Full-scale fire test on a composite floor slab incorporating long span cellular steel beams

As part of an international major research initiative, dealing with the behaviour of long span cellular beams in steel framed buildings under fire, a large-scale fire test incorporating 15m long cellular beams was carried out. The test incorporated unprotected secondary cellular steel beams acting compositely with the supporting floor slab. The floorplate in its entirety was designed to carry the load with unprotected beams, when subjected to a severe fire, by utilising membrane action of the floor slab. The overall structure performed very well supporting the full applied static load for the duration of the test. The unprotected cellular steel beams were subjected to distortional buckling, with only the top tee providing any support through catanary action. The test supported the assumptions adopted in the structural design approach and provided an accurate estimate of the strength of the floorplate. Comparison of the recorded time-temperature relationship of the fire with the design method presented in the Eurocodes shows that the code under-predicts the severity of the fire, although this was compensated to some extent by the conservative assumptions embedded within the structural model.