Comparison of Lateral Load Performance of Light Wood Diaphragms Built with Sawn Lumber and Wood I-Joists

Abstract

Diaphragm design provisions in North America were originally developed based on the performance of diaphragms constructed with sawn lumber framing members. Although these design guidelines have been applied to diaphragms built with wood I-joists, questions were raised as to whether they are equally applicable. More recently, the height limit of light wood frame buildings was increased across North America from four to six stories, leading to the need for high capacity diaphragms. This change raises further questions on the validity of using existing lumber diaphragm design provisions for diaphragms built with wood I-joists. In this study, tests were conducted to investigate the lateral load resistance of diaphragms built with wood I-joists by comparing with those built with solid sawn lumber joists. Since the lateral load resistance of wood diaphragm is highly dependent on the behavior of their individual nail connections, tests were first performed to examine the strength of nailed joints with point-side penetration into solid sawn lumber and flange of wood I-joists. After that, small-scale diaphragm tests were conducted to investigate the effect of multiple-row fastening on potential diaphragm performance in relative terms. Based on these results, it is tentatively recommended that the fastener row factor for diaphragms built with I-joists can be obtained by applying a 10% reduction to the corresponding value for sawn lumber diaphragm.