The Warping Constant for the W-Section with a Channel Cap

Abstract

It is common practice in crane runway beams to place a channel, open-side down, over the top flange of a W-section to increase its lateral stability. This is done because it is not always convenient to brace the compression flange between columns. The lateral-torsional buckling capacity of a singly symmetric section may be determined by the formulas without knowing the warping section constant. However, these formulas were developed from research on three-plate mono-symmetric sections. If one is to develop a similar equation for the case of the W-section with a channel cap, it is necessary to return to the basic theory of lateral-torsional buckling and that means that one must calculate the warping constant (Cwc) for the cross-section. It is not a difficult matter to do this with a computer, but since the program may not be available to everyone, it would be useful to develop a simple empirical equation for preliminary design, making use of the section properties already given in the AISC steel manual.