Lateral instability of steel beams in fire : behaviour, numerical modelling and design

The lateral torsional buckling behaviour and design of steel beams in fire are investigated in this paper. Finite element models able to replicate the lateral-torsional buckling (LTB) response of steel beams at elevated temperatures are developed and validated. The validated finite element models are used to carry out extensive parametric studies to explore the LTB behaviour of steel beams in fire, considering various cross-section shapes, member slendernesses, steel grades, elevated temperature levels and different fabrication processes. A design equation for the LTB assessment of steel beams at elevated temperatures is developed on the basis of the results from the extensive parametric studies. The high accuracy, safety and reliability of the proposed design approach are illustrated, which is also compared against the beam design rules existing in the European structural steel fire design standard EN 1993-1-2. The design proposals made in this paper are compatible with the new LTB assessment equations that are due to be incorporated into the next version of the European room temperature structural steel design standard EN 1993-1-1 and lead to more accurate ultimate strength predictions relative to the beam buckling design equations existing in EN 1993-1-2