Web Crippling Strength of Sigma-Shaped Cold-Formed Steel Studs Subjected to Axial Load

Abstract

Load-bearing light steel framing (LSF) systems have gained good acceptance to the low to mid-rise construction market in the U.S. in recent years. This construction market covers a wide range of building usage, including apartment and office buildings, hotels, and schools. For years, standard C-shaped metal studs have been the only option for designers and contractors when selecting a cross-section for load bearing studs. As design loads for the studs get larger with heavier floor systems or at lower levels of mid-rise buildings, designers have been required to either use multiple (built-up) C-shaped studs or switch to structural steel members. An alternative to the standard shapes, although seldom found in the U.S., is the sigma-shaped section, but this shape is primarily used as a roof purlin in Europe. The Steel Network, Inc. of Raleigh, North Carolina recognized the potential of this section for use within a LSF system and developed the SigmaStud. A testing program was developed for the SigmaStud and testing was conducted at North Carolina State University's Constructed Facilities Laboratory (CFL). Presented are the results of a series of tests to evaluate the web crippling behavior of a new sigma-shaped metal stud when subjected to lateral load in addition to axial load. Also presented is an analytical study that results in proposed modifications to the AISI web crippling equation to account for sigma-shaped sections with or without axial load.