Design of composite asymmetric cellular beams and beams with large web openings

The design of composite asymmetric cellular beams is not fully covered by existing guidance but is an area of important practical application. Asymmetry in the shape of the cross-section of cellular beams causes development of additional bending moments in the web-posts between closely placed openings. Furthermore, the development of local composite action influences the distribution of forces in the web-flange Tees. The design method presented in this paper takes account of high degrees of asymmetry in the cross-section and also the influence of elongated or rectangular openings. Web-post moments also influence buckling of the web-post between openings, which is accentuated by adjacent long openings. Simplified equations are presented for web-post buckling based on a compression field or 'strut' model, which is calibrated against the results of Finite Element Analyses (FEA). The FEA are also extended to cover the case of highly asymmetric sections and ring-stiffened openings. Closed solutions are presented that enable the designer to calculate the maximum shear force acting on the beam when its load resistance is limited by web-post bending or buckling. For long openings, high pull-out forces may exist in the shear connectors at the edge of the opening. When combined with possible second-order effects due to shear deflection across the opening, it is necessary to limit the magnitude of local composite action due to Vierendeel bending that can be considered in design