Investigations on structural-sized GLT beams reinforced with steel and FRP composite bars: experimental tests and nonlinear numerical approach

Abstract

The paper presents experimental and numerical investigations on structural-sized glued laminated timber beams made of coniferous wood with different reinforcing bars configurations (steel, BFRP and GFRP). Thirty-nine specimens were analysed in a four-point bending testing scheme. The highest improvements in stiffness (23.9% and 38.9%) and ultimate load-carrying capacity (13.6% and 29.4%) were observed for beams reinforced with steel bars. However, plasticisation in the steel occurred before wood failure. Beams reinforced with BFRP bars showed intermediate improvements in stiffness (8.2%, 14.2%) and ultimate load (9.6%, 17.5%), followed by those with GFRP bars (5.1% and 9.0%, and 6.2% and 10.7%). Most times, final failure occurred in the tension zone because of cracking at wood defects such as knots and was preceded by ductile failure in the compression zone. The entire experimental programme enabled to validate the FE model, based on the orthotropic Hill yield criterion for wood and cohesive surface for the adhesive behaviour. The proposed FE model shows the ability to predict accurately the failure load and the mid-span deflection. In addition, it can reliably forecast failure modes in both compression (upper lamella) and tension (lower lamella), as well as shear failure because of excessive shearing stresses in the adhesive. The model also supports the analysis of different reinforcement configurations and materials within the tension zone, accounting for varying wood properties.