Mechanical properties of partially damaged structural steel induced by high strain rate loading at elevated temperatures – An experimental investigation

Abstract

In structural engineering practice, understanding the behaviour of steel under extreme loading conditions is essential for accurate prediction of material response when subjected to a combination of severe load scenarios such as collision by heavy objects and a following fire. Hitherto, the combined effects of high strain loading and subsequent elevated temperature have not been widely investigated on the mechanical properties of structural steel. A comprehensive test program is carried out to investigate the post-impact fire properties of Grade 350 steel under well-defined conditions, the results of which are reported in this paper. Coupon specimens have undergone interrupting high strain rate (HSR) tensile loading at impact level, controlled locally at different levels of elongation, to account for different deformation states. Three different damage levels are introduced with respect to the displacement corresponding to the ultimate stress (fu). Subsequently, the partly damaged specimens are subjected to steady-state quasi-static tensile loading to failure at temperatures ranging from ambient to 600 °C. The overall stress–strain relationship, as well as the mechanical properties of pre-damaged steel, are presented at elevated temperatures and compared to those of each individual loading scenario. The test results demonstrate that the effects of these combined actions are profoundly different from those in which the structure is subjected to either high strain rate or thermal loading individually. It is shown that the strength and ductility of mild steel is significantly dependent on the rate of loading, the pre-deformation history and the temperature to which it is subsequently exposed. This necessitates the development of models which take into account the coupled effect of high strain rate and temperature in rational fire analysis and design of steel structures.