Seismic design of timber structures

Timber buildings have a good reputation when subjected to seismic events. Experience from North America and Japan states that wooden buildings can resist catastrophic earthquakes with minimal damage. Many modern timber buildings have resisted even without any visual signs of damage. The advantage of wooden buildings is based on low self-weight, ductile joints and in general very regular building geometry. An effective way to design for lateral loads, including seismic loads, in residential wooden houses, is the use of plywood panels in shear walls. These shear walls have high lateral force resisting capacity and the joints are in general very ductile. The ductility of the joints is very critical as it affects also the level of shear force to which the wall is subjected. The high performance of plywood shear walls is based on the ductility and energy dissipative characteristics of nailed or screwed joints on plywood in shear. Based on previous experience, modern design codes perform well for earthquakes. In the European region, Eurocode 5, Design of timber structures, and Eurocode 8, Design provisions for earthquake resistance of structures, are new design codes and these may be applied for example in the exportation of wooden buildings and building know-how to seismic areas. This report explains the use of Eurocodes in the seismic design of wooden residential buildings. Wooden buildings are usually regular, both in plane and in height, and in such case, a simplified modal response spectrum analysis may be used. The body forces created by the ground acceleration on the building are converted to a base shear force imposed to both principal directions. EC8 gives the methods to calculate this shear force. The structures resisting these lateral forces such as shear walls, floor diaphragms and anchorages are then designed against this base shear force.