An experimental investigation of the behaviour of composite reinforced-concrete/steel beams with corrugated webs under flexure is presented in this paper. This study focuses on the effect of a top steel flange on the failure mechanism of a composite concrete/steel beam. Accordingly, four full-scale composite concrete/steel beams are fabricated and tested. Two beams have concrete and steel flanges that consist of shear connectors. The other beams have concrete-only flanges with shear connectors and additional steel mesh. All specimens are loaded at points dividing the beam length into thirds. Consequently, the zero shear and constant moment regions are created by this loading distribution in the middle third of the specimens. Both the local and global failure mechanisms are influenced by the top steel flange composition. Moreover, the effects of the top steel flange on the beam stiffness, ultimate load, local buckling of the corrugated web, concrete slip, and failure mechanism of the concrete slab are discussed.