Local stability of normal and high strength steel plates at elevated temperatures

•Behaviour and design of high strength and normal strength steel plates in fire are investigated.•Advanced nonlinear finite element models able to mimic the local buckling response of steel plates at elevated temperatures are developed and validated using results from experiments.•New design rules for the local buckling assessment of high-strength and normal- strength steel plates in fire are established.•Proposed design rules lead to improved accuracy relative to the current design rules provided in EN 1993–1-2 and prEN 1993–1-2.•Accuracy, safety and reliability of proposed design rules are verified against extensive numerical data. This paper presents an investigation into the local buckling behaviour and design of normal and high strength steel plates at elevated temperatures. The considered high strength steel grades include grades S690 and S460 as well as the normal strength grades S355, S275 and S235 taken into consideration. Shell finite element models of normal and high strength steel plates are created to mimic their local buckling response in fire, whose accuracy is validated against experimental results from the literature. Extensive numerical parametric studies are then carried out by means of the validated finite element models, taking into account different plate slendernesses, elevated temperature levels, edge boundary conditions and steel grades. The accuracy of the design provisions provided in the current European structural steel fire design standard EN 1993–1-2 and its upcoming version prEN 1993–1-2 for the consideration of the local buckling behaviour of normal and high strength steel plates in fire is investigated. It is observed that the existing design rules given in both EN 1993–1-2 and prEN 1993–1-2 lead to rather scattered estimations of the local buckling strengths of high strength steel plates at elevated temperatures. New cross-section classification rules and effective width design equations for the ultimate strength predictions of normal and high strength steel plates in fire are developed. High accuracy and reliability of the proposed design rules are demonstrated.