Zhaowei Chen

1. Urban rail transit systems have expanded rapidly in densely populated areas, offering efficient and sustainable mobility [1]. However, operation-induced environmental vibrations increasingly und...

The increasing density of urban rail networks has resulted in substantial growth in metro-superstructure building development. These structures face dual engineering demands in high-seismic regions: ensuring occupant comfort by mitigating metro-induced vibrations while maintaining structural safety during seismic events. Traditional isolation bearing systems frequently fail to address both vertical and horizontal excitations simultaneously. To address this limitation, a novel three-dimensional seismic and vibration isolation bearing (3D-SVIB) is developed, exploiting the superelastic properties of shape memory alloy (SMA) materials. The 3D-SVIB incorporates thick laminated natural rubber (LNR) components and SMA wires arranged in a parallel configuration. The LNR module primarily accommodates vertical compression loads, while both components collectively resist horizontal shear forces, thereby achieving decoupled directional responses. Mechanical constitutive models were developed based on comprehensive experimental data, with testing demonstrating that the bearing’s vertical stiffness increases from 1[ ]559[ ]kN/mm to 2[ ]107[ ]kN/mm under progressive compression loading. Furthermore, the horizontal equivalent stiffness increases from 2.95[ ]kN/mm to 4.76[ ]kN/mm with increasing shear strain amplitude. The bearing system maintains structural stability under deformation levels reaching 150% and demonstrates superior energy dissipation capabilities. Coupling analysis reveals minimal interaction effects, with stiffness variations maintained below 10.05%, thereby validating the decoupled design philosophy. Additionally, frequency response analysis indicates significant resonance control improvements, with structural period elongation achieving 1.93[ ]times (horizontal) and 5.33[ ]times (vertical) compared to the original fixed-base structure. The −12[ ]dB isolation thresholds are reduced to 1.04[ ]Hz and 2.12[ ]Hz for horizontal and vertical directions, respectively, representing 85% and 82% improvements over baseline structural configurations. Dynamic analyses demonstrate substantial vibration reductions under both excitation types. Metro-induced vertical accelerations decrease by 31.65–34.95% across building floor levels, with insertion loss reaching 10.1[ ]dB. Under seismic loading conditions, the 3D-SVIB system limits top-floor displacement to 20.3% of fixed-base response levels, compared to 76.7% achieved by conventional isolation systems. Moreover, maximum interstory displacement ratios are reduced to 61.1% of non-isolated values. Engineering validation through a comprehensive Chongqing transit-oriented development (TOD) project confirms the system’s practical effectiveness for metro-superstructure applications in seismically active regions.

Pier settlement is inevitable in high-gradient elevated lines, which leads to vertical deformation of track structure. The uncoordinated deformation causes longitudinal slip and vertical gap between sleeper and ballast bed. In view of the above problems, this paper considers the vertical and longitudinal nonlinear mechanical characteristics of ballast bed, explores the influence of pier settlement on the contact characteristics of sleeper and ballast bed in rack railway system. The paper pays attention to the nonlinear contact characteristics of pier settlement and vehicle running load on the sleeper and ballast bed mechanical properties and dynamic responses. The results show that the influence of pier settlement on system characteristics is mainly concentrated in vertical direction, which directly leads to vertical gap between sleeper and ballast bed (i.e., the appearance of unsupported sleeper). Compared with pier settlement position, structure of adjacent pier area is more sensitive to the change of pier settlement. The vertical damping effect of ballast bed is worse than that of longitudinal damping effect at pier settlement and pier adjacent to pier settlement. The sliding caused by large slope lines and pier settlement has no effect on the mechanical characteristics of ballast bed.

During the operation of rack vehicles, gravity center offset is usually induced by the passenger distribution and the equipment layout, which greatly deteriorates the gear-rack dynamic meshing effect and the wheel/rail nonlinear friction contact behavior, and further threatens the safety and stability of the vehicle. Aiming at this problem, dynamic behavior of rack vehicle system subject to gravity center offset is investigated in this work. Considering the disturbance effect of gear-rack meshing impact and wheel/rail dynamic contact behavior, a complete dynamic model of rack vehicle is established based on multi-body dynamics, adopting which the influence of the carbody gravity center offset on the dynamic characteristics of rack vehicle and nonlinear meshing behavior of driven gear-rack system are explored. Results show that: The gear-rack dynamic contact force results in an impact under the rack vehicle carbody gravity center offset, and the impact increases with the increase of running speed. The gear-rack dynamic contact force reaches 73kN when the speed reaches 30km·h-1. The lateral offset of the gravity center has a linear effect on rack vehicle running safety, and the wheel/rail vertical force is affected by the gear-rack dynamic meshing and produce vibration. The rack vehicle running stability is more sensitive to the longitudinal offset of the gravity center. The carbody acceleration increases by 4.8 times when the carbody gravity center is 3.0m forward. The vertical Sperling index of the vehicle is optimal when the carbody gravity center is behind in 0~1 m. The conclusions of this study provide theoretical support for the worldwide rack railway design and safe operation.

To investigate the dynamic characteristics and safe operation speed threshold of metro train passing through curved bridge (CB) considering resilient wheels, the mechanical connection characteristics of rim and web are discussed firstly. Based on the train–track–bridge interaction theory, the coupled dynamic model of metro train-CB considering resilient wheels is established. Then, the vehicle–bridge coupled dynamic characteristics under the excitation of long-short wave track irregularity are researched. Finally, from the perspective of dynamics, the safe operating speed threshold of metro trains passing through curved bridge considering resilient wheels (RW) is discussed. Results show that the vertical wheel–rail force of RW is reduced, but the lateral wheel–rail force is amplified compared with the solid wheels (SW). The vertical vibration acceleration of the wheel is reduced, but the lateral vibration acceleration is increased. It is recommended that the speed of metro trains running on curved bridge is not more than 60 km/h. The vehicle–bridge coupling dynamic response is aggravated with the speed and load of metro train. The vibration of the inner side of the curved bridge is greater than that of the outer side, and the vibration reduction effect of the RW on the inner side is more significant than that on the outer side. The RW has a vibration absorption effect on the wheel–rail vertical and the vibration of the curved bridge force within 40–140 Hz.

Urban rail transit is rapidly evolving, with long-span cable-stayed bridges becoming increasingly popular among engineers because of their adaptability. However, as the operation time of bridges with tracks increases, the combined effects of repeated wheel loads and various bridge system excitations, including temperature changes and shrinkage–creep, gradually alter the alignment of the main beam. Similarly, the track structure on the bridge deck also undergoes vertical displacement, leading to corresponding degradation in rail alignment. This study applies singular function theory and verifies its effectiveness in bridge mechanical analysis. For the steel spring floating plate track cable-stayed bridge system, the mapping relationship between the deformation of the bridge’s main beam and the track’s deformation under bridge system excitation is derived, integrating singular function theory with the theory of train–track–bridge dynamic interaction. By analyzing the force transfer mechanism of the track–bridge system under system excitation, this research examines the effects of different excitations on the coupled dynamic response of the train–track–bridge. These findings suggest that system excitations increase the dynamic response of the train–track–bridge system, which is crucial for improving the durability and reliability of urban rail transit infrastructure.