Elastic Distortional Buckling Analysis of I-Steel Concrete Composite Beam Considering Shear Deformation

Elastic distortional buckling is one of the essential buckling modes of the I-steel concrete composite beam (ISCCB); such buckling often occurs under the gradient of negative moment. The key factors affecting the kind of buckling are the “torsional” and “lateral” restraint stiffnesses of the bottom flange of the beam. This paper investigates the equivalent lateral and torsional restraint stiffnesses of the bottom flange of the ISCCB under the gradient of negative moment. The relations for estimating the lateral and torsional restraint stiffnesses are used to determine the critical distortional buckling stress and associated buckling moment of the beam under the gradient of negative moment. A new method is proposed for assessing the buckling of the elastic-foundation beam, by which the related factors are considered: (1) The coupling effect between the applied forces and lateral/torsional restraint stiffness of the bottom flange of the beam, (2) the effect of gradient of a moment and (3) the effect of shear deformation of the web. The proposed method has been compared with those available by using the data of 15 cases under different loading conditions; the results show that the present method is much more accurate and reliable than the existing ones. The method as proposed herein is recommended for further research in relation to the buckling of the ISCCB.