High‐Cycle Fatigue Performance of Fillet Welds in Bridges

Fatigue performance of welded joints is a critical consideration in the design, assessment, and maintenance of steel railway bridges, particularly under high‐cycle loading conditions imposed by repeated train passages. In New Zealand, fillet welds are encouraged to be used in bridge components due to their simplicity of fabrication, reduced construction time, and cost‐effectiveness; however, these welds are generally regarded as being more susceptible to fatigue cracking because of geometric discontinuities and stress concentrations at the weld toe and root. As KiwiRail advances its national infrastructure upgrade and bridge standardisation programmes, a reliable and quantitative evaluation of the fatigue behaviour of welded details is essential to ensure adequate durability, structural reliability, and safe service life.

This study is about experimental investigation into the high‐cycle fatigue performance of fillet‐welded T‐joint specimens representing typical welded details used in New Zealand steel railway bridges, including flange‐to‐web and stiffener‐type connections. The specimens are being fabricated from G350 structural steel using local welding procedures and are to be tested under sinusoidal cyclic loading using a 250 kN servo‐hydraulic MTS dynamic actuator in a purpose‐designed test rig. The loading parameters, including stress range and frequency, are selected to simulate realistic service conditions while satisfying high‐cycle fatigue testing requirements. Strain gauges, LVDTs, and visual monitoring are to be employed to record structural response, crack initiation, and crack propagation behaviour. The results will provide experimental S–N data and will be used to support and assess structural stress‐based fatigue evaluation methods for future application in bridge design and assessment.