Fire Exposed Composite Steel-Concrete Slabs

Composite steel/concrete slabs, consisting of cold-formed profiled thin-walled steel decking and concrete cast on top, are a popular flooring system in modern steel framed buildings. The fire resistance is an important performance criterion. The behaviour of composite slabs in fire is rather complex, amongst others due to the highly non-linear material behaviour at elevated temperatures. In order to determine whether the behaviour in fire meets the requirements as specified in the building regulations, simple calculation rules are available, which are based however, on limited experimental evidence, and are therefore lacking a fundamental basis. The main goal of this research was to provide this fundamental basis and along with it the establishment of new more accurate calculation rules. A significant part of the work has been carried out within the scope of an ECSC co-sponsored research project From a literature survey it became apparent that with a view to validation of numerical models, experimental evidence on the behaviour of fire exposed continuous span slabs was scarce. Full scale well-instrumented fire tests have therefore been performed on various types of composite slabs to study the thermal behaviour near internal supports and the mechanical behaviour of continuous two-span systems. The parameters investigated comprise: reinforcement ratio, load level, insulation of internal support and type of steel decking (Section 2). Finite element models have been developed and validated for the simulation of the thermal and mechanical response. The numerical models were validated on the basis of experimental evidence and appeared to be suitable for parametric studies (Section 2). A new set of simple calculation rules for the assessment of the fire resistance of composite slabs has been established. These are based on extensive parametric studies, in which the geometry of the steel decking was varied systematically and which furthermore comprised all existing types of steel deckings. Intermediate results of the parameter study were confronted with the existing calculation rules to show the improvement (Section 3).