Buckling behaviour of steel and composite beams at elevated temperatures

The objective of this research was to study the buckling behaviour of steel and composite beams at elevated temperatures. Both global buckling in the form of lateral torsional buckling and local buckling were studied. The first part of the study focused on the lateral torsional buckling behaviour of bare steel beams with an aim to develop design approaches for laterally unrestrained steel beams at elevated temperature. The second part focused on the local buckling behaviour which limits the ductility of beams. Both bare steel beams and composite deck slab with re-entrant steel decking were considered for the second part to investigate the ductility issue related to inelastic behaviour in the hogging moment regions under fire conditions and to propose the model of the moment-rotational relationships. Numerical analysis using MSC.MARC Mentat and published test results were used to study the lateral torsional buckling of steel beams at elevated temperatures. Subsequently, a general approach, different from the current approach, called an alternative approach was suggested. Besides, a simple analytical approach, based on Rankine principle, was applied to estimate the lateral torsional buckling failure of steel beams in fire. Both proposals were shown to provide a good correlation with the numerical and test results. The investigation of the local buckling behaviour at elevated temperatures comprised of both experimental and numerical investigation. The experimental investigation consisted of two series of tests, namely, investigation on steel beams as the first series and investigation on composite beams as the second series. The numerical investigation involved fairly extensive parametric studies using the numerical model which had been validated with test results. Finally, the analytical models for the moment-rotational relationships under fire conditions were proposed.Doctor of Philosophy (CEE