Current seismic damage assessments for high-speed railway (HSR) bridges primarily focus on the overall structural safety, lacking evaluations from multiple performance perspectives, which affects the post-earthquake traffic decision-making for the bridges. This study proposes a performance-based comprehensive functional damage probability assessment framework for high-speed railway simply supported bridges (HSRSSBs) under earthquakes. The framework categorizes the functions of HSR bridges into three levels: post-earthquake traffic function (PTF), structural bearing function (SBF), and collapse resistance function (CRF), corresponding to the operational, structural safety, and structural integrity requirements of HSRSSB, respectively. By analyzing the damage states of key bridge components during earthquakes, the functional damage probability assessment indicators and classification thresholds are established according to various performance requirements. Damage probability calculations are conducted using the probability density evolution method and vulnerability method. Finally, based on the relationship between damage probabilities at different functional levels, a comprehensive damage probability assessment framework considering the three-level performance requirements of HSRSSBs is developed, and the influence of varying pier heights on the functional damage probability relationship is examined. The results indicate that current HSRSSB designs meet all performance requirements under frequent earthquakes. Under design-level earthquake conditions, the SBF remains in a slight damage state, while the PTF exhibits varying degrees of damage, which worsens as pier height increases. The pier structure satisfies seismic demands even under rare earthquake conditions.
Effective maintenance of railway infrastructure is crucial for safe and comfortable transportation. Among the various degradation modes, track geometry deformation due to repeated loading significantly impacts operational safety. Detecting and maintaining acceptable track geometry involve the use of track recording vehicles (TRVs) that inspect and record geometric parameters. This study aims to develop a novel track geometry degradation model that considers multiple indicators and their correlations, accounting for both imperfect manual and mechanized tamping. A multivariate Wiener model is formulated to capture the characteristics of track geometry degradation. To address data limitations, a hierarchical Bayesian approach with Markov Chain Monte Carlo (MCMC) simulation is employed. This research contributes to the analysis of a multivariate predictive model, which considers the correlation between the degradation rates of multiple indicators, providing insights for rail operators and new track-monitoring systems. The model’s performance is validated through a real-world case study on a commuter track in Queensland, Australia, using actual data and independent test datasets. Additionally, the study demonstrates the application of the proposed multivariate degradation model in developing a condition-based inspection policy for track geometry, potentially reducing the number of TRVs runs while maintaining abnormal detection levels and failure rates.
The stick–slip vibration of the disc brake system at low speed is caused by the interaction of multiple factors. This paper focuses on the disc brake system of the high-speed train as the research object, establishing three- and four-degree-of-freedom (DOF) dynamic models considering wheel–rail adhesion and nonlinear friction, and the model’s accuracy was confirmed through line testing. The system stability, stick–slip bifurcation characteristics, and key factors affecting stick–slip vibration are analyzed through models simulation. The results demonstrated that compared with the three-DOF model, the over-evaluation of the system stability can be avoided after considering the normal motion. In the three-DOF model, the main factor inducing chaotic stick–slip vibration is the tangential stiffness. In the four-DOF model, the tangential stiffness mainly changes the amplitude, while the normal stiffness is the main factor causing vibration chaos. Additionally, damping has a minimal impact on the occurrence of chaotic stick–slip vibration. Optimal ranges for brake disc rotational inertia (5–9 kg·m2 and 11–22 kg·m2) and friction pad mass (7–17 kg) were further identified, effectively mitigating the occurrence of chaotic stick–slip vibration.
The railway signalling system is a key player in controlling train traffic, with the purpose of guaranteeing safety while respecting transport demand. For rail vehicles, visual-based driving is unfeasible, and thus, railway signalling systems have been developed as answers to this issue. Moreover, the increasing demand for railway traffic requires improved signalling system performances. Recent developments have led to the theoretical definition of the Moving Block signalling system as an approach to overcome the limitations of the Fixed Block system, currently adopted in many applications worldwide. This paper focuses on the development of a modular time-based simulation tool for Fixed Block and Moving Block railway signalling systems. The simulator incorporates all main elements for the assessment of signalling system’s performances, including the model of the Radio Block Centre, used for the communication among the trains, the On-Board Unit, which generates the reference speed profile, the vehicle longitudinal dynamics, and the speed control algorithm, emulating a human driver’s behaviour. Different operational conditions have been considered to show the capabilities of the simulator, which may represent a first step towards the reduction of on-site testing of railway signalling systems.
The issue of fatigue damage to rails has become increasingly prominent with the rise in subway traffic and speed. The hazardous space of the turnout frog significantly intensifies the dynamic interaction between the vehicle and the frog rail, leading to more pronounced fatigue damage in the turnout rail. This paper focuses on the No. 9 turnout fixed frog commonly used in subway lines. A three-dimensional explicit transient rolling contact finite element model of the fixed frog is established. The dynamic response of wheel–rail rolling contact is analyzed under various speeds and vertical stiffness conditions. Rolling contact fatigue crack locations, angles, and initiation life were investigated. The research indicates that the 30 mm top width cross-section of the nose rail is most susceptible to fatigue cracks, which initiate on the rail surface. The angle between the crack initiation surface and the lateral direction is between 70° and 95°. Higher speeds result in shorter fatigue life, while the vertical stiffness of the fastener has less of an effect. The simulation results align with findings from field surveys. The established model and research conclusions can provide theoretical support for optimizing fixed frog structures and predicting fatigue life.
Predicting rolling contact fatigue crack hot spots or regions with increased local driving forces in rails is challenging due to the wide range of factors that influence crack initiation. Rail sections experience fluctuating creepage conditions, contact positions, and loads throughout their lifespan, influencing the development and location of fatigue cracks. A new computational method is proposed that predicts the orientation and regions prone to rolling contact fatigue cracks under realistic service loading. It combines multi-body simulations, finite element analysis, and critical plane approaches. A novel multi-variable sampling technique simplifies loading spectra into representative traction profiles, which are then analyzed using finite element analysis and the Smith–Watson–Topper damage indicator parameter (DIPSWT). The maximum DIPSWT value identifies the critical plane and potential crack orientation. A case study on the Swedish heavy haul train line (Malmbanan) considers measured traffic and loading conditions, analyzing the wheel load spectrum for a 384 m long section of a R=450 m curve. Results show that the DIPSWT is highest for the locomotive with a loaded payload configuration, with a maximum value of 3.84×10−8 located at 38.59 mm from the lower gauge face corner. The DIPSWT critical plane aligns with experimental measurements of RCF cracks orientations near the gauge corner. This computational method, when combined with other predictive tools, can efficiently identify conditions that lead to RCF cracks and determine their possible locations and orientations in railway tracks.
Combining the improved delayed detached eddy simulation and Ffowcs Williams–Hawkings equation, a numerical study is conducted to explore the potential of base-frame fairings in aerodynamic noise reduction of high-speed pantographs and deepen the understanding of related flow physics. The fairing models for noise control are designed without changing the bottom structures of the pantograph. The aerodynamic and acoustic results indicate that the flow deflection and acceleration effects caused by the fairings when shielding the bottom components of the pantograph as well as the self-noise generated by the interaction between the wake of unshielded components and the fairings may compromise the noise reduction effects. Compared with the solid fairing, the perforated fairing has additional advantages in noise reduction. The presence of through-holes leads to a flow redistribution around the fairing, alleviating the flow deflection and acceleration effects. Besides, the airflow ejected from the holes on leeward side can suppress the formation of vortex structures in the fairing wake and push them downstream, thereby effectively weakening the flow field fluctuation near the fairing tail. The investigation of the aerodynamic drag of the pantograph and lift fluctuation of the strip further confirms the superiority of the perforated fairing over the solid one.
In recent years, the issue of structure-borne noise generated by steel–concrete composite (SCC) bridges has become increasingly severe. To control this noise by adjusting the cross section parameters of SCC bridges, this study first established a numerical model based on the hybrid finite element–statistical energy analysis (FE-SEA) method. The overall sound pressure levels calculated by numerical model are compared with field measurements, showing discrepancies of 0.4 dB and 1.1 dB, respectively. The comparison confirms the accuracy of the numerical model. Then, a high-accuracy radial basis function neural network (RBFNN) was trained using samples generated from the numerical model with uniform design. To achieve greater noise reduction with lower costs, the non-dominated sorting genetic algorithm (NSGA-II) was used for multi-objective constrained optimization, resulting in the Pareto frontier for sound power levels (SWLs) and material cost. Finally, the solution set was evaluated using the technique for order preference by similarity to an ideal solution method, and the optimal combination of cross sectional parameters was obtained. This combination resulted in a 5 dB reduction in the SWL of the structure and a 23.9% reduction in material cost.
Turnout irregularity significantly affects the stochastic vibration behavior of vehicle–turnout structures. This study proposes a fitting formula for the turnout irregularity spectrum and develops a turnout irregularity full information expression model (TIFIEM) using a stochastic harmonic function. The model is applied to vehicle–turnout structure stochastic vibration and reliability analysis. Findings suggest that the Hamming window method, with a window length of 4096 points, is optimal for estimating the turnout irregularity spectrum. It is recommended to fit the power spectral density (PSD) using a 5th-order polynomial for better accuracy. The TIFIEM effectively addresses randomness in amplitude, frequency, and phase. An analysis of 250 irregularity samples is sufficient for the desired accuracy. Additionally, the PSD amplitude at various frequency points follows a Chi-square distribution with 2° of freedom. Regions 3–7 m from the tip of the switch rail on the straight switch rail and 53–54 m on the point rail are most susceptible to wear. When the vehicle passes through the turnout at 300 km/h, the reliability of vehicle–turnout structures at the crossing panel decreases to 95.8%.
The use of asphalt mixtures for sub-ballast layers in railway infrastructure, which is becoming a preferred design solution in in the high-speed and high-capacity lines in some European countries and in the United States, offers several structural, functional and economic benefits. The assessment of physical–mechanical characteristics of these mixtures still occurs with methods that are well-established in the road paving industry, though these methods are not consistently capable of highlighting the peculiarities of the railway operations, such as the ballast/sub-ballast interaction and the granular behavior of the overlying unbound layer. Specifically, the interface between the crushed stone elements of the ballast bed and the underlying asphalt layer deserves specific attention. Thus, this study presents a new conceived experimental method for the mechanical characterization of mixes intended for asphalt sub-ballast, based on punching test. The test employs an adaptive indentation plate (AIP), which was designed to replicate the interaction between ballast particles and the sub-ballast. Cylindrical asphalt specimens (ϕ150 mm) were subjected to vertical point loads using the AIP, considering different temperatures (5, 20, 35 °C) and deformation rates (5.08, 25.4, 50.8 mm/min). The validation of the experimental procedure involved the analysis of two asphalt mixes of different stiffness, which conformed to the Italian standard for asphalt sub-ballast. The results showed that the punching test offers an effective evaluation of resistance to plastic deformation and additional information on the indentation phenomenon, which is not currently considered in existing specifications. This approach could be used alongside standard tests to better evaluate the performance of different materials in railway sub-ballast applications.