## 1 Introduction
The slope of S-N curve changes from low to high cycles in the fatigue design codes, such as Eurocode3 [9] and the International Institute of Welding (IIW) [12]. Therefore, the slope of the master S-N curve at high cycles and its influence on the bridge fatigue life are also discussed in the present study. The studies on the fatigue behaviors of rib-to-deck welded joints in orthotropic steel decks using equivalent structural stress have been given by [PERSON] et al. [20] and [PERSON] et al. [21]. However, these research efforts on the fatigue performance of rib-to-deck welded joints in OSDs occurred under experimental conditions. In the present study, the research is oriented towards an actual bridge: Jiangyin Bridge. The actual bridge model and fatigue vehicle load model are given, and the vehicle daily traffic volume data were obtained through bridge structural health monitoring. The change of the weld size affects the fatigue performance of welded joints. [PERSON] et al. [22] pointed out that one of the main methods to improve the weld joint fatigue properties is to change the weld size. The new improving deck-rib welding details in OSDs include increasing the size of the weld itself and increasing the thickness of the U-rib edge close to the weld seam, both of which increase the distance from the weld toe to the weld root. The parameters, including the relative weld height and deck toe flank angle, have an effect on the weld root notch stress intensity factors for rib-to-deck welded joints, as proposed by [PERSON] et al. [23]. They also investigated the fatigue performance of an innovative rib-to-deck welded joint which has an increased weld depth due to the rolled U-rib with thickened edges [24]. The rolled U-ribs with thickened edges may significantly change the stress distribution around the rib-to-deck joint. [PERSON] et al. [25] evaluated the fatigue performance of the rib-to-deck welded joints in OSDs with thickened edge U-ribs (TEUs) and investigated the effects of weld penetration and the open angle of the rib-to-deck joints. The findings showed that as the penetration depth in TEU specimens decreased from 12 to 4 mm, the maximum notch stress was only increased by 2.8%. The use of TEUs significantly improved the robustness of the welded joints in terms of sensitivity to variations in the weld penetration. The appropriate increases in the open angle of the rib-to-deck joints in OSDs with TEUs further improved fatigue performances. [PERSON] et al. [26] pointed out that increasing the weld size is effective in improving the fatigue performance within a certain range. The transition angle and radius between the weld and the deck have an important impact on the fatigue strength of butt weld joints. When the transition angle is fixed (i.e., the weld shape remains the same), the weld fatigue strength does not change with the weld width and height. [PERSON] et al. [27] highlighted that the open angle between the deck and weld seam had a significant effect on the effective notch stress at the weld toe. Therefore, in the present study, the weld geometry size was measured in the experiment, which was within the range of the weld manufacturing errors, without any treatment, such as thickening of the U-rib or enlarging of the weld seam. The influence of the weld size differences caused by weld manufacturing errors on the fatigue performance of the deck-rib welding details in the OSD of Jiangyin Bridge is discussed based on the stress integration approach. In order to improve the fatigue performance of the weld seams, scholars have put forward different treatment methods, such as ultrasonic treatment, the crack stop hole treatment, the grinding treatment, and so on. The ultrasonic impact is an effective method to decrease welding residual stress and thereby improve the fatigue strength of welds for steel bridges [28; 29; 30]. The crack stop hole treatment could reduce stress concentration and prevent cracks from growing [31; 32].