Performance of Post-Frame Shear Walls with Wood Plastic Composite Skirtboards Subjected to Monotonic Racking Loads

Abstract

Shear walls in post-frame buildings are commonly constructed with timber posts and horizontally framed wall girts. The bottom wall girt, called the skirtboard or splashboard, is typically pressure preservative-treated (PPT) due its location near the ground. Wood plastic composite (WPC) lumber is an environmentally benign alternative to PPT lumber, and WPCs avoid the copper-rich chemical formulations found in PPT lumber that potentially accelerate the corrosion of the steel panels and fasteners. WPC products have mechanical properties different from those of lumber, so testing is required when substituting WPC products for PPT lumber in post-frame shear wall assemblies. In this study, a commercially available WPC product and PPT lumber were used as skirtboards in two common framing configurations of post-frame endwalls to evaluate possible effects on shear strength and stiffness. The study found that two 38 × 140 mm WPC boards can be substituted for a single 38 × 235 mm PPT board without significantly affecting the strength or stiffness of the shear walls. A high-density polyethylene WPC formulation was chosen for this study due to its relatively low modulus of elasticity as compared to other commercially available WPC formulations (e.g., using polypropylene or polyvinyl chloride). No significant buckling of the WPC members was observed during the tests. The dominant failure mode of the shear walls was buckling of the ribbed steel sheathing. It should be noted that this study only included a relatively limited sample of two wall constructions. Additional testing is recommended for wall constructions and materials not studied herein.