Investigating the Performance of Reinforced Glulam Beams Under Shock Tube Induced Blast Loading

Abstract

Glulam beams are widely used in timber construction due to their strength and versatility; however, they are prone to brittle failure under flexural loading, particularly in the tension zone. This study explores the effectiveness of Near-Surface Mounted (NSM) reinforcement using steel rebars and plates as a retrofit strategy to improve the structural performance of glulam beams, especially under extreme dynamic loads such as blast events. The reinforcement was applied by embedding steel elements into pre-cut grooves along the tension face of the beams and bonding them with epoxy. Three reinforcement ratios (0.8%, 1.6%, and 2.5%) were examined using 10M, 15M, and 20M rebars, respectively. In addition, steel plates were employed with a reinforcement ratio equivalent to the 15M configuration. Variations in plate positioning were investigated to assess the impact of horizontal versus vertical placement, offering practical solutions where side access to beams is limited.

A total of sixteen reinforced beams were tested under both static four-point bending and dynamic blast loading, the latter simulated using a shock tube device at the University of Ottawa Structural Laboratory. The experimental results revealed that NSM reinforcement significantly enhanced the load-carrying capacity, stiffness, and ductility of the beams. Strength increases ranged from 23.0% to 83.3%, while stiffness improvements were between 7.8% and 38.1%. Ductility ratios improved substantially, ranging from 1.1 to 7.2, and failure modes transitioned from brittle tensile rupture to more ductile compression crushing, indicating enhanced energy absorption and deformation capacity.

The epoxy bonding system showed excellent performance, with no significant debonding or slippage observed during testing, except near ultimate failure. While some plate-reinforced specimens exhibited slip failures at the wood–epoxy or plate–epoxy interface, overall bonding integrity was maintained throughout the critical stages of loading. In dynamic tests, the reinforced beams exhibited higher resistance compared to unreinforced controls, confirming the potential of NSM systems for blast-resistant timber design.

An analytical model based on layered-section analysis was developed to simulate the behavior of the reinforced beams. The model accounted for elastic, inelastic, and plastic hinge stages and treated the steel reinforcement as concentrated elements. Analytical predictions demonstrated strong agreement with experimental data, accurately capturing trends in strain, displacement, and force response.

Overall, this research confirms that NSM reinforcement using steel rebars and plates is an effective and practical technique for improving the structural performance and blast resistance of glulam beams. The results contribute valuable insights into the design, application, and modeling of timber reinforcement systems under both static and extreme dynamic loading conditions.