Composite joints under M-N at elevated temperatures

The Eurocodes recognise robustness as a way to ensure the structural integrity of a building frame subjected to an unforeseen event and therefore to avoid a so-called “progressive failure” mode in extreme loading situations. However, few practical guidelines exist nowadays which would allow a designer to design a structure accordingly. Within the European RFCS ROBUSTFIRE project, the behaviour of steel and composite car parks subjected to localised fire leading to a column loss was investigated. Under such a scenario, the beam-to-column joints play a key role in the global structural response. Indeed, these joints, initially loaded in bending, may be subjected to elevated temperatures and to combined axial load “N”, bending moment “M” and shear forces “V”. In this paper, a methodology to predict the mechanical response of bolted composite beam-to-column joints at elevated temperatures under M-N is presented and validated through comparison with detailed numerical results and experimental tests. This methodology is based on an analytical method able to predict M-N resistance interaction curves for steel and composite joints and which is in full agreement with the component model recommended by the Eurocode.