Corrosion effects in the structural design of metal fasteners for timber construction

Abstract

There has been growing recognition of the need for a more explicit consideration of material degradation effects in structural design. This article presents a procedure for the design of metal fasteners used in exposed timber structures that is suitable for use in modern reliability-based engineering design codes. The procedure is focused on the computation of the effective loss of structural section that is related to a specified service life. The fasteners are considered to be subjected to two types of corrosion: (1) the corrosion of exposed parts of the fasteners, where the corrosive agents are airborne salinity and pollution agents and (2) the corrosion of parts of the fasteners embedded in wood, where the corrosive agents are the wood acidity and preservatives. The corrosion of zinc and steel, and the effects of copper chrome arsenate preservative treatment are considered. The main design method, illustrated through a worked example in an Australian context, is applicable to most common types of mechanical joint in timber structures, but a special design procedure is required – and presented – for the shanks of bolts. The concept and format are applicable worldwide, when suitably modified according to local data and experience. Limitations and future research are suggested.