Reinforcement of softwood beams using unglued composite laminates

This article describes aspects within an experimental programme aimed at improving the structural performance of solid fir-wood beams reinforced with unglued composite laminates applied on the beam tension zone. Softwood is from gymnosperm plants and it is the basis of approx. 85% of the world’s production of wood elements. Fir wood is characterised by low weight density, low compression strength and high level of defects, is likely to distort when dried and tends to fail in tension due to the presence of cracks, knots or grain deviation. The addition of modest ratios of FRP composite reinforcement can suppress tension failure in beams. However the application of epoxy adhesives presents problems of reversibility, compatibility with timber, durability and poor performance at temperatures higher than 60-80°C. The study of failure modes, particularly in tension-reinforced beams, is the main focus of this paper. The experimental campaign is dealing with the evaluation of bending strength and deformation properties of a significant number of un-reinforced and reinforced beams strengthened with unbonded carbon (CFRP) plates or basalt (BFRP) spikes. Increases of beam capacity, bending strength and of modulus of elasticity and analysis of failure modes were measured and discussed.