Behaviour of composite floor slabs under fire conditions

This paper is concerned with the ultimate behaviour of composite floor slabs during fire scenarios. Steel/concrete composite structures are increasingly common in the UK and worldwide, particularly for multi-storey construction. The popularity of this construction form is mainly due to the excellent efficiency offered in terms of structural behaviour, construction time and material usage all of which are attractive given the ever-increasing demands for improved sustainability in construction. In this context, the engineering research community has focused considerable effort in recent years towards understanding the response of composite structures during fires. In particular, the contribution made by the floor slab system is of crucial importance as its ability to undergo secondary load-carrying mechanisms (e.g. membrane action) once conventional strength limits have been reached may be the key to preventing disproportionate collapse of the overall structure. Researchers have focused on developing the fundamental understanding of the complex behaviour of floor slabs and also improving the methods of analysis. Building on this work, the current paper describes the development and validation of a finite element model which can simulate the response of floor slab systems until failure, both at ambient and elevated temperature. The model can represent the complexities of the behaviour including the temperature-dependent material and geometric nonlinearities. It is first developed at ambient temperature and validated using a series of experiments on isolated slab elements. The most salient parameters are identified and studied. Thereafter, the model is extended to include the effects of elevated temperature and is employed to investigate the behaviour under these conditions. Comparisons with current design procedures are assessed and discussed

Assessment of the ultimate response of composite slab panels

It has been shown that steel-concrete composite floor systems can withstand loads and deflections far greater than those calculated by the traditional methods of design under fire conditions. In recent years, there has been considerable research focus directed towards developing the fundamental understanding of the complex behaviour of floor slabs and also improving the methods of analysis. Building on this work, the current paper describes the development and validation of a finite element model, developed using the ABAQUS software, which is capable of simulating the load-displacement response until failure. The model can represent the complexities of the behaviour including both the material and geometric nonlinearities and has been developed in five phases, including (i) unrestrained isolated strips (ii) restrained isolated strips (iii) unrestrained slabs (iv) restrained slabs and (v) an arrangement of three by three slab panels. The first four phases have been validated using data from tests on isolated elements and the current paper focuses mainly on the response of unrestrained two-way spanning slabs. The most salient parameters including boundary conditions, continuity and various other material and geometric properties are identified and studied. Comparisons with current design procedures are also discussed. The results of this investigation offer detailed insights into the key factors that govern the ultimate behaviour of buildings with composite floor systems under extreme loading conditions, and provide the essential background to enable the development of more performance-based design expressions