Combined Shear and Wind Uplift Resistance of Wood Structural Panel Shearwalls

Abstract

Shearwalls constructed with wood structural panels, such as plywood and oriented strand board (OSB), have been used to resist combined shear and wind uplift forces for many years in the U.S. For example, the Southern Building Code Congress International (SBCCI) published SSTD 10, Standard for Hurricane Resistant Residential Construction, in 1999, which provided the shear resistance table for wood structural panels. When wood structural panels are used in combined shear and wind uplift, SSTD 10-99 also tabulated the wind uplift resistance of wood structural panels with a minimum thickness of 12 mm (15/32 in.) when used in conjunction with the shear resistance table. Working with researchers at the National Home Builders Association Research Center (NAHB RC), Norbord Industries sponsored full-scale combined shear and uplift tests, showing that the cross-grain bending of the bottom plate, which is a brittle failure mode, could be avoided by using 5.8 x 76 x 76 mm (0.229 x 3 x 3 in.) plate washers with anchor bolts. The NAHB RC tests were conducted in lateral shear and tension (uplift) separately, and the effect of combined shear and uplift was evaluated based on an engineering analysis. After reviewing the NAHB RC study, APA and Norbord jointly conducted full-scale combined shear and wind uplift tests at Clemson University to gather more data on this subject. The test setup at Clemson University was capable of increasing the shear and wind uplift forces simultaneously until failure was reached by using a pulley system controlling the bi-axial forces in both lateral and vertical directions. Results of the Clemson study were used to support the development of engineering standards and changes to the national building code in the U.S., and are reported in this paper. In 2007, APA constructed new combined shear and wind uplift test equipment that is capable of bi-axial loading in both lateral and vertical directions with independent but synchronized loading mechanisms. The vertical load can be applied as either an uplift force or a downward gravity load. Research results using this new equipment are utilized to enhance the understanding of the design on the bi-axial combined shear and wind uplift. This paper describes the latest finding from this research.