## 3 Fine Element Modelling  
### The Slim Floors  
During this study, FEM is performed for the thermal and thermo-mechanical (structural) response of slim floor systems in 2D is performed using SAFIR while the same in 3D is conducted using ABAQUS. Non-linear temperature thermal related material properties of steel and concrete, the specific heat, density and thermal conductivity, were taken from the Eurocodes [21] (Figure 4). Mechanical properties for steel and concrete were also been taken from the Eurocodes [22,23] (see Figure 4) with the exception that the actual yield strength of steel obtained from the material tests is used instead of its nominal value. Due to changes related to the shape of docking, two sections are selected along the span, section A-A' with the highest depth and width of concrete around the steel web and section B-B' with the minimum width and depth of concrete slab (see Figures 1 and 2). During 2D thermal analyses, FE modelling are performed for section A-A' and section B-B' separately, while during 3D modelling, full-size models are developed for the test assemblies. External loadings, fire exposure and boundary conditions for both slim floor beams are kept the same during the analysis as those reported for each test. The authors have earlier conducted a study on the thermal response of slim floor systems using FEM. In these studies, it  
Figure 3: The tested specimen for intumescent coating (**a**) Test assembly, (**b**) The steel member. was found that the predicted results for 2D modelling using both software, ABAQUS and SAFIR, were similar. Hence, during this study, FEM in 2D will only be performed using SAFIR. During the 2D modelling, 43-node linear quadrilateral heat transfer elements are employed, while for 3D modelling, 8 node hexahedral solid linear heat transfer elements, DC3D8 are used to perform the thermal analysis. Following the recommendations of the Eurocodes [18], convection coefficients for unexposed and exposed edges/surfaces are taken as 9 W/m\({}^{2}\)K and 25 W/m\({}^{2}\)K, respectively. Radiation emissivity for the exposed steel and concrete edges/surfaces is taken 0.5 and 0.25, respectively, as reported previously [24]. During the thermal analysis, any heat losses resulting from radiation from the unexposed edges/surfaces have been ignored. The temperature predictions obtained during this part of the analysis are later applied to ASBs to examine the influence of fire on their structural response. During the second part, structural analyses were conducted in two steps. In the first step, external loads were applied on the slim floor beam assembly, while in the second step, the beam assembly was exposed to temperature predictions obtained during the first part, the thermal analysis. The non-linear behaviour of concrete was modelled using 'the concrete damaged plasticity model' while the same for steel has been modelled using '[PERSON] plastic model'. The dilation angle for concrete was set to 55\({}^{\circ}\) as suggested previously by researchers [24]. A uniformly distributed load representing the test loads was applied during FEM. Structural FE analysis in 2D using SAFIR was performed using 43-node beam elements and section A-A' and section B-B' was were assigned to the specimen at respective locations  
Figure 4: Temperature-dependent properties, (**a**) Stress-strain curve of structural steel, (**b**) compressive behaviour concrete, (**c**) Tensile Behaviour Concrete, (**d**) Thermal conductivity of concrete. along its span. In particular, the 2D beam's mechanical model consists of an alternation of sections section A-A' and section B-B', to simulate the presence of different cross-sections also in the 2D model (see Figure 1). The structural analysis in 3D with ABAQUS was performed using different analysis elements for concrete and steel.