Modeling of Metal-plate-connected Wood Truss Joints

Abstract

A commercially available, three-dimensional finite-element analysis software was used to model the load- displacement behavior of metal-plate-connected (MPC) joints in wooden trusses. Model features included consideration of material properties, teeth-to-grain-to-direction-of-force orientation, wood-to-wood interaction, and gaps between wood members. To simulate wood-to-plate interaction, the main feature of the model, each tooth of the metal plate is represented by one set of three spring elements. Each spring element accounts for tooth-wood behavior (stiffness) in one major plate direction: parallel to slots, perpendicular to slots in the plane of the plate, and perpendicular to the plane of the plate. For each element, nonlinear load-slip (stiffness) curves are defined based on tension splice joint tests at various teeth-to-grain orientations. One advantage of the spring-element-based approach is that once incorporated in the model, the per-tooth stiffness need not be adjusted for different loading conditions applied later to the joint model The load-displacement (L-D) results from the model compared very well to the experimental results from tensile and bending tests of splice joints with several different teeth-to-grain orientations. For the investigated plate size, the governing factor for joint behavior was the plate-wood interaction (spring elements). Several possible model simplifications were investigated. Models with lumped teeth properties predict joint L-D behavior reasonably well. Keywords. Wood engineering. Trusses, Joints, Metal-plate-connectors, Modeling, T he behavior of metal-plate-c onnected (MPC) joints in service is complex and difficult to analyze without experimental data and validation. Better analyses of joints contribute to an understanding of the overall behavior of MPC trusses, and could lead to improvements in current design practices, and in turn improved cost effectiveness and safety of engineered trusses. To date, one of the most advanced methods for determining properties of MPC joints was a model developed by Foschi (1979), who used a three-paramete r equation to characterize the nonlinear load-slip behavior of connections. The basic load-slip properties associated with the entire wood-member areas covered by the plate are determined from the four tests defined by the Canadian Standards Association (1980). Foschi's connector model was implemented in a computer program Structural