Study of the Capability of Multiple Mechanical Fasteners in Roof-to-Wall Connections of Timber Residential Buildings

Abstract

One of the most critical connections in wood frame construction is that of the roof rafter and the top plate of the wall. This type of connection typically uses mechanical fasteners, such as metal straps or clips fastened with nails. Manufacturers base the allowable capacity of connections with one fastener on results of tests performed on such connections. However, it is assumed in current design practice that the capacity of a connection with two mechanical fasteners is twice the capacity of a connection with a single fastener. Implicit in this practice is the assumption that the connection’s capacity is proportional to the number of fasteners per connection joint. This approach, based as it is on testing a single fastener per joint, disregards the fact that the failure modes of a connection joint may depend on the number of fasteners per joint. This paper presents results of tests that establish this fact. The results, based on testing with three types of wood (spruce pine fir, southern yellow pine, and douglas fir), are used to modify the current design approach and propose a realistic relationship between the capacity of the connection joint and the number of fasteners in the joint. The results show that current design practices may overestimate the capacity of these joints and can therefore be the cause of roof-to-wall connection failures in extreme wind events. The research reported herein is limited to the case of unidirectional loading. Future research is planned on the case of multidirectional loading.