In order to investigate the damage process caused by the seismic pseudo-static load, quasi-distributed fiber bragg grating (FBG) sensors were placed in CRTS III ballastless track specimens. Low-cyclic reversed load experiments were then carried out. We studied the strain conditions at various points along the ballastless track under cyclic loading as well as the damage modes, strain curves, residual strains, and cross-sectional stresses of the self-compacting concrete layer and foundation slab. The damage process may be broken down into three stages: First, fractures show up at the base plate anchors; second, the shear reinforcement deforms; and third, the concrete layer is lifted until it is crushed. The CRTS III ballastless slab's maximum transverse tensile strain is greater than its maximum longitudinal tensile strain. Premature cracking of the self-compacting concrete layer will result from greater strain at the edge and corner of the groove and from a lack of reinforcing. It is tough to monitor the deformation of the groove area at simultaneously, which is not possible with more conventional monitoring methods like strain gauge sensors. Quasi-distributed FBG sensing can effectively observe the detailed strain development of the groove and its surrounding areas.

Due to the extensive construction of high-speed rail lines that traverse through seismically active areas, the possibility of a sudden earthquake occurring during train operation is very high. Additionally, the earthquake will intensify the dynamic response of trains and bridges, causing serious bridge damage. In this work, the dynamic response behavior of the bridge structures in the coupled train-bridge system under the earthquake is investigated based on the 4-table shaking table system. Shaking table experiments are also conducted on a high-speed railroad model of simple-supported girder bridge at a scale of 1/10 with the simulated layers of China Railway Track System type II (CRTS II) ballastless track slabs. The strain responses of rails, track plates, base plates, and beams were measured on the bridge using quasi-distributed fiber optic gratings both with and without seismic actions. The seismic isolation characteristics of the fasteners and the CA mortar layer were investigated, and the dynamic performances of the coupled train-bridge system under earthquakes was studied in the time and frequency domains.

Ballastless track structures are widely employed in high-speed rail networks because of their superior safety and durability. Among the various types of ballastless track, the Type II slab is currently one of the most extensively used and mature technologies in practice. Over the course of its service life, the damage within the ballastless track structure gradually accumulates in response to increased external loads. Therefore, it is crucial to continuously monitor the health condition of the track structure. In this study, a quasi-distributed fiber optic sensing system is adopted to monitor the deformation capacity and force performance of a Type II ballastless track slab under vertical load. The investigation aims to analyze the damage mechanism of the track structure under vertical pressure by assessing the deformation differences among its different components. The findings reveal that the incorporation of vertical reinforcement can enhance the pressure bearing capacity of the cement asphalt mortar layer to a certain extent, subsequently affecting the stress dilation. The stress performance of the ballastless track slab can be effectively monitored using the quasi-distributed fiber optic sensing technology under pressure. The outcomes of this research offer valuable insights for controlling displacement and analyzing damage in ballastless railway systems subjected to compression.

In addressing the challenges of analyzing seismic response data for high-speed railroads, this research introduces a hybrid prediction model combining convolutional neural networks (CNN) and long short-term memory networks (LSTM). The model's novelty lies in its ability to significantly improve the precision of fiber grating monitoring for high-speed railroads. Employing quasi-distributed fiber optic gratings, seven grating monitoring points were strategically placed on each fiber to capture responses of the track plate, rail, base plate, and beam during seismic activities. Using data from peripheral gratings, the model predicts the central point's response. A continuous feature map, formed via a time-sliding window from the rail's acquisition location, undergoes initial feature extraction with CNN. These features are then sequenced for the LSTM network, culminating in prediction. Empirical results validate the model's efficacy, with an RMSE of 0.3753, MAE of 0.2968, and a R 2 of 0.9371, underscoring its potential in earthquake response analysis for rail infrastructures.

As an advanced high-speed railway technology, ballastless track type II slabs have found widespread application in the development of high-speed train networks. However, the performance of ballastless track type II slabs deteriorates over time, making it crucial to investigate the performance of structural interlayer forces under load. This study explores the interlayer forces in ballastless track type II slabs under shear loads, the variation in interlayer force performance within the track slab, CA mortar layer, and base plate, and the impact of increasing the cross-sectional area of shear reinforcement on the mechanical performance of ballastless track type II slabs. Quasi-distributed fiber optic sensing is employed for these investigations. The results demonstrate the effective monitoring capability of a quasi-distributed fiber optic sensing network, setting a precedent for the utilization of fiber optic sensing technology in high-speed train structural health monitoring.

With the continuous development of high-speed railway technology, there are higher expectations for train operation and running safety. Shear failure is the main form of damage to the ballastless CRTS II slab as an essential part of the ballastless track system, and its interlayer shearing performance and damage mechanism play an important role in ensuring railroad safety. This paper employs quasi-distributed optical fiber technology to investigate the force characteristics, ductility performance, and damage mechanism of ballastless CRTS II plate in shear failure. The influences of shear reinforcement on the shear bearing capacity of ballastless track structure are also investigated. It is concluded that shearing force in each layer of the CRTS II ballastless track exhibits obvious nonlinear characteristics, and the introduction of shear reinforcement can improve the seismic perfor-mance. The quasi-distributed optical fiber sensing has good performance in the field of ballastless track moni-toring, which compensates for the limitation that traditional monitoring methods are difficult to be used in concealed CA mortar layer in long-term service and provides reasonable recommendations for ballastless track design and subsequent maintenance.

With the rapid expansion of the high-speed railway (HSR) network, high-speed train running safety (TRS) over bridges is increasingly highlighted in the world. Previously, spectral intensity (SI) was proposed and considered as a performance-based index for discussing TRS over HSR bridges in seismic design. However, the speed independence of the conventional SI index greatly limits its rationality and generalisation in the performance-based bridge design under earthquake. To this end, the velocity-related SI index is proposed for the first time and improves the limitations of the conventional index in this research. The discrepancy between the proposed SI and the conventional SI is explained theoretically, and the correlation between the proposed SI and train running speed is illustrated in detail. Additionally, a series of scale model experiments are conducted to validate the feasibility of the train-bridge coupled (TBC) system. The probability analysis of the proposed SI index is presented to help discuss the randomness and economy of HSR bridges. Furthermore, systematic parametric analyses are finished by taking the train running speed as the kernel parameter based on the TBC model. The simulation results show the conventional SI index unduly neglected the velocity-induced vibration of the train under an earthquake. Within the common train running speed range, the proposed SI indices have the same varying pattern with the derailment factors and are comprehensively larger than the conventional SI indices. The vibration induced by train speed seriously threatens TRS under earthquake, but it was ignored in the seismic design for the HSR bridge before.