A composite slab consists of a concrete topping cast on the top of a steel deck. The concrete is
usually reinforced with a steel mesh on the top and may also be reinforced using individual rebars.
The steel deck also acts as reinforcement and may be directly exposed to accidental fire
conditions. This composite solution is widely used in every type of buildings which require fire
resistance, in accordance to regulations and standards. The scope of this investigation concerns
the fire rating for insulation (I). Numerical simulation was developed, using Matlab PDE toolbox
and ANSYS, to find out the thermal effects of standard fire exposure. The results of the numerical
simulation are compared with experimental results available in the literature in order to validate our approach. The results are also compared with the simplified
method proposed by Eurocode 4-part 1.2.
A composite steel-concrete slab consists of a concrete topping cast on the top of a profiled steel
deck. Normally, the concrete is reinforced with an anti-crack mesh positioned on the upper part
and individual reinforcing bars placed within the ribs, see Figure 1. The steel deck acts as a
permanent formwork and the composite action between the steel and concrete is generally
achieved by indentations or embossments in the steel deck. Due to the reinforcement provided
by the steel deck, composite slabs are generally slenderer and more efficient than flat concrete
slabs because require less additional reinforcement and less concrete as well. The reduction of
the construction time, simplicity of installation and reduction/elimination of struts are other
advantages of composite slabs that should be highlighted.
A composite steel-concrete slab consists of a concrete topping cast on the top of a profiled steel deck. Normally, the concrete is reinforced with an anti-crack mesh positioned on the upper part and individual reinforcing bars placed within the ribs. The steel deck acts as a permanent formwork and the composite action between the steel and concrete is generally achieved by indentations or embossments in this component.
Composite slabs play an important role in the overall stability of buildings during fire exposure, and should be designed in accordance with regulations and standards. The fire rating of this structural element is defined with respect to fire exposure from below and is normally determined through standard fire tests. Three different criteria should be taken into consideration: load bearing (R), integrity (E) and thermal insulation (I).
The Annex D of the EN 1994 – 1-2 and the Annex C of the NBR 14323 provide guidelines for the calculation of the fire resistance (I), as well as the temperature of the rebars and the parts of the steel deck of unprotected fire exposed composite slabs. However, no revisions were made to these methods during the last two decades.
The underlying work presents the development of numerical models for 3-D thermal analysis in the software ANSYS Mechanical APDL 18.2, and MATLAB R2018a through the PDE Toolbox. A total of 208 numerical simulations should be performed considering perfect thermal contact between all the materials, with the aim to investigate the influence of different parameters on the fire resistance (I) and the temperature of the steel components.
During experimental fire tests, the steel deck separates from concrete, which increases the thermal resistance in this interface. In order to simulate debonding effects, another thermal model is established for more 40 numerical simulations, including an air gap with a constant thickness between the steel deck and concrete topping.
The thermal models shall be validated against the results of different experimental fire tests. It is concluded that the calculation rules given in the European and Brazilian standard are generally on the unsafe side and do not consider important parameters. This work proposes improved equations for the estimation of the fire resistance (I) and the temperature of the parts of the steel deck and the rebars as well.
