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A novel leaning-type spatial arch bridge without thrust was designed as a landmark in a major urban city. In order to alleviate the higher negative reaction force at side span and enhance the lateral stability, commonly the case within this type bridge, a large-size replaceable box-shaped steel rod with pinned connections was introduced. The fatigue behaviour of the box-shaped steel rod and related upper and lower anchorage segments was investigated through a full-scale constant-amplitude fatigue test under axial loading. In comparison to the fatigue test results, the fatigue evaluation based on Eurocode 3 nominal stress design curve FAT56 considerably overestimated the fatigue strength of critical welded detail in box-shaped steel rod, which was underrated according to the universal International Institute of Welding effective notch stress design curve FAT225. The presented full-scale programme also validated the applicability of the latter method, which presented conservative results, to large-size thick-plate (80？mm) welded joints. The conclusion based on the test and theoretical results may provide a reference for the fatigue design of adopting box-shaped steel rod in spatial arch bridges