Low-grade glued laminated timber beams reinforced using improved arrangements of bonded-in GFRP rods

This paper describes an experimental test programme which examines the strengthening in flexure of low-grade glued laminated timber beams (glulam) using bonded-in glass fibre reinforced polymer (GFRP) rods. Reinforcement configurations and arrangements previously not studied in the literature are reported on. The performance of unreinforced glulam beams, strengthened glulam beams using varying groove arrangements and different GFRP sized rods with single and double reinforcement was examined. The test results indicate that the geometrical arrangement of the routed out grooves is important and enhancements in the mechanical performance of the reinforced beams can be improved by reducing the effects of stress concentrations. The use of a number of smaller diameter rods per groove to increase the bond surface area proved to be of no advantage when reinforcing the beams. The unreinforced low-grade glulam exhibited linear elastic behaviour with brittle tensile failures in comparison to the nonlinear behaviour of the beams strengthened on their tensile face. Using a reasonable reinforcement percentage of 1.4% in the tension zone with circular routed grooves, mean stiffness enhancements of 11.2% and 13.9% for the global and local measurements were achieved respectively and a mean improvement in the ultimate moment capacity of 68% was achieved in comparison to the unreinforced glulam beams.