Partial Factor Approach to Repetitive-Member System Factors

Abstract

Beneficial system behavior has been acknowledged in the design of repetitive-member systems. Current design specifications for wood (both National Design Specification and LRFD) permit the use of a repetitive-member factor to account for load-sharing or redistribution of load between framing members and partial composite action. The factors, however, were developed based on a simple statistical model rather than a more rigorous or comprehensive analytical study. The paper reports on a study to investigate load-sharing and system effects in light-frame wall systems and evaluate system factors for codified design that rationally account for load sharing and other system behavior. An objective at the study was to develop system factors that could be used in the design of individual wall members, much as repetitive member factors are used in the design of parallel-member floor and roof systems. Wall studs typically are much smaller in cross section than floor joists. In addition to having greater flexibility than floors, wood stud walls may be subject to the actions of combined loads and their load-sharing behavior may be influenced significantly by the presence of openings. A single system factor may, in fact, not be adequate to account for a wide range of system configurations, loading types, and so forth. This paper presents a new framework based on partial system factors to account for different system effects in parallel-member wood systems.