Analytical and experimental analysis of timber–concrete composite beams: Influence of connection system and fiberglass reinforcement

The use of timber–concrete composite structures offer several advantages, particularly from an environmental standpoint, as they result in lower environmental impacts compared to others structural solutions. In addition, timber–concrete composite beams can be strengthened with fiber reinforced polymers (FRP), thereby increasing their flexural strength. In this context, the present study provides an experimental investigation of factors influencing the behavior of timber–concrete composite beams, specifically the connection system and the use of FRP. Furthermore, the experimental results were compared with predictions obtained from an analytical model available in the literature. Two connection systems were considered: one consisting of inclined steel bars and another consisting of inclined steel bars associated with triangular notches. Glass fibers were used as the FRP reinforcement. The composite beams were subjected to three-point bending tests in order to evaluate load–deflection behavior at mid-span, load–slip response between timber and concrete, strain distribution across the cross section, and failure modes. The results indicated that both the connection system and the use of FRP influenced the failure mode, ductility, and interfacial slip between the constituent materials. A 2.5% reduction in the ultimate load was observed for the beams with notched connections compared with those connected exclusively by steel bars, whereas, for the beams with inclined steel bars, the use of FRP increased the maximum load capacity by 22.6%. In beams with notched connections, the concrete exhibited only compressive strains, while the timber exhibited both tensile and compressive strains. For the beams with RB connections, both the timber and concrete components exhibited tensile and compressive strains in the unreinforced specimens, whereas in the GFRP-reinforced specimens, the concrete exhibited compressive strains, while the timber component exhibited both tensile and compressive strains. For the beams investigated, the experimentally determined service stiffness was 3–17% higher than that predicted by the analytical model.