and longitudinal FRP for combined shear and flexural strengthening. Parameters of interest in the study included the influence of fiber type (glass versus carbon), fiber orientation (uni- versus bidirectional FRP U-wraps), and fiber bond (bonded versus unbonded U-wraps). Consideration was also given to the influence of U-wrap anchorage on the retrofit performance. Retrofit performance was evaluated by testing eight large-scale glulam beams with a low shear-span-to-depth ratio (a/d = 2.39). Results of the study demonstrated that both the fiber orientation of the U-wraps and the bond between the FRP and wood impacted the effectiveness of the retrofit. Overall, the use of FRP U-wraps was found to increase the beam strength and ductility relative to the control beam by 1.2 and 1.7 times, respectively. The combination of U-wraps and longitudinal FRP sheets for flexural strengthening increased the beam capacity by up to 1.4 times the control beam. The results demonstrated that longitudinal FRP strains reached up to 7,000 µε, while strains in the FRP U-wraps exceeded 2,900 µε in some configurations. The distributions of the longitudinal and transverse strains in the FRP measured using distributed fiber optic sensors are also discussed.