Steel Buildings in Europe

Part 7: Fire Engineering 7 - 27 The value of the adaptation factors κ 1 and κ 2 should be taken according to EN 1993-1-2. Members subject to combined bending and axial compression A simplified design method is also available to verify the fire resistance of steel members subjected to combined bending and axial compression, such as slender columns under eccentric load and long beams with lateral buckling. For this situation, the simple calculation model takes into account the combination effect of bending and compression by combining above two models for the simple loading condition. Detailed information is given in EN 1993-1-2. 5.3.3 Determination of fire protection material thickness In situations where requirements with respect to fire resistance are high (generally more than R30), the application of prescriptive rules usually leads to the fire protection of steel structures. When passive fire protection is necessary, the knowledge of the critical temperature, the section factor and the fire resistance time required, allow for a given fire protection system (spray, board, intumescent coating), determination of the thickness to apply. Only products which were tested and assessed in standard fire tests according to the European standard EN 13881 may be used in practice. The required thickness can usually be determined from manufacturer’s published data. Such manufacturer’s data can be given in form of table or diagram as illustrated in Figure 5.7. The data generally relates the thickness of fire protection material to the section factor of the steel member ( A p / V ), the critical temperature and the fire resistance time required. For typical building construction using standard I and H steel profiles, the value of A m / V is usually in the range 30 – 450 m -1 . Fire resistance rating R60 Section factor A p / V (m -1 ) Steel temperature (°C) Figure 5.7 Example of French diagram for boarded fire protection In practical design, for a given fire protection material, the thickness may be determined according to following steps:  Choose the data related to the fire resistance time required  Calculate the section factor according to the shape of the steel profile, the presence of any shading of the structural member against heat transfer from