Critical Crack Lengths in FRP Reinforced Glulam Beams

Tension reinforcement of glued-laminated (glulam) timber beams has been shown to be an effective way to utilize lower grade wood in structural applications. Fibre reinforced polymer (FRP) composites are a particularly good reinforcement because they can be fabricated to be compatible with the compliance properties of the wood substrate. While the reinforcement has been shown to be effective at improving strength and to some degree stiffness, there is a concern that long-term exposure to moisture and freeze-thaw cycles could lead to some delamination between the wood and the reinforcement. This is a particularly important issue when reinforced beams are used as bridge girders, as environmental exposure can be severe. In order to make quantitative assessments of the effects of these potential delaminations, a laboratory study of mixed mode fracture toughness was combined with numerical simulations of in-service load conditions. The goal was to make reasonable estimates of allowable delamination sizes for inservice conditions.