Failure of Wood Connections and the Evolution of Connection Design

Wood has been used as a construction material long before concrete and steel were available as structural materials. Wood is easy to work with and can be used for many different types of framing. Wood trusses have been used for long span roof framing in the United States since the 1800's. Over time the material, wood, has remained largely unchanged; however, the connections have evolved as well as the standards to which they are designed. Before the 1850's, truss connections typically consisted of mortise and tenon joinery. These connections make good use of the inherent strength of the wood members with little or no reliance on fasteners or engineering analysis. During the late 1800's and early 1900's these connections evolved into side lapped joints with steel bolts which bear on the wood in order to transfer shear through the joint. During the mid 1900's the invention of shear plates and split rings allowed joint forces to be transferred with fewer bolts. During the late 1900's pressed plate connections were developed which permited wood trusses to be readily pre-fabricated. In addition to the evolution of the connections, advancements in the testing of materials and creation of design standards have evolved into what they are today. This paper provides examples of actual woods connection failures from the different time periods mentioned above and discusses the cause of the failures. Also provided is a comparison of historic references versus modern design methods for the evaluation of the failed connections.