Metal Plate Connection Failures in Wood Trusses: Lessons Learned from Damage Investigations

Abstract

Metal plate connected (MPC) wood trusses are a popular structural framing system used in floors and roofs often for residential and light commercial construction. In the past several years, the authors have investigated multiple occurrences of failures of MPC parallel chord wood floor trusses related to large gatherings inside private dwelling units as a result of excessive occupancy conditions, and of MPC parallel chord wood roof trusses due to snow accumulations. The failures observed include MPC plate deformations; connector plate teeth partially or fully pulling out or separating away from the structural wood elements; or some combination of both conditions. Fortunately, these failures did not lead to catastrophic collapse. However, in several cases, they placed occupants in dangerous situations, and the repair and remediation resulted in a wide range of economic losses. In each case, the authors studied the conditions associated with the probable loads imposed on the truss framing that led to the structural and performance failures. This paper will present the reader with observations of typical patterns of MPC wood truss connection failures. In addition, discussion will include lessons learned from several case studies, a review of the event loading conditions associated with each case, a discussion of the observed MPC failure relative to the loads imposed, and recommendations for when investigating similar cases in practice.