دانلود رایگان مقاله مدلسازی عددی موضوع اسلب طبقه کامپوزیت برای تغییر شکل بزرگ

Abstract

This paper is concerned with the ultimate behaviour of composite floor slabs. 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 particularly 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 extreme events, such as 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 prevent overall collapse of the 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 so it can be employed to investigate the behaviour under these conditions. Comparisons with current design procedures are assessed and discussed.

5. Conclusions

This paper has presented numerical studies into the behaviour and ultimate response of one-way spanning strip and two-way isolated, lightly reinforced slab elements such as those encountered in steelframed composite structures. Particular attention has been given in creating a reliable FEM able to predict with good accuracy failure either by reinforcement rupture or concrete crushing. Towards this end, the results of an experimental test series consisting of sixteen ambient tests on one-way and fourteen tests of two-way isolated elements were utilised to calibrate and validate the model. It was shown that the numerical model which has been developed in the ABAQUS software can realistically represent the behaviour at large deflections. Importantly, this model accounts for the relationship with the steel reinforcement and surrounding concrete. This, in turn, led to the validation of the model using the previouslyvalidated VULCAN software, and compared the results to the BRE simplified design method for both ambient and elevated temperature. Important parameters that influence the outcome of the FEM have been identified and discussed where appropriate. The work described in this paper is the first step in a larger research programme and the future targets include: − Validating the model against experimental data on isolated slab elements at elevated temperature; − Expanding the model to include the influence of neighbouring compartments on the overall behaviour in fire; − Using the validated model to develop an understanding of the most salient parameters such as boundary conditions, continuity, bond strength and various other material and geometric properties under ambient and elevated temperatures on the overall response; and − Proposing performance-based expressions which can be used in design for the ultimate response of floor slabs under fire conditions The results of this investigation will 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.