# Response of Seismically Damaged Steel Reduced Beam Section Joints under Fire
## 4 Results of Parametric FEAs
### Fire Behaviour  
The results of FEAs of the undamaged joints subjected to the three considered fire scenarios (S1, S2, and S3) are presented in terms of time-rotation and temperature-rotation curves in Figure 8, where the Von Misses stress distribution of the EJ-80%-ND-S2 and IJ-80%-ND-S2 joints are also depicted.  
All temperature-rotation curves have an initial rotation before at ambient temperature, which corresponds to the rotation induced by the gravity loads (both dead and live loads).  
As previously described, the external joints have an RBS connection on one side of the column, and a flush end-plate connection on the other side. This configuration is strongly influenced by fire loads. As depicted in Figure 8a,b, both external RBS-80 and RBS-65 s exhibit good behaviour in the S1 scenario up to 800 \({}^{\circ}\)C. In contrast, for S2 and S3, the flush end-plate connection experiences a significant reduction in resistance due to the large concentration of damage into the end-plate and first bolt row (see Figure 8e). In the case of RBS-80 in the S1 scenario, the stiffness degradation becomes evident when a temperature of 650 \({}^{\circ}\)C is reached at the lower flange of the beam (see Figure 8f).  
The resistance of the RBS, namely the width of the cut flange, highly influences the fire behaviour of the joints. For instance, comparing the response of the EJ-RBS-80 and EJ-RBS-65 joints in the S1 scenario, it can be observed that the weaker the RBS, the worse its fire response (see Figure 9); indeed, the EJ-RBS-80 shows a good fire performance up to 55 min, while the corresponding RBS-65 shows a complete loss of stiffness after 38 min.  
Figure 7: Cyclic behaviour of the investigated joints in terms of moment–rotation curves and equivalent plastic deformation (PEEQ).  
The results of the internal joints are depicted in Figure 10. It should be observed that, in contrast to the external, the internal joints are symmetric, having the same connections and beams on both sides of the column. Therefore, only the results belonging to the right beam are pointed out hereinafter. Moreover, for the sake of brevity and since the results are perfectly comparable, only the results of the IJ-RBS-80 joints are presented.  
Figure 8: FE results of undamaged external joints subjected to elevated temperature in terms of time-rotation curves (**a**,**c**), temperature rotation curves (**b**,**d**) and Von Misses and PEEQ distribution (**e**,**f**).  
Figure 9: Comparison between the external RBS-65 and RBS-80 joints in terms of time-rotation (**a**) and temperature-rotation (**b**) curves.  
For the S1 scenario, the considerations made for the external joints can be extended, while a higher performance can be observed in the S2 and S3 scenarios (see Figure 10a,b).  
As expected, since the beams and the connection are the same, the results of the S1 and S2 scenario are rather similar. However, increasing the temperature of the IJ-RBS-80-ND-S2 affected the loss of stiffness. This difference is due to the instability of the column that is subjected to fire on both sides in the S2 scenario (see Figure 10c).  
In the case of the S3 scenario, the worst response for all examined cases can be observed. These results depend on the severity of the fire scenario, where elevated temperatures are applied throughout the surfaces of the assemblies.