Steel Buildings in Europe

Title Worked Example – Fire safety strategies and design approach of steel floor beam 7 of 10 6 - 55 The ratios for local buckling of the section elements are: Flange: c f / t f = 5,28 < [ c f / t f ] lim = 9 ε = 7,07 Web: c w / t w = 35,01 < [ c w / t w ] lim = 72 ε = 56,57 The section is class 1. Resistance of beam after 60 minutes fire exposure The moment resistance of a beam with non-uniform temperature along the depth of its cross-section can be calculated as: M fi,Rd = M fi,t,Rd = k y, θ W pl,y f y /( κ 1 κ 2 ) Where k y, θ is the reduction factor for effective yield strength κ 1 , κ 2 are adaptation factors for non-uniform temperature across the cross-section and along the beam EN 1993-1-2; Table 3.1 EN 1993-1-2; §4.2.3.3 Unprotected beam The temperature of the unprotected beam after 60 minutes fire exposure as obtained from the figure on Sheet 6, is: θ at = 935  C The reduction factor for effective yield strength can be obtained for: θ a = 900  C k y, θ = 0,060 θ a = 1000  C k y, θ = 0,040 By interpolating for θ a = 935  C, we obtain: k y, θ = 0,052 For an unprotected beam exposed on three sides, with a composite or concrete slab on side four: κ 1 = 0,70 for any case where the supports of the beam are not statically indeterminate: κ 2 = 0,85 Therefore the moment resistance of the beam is: M fi,Rd = 0,052  628  10 3  275/(0,7  1,0)  10 -6 = 12,83 kNm < = 80.9 kNm Therefore the unprotected section is not safe.  FAIL 10 mm board protection Hence some protection is required for the beam. Following from the findings of the previous simplified calculation based on the temperature, the first option to be explored is the 10mm fire board protection. This solution has already been found to be safe. From the above Figure the temperature of this solution after 60 minutes of fire exposure is: θ at = 594  C