An optimisation strategy for the (in- and out-of-plane) resistance of steel beams in demountable composite floor systems

Demountable and reusable composite floor systems enable the decoupling between the use of construction materials and economic activity, and hereby contribute to the sustainability of the built environment. Efficient material use through optimised cross-section design reduces construction material demand. Demountable steel-concrete composite floor systems are perceived as competitive when consisting of steel beams and large prefabricated concrete floor elements, with composite interaction achieved by demountable shear connectors. Compared to traditional monolithic floor systems, the demountable composite floor systems have an increased sensitivity to lateral-torsional buckling during execution, mostly because of unsymmetrical loading and the absence of rotational constraints in the execution phase. This increased sensitivity implies that the cross-section of the steel beam should not only be designed based on the required in-plane resistance, but should also maximise the out-of-plane resistance. The Energy method and Rayleigh-Ritz methods are combined to develop a prediction model for the critical bending moment of monosymmetrical web-tapered steel beams. The key cross-sectional dimensions and parameters that affect the in-plane and out-of-plane resistance are identified. An overarching strategy for the concurrent optimisation of the in-plane and out-of-plane resistance of monosymmetrical cross-sections is presented without compromising on material efficiency. The beneficial effects of the proposed optimisation strategy are quantified through a case study example.