Response of idealised composite beam-slab systems under fire conditions

This paper presents a numerical model for beam-slab floor systems in which a single compartment is subjected to fire. The system consists of a composite steel-concrete slab and a bare steel beam. Several idealisations are made in order to illustrate important behavioural patterns which occur under fire conditions. Nonlinear analyses are undertaken using an advanced yet computationally efficient computer program which accounts for the large displacement behaviour at elevated temperatures. The model is shown to capture the main parameters influencing the performance of the system under fire. In particular, the significance of axial restraint and thermal expansion on the overall deformation and capacity of the system is demonstrated. It is indicated that thermal expansion may have beneficial as well as detrimental consequences on the performance, depending on the particular structural configuration under consideration. The paper also closely examines the level of dependency of the response on the sequence of application of loading and elevated temperature as well as the assessment of the overall system response from consideration of the respective responses of individual components. It is shown that such concepts may be effectively employed in undertaking detailed studies for improved quantification of the fire resistance of beam-slab systems with a view to the development of more rational performance-based design procedures.