C O N T E X T 1 3 4 : M A Y 2 0 1 4 39 RICHARD HARRIS, WEN-SHAO CHANG, PETER WALKER and JON SHANKS Research into traditional timber joints Engineers’ proper understanding of the performance of timber joints should help ensure that traditional methods can be used in repairing oak-frame construction. The most common form of joint in traditional oak-frame construction is the all-timber, oak-pegged morticeand-tenon joint. Although this is the stock-in-trade of the traditional carpenter, there has been little research work to investigate the joint’s engineering behaviour. Why so little interest in this important topic? In Japan, where there are many historic timber buildings, there is a considerable body of research work investigating the engineering performance of buildings. Earthquakes do not respect the historic value of buildings, so it is important to have modern methods of assessment to preserve human safety. For example, the joints of Kiyomizu Dera in Kyoto have been the subject of much research work to determine their strength and performance under seismic loads (Chang et al 2009). In the UK we are fortunate not to have serious earthquakes. In most situations the design and fabrication of joints in traditional timber frames can be left to carpenters, who will size them by means of well-established principles of minimum size, spacing and proportion. Kiyomizu Dera Temple, Kyoto, and detail on the following page However, there are situations where it is useful to know a traditional joint’s capacity. This may be in assessing a building for change of use to determine long-term safety, in making new extensions or repairs using a replication of historic detail, or in structures that draw on historic techniques in contemporary building design. For whatever reason, it is clear that having an engineering assessment of mode of failure and mechanical performance can be very useful. Prior to a study at the University of Bath, culminating with a PhD thesis (Shanks and Walker 2005), the majority of pegged all-timber connection research had been carried out in the US (Brungraber 1985, Mackay 1997, Bulleit 1999, Daniels 1999, Scholl 2000). The Shanks work developed a new understanding of the mode of failure of traditional mortice-and-tenon joints and provided information on the mechanical properties. Being anisotropic (having different values when measured in different directions), timber is a challenging material. Traditional joints have evolved over the centuries to resist loads efficiently. When working on
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