Effects of a Flexible Foundation on the Response of a Timber Shear Wall

Abstract

A parametric study was performed to determine the effect of flexible foundations on the response of timber shear walls. Timber shear walls, which typically consist of structural-use panels, such as plywood or oriented strand board (OSB), attached to a frame made from dimension lumber with dowel-type fasteners such as nails, provide resistance to lateral loading for many low-rise structures in North America. Research performed on shear walls has assumed that a wall is supported by a relatively stiff foundation, such as a concrete block wall, along the entire length of the wall. However, walls are sometimes supported by a relatively flexible foundation, such as a floor joist, which would alter the stiffness, and therefore the response of the wall. Research on flexible foundations is limited at best, and there is a string need to examine the behavior of shear walls on flexible foundations.

The study consisted of creating a shear wall numerical model, varying the conditions at the foundation of the model, and analyzing the model when subjected to both monotonic and dynamic loading for each foundation. The system modeled corresponded to a 2.4 m (8 ft) high by 3.7 m (12 ft) long shear wall supported by and parallel to a 7.3 m (24 ft) long joist with hold-downs at each chord of the wall. The joist was supported at each end, with one chord of the wall at an end of the joist and the other chord located at the center of the joist. Eleven joist cross-sections, with sizes determined based on deflection criteria ranging from L/180 to L/720, and a rigid base were included in the study, along with three different hold-down bolt sizes, for a total of thirty-six different foundations. The wall model was analyzed using WALSEIZ1, which is a modified version of the finite element program WALSEIZ (White and Dolan, 1995). Maximum displacements, internal forces, and maximum load were recorded when the model was subjected to monotonic loading, while the maximum displacements and base shear were recorded when the model was subjected to dynamic loading. Results from the study were examined to determine if modifications to the current design practices should be considered.