Keywords: composite floors, finite element method, ANSYS, concrete slab, elevated-temperature, fire.

The research presented in this paper focuses on investigating the behaviour of a concrete slab in fire conditions using a finite element program. A three-dimensional finite element model has been created using ANSYS, the concrete slab is simulated subject to exposure to the ISO834 standard fire [1]. A two hour fire analysis is considered. The results of the fire test conducted by BRANZ (Building Research Association of New Zealand) are used for validation [2]. In this research, the first step is to conduct the thermal field analysis, to obtain the temperature distribution over the concrete slab, and then the element type and material properties must be changed from a thermal field to a structure field, based on the results of thermal analysis, to apply the uniform pressure on the top surface of the concrete slab. The thermal field analysis indicates that the temperature distribution in the same section of the concrete slab is different along a plane. The greater difference in temperature on the concrete slab surface will cause greater differences in local stresses. Due to the different thermal properties of the concrete and metal decking, heat transfer in metal decking was much faster than in the concrete material. After two hours the temperature of metal decking increased to 1049°C, but the temperature in the top concrete slab was just around 400°C. A large vertical displacement was found in the concrete slab. In the beginning of the analysis, the vertical displacement in the midspan of the concrete slab developed slowly, However, it increased significantly, at the end of the two hours fire duration, the vertical displacement in the midspan of concrete slab increased to 168mm. The results from the three-dimensional analysis of concrete slab using the ANSYS software have shown good agreement with the fire test results. Both the ANSYS analysis and the fire tests demonstrate that simply supported concrete slabs have excellent fire resistance.

1

ISO834, "Fire resistance tests on elements of building construction", International Organisation for Standardisation, 1975.

2

L. Lim, C. Wade, "Experimental fire tests of two-way concrete slabs", Fire Engineering Research Report 02/12, University of Canterbury and BRANZ Ltd, New Zealand, 2002.

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