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In a composite beam, transverse web stiffeners are often provided to the steel section at regular intervals along the beam span to eliminate local shear buckling as well as to reduce web distortion in the steel section. These transverse stiffeners are also found to be effective in providing intermediate lateral restraints from the stiff concrete slab to the compressive steel flange, forming a 'discrete inverted U-frame' action so that the resistance of the composite beam against distortional lateral buckling is significantly enhanced. In general, the load carrying capacity of a continuous composite beam depends on a number of factors such as initial imperfections, residual stresses, and material nonlinearity. A general design method to evaluate the contribution of transverse web stiffeners to the capacity of a continuous composite beam, is however yet unavailable.This paper presents an advanced numerical investigation into the structural behaviour of composite beams under the discrete inverted U-frame action. Based on a comprehensive finite element study, the following key parameters affecting the load carrying capacity of the beam are studied: i) the flexural stiffness of the concrete slab, ii) the stiffness of the web stiffeners, iii) the ratio of the depth to thickness of the steel web, and iv) the ratio of the spacing of the web stiffeners to the beam span. It has been verified that in the presence of properly designed web stiffeners, the buckling moment resistances of composite beams will be significantly increased while the lateral deflection of the compression flanges is greatly reduced. [ABSTRACT FROM AUTHOR]