Abstract
The present paper investigates fire resistance of a simply-supported composite concrete-trapezoidal steel sheet slab. The objective is to find out if a steel sheet, as a moisture diffusion barrier, may substantially effect the hydro-thermal situation in the concrete part of the cross-section. The numerical integration of the equations of a coupled hygro-thermal boundary-value problem (Tenchev, R.T., Li, L.Y. and Purkiss, J.A. (2001) Num. Heat Transfer Part A, 39(7), 685-710), with and without considering the barrier, shows that the barrier does not really effect the magnitude and the development of temperatures over the cross-section, while there is a significant effect on the pattern of moisture transport and the magnitude of vapour pressure. Particularly high magnitudes of vapour pressure (about 4.5 MPa) were shown in cases where the steel sheet was considered in analyses, which indicates a possible micro damage of concrete in the web of the section, although spalling probably cannot take place due to the steel sheet cover. As the typical composite slab investigated here is not sufficiently fire resistant without any additional reinforcement bars placed in the web, further in-vestigations are directed to finding an optimal position and area of these bars. Following a simplified procedure given in EC2 (Eurocode 2, Design of Concrete Structures, Part 1.2 (2004) Structural fire design, European Committee for Standardization) and assuming that the present composite slab is subject to the uniform traction , yields that placing one bar with the area 1.153 cm2 4 cm away from the edge suffices for the 60 min fire resistance of the slab.
Highlights
Composite concrete-trapezoidal steel plate slabs are widely used structural elements in buildings and bridges
As the typical composite slab investigated here is not sufficiently fire resistant without any additional reinforcement bars placed in the web, further investigations are directed to finding an optimal position and area of these bars
To assess the effect of steel sheet as the diffusion barrier, we present in Figure 3 the increase of temperatures with time in some characteristic points within the web of the cross-section, whose positions are convenient for placing additional reinforcement bars to achieve a sufficient fire resistance
Summary
Composite concrete-trapezoidal steel plate slabs are widely used structural elements in buildings and bridges. A somewhat modified model of Tenchev et al [5] is employed to investigate the hygro -thermal behaviour of a composite concrete-trapezoidal steel plate slab in fire. This numerical model enables us to estimate the distribution of temperature, moisture and pore pressure over the concrete cross-section at any time during a fire. These are vital data for predicting the fire resistance time, and spalling of concrete [4]. In what follows we make a short overview of the equations of heat and moisture transport in concrete and describe relevant variables; subsequently we discuss the hygro-thermal behaviour of the composite slab in fire
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