Modification of timber joint performance through selective epoxy addition

A study was undertaken to investigate the performance enhancement of two innovative connection systems useful for timber frame and other building construction applications. Timber connections included the Timberlok™ system developed by Green Mountain Precision Frames and a European fastener system distributed by Bulldog-Simpson. Both joinery methods rely on bolts for load transfer as opposed to the more traditional practice of timber frame joinery. A primary study objective was the investigation of epoxy addition to improve mechanical behavior. The devised epoxy treatment was believed to be an inexpensive approach to improve upon assembled timber joint performance. Specifically, the treatment involved the selective incorporation of an epoxide resin relative to the installed bolt dowel within the side member attachment. Side-to-main glulam member specimens were fabricated as controls for comparison to epoxy-treated groups with subsequent loading evaluation through axial tensile (withdrawal) and lateral (shear) test conditions. For testing purposes, southern pine and red maple glulam material were fabricated into the timber joinery specimens for subsequent experimental trials. Performance properties measured included determination of joint stiffness and 5 percent offset load (P5%) values. The epoxy fill treatment was found in most cases to be statistically significant to enhance joint properties. One exception was for Timberlok with no statistical difference between epoxy-treated and the control group specific to the P5% mean value corresponding with the lateral resistance trial data. This research shows selective epoxy addition can be successfully incorporated with minimum difficulty for beneficial modification of joint performance.