Global Imperfections and Dimensional Variations in Cold-formed Steel Members

The objective of this paper is to provide the results from an experimental program to measure global imperfections and dimensional variations in cold-formed steel-lipped channel members. Measurements were conducted at seven different manufacturing plants in the United States. A total of 210 cross sections were measured for global imperfections. Each cross section was measured at three locations, and every 305 mm (12 in.) along the length. The data is used to characterize global bow, camber, and twist. The majority of the data exhibits global imperfections well approximated by a half sine-wave. Further, global bow imperfections are shown to have a systematic bias in the direction of bow. The measured data is compared with manufacturing tolerances (e.g., L/384) and assumed imperfection sizes from column curves (e.g., L/960) as utilized in design practice in the United States. The measured imperfections served as justification for tightening manufacturing tolerances in the United States (e.g., to L/960). Dimensional variation of typical cold-formed steel members is also measured and compared with tolerances. The measured data provides much needed input for nonlinear analysis of cold-formed steel structures.