Abstract
Elastic and inelastic lateral torsional buckling of simply web tapered I beam is studied using the finite element method. The length of the beams is 8000 mm for elastic lateral torsional buckling and 4000 mm for inelastic lateral torsional buckling. The depth of cross section at one end is 500 mm and at the other end it is varied. The thickness of the flange is 16 mm and the thickness of the web is 10 mm. The section of the beams is compact. The beams are loaded by end moments. The ratio of end moments at one end and the moments at the other end are varied. The beams are assumed to have geometric imperfection and the distribution of imperfection follows the shape of the first buckling mode of elastic lateral torsional buckling of the beam. The amplitude of the imperfection is taken one milimeter at the top flange in lateral direction. The load is increased until the beams collapse. The ultimate load is considered as the critical moments of the beams. The results of the analysis are compared to nominal lateral torsional buckling moments using the method presented in the AISC Design Guide 25 (Design Guide for web tapered members). It can be concluded that usually the critical moments of the collapse analysis are close to the critical moments of the design guide. But sometimes it is less than the design guide and it means design guide is sometimes is not on the safe side.
Highlights
Web tapered steel beams are usually used due to economic aspects
This paper presents the results of a study about lateral torsional buckling of web tapered I beams loaded by end moments
For beam with an 8000 mm span, elastic buckling formula governs the calculation of the critical moment and the results of collapse analysis show that the stresses at peak load is still in elastic range
Summary
Web tapered steel beams are usually used due to economic aspects. In beam design, one of the consideration is lateral torsional buckling. Miller [2] studied lateral torsional buckling of web tapered I beams using nonlinear finite element method. J.S Park et al [3] studied lateral torsional buckling of stepped beams using the linear finite element method. Vandermeulen et al [4] studied lateral torsional buckling of tapered beams using the linear and nonlinear finite element method, but residual stress was not considered. [7] studied elastic lateral torsional buckling of web tapered I beams using the 1D and 3D FEM method. He developed the 1D element and compared it to the 3D shell element model. The results of analysis are compared with the critical moment computed using the AISC Steel Design Guide 25
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