Fatigue Performance of High-Frequency Welded Steel I-Beams

INTRODUCTION

High-frequency (HF) welding is a solid-state welding process that is also referred to as “electrical resistance welding.” HF currents heat up the surfaces to be joined together near their melting point; then, the surfaces are mechanically forced, or forged, together to form a welded joint.

Compared to conventional processes, HF welding is extremely fast and does not require welding consumables. For bridge fabrication, the I-shape is of interest. I-shapes can be hot-rolled or built up from three plates welded together with two joints. Using a conventional weld process, three plates are joined with four fillet or partial-penetration welds, two at each web and flange intersection. To orient the molten weld pool most favorably to gravity, likely only two welds can be made simultaneously; then, the work piece is flipped to finish the remaining two welds. With HF welding and dedicated fixturing, however, three plates are simultaneously brought into alignment and HF welded together through the creation of two complete joint penetration (CJP) welds. The HF CJP welds may lead to less injurious weld defects than fusion welds, and less heat input leads to less distortion of the work piece and smaller heat-affected zones. The speed of HF welding is at least an order of magnitude greater than conventional processes.

The primary objective of the research performed in this study was to evaluate the fatigue performance of HF-welded steel I-beams and make recommendations for the use of such I-beams in bridge design that are consistent with current practice. Stated more specifically, the desire was to make a preliminary determination of which American Association of State Highway and Transportation Officials (AASHTO) fatigue design category is appropriate for use in the design of HF-welded steel I-beams in resisting load-induced fatigue failure.⁽¹⁾ This was accomplished by performing fatigue testing on a series of six beam specimens with identical nominal dimensions and steel specification. All testing was conducted at the Federal Highway Administration Turner–Fairbank Highway Research Center.