Experimental and numerical study of steel joist and girder cold-formed web members with periodically-varying section properties

This research work is aimed at the development of design equations for cold-formed web members with non-uniform sections. This type of member regroups periodically closed channels, stitched channels and back-to-back channels with batten plates. The first two types of members can be used in joists as an alternative to a seamless welded closed section, while the double member assembly is to be utilized with girders. The proposed design algorithms either result in an adaptation of classical design methods for batten columns (Engesser, Bleich, critical shear ratios), or in the development of new analytical expressions (Fourier series description of periodically varying properties). In all cases, the proposed equations are incorporated into the actual design standards for cold-formed structural members.; To validate the developed design algorithms, stub columns tests as well as full scale joist experiments are statistically conducted and analyzed. Factors such as the effect of eccentricity and restraint resulting from the weld pattern connecting the webs to the hot-rolled angle chords are considered. Other design parameters such as appropriate effective length coefficients, the influence of the sheet anisotropy, of the yielded corners or the restraint associated with one or two batten plates are investigated. These variables are also incorporated in various finite element models to validate the proposed design schemes. This work finally includes discussions and conclusions on the new design procedures as well as proposals for further research work.