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Comparative study of the equivalent moment factor between international steel design specifications
[摘要] ENGLISH ABSTRACT: Lateral-torsional buckling (LTB) is an important failure mode that needs to be taken into account duringthe design of steel beams. The fundamental equation for determining the elastic critical moment ofa beam was derived with the assumption that the beam is subjected to a uniform bending momentdistribution. Loads on steel structures generate a great variety of bending moment distributions. Theeffect of the bending moment distribution is taken into account by a parameter known as the equivalentmoment factor. The procedure outlined in the South African National Standard for limit-states design ofhot-rolled steel work, SANS 10162-1:2011, for determining the equivalent moment factor was originallydeveloped for a bending moment that is uniformly or linearly distributed, however it is currently usedfor all bending moment distributions.A Finite Element (FE) model was developed in this investigation for determining the equivalent momentfactor. The numerical model included residual stresses and initial geometric imperfections commonlyfound in hot-rolled steel beams. To validate the assumptions made during the development of the FEmodel an in-depth experimental investigation was conducted on simply supported beams. Three differentload configurations were considered in the experimental study in order to simulate various bendingmoment distributions. A comparison of the equivalent moment factor between the numerical results andthe results obtained from various steel specifications, including SANS 10162-1:2011, was carried out inan attempt to quantify the positive and negative attributes of the various methods employed by steeldesign specifications.The experimental investigation concluded that the FE model is able to successfully represent a simplysupported beam with realistic characteristics that include residual stresses and imperfections. The comparativestudy illustrated that for a bending moment distribution with a constant moment gradient,SANS 10162-1:2011 provides excellent results. However, for the other distributions considered in this investigationhighly conservative results were obtained for the equivalent moment factor. The relevance ofthese findings were made clear by considering three design cases found in steel structures. The resistancemoment of the beams in each of these cases was calculated according to each of the steel specifications. Itwas found that the use of a highly conservative procedure for determining the equivalent moment factorcan lead to the uneconomical design of a structure.
[发布日期]  [发布机构] Stellenbosch University
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