Influence of the local buckling of web on the bearing capacity of a castellated beam/composite beam under pure bending

The buckling and post-buckling behavior of 'tee' webs in thin-webbed castellated beams with deeper tee-sections under pure bending, which have received limited attention in previous studies, are comprehensively examined within this paper. An experimental study was conducted on 5 castellated beams/composite beams, and a finite element analysis was performed using 417 castellated beam/composite beam models to investigate the following. (1) The influence of the opening parameters (opening rate and opening spacing), (2) castellated beam section parameters (beam depth, flange width, flange thickness, and web thickness), (3) floor slab, and (4) transverse stiffener on the buckling load, peak load, buckling mode, and failure mode of a castellated beam/ composite beam under pure bending. The results show that the normal stress of the section and buckling critical stress of the compression plate have a considerable effect on the buckling load of the castellated beam and that the local buckling of the web may cause torsion of the beam flange. Furthermore, the bearing capacity of the castellated beam/composite beam could be increased by 27.3 % and 31.9 %, respectively, following local web buckling. The failure modes of the castellated beam were bending-torsion failure or bending failure of the beam flange and that of the castellated composite beam was the bending failure of the beam flange after concrete slab failure. The concrete slab can effectively limit the torsion of the beam flange, reduce the height of the compression web, and limit the buckling development of the web, and the stiffener can effectively prevent webpost buckling. The buckling and peak load prediction method of the castellated beam (the buckling mode is the buckling of the open-section compression web, and the failure mode is the bending-torsion or bending failure of the beam flange) under pure bending is proposed. The research findings provide a supplement to related studies on castellated beams and a reference for related design and engineering.