NUMERICAL AND ANALYTICAL STUDIES OF JOINT COMPONENT BEHAVIOUR IN FIRE

Full-scale fire tests have clearly shown that joints in composite steel-frame buildings have a considerable effect on the survival time of the structure, due to their ability to transfer forces from hot parts of the structure to cooler zones. Realistic modelling of joints in global analysis could be of great importance in structural fire design calculations, which can either be used to give confidence about safety margins or to help to reduce the cost of fire protection strategies. A versatile approach for predicting the high temperature behaviour of joints is the “Component Method”, in which a joint is considered as an assembly of a number of individual basic components, allowing a large number of possible variables in a beam-to-column joint to be considered simultaneously. This method provides a practical analytical approach to joint modelling under the simultaneous effects of loading, thermal degradation of materials and forces due to restraint of thermal expansion, all of which occur concurrently in a building fire. This paper describes the main findings from an ongoing study of the column web compression zone in fire, including the effect of superstructure loading. A range of column sections has been analysed at different temperatures and axial load ratios under transverse loading using ANSYS. From this study a temperature-dependent reduction factor for the transverse resistance of the column web and a simplified analytical approach have been developed to predict the force-displacement behaviour of the compression zone. The results have been compared with high temperature experiments and generally good correlation has been found. The test setup for a further series of bi-axial high temperature compression experiments is described.