Steel and concrete composite diaphragms
Stressed skin design has now been developed into an important tool for designing buildings. In developing stressed skin theory, it has been shown that the inherent inplane stiffness of the materials considered is of predominate importance in the distribution of lateral forces within a structure. The materials that have been incorporated in the theory so far are profiled steel and aluminium sheeting. Lately, work on multi-storey buildings has shown the advantage of using infill panels in the vertical plane to control the sway deflection of the building. No account, however, has been taken of the horizontal floors acting as diaphragms. Incorporating the floor into the sway analysis would clearly model the building more realistically. A typical floor construction commonly adopted in steel framed buildings is the composite slab. This consists of trapezoidally profiled steel sheeting fastened to the structure and overlain by concrete. Design formulae are derived for the shear strength and flexibility of the above floor construction and verified by experimental work. In the basic stressed skin concept the shear distortional flexibility of profiled sheeting has been shown to be dependent on the overall dimensions of the diaphragm, the shape of the profile and the fastener arrangement. At present the analysis considers a typical corrugation to lie within a large "field or corrugations" and so edge effects are neglected. A Finite Strip program has been written to analyse these fields of corrugations under the action of a shear flow and to investigate the effect of edge members on the shear flexibility. The large end distortions of the profiled sheeting, that arise as a result of the action of the shear flow on the profile, can cause failure of the sheeting and fasteners in this region. A study has been undertaken to investigate the possible failure modes, as a result of which three modes have been identified, namely, failure of the sheet / purlin fasteners, buckling of the profile web and a sideways collapse of the profile. Numerical expressions are developed for these failures and compared with experimental results.