Steel Buildings in Europe

Title Worked Example – Fire safety strategies and design approach of steel floor beam 4 of 10 6 - 52 3.1.2. Fire protection boards The section factor of the beam section A m / V = 200 m -1 < [ A m / V ] max = 260 m -1  20mm thick fire board is adequate for R60. Table 3.1 3.1.3. Sprayed coatings A m / V = 200 m-1, 16mm thick sprayed coating is adequate for R60. Table 3.2 3.1.4. Intumescent coatings A m / V =200 m-1, 0,69 mm thick intumescent coating is adequate for R60. Table 3.3 3.2. Alternative structural solutions To avoid the costs of protection materials and reduce the cost of construction, it is preferred to use unprotected sections, as long as the R60 requirement is satisfied, by using alternative structural solutions. These include encasing the beam in concrete or using a composite slab. These options are discussed in the sections that follow. 3.2.1. Partially encased beam Load level: η fi = 0,477 < 0,5 Section ratio: h / b = 300/150 = 2,0 > 1,5. Hence, for R60 fire resistance, a partially encased beam using concrete without reinforcement can satisfy the R60 requirement. Note that the extra weight of the concrete should be added to the permanent action. Table 3.7 3.2.2. Integrated beams Integrated construction makes use of asymmetric steel sections containing the steel beam within the depth of the precast concrete slab. This solution may satisfy the R60 requirement without the need of fire protection. Section 3.3.2 3.3. Simple calculation models To verify the fire resistance of the beam at its fire ultimate limit state, the simple model given in EN 1993-1-1 is used, following the flowchart given in Section 4.4 of this publication. This model is applied to unprotected sections and to sections protected with fire boards. The next section presents the calculation using the load bearing resistance approach. In order to obtain an optimised design, the worked example uses different protection thicknesses until the optimal is found. The critical calculation approach can only be used when the temperature across the cross-section is uniform and it is not shown in this example.