Impact of thin-walled high-strength steel structural sections

An experimental programme is reported which examines the progressive collapse behaviour of some thin-walled closed-section structural sections made from high-strength steels under quasi-static and impact axial loads. A comparison is made with theoretical formulae, which have been used successfully for predicting the behaviour of mild steel thin-walled structures. Ten quasi-static crush tests and 46 impact tests were conducted on spot-welded top-hat and laser-welded square sections. The thin-walled sections were made from two different types of high-strength steel and one mild steel, the mechanical properties of which were determined experimentally from quasi-static and dynamic tensile tests. Although no specific change in the collapse mode was observed, the limited weight-specific energy absorption efficiency of the high-strength steels under dynamic loadings hinders the weight-reduction potential of crashworthy designs. An unexpected difference in the structural effectiveness of spot-welded top-hat sections made from mild steels and high-strength steels was identified, but was not present for similar square sections. This difference further accentuated the loss in the advantage of high-strength steels over mild steels, especially for spot-welded top-hat sections, and led to differences in the agreement between the experimental results and the theoretical predictions.