Investigating the Performance of Straight and Bent GFRP Bars as Flexural Reinforcement for Glulam Beams

Abstract

The heightened interest in using wood as a sustainable building material contributed to an increased demand for glued-laminated timber (glulam). Despite this, fundamental research is required on how to rehabilitate and retrofit deficient structural wooden members to extend the service life of the structure. The research focuses on the effects of reinforcement configurations consisting of glass-fibre reinforced polymer (GFRP) bars on the flexural behaviour of glulam beams. Of particular interest are the effects of reinforcement length, adhesive type, and knurling on the failure modes of the reinforced members when compared to unreinforced glulam. A total of eighteen pullout specimens were tested to investigate the effects of adhesive and knurling patterns on bond strength, and fourteen full-scale glulam beams were tested to failure under four-point static bending, including four unreinforced and ten GFRP-reinforced. The pullout test results showed that the texture and density of an adhesive had a critical role on the overall behaviour with improved behaviour in specimens using a fluid density in comparison to those with dense. The addition of GFRP reinforcement to the glulam beams contributed to an increase in strength, failure displacement, and stiffness by factors ranging between 1.16 – 1.30, 1.04 – 1.24, and 1.13 – 1.18, respectively, in comparison to unreinforced glulam irrespective of the failure mode obtained. The effects of reinforcement length and termination point showed that the change from short to long bars resulted in improvements in maximum resistance and stiffness by factors of 1.10 and 1.19, respectively, for the bent bar reinforced specimens, and insignificant improvements for the straight bar reinforced specimens. Additionally, the change from straight to bent bars resulted in improvements in maximum resistance and stiffness by factors of 1.06 and 1.03, respectively, for the specimens with longer lengths of bars, and insignificant improvements for the specimens with short lengths of bars. The addition of knurling in the full-scale GFRP-reinforced beams resulted in increases of 1.07 and 1.03 for the maximum resistance and stiffness, in comparison to beams without knurling. Additionally, a change in failure mode from shear to flexure was observed with the addition of knurling. A material model was developed to predict the flexural behaviour of unreinforced and GFRP-reinforced glulam beams, and the two proposed approaches were shown to generally captured the overall behaviour with a tendency to overpredict displacements at initial failure. Finally, the improvement in tensile failure strains in flexure due to the reinforcement was not observed to be present due to the mixed failure modes of shear and flexure. Strains from the digital image correlation system were observed to be lower than those measured by localized strain gauges, suggesting that measuring strains over a large area is critical.