Strengthening Glulam Beams with Steel and Composite Plates

The limiting factor when it comes to design timber structures is often the stiffness properties of timber products. The stiffness requirements in serviceability limit state, both short-term and final deformation especially in horizontal members, is a factor that often makes it necessary to increase the dimensions of the member. This cause increased material use and thus higher production costs. In this paper, both the results from an experimental study and the results from the analytical modelling are presented. In the experimental investigation, nine glulam beams strengthened with bonded steel plates or CFRP-laminates were tested to failure. The effect of various geometrical and material properties for the plates was investigated, as well as strengthening with different amounts of laminates on the tension and compression side. A simple analytical model for wood with plasticity of the compression was developed to analyse the behaviour of the beam. All types of reinforcement resulted in higher stiffness as well as higher ultimate moment capacity. The experimental results agreed very well with the proposed models for calculating both stiffness and moment capacity of reinforced beams