Steel Buildings in Europe

Part 7: Fire Engineering 7 - 25 where:  is the imperfection factor for the appropriate buckling curve given by y 0.65 235 / f   with f y is characteristic yield strength of steel. The non dimensional slenderness at temperature θ is given by: θ E, θ y, θ / k k    (19) where: θ y, k is the reduction factor for the yield strength of steel at the temperature  θ E, k is the reduction factor for the slope of the linear elastic range at the temperature   The non dimensional slenderness at normal temperature, according to EN 1993-1-1 The non dimensional slenderness at normal temperature is given by: E f i y cr π 1    (20) where: cr  is the buckling length in the buckling plane considered i is the radius of gyration about the relevant axis, determined using the properties of the gross cross-section For a practical use, the reduction factor i f  for flexural buckling can be directly calculated from values given in Table 5.3, according to the steel grade and the non dimensional slenderness of steel member at normal temperature  . Values of reduction factor fi  in Table 5.3 were calculated assuming a slenderness in the fire situation equal to   1.3 θ  . For intermediate value of non- dimensional relative slenderness, linear interpolation may be used.