New AISC and EC3 design for S690 plate girders at elevated temperatures

Abstract

Recently, the determination of the strengths of bridge girders exposed to fire has become of great importance as a result of the failure of some famous bridges for the same reason (e.g. Birmingham and MacArthur Maze Bridges (USA)). On the other hand, S690 high strength steel is widely examined and used in bridges all over the world, such as Mttådalen Bridge in Sweden. With respect to the effect of elevated temperatures on the strength of flexural members, stocky I-section beams have been studied in the literature. On the opposite, the lateral-torsional buckling (LTB) strengths of laterally-unrestrained plate girders with slender webs, which are used extensively in bridges such as those of Birmingham and MacArthur Maze Bridges (USA), and particularly formed from S690 at elevated temperatures have not been addressed. Additionally, AISC (2016) and EC3–1-2 (2005) do not neither cover S690 steel elements nor IPGs with slender webs. Therefore, these girders are simulated in this paper using ABAQUS programme. Currently, the simplified finite element method used successfully by Chen and Young (2008) and Fang and Chan (2019), which utilises the reduced material properties of S690 above the room temperature, is used, which means assuming a balanced structure and a uniform temperature range. The parametric studies consider the variations of the cross-sectional radius of gyration and elastic section modulus. Since the main focus of this paper is strength predictions, strengths are first compared to design models initially proposed according to AISC and EC3–1-2, which are found to yield very conservative predictions. Then, modified AISC and EC3–1-2 design models are recommended, which can safely predict the strengths of S690 IPGs with slender webs at elevated temperatures.