A Review of the State-of-the-Art International Guidelines for Seismic Design of Timber Structures

The timber construction industry is expanding rapidly, fuelled by a growing awareness of the importance of providing sustainable buildings and the advantages timber buildings can offer off- and on-site, such as pre-fabrication and speed of assembly. While this market is also spreading into highly seismic areas in both developed and developing countries, research into the seismic behaviour of timber is relatively behind, compared with more conventional materials such as concrete and steel. Several national and international structural design codes (such as EC8, CSA-086, ASCE7 and ASCE41), now contain behaviour/response modification factors for timber that allow the designer to make use of dissipative zones in timber connections to provide ductility and allow deformations. However, the guidance is still generally very limited and primarily focused on light frame buildings using plywood/OSB shear wall systems, with little consideration of more modern systems such as heavy timber structures and CLT. This paper provides an introduction to timber design in seismic areas, drawing on international codes, guidelines and published research to describe why timber has performed well historically, how a ductile response can be achieved in timber structures, and how one should approach seismic timber design. The paper then discusses the most common timber lateral load-resisting systems – light-frame, CLT, moment frame and braced frame – as well as a few less common ones and new technologies under development. Timber guidance in EC8, CSA-086, ASCE7 and ASCE41 is presented, and a few recommendations are made where gaps or potential areas of unconservatism in these codes were found. Because these codes are new and research is still limited in comparison with steel and masonry, structural engineers should supplement the guidance from these standards with other published research and general engineering and seismic best practice. The paper concludes with recommendations on modelling timber structures for seismic design, and areas of future research and possible code development.