Experimental study on the static tensile and fatigue performance of resistance spot-welded reinforcement in prefabricated box girders for high-speed railways

• Crack initiation in resistance-welded steel reinforcement was localized at the nugget–base metal transition zone • Fatigue performance of large-diameter-ratio welded joints was quantified, and critical thresholds for design were proposed. • A design-oriented formula for allowable fatigue stress amplitude was developed for high-speed railway applications. For resistance spot-welded reinforcement with large diameter ratios used in prefabricated box girders of the Xiong’an–Xinzhou high-speed railway, we conducted indentation-depth and micro-morphology inspections, monotonic tensile tests, and high-cycle fatigue tests. All indentation depths met the code limit; the fusion-nugget region was dense and continuous with uniform elemental distribution; tensile performance was sound. Parametric analysis shows that increasing the diameter ratio from 1.0 to 1.8 reduces the high-cycle fatigue limit by about 23 percent and lowers the degradation-rate descriptor from roughly 600,000 to 340,000 cycles; once the diameter ratio exceeds 1.5, the high-cycle limit drops rapidly. As the stress ratio increases from 0 to 0.5, the high-cycle limit decreases nearly linearly to about 86 MPa while the degradation-rate descriptor increases monotonically. In addition, all fatigue data outperform those of the base material and conventional joints. A design expression for the allowable fatigue stress amplitude is developed, providing experimental support and an engineering calculation method for long-life design of prefabricated box girders.