Steel Buildings in Europe

Part 6: Fire Engineering 6 - 22 There are two types of open section integrated beams: asymmetric steel beam (ASB) and integrated fabricated beam (IFB), as shown in Figure 3.8 and Figure 3.9 respectively. Generally, integrated beams can achieve up to 60 minutes fire resistance without being fire-protected. With the inclusion of additional longitudinal reinforcement, 90 minutes fire resistance is possible with an unprotected bottom flange. The total structural depths and typical spans of integrated beams are summarised in Table 3.6, which may be referred to at the preliminary design of multi-storey buildings. Table 3.6 Structural depth and typical span of integrated beams Type of floor Depth (mm) Span (m) ASB Integrated beam 280 to 400 6 to 9 IFB Integrated beam 250 to 450 6 to 9 3.3.3 Partially encased beams and columns Partially encased beams and columns are constructed by filling the space between the flanges of I-sections using plain or reinforced concrete, as shown in Figure 3.10 and Figure 3.11. Compared with the unprotected I-sections, which only have about 15 minutes fire resistance, partially encased sections can achieve over 60 minutes, which normally meets the fire resistance requirements of many multi-storey buildings. The increase in fire resistance period is due to the coverage of most parts of the surface area of the steelwork using concrete, which has a low thermal conductivity. Longer periods of fire resistance can also be achieved by increasing the amount of reinforcement embedded within the concrete, to compensate the loss of the strength of the steelwork in fire. u u 1 e e f h h c c b eff w 2 b A A s f f A = b x e Figure 3.10 Partially encased beam EN 1994-1-2 offers relatively simple rules and established datasheets in clauses §4.2.2 and §4.2.3 for fire design of composite beams and columns, including partially encased steel sections. These rules relate the fire resistance of