Steel Buildings in Europe

Part 6: Fire Engineering 6 - 24 Table 3.7 Typical datasheets for fire design of partially encased sections Width b min (mm)/Reinforcement A s,min ratio (%) for the required fire resistance period (min) Member Section Ratio h / b Load level R30 R60 R90 R120 R180  fi,t ≤ 0,5 80/0,0 150/0,0 200/0,2 240/0,3 300/0,5 >1,5  fi,t ≤ 0,7 80/0,0 240/0,3 270/0,4 300/0,6  fi,t ≤ 0,5 60/0,0 100/0,0 170/0,2 200/0,3 250/0,3 Beam >3,0  fi,t ≤ 0,7 70/0,0 170/0,2 190/0,4 270/0,5 300/0,8  fi,t ≤ 0,47 160/- 300/4,0 400/4,0 Column Minimum h and b  fi,t ≤ 0,66 160/1,0 400/4,0 As an example, consider the case of a partially-encased beam with a ratio h / b > 3, under moderate load (  fi,t ≤ 0,5). For a fire resistance period of 60 minutes (R60):  The width should not be less than 100 mm, which leads to h > 3 b = 300 mm. So the minimum cross-sectional area is 100  300 mm  No reinforcement is required, A s = 0. To achieve a fire resistance period of 120 minutes (R120):  The width should not be less than 200 mm. Therefore the height h > 3 b = 600 mm and therefore the minimum cross-sectional area is 200  600 mm  The reinforcement area, A s , should not be less than 0,3% of the encased concrete area A c , i.e. , A s ≥ 0,003 A c . 3.3.4 External steelwork In some circumstances, the main structural members, such as columns and beams, may be located outside the building envelope without any fire protection, as shown in Figure 3.12. The fire protection requirements of external steelwork are significantly reduced, as the temperature of the external steelwork is lower compared to members inside a compartment. Further guidance on use of external steelwork for fire design can be found in EN 1993-1-2, §4.2.5.4.