# Study on the Mechanical Characteristics of the Sleeper Slab Track on a Long-Span Steel Truss Bridge
## 1 Introduction  
With the development of railway construction in China, the proportion of bridges in railway lines has gradually increased. When a vehicle passes through the bridge, the wheel-rail force is transmitted to the bridge through the track structure, which causes strain and deformation of the bridge, consequently affecting the safety and comfort of the track structure on the bridge. [PERSON] et al. proposed a bridge-track-vehicle unit model to study the interaction among the mobile vehicle, track structure, and bridge. The results show that the bridge has a great influence on the dynamic response of track structure [1]. [PERSON] et al. found that the effects of track structure on vertical displacement and vertical acceleration of the arc body are significant [2]. [PERSON] et al. demonstrated that the effects of the track on the lateral responses of vehicle and bridge cannot be ignored and the reasonable and comprehensive analysis of vehicle-track-bridge interaction should consider the effects of the track [3]. In summary, the selection of track structure on a railway bridge is of considerable importance. At present, the ballasted track, slab ballastless track, and wooden sleeper (composite sleeper) track on the open deck are the main track forms used on bridges. The ballasted track is a common track form on the steel bridge deck. It has the characteristics of low engineering cost and strong adjustment ability. However, the use of a ballasted track will increase the height of the track structure and the secondary dead load of the bridge. In addition, under the repeated load of the vehicle, the deformation of the ballastbed will accumulate. In severe cases, the ballast will be broken and powdered. Therefore, it is very important to study the mechanical properties and identify the ballast. [PERSON] et al. analyzed the random vibration characteristics of the vehicle-track-bridge coupling model under different vehicle speeds, and proposed a problem of possible destabilization of macadam ballastbeds on railway bridges. One possible solution is applying the ballastless track structure [4; 5; 6]. By comparing the results from the cyclic loading test on the ballast using a large-scale triaxial test apparatus with the full-scale laboratory test in the railway test facility (RTF), [PERSON] et al. analyzed the permanent axial strains and particle size distribution under traffic loading [7]. [PERSON] et al. used an image analysis approach based on machine vision algorithms to assess ballast condition and degradation levels [8]. However, due to the structural characteristics of the ballasted track on the bridge, it is difficult to inspect the bridge deck and maintain the ballast bed. Consequently, this will lead to an increase in maintenance workload. Different from the ballasted track, the slab ballastless track can reduce the secondary dead load of the bridge and the maintenance workload. In the meantime, the mechanical characteristics of ballastless tracks will also be affected by the behaviors of bridges. [PERSON] et al. studied the interaction between the track and bridge under the action of vehicle loading and seasonal temperature change and proposed that stresses in track structure on bridges are strongly influenced by the coupling interface between track and bridge in the longitudinal direction [9]. Full-scale fatigue tests and post-fatigue loading tests were carried out by [PERSON] et al. to research the mechanical behaviors and fatigue performances of ballastless tracks laid on long-span cable-stayed bridges [10]. The results indicate that ballastless track on bridge has good performance in fatigue property. In the work of [PERSON] et al., a segmental model was developed in the laboratory, on which various types of ballastless tracks were paved [11]. The authors suggested that appropriate track type can improve the mechanical performance of the structure. Previous research has established that the slab ballastless track can improve track regularity and stability.