Finite element analysis of unsupported metal plate connector areas of timber joints under buckling loads

Metal plate connected (MPC) joints are used to construct wooden roof and floor trusses that are built into residential and light commercial buildings in the U.S. To save time and money, the industry has changed its fabrication method to eliminate the custom cutting of members' ends that meet in the joints. The ends are now left square, increasing the amount of unsupported MPC area and greatly reducing contact area between members. The ultimate result is the increased transmission of load and stresses by the MPC with less lateral support from the joint members. The unsupported area of the MPC is more vulnerable to buckling under compressive loads. The Truss Plate Institute (TPI) published guidelines on the allowable amount of unsupported MPC but offered very little experimental or empirical validation of these guidelines.; A finite element analysis was employed to investigate the TPI guideline's validity. A simple right angle joint is modeled in the finite element analysis program, COSMOS. Joint models with four different unsupported MPC areas were created. The analysis included varying the MPC gauge for each unsupported MPC area. The models were in three dimensions, incorporated orthotropic mechanical properties, and model the MPC connection using per MPC tooth stiffness values.; The analysis demonstrated the importance of including orthotropic mechanical properties when modeling wood members. It also showed the need for further MPC research on a per tooth basis before larger scale analytical analysis is accurate. The study's result is the demonstration of increased load-bearing capacity by using thicker MPC gauges and decreasing the unsupported MPC area between joint members.