## 1 Introduction  
With the large-scale construction of the railway in China, super-long-span suspension bridges have gradually been popularized and applied in high-speed railway construction [1], considering the engineering economic factors when crossing complex river systems and geology. Although the suspension bridge is known for strong crossing capacity, convenient construction, and beautiful appearance, the bridge and the CWR laid on it form a complex spatial coupling model. Hence the bridge-track interaction is inevitable. CWR on suspension bridges not only imposes the difficulties of CWR itself to the common long-span bridge but also gives rise to a series of other technical difficulties. Specifically, the nonlinear factors of line resistance, as well as the large displacement of the structure, the initial stress of the main cable and suspender, the cable sag, etc., should be considered in the design and calculation of CWR. The track and large-span bridge have been investigated in different aspects, including: analytical algorithm of the bilinear resistance model [2]; nonlinear finite element model (FEM) [3, 4, 5, 6, 7]; nonlinear static analysis program using a truss model [8]; static and dynamic analysis of cable structures based on catenary cable element [9]; design optimization for primary beam shape and plate thicknesses of long-span suspension bridges [10]; and the distribution of rail longitudinal force on large-span bridges [11, 12, 13, 14]. Additional rail forces, as permitted by different countries, for addressing bridge-track interaction are summarized in [15]. Nevertheless, most existing studies only focus on cable-stayed bridges, to the neglect of the suspension bridge. The latter will drive CWR to produce larger deformation under the load of the train, because of its flexible system, thus posing a huge challenge to the stability and comfort of high-speed railway. Therefore, it is necessary to figure out the interaction mechanism of CWR on suspension bridges. REJ is a crucial structure of CWR. It consists of the stock rail and switch rail. The switch rails are fixed while stock rails expand. Under the ideal working condition, the stock rail and switch rail are always close to each other. It is beneficial to significantly reduce rail stress and coordinate bridge-track displacement. The limited bridge lengths with different configurations of rail and deck expansion joints are suggested in [16]. In terms of the REJ layout optimization, the position of the fixed pier is adjusted [17]. The relative position of stock rail and switch rail of REJ is swapped, and the laying length of small resistance fasteners is optimized [18; 19]. In terms of dynamic characteristics, nonlinear wheel-rail contact is considered [20; 21]. A simplified REJ model under train load is established [22], and experiments on the dilation length [23] as well as the dynamic performance of REJ [24] are carried out to evaluate the service status of REJ on bridges. It can be seen from the previous studies that, most of the REJ layout optimizations only pay attention to the mechanical characteristics of the bridge and track structure under static loads, but neglect the extending-retracting response of REJ under dynamic loads. As the weak link of CWR, the layout of REJ should be optimized in view of not only the statics, but also the dynamics. This work has two objectives: on the one hand, to explore the interaction between CWR and suspension bridge, based on a suspension bridge with a main span of 1092 m in South China And, on the other hand, to research the dynamic mechanical characteristics of REJ on the suspension bridge. Based on the above, an optimization method for choosing the installation location and range of REJ on the suspension bridge is put forward, to further improve the design method of CWR for high-speed.