## 1 Introduction  
Steel truss arch bridges are widely used in high-speed railway construction due to their high strength, light weight, large span, and aesthetic appeal [1, 2, 3]. As the span of railway bridges continues to increase and train speeds continue to rise, the interaction between large-span bridges and high-speed trains has garnered increasing attention [4, 5, 6, 7]. High-speed train operations exert significant dynamic impacts on bridges [8, 9, 10], affecting both the safety and economic viability of the structure. The impact coefficient is a dynamic amplification factor, which is defined in railway design standards as the ratio of the dynamic response to the static response of the structure, reflecting the magnitude of the impact effect. In recent years, numerous researchers conducted extensive research on the impact coefficients of bridges under moving train load effects [11; 12; 13; 14]. [PERSON] et al. [15], focusing on a large-span railway cable-stayed bridge, established a vehicle-bridge coupling model to investigate the impact on the main girder, stay cables, bearings, and bridge towers at various train speeds. [PERSON] et al. [16], using Monte Carlo simulation techniques, modeled the effect of reinforced concrete slabs on steel bridges and studied the effect of the impact coefficient on the fatigue performance of RC slabs. [PERSON] et al. [17] considered three different configurations and performed finite element analysis on a full-scale 3D bridge model to determine the impact factor (IF), while also accounting for the influence of soil-structure interaction (SSI) under three different soil conditions. [PERSON] et al. [18] discussed the dynamic behavior of twin-box girder bridges under high-speed railway traffic and found that the predicted dynamic response might unexpectedly exceed the static effects caused by the design load, even when the maximum vertical vibration levels in the deck are not severe, potentially leading to intense impact coefficients. [PERSON] et al. [19] conducted field measurements on a steel plate girder bridge in operation and, considering train speeds, derived the impact coefficients for the track structure and its main girder. [PERSON] et al. [20] analyzed the influence of vehicle speed and road roughness on a spatial Y-shaped steel arch bridge and calculated the impact coefficient of vehicles on a flat bridge deck at design speed. [PERSON] et al. [21] investigated the vibration serviceability and impact coefficient of a seven-span continuous cable-stayed bridge planned for an expressway extension using a three-dimensional vehicle-bridge coupled vibration analysis. Previous research on impact coefficients largely focused on simply supported beam bridges, cable-stayed bridges, suspension bridges, and other types of bridges, with relatively limited studies on large-span steel truss arch bridges for railway applications. Furthermore, most of the existing studies concentrated on the global impact coefficient of the bridge as a whole, while the local impact coefficients of the bridge are equally significant and should not be overlooked [22; 23; 24]. Given that steel truss arch bridges consist of numerous individual members, the impact effects on some of these members are more strongly correlated with the local dynamic characteristics of the bridge. Therefore, it is essential to investigate both the global and local impact behaviors of large-span steel truss arch bridges. This study focused on the Nanning Three Banks Yongjiang Special Bridge and investigated the dynamic interaction between the bridge and vehicles. To conduct this analysis, advanced computational tools, including multibody dynamics software SIMPACK and finite element software ABAQUS 2022, were employed to perform a coupled simulation of the vehicle-bridge interaction system. The primary aim of this simulation was to create a robust model that could accurately replicate real-world conditions.