Reliability of Light-Frame Wall Systems Subject to Combined Axial and Transverse Loads

Abstract

Wood frame walls are essential subassemblies used to transmit roof, floor, wind, and seismic loads into lower stories and eventually into the foundation of light-frame structures. There has been some discussion and debate in recent years over appropriate system factors for use in the design of repetitive wall members, which typically are much smaller in the cross section than floor joists. In addition to having greater flexibility than floors, wood stud walls also may be subject to the actions of combined loads, and their load-sharing behavior may be significantly influenced by the presence of openings. As a precursor to evaluating system factors for design, this study investigated load-sharing and system effects in light-frame walls subject to combined axial and transverse loads. An analytical model was developed to account for partial composite action, load-sharing, two-way action, and openings in the wall system. The model consisted of two main components: A system model and a member model. The system model was a beam-spring analog model with spring stiffnesses obtained from the member model. The member model was a beam-column model which took into account partial composite action between the stud and the sheathing and possible end restraints. After validating the model using experimental test data from other studies, it was incorporated into a Monte Carlo simulation to evaluate the strength and reliability of light-frame wall systems subject to combined axial and transverse loads. Sensitivity studies were performed to investigate how system parameters affected the wall system strength and reliability. Critical load combinations were determined external to the reliability analysis. Reliabilities were then evaluated using a portfolio of representative light-frame wall systems designed according to current code provisions.