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 composi te steel-concrete slab and a bare steel beam. Several idealisations are mad e in order to illustrate important behavioural patterns which occur under f ire conditions. Nonlinear analyses are undertaken using an advanced yet com putationally efficient computer program which accounts for the large displa cement behaviour at elevated temperatures. The model is shown to capture th e main parameters influencing the performance of the system under fire. In particular, the significance of axial restraint and thermal expansion on th e overall deformation and capacity of the system is demonstrated. It is ind icated that thermal expansion may have beneficial as well as detrimental co nsequences on the performance, depending on the particular structural confi guration under consideration. The paper also closely examines the level of dependency of the response on the sequence of application of loading and el evated temperature as well as the assessment of the overall system response from consideration of the respective responses of individual components. I t is shown that such concepts may be effectively employed in undertaking de tailed studies for improved quantification of the fire resistance of beam-s lab systems with a view to the development of more rational performance-bas ed design procedures. (C) 2000 Elsevier Science Ltd. All rights reserved.