•Large-scale phased cyclic loading of asphaltic railway tracks.•Investigation of asphalt railroad performance at a subgrade transition zone.•Asphaltic track shown to outperform ballast track in terms ...of settlement and subgrade pressure reduction.
The use of structural asphalt layers inside ballasted railway tracks is attractive because it can increase track bending stiffness. Therefore, for the first time, this paper investigates the long-term settlement characteristics of asphaltic track in the presence of a subgrade stiffness transition zone. Phased load cyclic compression laboratory tests are performed on a large-scale hybrid asphalt-ballast track, supported by subgrade with varying stiffness. It is found that an asphaltic layer acts as a bridge to shield the subgrade from high stresses. It is also found that the asphalt reduces track settlement, and is particularly effective when subgrade stiffness is low.
"Power Quality in Electrified Transportation Systems" has covered interesting horizontal topics over diversified transportation technologies, ranging from railways to electric vehicles and ships. ...Although the attention is chiefly focused on typical railway issues such as harmonics, resonances and reactive power flow compensation, the integration of electric vehicles plays a significant role. The book is completed by some additional significant contributions, focusing on the interpretation of Power Quality phenomena propagation in railways using the fundamentals of electromagnetic theory and on electric ships in the light of the latest standardization efforts.
Display omitted
•Recent development of fiber optic sensing (FOS) technology for railway infrastructure monitoring is comprehensively reviewed.•Various FOS technologies and their respective working ...principles have been discussed.•Application of FOS for train operation and structural health monitoring is briefly discussed.•Aspects of the FOS design, installation, performance/accuracy, signal processing and data analysis algorithms are discussed.
In recent years, railway infrastructures and systems have played a significant role as a highly efficient transportation mode to meet the growing demand in transporting both cargo and passengers. Application of these structures in extreme environmental situation under severe working and loading conditions, caused by the traffic growth, heavier axles and vehicles and increase in speed makes it extremely susceptible to degradation and failure. In the last two decades, a significant number of innovative sensing technologies based on fiber optic sensors (FOS) have been utilized for structural health monitoring (SHM) due to their inherent distinctive advantages, such as small size, light weight, immunity to electromagnetic interference (EMI) and corrosion, and embedding capability. Fiber optic-based monitoring systems use quasi-distributed and continuously distributed sensing techniques for real time measurement and long term assessment of structural properties. This allows for early stage damage detection and characterization, leading to timely remediation and prevention of catastrophic failures. In this scenario, FOS have been proved to be a powerful tool for meticulous assessment of railway systems including train and track behavior by enabling real-time data collection, inspection and detection of structural degradation. This article reviews the current state-of-the-art of fiber optic sensing/monitoring technologies, including the basic principles of various optical fiber sensors, novel sensing and computational methodologies, and practical applications for railway infrastructure monitoring. Additionally, application of these technologies to monitor temperature, stresses, displacements, strain measurements, train speed, mass and location, axle counting, wheel imperfections, rail settlements, wear and tear and health assessment of railway bridges and tunnels will be thoroughly discussed.
In the past two decades, the interest in fire safety science of tunnels has significantly increased, mainly due to the rapidly increasing number of tunnels built and the catastrophic tunnel fire ...incidents occurred. This paper presents an overview of research on fire safety in underground road and railway tunnels from the perspectives of fire safety design. The main focuses are on design fires, structural protection, smoke control and use of water-based fire suppression systems. Besides, some key fire characteristics, including flame length, fire spread, heat flux and smoke stratification, are discussed.
Wheel–rail impact loads and noise at railway crossings are calculated by applying a hybrid prediction model. It combines the simulation of non-linear vertical dynamic vehicle‒track interaction in the ...time domain and the prediction of sound pressure level using a linear frequency-domain model. The two models are coupled based on the concept of an equivalent roughness spectrum. The time-domain model uses moving Green's functions for the linear vehicle and track models, accounting for wheel structural flexibility and a discretely supported rail with spatially-varying beam properties, and a non-Hertzian wheel–rail contact model. Three-dimensional surface geometry of the wheel and crossing is accounted for in the solution of the wheel–rail contact. The hybrid model is compared against field measurements and is demonstrated by investigating the influence of vehicle speed and crossing geometry on the radiated impact noise. Based on simulation results, it is concluded that the impact loads and noise can be mitigated by reducing the effective dip angle at the crossing, which is determined by the vertical trajectory of the wheel when making the transition between wing rail and crossing nose.
•We study an integrated train timetabling and track maintenance scheduling problem.•We present a new bi-objective microscopic optimization model for this problem.•We propose an iterative algorithm to ...compute near-optimal solutions in a short time.•The iterative algorithm outperforms previous methods and a commercial solver.•We provide new best-known solutions to INFORMS RAS 2016 PSC instances.
This paper addresses the problem of improving the integration between passenger timetabling and track maintenance scheduling. We propose a microscopic optimization model and an iterative algorithm for solving this problem efficiently. Block sections are considered as the basic microscopic elements for train movements in a railway network. A mixed-integer linear programming formulation is proposed for the integrated optimization problem in which train timing, sequencing and routing are the timetabling variables, while timing and sequencing of maintenance tasks are the track maintenance variables. The objective function is to minimize the total train travel time and the maintenance tardiness cost. The constraints proposed in this work address the practical specifications of the INFORMS RAS 2016 Problem Solving Competition (2016 PSC). In this context, the main decision variables are the entrance and exit times of the trains on each block section plus the start and end times of each maintenance task. Since the integrated optimization problem is strongly NP-hard, an iterative algorithm is proposed to compute near-optimal solutions in a short computation time. The algorithm is based on a decomposition of the overall problem into sub-problems related to train scheduling and/or routing with or without track maintenance task scheduling. The connecting information between the two sub-problems concerns the selected train routes plus the start and end times of the maintenance tasks. Computational experiments are performed on a set of realistic railway instances, which were introduced during the 2016 PSC. The iterative algorithm outperforms a standard MILP solver and the first-place team of this competition in terms of both solution quality and time to deliver the new best-known solutions. The scalability of the iterative algorithm is investigated when increasing the number of trains and track maintenance tasks.
Model testing in laboratory, as an effective alternative to field measurement, provides valuable data to understand railway׳s dynamic behaviors under train moving loads. This paper presents ...comprehensive experimental results on track vibration and soil response of a ballastless high-speed railway from a full-scale model testing with simulated train moving loads at various speeds. A portion of a realistic ballastless railway comprising slab track, roadbed, subgrade, and subsoil was constructed in a larger steel box. A computer-controlled sequential loading system was developed to generate equivalent vertical loadings at the track structure for simulating the dynamic excitations due to train׳s movements. Comparisons with the field measurements show that the proposed model testing can accurately reproduce dynamic behaviors of the track structure and underlying soils under train moving loads. The attenuation characteristics of dynamic soil stresses in a ballastless slab track is found to have distinct differences from that in a ballasted track. The model testing results provide better understanding of the influence of dynamic soil–structure interaction and train speed on the response of track structure and soils.
•Train moving loads were implemented in the model testing of railway infrastructure.•Highest train speed of 360km/h was achieved in the physical model testing.•Roadbed plays a critical role in vibration reduction of ballastless tracks.•Dynamic soil stress differs noticeably between ballastless and ballasted railways.•A new formula on dependency of dynamic soil stress on train speed is proposed.
The increase of train speed and axle load is an essential goal to make the railway transport more and more competitive for passengers and freights. On this basis, the unevenness of the railway track ...is crucial for the safety of the railway due to the high speed of the vehicle. Although ballasted tracks represent by far the most used railway track substructure, in recent years the modernization process has led the development of the ballastless track substructures.
In deciding between the use of ballasted or ballastless track substructure there are many important technical, economical and environmental factors that have to be addressed. Based on the above, the principal objective of this study was to evaluate the environmental impact of different railway track substructures including ballast, cast-in sleeper and embedded track systems on the short, medium and long term. To accomplish this task, a life cycle assessment (LCA) was carried out throughout the entire life cycle of the railway infrastructure by using the ReCiPe (H) method. Although such approach is commonly included in the environmental assessment of building products and buildings, it was rarely applied in the analysis of the environmental impacts of railway track substructure.
Thus, the result of these LCA showed that ballasted tracks cause the lowest environmental impact for service lives of up to 75 years. On the other hand, the embedded track beds cause the highest environmental impacts, regardless of their service life. The highest contributor for the environmental impacts of the track beds was the steel production.
The results of this study will provide relevant environmental information for engineers and decision makers to select the most adequate railway track substructures for addressing issues related to the pursuit of sustainable development.
•Rail construction and maintenance phases should not be neglected in LCA approach.•LCA of rail track require more standardized assessment procedures.•Environmental LCA of different railway track substructures were analyzed.•Damage categories have been normalized for the total environmental impact.•Future LCA of rail projects should also consider the time effect.
•This the world's first to establish a probabilistic Bayesian model for railway operations.•Model verifications against the long-term FRA's data exhibit excellent accuracy >95%.•Both of decision tree ...and Petri-nets models are embedded for risk assessment.•Both DT and PT models can be practically used by any railway authorities.•Railway accident reduction and reliability can be achieved by model adoption.
Not only has the railway accidental prevention been a prime focus, but it has also become a key challenge for the industry in recent years. For many decades, rail authorities have attempted to significantly improve rail safety, whilst facing various passengers’ risks and uncertainties. The overarching goal of this study is to develop a new posterior probability model to quantify uncertainties for benchmarking. This is the world's first to establish new insights from the benchmarking of risk and safety across different rail networks. The insights will point out the advantages and practicability of launching safety policies and reducing railway accidents for other rail networks. The new model has been developed using unparalleled long-term accidental data sets, including ‘a trailer an accident’ and ‘causes of the accident’. The investigation adopts a Bayesian approach (via Python) to codify the novel model. The new findings lead to the better understanding into the uncertainty of railway accidents. Five notable rail networks have been selected as case studies. This study has also compared the effectiveness of the decision tree and Petri-net models using the posterior probability and number of injuries and fatalities. Based on the benchmarking outcomes, Chinese and Japanese railway systems denote the lowest risk over other networks, followed by Spanish, French and South Korean rail networks. The study also demonstrates that the novel benchmarking criteria can effectively measure and compare any rail networks’ risk and uncertainties. Its adoption will lead to performance improvement in terms of safety, reliability and maintenance policies of railway networks globally.
PDF
