Steel Buildings in Europe

Part 6: Fire Engineering 6 - 35 Resistances of unrestrained beams and columns The simple models for calculating the buckling resistances of unrestrained beams and columns with a uniform temperature are given in §4.2.3.3, §4.2.3.4 and §4.2.3.2 of EN 1993-1-2. These rules were developed by imposing the following modifications on the relevant models given in EN 1993-1-1 for normal design to account for the effect of elevated temperature:  Reduced yield strength for elevated temperature  Use of partial factors for fire design  Increased non-dimensional slenderness  Buckling length of columns in fire is taken as 0,5 and 0,7 of the system length for the top storey and for the other storeys, respectively  Specific buckling curves for the fire condition. Resistance of composite members in fire The simple models to calculate the resistances of composite members in fire are given in §4.3 and Annexes D, E, F, G and H of EN 1994-1-2 for composite slabs, composite beams, encased beams, encased columns and filled columns. Since the temperature generally is not uniformly distributed over the cross-section, the design resistance of a composite member in fire generally has to be calculated by dividing the section into a number of elements. The temperature and the corresponding reduction factors for steel and concrete strengths in each element are determined and the design resistance of all the elements are added to calculate the resistance of the entire cross-section. The simple models for composite members are more complex than the calculation for bare steel members. For this reason, most calculations for temperature rise and load bearing resistance of composite members are carried out using computer software. In addition, the resistances of many fire design solutions for composite members have been tabulated, as given in §4.2 of EN 1994-1-2. Resistance of composite slabs The simple models for fire design of composite slabs are specified in §4.3.1, §4.3.2 and §4.3.3 of EN 1994-1-2. As partition members, composite slabs are required to meet the criteria of insulation ‘ I ’, integrity ‘ E ’ and the load bearing resistance ‘ R ’. These must be demonstrated through fire tests, design calculations or both. The calculation of sagging and hogging moment resistances of slabs are based on different assumptions and temperature distributions as given in D.2 and D.3 of EN 1994-1-2. The contribution of the steel decking is generally included in the calculation of the sagging moment resistance, but conservatively ignored in the calculation of the hogging moment resistance. Resistance of composite beams Composite beams comprise steel sections structurally attached through shear connectors to a concrete or composite slab, with or without concrete encasement. Generally, the voids created by the deck shape over the beam