Lateral-distortional buckling of steel-concrete composite beams: Kinematics, constrained-mode GBT and analytical formulae

Abstract

This paper investigates and sheds fresh light on the kinematics and mechanics involved in the lateral-distortional buckling (LDB) behaviour (involving web single or double curvature) of simply supported I-section steel beams elastically restrained by concrete slabs under uniform negative (hogging) bending. The findings obtained are used to derive and illustrate the application of analytical formulae to calculate LDB moments of the steel-concrete composite beams considered. The study is based on a Generalised Beam Theory (GBT) approach to perform buckling analyses using constrained deformation modes that incorporate the displacement/rotation restraints, thus making it possible to obtain accurate buckling results with only a few deformation modes. The formulae provide the solution of the LDB equilibrium equation when only one or two constrained deformation modes are involved. Their merits and accuracy are assessed through the application to problems of practical interest – the LDB moments determined are compared with values (i) provided by other available formulae and/or (ii) obtained from conventional GBT, finite strip and/or Ansys shell finite element analyses. It is found that (i) the proposed constrained-mode GBT clearly outperforms the conventional one, both in structural insight and computational efficiency, and (ii) the derived analytical formulae consistently yield accurate LDB moment estimates.