Effect of load height on elastic buckling behavior of I-shaped cellular beams

Abstract

The effect of load height on the elastic moment gradient factor (Cb) for laterally unsupported I-shaped cellular steel beams under uniformly distributed load is numerically investigated in this paper. This study is carried on simply supported cellular beams for different cross-sections, beam slenderness, size and spacing of circular openings. The effect of web and flange slenderness on the elastic buckling behavior of cellular steel beam is also investigated in the present work. For determining the effect of load height on Cb, three different possible levels of loading positions; viz., uniformly distributed load applied at the shear center, at the top flange, and at the bottom flange are considered and the numerical results are compared with the standard case of uniform moment condition.It is observed that the presence of web perforations in the case of cellular steel beam significantly affects the elastic stability of beams. Numerically obtained Cb factors for cellular beams are compared with those obtained from equations mentioned in SSRC guidelines applied to the cellular beams. A significant variation is observed between Cb factors obtained from numerical finite element analysis and the equations mentioned in SSRC guidelines applied to cellular short span beams having slender webs and closely spaced openings for considered three different levels of loading positions. This variation is due to the fact that the instability in the cellular steel beam is associated with severe web distortion which is ignored in the formulations of SSRC guidelines. The equations of SSRC guidelines to cellular steel beams are applicable for longer span beams wherein the lateral-torsional buckling mode is governing. The uniformly distributed load applied at the top flange of the cellular beam is the most critical condition and resulting in the least Cb factors.