Steel Buildings in Europe

Part 6: Fire Engineering 6 - 37 5 TENSILE MEMBRANE ACTION Full scale fire tests and real fire investigations in multi storey buildings have shown that when a floor develops tensile membrane action, it can achieve a higher fire resistance than calculations and tests on isolated members indicate. In order to take account of this beneficial behaviour of multi-storey buildings in fire, a new design model has been developed, which allows for a more economic solution to fire design. The model has been validated by tests. 5.1 Cardington fire test The prescriptive approach and the simple calculation models described in this guide are well-established methods to carry out the fire design of a multi-storey building. The application of such methods to an unprotected multi-storey steel building determines the fire resistance period as no more than 30 minutes. However, large-scale fire tests and real fire investigations over the years have demonstrated that some savings can be achieved in the fire design of the frame, and a new simple design method (BRE-BM) has been developed. 5.1.1 Full-scale fire tests Following the investigations on real fire-damaged buildings in the UK at Broadgate and Basingstoke, fire tests were conducted in Cardington (UK) on a full-scale eight-storey steel-composite framed building with unprotected steel beams and trapezoidal composite slab, as shown in Figure 5.1(a). 0 50 100 150 200 250 300 350 0 100 200 300 400 500 600 0 200 400 600 800 1000 1200 Time (mins) Maximum vertical displacement (mm) Maximum steel temperature (°C) Maximumvertical displacement Maximum temperature (a) Full-scale building tested in Cardington (b) Temperature and displacement of secondary beam Figure 5.1 Cardington fire tests Observations from the tests and the real fire investigations have consistently shown that the performance of a whole steel-framed building in fire is very different from that of its individual members. Under applied actions and a real fire, significant interactions between different types of structural members and important changes of their load-carrying mechanisms take place in real structures. The inherent fire performance of unprotected steel elements in