## 4 Results and Observations
### Slim Floor Systems Protected with Intumescent Coating  
FEM for the slim floor beams assumed to be protected by a layer of intumescent coating on the exposed edges/surfaces of the lower flange is conducted by combining the verified models for unprotected slim floor beams and steel members with intumescent coating. The thermal estimates obtained from numerical modelling for the protected slim floors are plotted against the test data for unprotected tests WFRC 66162 and WFRC 67756 in Figures 10 and 11, respectively. Figure 9: Test data and analytical results for Intumescent Coating test: (**a**) Results at the end of 120 min of analytical modelling, (**b**) Comparison of analytical results and the test data. As expected, it is found that the applied intumescent coating (1200 \(\upmu\)m) significantly restricts the temperature developments on the steel section when compared to those recorded for the unprotected ASBs. The parts of the steel beam section which are closer  
Figure 11: Effectiveness of IC in terms of temperatures predictions for protected vs. recorded for unprotected, WFRC 67756: (**a**) Thermal contours for the protected beam at section AA’ after 90 min, (**b**) Thermal contours for the protected beam at section BB’ after 90 min, (**c**) Protected vs. Unprotected at section AA’ (**d**) Protected vs. Unprotected at section BB’. Figure 10: Effectiveness of IC in terms of temperatures predictions for protected vs. recorded for unprotected, WFRC 66162: (**a**) Thermal contours for the protected beam at section AA’ after 120 min, (**b**) Thermal contours for the protected beam at section BB’ after 120 min, (**c**) Protected vs. Unprotected at section AA’ (**d**) Protected vs. Unprotected at section AB’. to exposed surface/edges, the temperature reduction in temperature is more significant. This difference reduces with the increase in the distance towards the unexposed upper surfaces/edges. The steel parts away from the protection layer are less influenced by its application of intumescent coating as they are already encased in the concrete slab which protects them from direct exposure to fire by providing adequate insulation. In both cases, the temperatures recorded on the steel section are below 400 \({}^{\circ}\)C even after a fire exposure of more than 60 min, hence, the specimens retain their full strength/capacity and stiffness for this duration of fire exposure. Further, the structural response has improved significantly for both SFB assemblies. Figures 12 and 13 show that both protected slim floor beams offered an enhanced fire resistance against the standard fire curve. Both slim floor beams continued to support the external loads for more than 120 min. At 120 min, the FE analysis was discontinued and the mid-span deflection for both beams was predicted to be less than 60 mm for both FEM approaches, 2D and 3D. Hence, the slim floors protected using a 1200 \(\upmu\)m thick layer of the intumescent coating can offer fire resistance of more than 120 min for the same utilisation factors as those used during the tests. Moreover, the slim floor beams protected with 1200 \(\upmu\)m can satisfy the performance levels IV with limited damage of the structure after fire exposure; indeed, the maximum displacement is less than 50 mm for 120 min. For satisfying the performance level V, a greater thickness of protection is necessary for reaching 120 min; indeed, Figures 12 and 13 show that the maximum displacement is lower than the limit one for a time of 30 min. It should be noted that the protected specimen continued to support the loads beyond 120 min, however, the FE analysis was discontinued at this point. The structural response of protected slim floor beams is analysed using the same approach as that used for the unprotected slim floors where loads are applied in the first step on the upper flange of the steel section and in the second step, the specimen is heated using the temperature predictions obtained from the thermal analysis.