## 2 Validation of the Numerical Model
### Validated Model  
The material properties used in the numerical models are according to the fire design Eurocodes [17; 25; 26; 27]. For the thermal analysis, the emissivity used was 0.7 for both steel and concrete, on heated surfaces as well as on unheated surfaces, whereas the coefficient of convection was 25 W/m\({}^{2}\)K on heated surfaces and 4 W/m\({}^{2}\)K on unheated surfaces, for both materials. The upper limit of the thermal conductivity was considered for concrete. For experiment No. 66162, the value of concrete density was considered 2300 kg/m\({}^{3}\). For experiment No. 44174, the measured concrete density was 2200 kg/m\({}^{3}\) for normal weight concrete and 1850 kg/m\({}^{3}\) for light weight concrete. The moisture content of the concrete was taken in accordance to the technical notes of the experimental tests [23; 24]. For experiment No. 44174, the measured moisture content was 39 kg/m\({}^{3}\) for normal weight concrete and 47 kg/m\({}^{3}\) for light weight concrete. For experiment No. 66162, the moisture content was 42 kg/m\({}^{3}\). Safir software takes into account the energy dissipated by the evaporation of free water, in concrete. This energy is resealed at a constant rate from 100 \({}^{\circ}\)C to 115 \({}^{\circ}\)C, and then the energy release rate is linearly decreasing from 115 \({}^{\circ}\)C to 200 \({}^{\circ}\)C [22]. The cross-sections of the beam were exposed to the ISO fire only from below, the temperature in the air on the top of the floor being considered 20 \({}^{\circ}\)C.  
To describe the geometry of the cross section and the temperature distribution, linear isoparametric finite elements were used [22]. A 2D thermal analysis was realized on the cross-sections with triangle shape elements to describe the meshing. For the mechanical model, 2D beam finite elements were used, with constant cross-section along the longitudinal axis. The thermal analysis and the mechanical analysis were realized separately and subsequently, which means that the temperature distribution would obviously influence the  
Figure 4: Cross-section of the experimental test configuration: (**a**) WFRC 44174 [23]; (**b**) WFRC 66162 [24]. mechanical response, but the opposite was not true [22]. In the cases with non-composite behaviour, the concrete material was considered only with thermal properties, but no mechanical properties. Thus, the presence of the concrete influenced the thermal analysis, but not the mechanical one. The boundary conditions and the loads were considered as in the fire resistance tests. The mechanical models, for both tests, consisted of 4.5 m simply supported beams, heated over 4 m, loaded with four concentrated loads, as described in Section 2.1. The materials were isotropic, not submitted to movements, not compressible and had no mechanical dissipation. No heat flux was considered along the longitudinal axis of the beam finite element [22]. Figure 5 shows the meshed cross-section for the WFRC 44174 test, while Figure 6 shows the meshed cross-sections for the WFRC 66162 test. Due to the deep-decking metal sheet, the cross-section of the WFRC 66162 beam varies along the length of the beam. Therefore, three cross-sections were modelled: a cross-section with a thinner depth of the concrete slab (Figure 6a), a cross-section with a concrete slab standing on the lower flange of the I section (Figure 6c), and an intermediate cross-section (Figure 6b) which makes the transition between the other two. The temperature variation on the cross-section was analyzed in the same points where the thermocouples were placed during the experimental test. The article presents the comparison in the points where the temperature was reaching important values i.e., above 400 \({}^{\circ}\)C. Figures 5 and 6 present the points where the temperatures obtained through the numerical simulation were compared with the values recorded during the experimental model.