Monotonic and cyclic behaviour of wood frame shear walls for mid-height timber buildings

Abstract

The Chilean forestry industry has a significant presence in the economy of the country. Due to pollution problems and the high seismicity of the region, timber is a suitable material for new buildings. However, because of cultural customs and high demands of regulations, nowadays it is difficult to construct buildings higher than three stories in Chile. However, several international projects have shown that is feasible to construct mid-height timber buildings. Sturdy end studs and strong hold-downs are needed in mid-height wood buildings (up to 6 stories high) to resist large vertical and horizontal loads. However, design parameters provided by current seismic design provisions for those shear walls do not consider the effects of sturdy end studs and strong holddowns in lateral strength and stiffness of the walls. In order to address this issue, a multidisciplinary team at the Catholic University of Chile has conducted an extensive experimental and numerical research program. This paper presents the results of seventeen in-plane monotonic and cyclic shear tests in wood frame shear walls of different lengths (1200, 2400 and 3600 mm) and 2470mm height. The walls have five 2×6″ end studs, strong hold-down anchorages and standard 11.1mm structural OSB panels (1200×2400 mm) on both faces of the wall and with nails in the edge of the OSB panels spaced at 50 or 100 mm. The main objectives of this research are to evaluate the seismic response of these shear walls and to assess the current code expressions applied to shear walls with sturdy end studs to be used in mid-height timber buildings. The results show that, while cyclic loads reduce the monotonic shear strength of walls, cyclic loads do not influence the ultimate displacement and stiffness. The main benefits of a smaller nail spacing are the increase of the strength and delay of stiffness degradation. The unit shear was influenced by wall length: 1200mm walls presented a better unit shear capacity than 2400 and 3600 walls, and there were not observable differences between 2400 and 3600mm walls. The characteristic damping of the walls varied between 7 and 10%. Finally, the current design provisions underestimate the shear strength and overestimate the stiffness of walls to be used in mid-height timber buildings.