Behaviour and resistance of composite slabs : experiments and finite element analysis

Abstract: Composite slab flooring systems are used in steel framed buildings as well as in conjunction with concrete, prestressed concrete and timber structures. Composite slabs consist of a thin-walled profiled steel sheet, reinforcement and in-situ cast concrete. The profiled sheeting acts as permanent formwork and once the concrete has hardened as an outer reinforcement. Unlike a bar reinforcement, the sheeting does not benefit from being totally embedded in concrete. Partial connection between the sheeting and concrete takes place after the adhesion is broken. Composite slab design is usually based on parameters of partial connection obtained from full scale bending test. The objective of this thesis is to analyse composite slabs which fail in longitudinal shear and flexural failure. An analytical approach based on FE simulations and data from small scale tests (detail tests) has been used. A new test rig has been designed and a procedure developed to evaluate the characteristics of the interaction. Mechanical interlocking resistance, reduction of mechanical interlocking due to high strains in the sheeting, and friction between sheeting and concrete has been assessed. Cracking of concrete in composite slabs has a major influence on the distribution of horizontal shear forces between the sheeting and concrete, and consequently on the behaviour of the composite slab. An intensive FE nonlinear study has therefore been performed to examine various concepts of concrete cracking. FE predictions have been validated with the full scale tests and the good agreement obtained shows that modeling and input data were correct. Results of small scale tests and FE calculations have increased the knowledge of composite slab behaviour. A parametric study of the influence of load arrangements and various characteristic of partial connection have created the basis for an improved design method. A design method based on small scale tests and FE calculation is proposed. It uses a simple structural model and a new concept of transfer length to properly define a parth of slab length mobilized for longitudinal shear connection. The design method is an improved version of existing partial connection strength method described in Eurocode 4. The method is applicable for ductile and non ductile slabs and accounts for various loading arrangements in a consistent manner. Design recommendations for a general load arrangement are given.