Flexural Strengthening of Glued-Laminated Timber Beams Using Externally Bonded FRP Sheets

The ability to retrofit and repurpose existing infrastructure creates a significant opportunity for more sustainable building practices in our changing climate. One advanced retrofitting technique is the use of externally bonded fibre-reinforced polymer (FRP) sheets, which has proven to be an effective method to increase the capacity of existing concrete, steel and masonry structures, and well-established techniques to design FRP retrofits have been incorporated into modern design codes (e.g. ACI 440 or CSA S806). However, research pertaining to the use of FRP sheets to retrofit timber structures remains limited, and as such, guidelines for the use of FRP to retrofit timber structures have not been incorporated into modern design codes. The aim of this research is to gain insight into the ability of externally bonded FRP sheets to increase the flexural capacity of glued-laminated (glulam) timber beams. A series of experiments are carried out on flexurally dominant glulam beams tested in four-point bending. Design approaches for different failure modes of potential retrofits with increasing layers of flexural FRP are assessed and an appropriate retrofit is chosen. Results of the study demonstrated that the FRP retrofitted specimen had an increase in flexural strength of 47.5% when compared to the control. Furthermore, the retrofit successfully changed the failure mode from a brittle tension failure to a ductile compression failure.