Improved crack width calculation method to BS 8007 for combined flexure and direct tension

The domestic and light industrial floor market in South Africa comprises a floor system referred to as the rib and block floor slab. The floor system is a concrete composite, composed of in situ concrete, precast ribs and hollow block void formers. The system is noted for its speed of construction and formwork is not required. However, transportation costs of the precast ribs and the need for lifting equipment renders the system uneconomical beyond a limited radius from the factory. To minimise costs, a new system is proposed, which replaces the precast rib with a cold-formed lipped channel. A set of design equations, adapted from the code, are compared with a set of experiments. The investigation indicated the proposed system is a viable alternative, but embossment or means to mechanically bond the concrete to the steel is required to achieve composite action. M. Gohnert, BSc, MEM, PhD, CEng, Pr Eng, AIStructE University of the Witwatersrand, South Africa M. J. Komakec, BSc, GDE, MSc University of the Witwatersrand, South Africa