Experimental Study on the Behavior of Full-Scale Composite Steel Frames under Furnace Loading

In current design codes, structural fire behavior is evaluated by conducting experiments on isolated structural elements in a standard fire condition. In such tests involving single isolated elements, many aspects of structural behavior that occur due to the interaction between adjacent members as well as the role of connections cannot be studied. Performance of real structures subject to fires is often much better than that predicted from standard tests due to structural continuity and the interaction between members. In addition, tests performed under the current design codes subject the structural element to a heat up phase only and do not consider the cool-down phase during which local/global failure of the structure may occur. This paper describes the results of a furnace test conducted on two full-scale composite steel frames. In one frame the beam-to-column connections were protected while in the second frame the columns as well as the beam-to-column connections were protected. A special test furnace was built in which full-scale frames could be tested under load. The structural frame was subjected to a heat up phase followed by a cool-down phase. During the test, the furnace temperature, steel and concrete temperatures as well as the horizontal and vertical deflections were recorded. The complete deformation process of the test frame observed during the heating phase and the cooling phase, including failure of the frame is described in this paper. A comparison of the data obtained from the two tests indicates that the fire resistance of a composite beam is significantly better than that of a steel column. Finally, experimental data on fire resistance of composite frames with conventional floor slab construction was compared with data from slim floor slab construction. Results indicate that the fire resistance rating of frames constructed with slim floor slabs is at least as good as that of frames with conventional floor slab construction. It is proposed that in certain engineering design scenarios, the composite beam may not have to be protected due to its higher fire resistance rating, while the steel column should be protected from fire heating.