Dynamic Response of an Over-Track Building to Metro Train Loads: A Scale Model Test

In railway engineering research, there is a notable gap as existing studies often focus separately on train-induced vibrations or freeze–thaw cycle impacts on subgrades, lacking a comprehensive analysis of their combined effects on subgrade dynamic responses. This study developed a three-dimensional finite-element model of a double-track ballastless track railway subgrade. The model considers various conditions, including train speeds of 180 km/h, 200 km/h, and 220 km/h, and soil temperatures of 5 °C, −5 °C, and −15 °C, with typical subgrade materials. The results show that under train load, the maximum vertical displacement of the subgrade decreases as train speed increases. Conversely, the maximum vertical stress and acceleration are directly proportional to the train speed. When the train speed rises from 180 km/h to 220 km/h, the maximum vertical stress of the subgrade increases by 1.1% and 3.1%, respectively. As the soil temperature drops from 5 °C to −15 °C, the maximum vertical displacement of the subgrade decreases. The displacement reduces with increasing distance from the train load. At a specific point A, the maximum vertical stress increases by 2.02% and 1.43%, respectively. Additionally, the deformation of the railway subgrade is directly proportional to the temperature difference. These findings are valuable for understanding subgrade behavior and guiding railway construction in freeze–thaw-affected areas.

Evolution of trackbed performance and ballast degradation due to passages of million train wheel axle loads

In many dynamic systems such as robot and aerospace areas, flexible structures have been extremely employed to satisfy various requirements for large scale, light weight and high speed in dynamic motion. However, these flexible structures are readily susceptible to the internal/external disturbances (or excitations). Therefore, vibration control schemes should be exerted to achieve high performance and stability of flexible structure systems. Recently, in order to successfully achieve vibration control for flexible structures smart materials such as piezoelectric materials [1-2], shape memory alloys [3-4], electrorheological (ER) fluids [5-6] and magnetorheological (MR) fluids [7] are being widely utilized. Among these smart materials, ER or MR fluid exhibits reversible changes in material characteristics when sub‐ jected to electric or magnetic field. The vibration control of flexible structures using the smart ER or MR fluid can be achieved from two different methods. The first approach is to replace conventional viscoelastic materials by the ER or MR fluid. This method is very effec‐ tive for shape control of flexible structures such as plate [5]. The second approach is to de‐ vise dampers or mounts and apply to vibration control of the flexible structures. This method is very useful to isolate vibration of large structural systems subjected to external excitations [6-7]. In this work, a new type of MR mount is proposed and applied to vibration control of the flexible structures.

Dynamic responses and fatigue assessment of OSD in heavy-haul railway bridges

Active robust vibration control of flexible structures

The synthesis of structural health monitoring and vibration control is important in order to provide facilities for constructing smart structures. In recent years, some techniques have been developed to integrate structural identification and optimal vibration control. However, it is still challenging to integrate the identification and vibration control of time-varying structures subject to unknown earthquake excitation. The main difficulties are that structural dynamic responses collected by a simple harmonic motion system are absolute responses under unknown earthquake ground motion while previous identification approaches for unknown external excitation are not applicable for this situation and the need of an efficient algorithm to accurately track the various scenarios of time-varying structures with inexpensive computation to ensure the real-time performance requested by structural vibration control. In this paper, a novel algorithm is presented, in which structural time-varying parameters are treated as ‘virtual unknown inputs’ to the underlying time-invariant structure, a generalized Kalman filter with unknown inputs is proposed for joint identification of joint structural state, unknown earthquake excitation and ‘virtual unknown inputs’ with only partially measured structural absolute responses, and the identification results are integrated in real-time with the instantaneous optimal control scheme to reach the goal of optimal semi-active control provided by magneto-rheological dampers. Some numerical examples of integrated identification and vibration control of various time-varying structures subject to unknown earthquake excitation are used to demonstrate the performances of the proposed algorithm.

Accurately understanding the travel demand of urban rail transit (URT) systems is crucial for effective operational management. Despite the recognition that the diversity in human activity patterns results in different travel demands, few studies have thoroughly investigated the heterogeneity among passengers and its impact on URT ridership. This study utilizes smart card data collected from the Beijing Subway to categorize passengers into four groups: tourist passengers, flexible commuters, regular commuters, and life‐oriented passengers, based on their spatiotemporal travel patterns. Furthermore, a Multiscale Geographically Weighted Regression (MGWR) model is employed to examine the relationship between station‐level ridership of URT and its determinants, including the built environment and station properties, for each passenger group. The results indicate that the influence of these determinants on station‐level ridership varies across passenger groups and spatial scales. For instance, regular commuters exhibit lower sensitivity to accessibility on workdays, whereas those unfamiliar with the URT network are more concerned about the bus accessibility in pedestrian‐ or bicycle‐unfriendly areas. Notably, for tourist and life‐oriented passengers, the stations significantly affected by population density are concentrated in areas with a higher proportion of elderly individuals. Conversely, for flexible and regular commuters, these stations are predominantly situated in areas associated with internet technology and scientific research. These findings are valuable for policymakers in designing strategies tailored to different passenger groups to balance trip demand and capacity, thereby improving URT services and promoting a sustainable urban environment.

The ballasted trackbed plays a crucial role in railway infrastructure. However, as train speeds escalate, it experiences heightened vibrations and substantial permanent deformation, posing a notable threat to normal train operations. This study is dedicated to investigating the dynamic response and associated irreversible deformation of railway ballast under varying train speeds, with a specific focus on particle-scale manifestations. To accomplish this, a comprehensive ballasted trackbed model, encompassing the entire transversal cross-section, was built using the discrete element method (DEM) with realistic polygonal elements. The DEM model underwent preliminary validation against measurements from full-scale model tests and was subsequently employed to simulate the mechanical behavior of the ballasted trackbed under various train speeds. The findings reveal that increased train speeds lead to vigorous shaking of ballast particles, manifesting as intense vibration at the macroscopic level of the track structure. The heightened particle activity indicates instability in the inter-particle contact network and distinctive particle migration. Consequently, a notable accumulation of permanent deformation occurs in the granular trackbed. Notably, once the train speed surpasses a certain threshold, there is observable migration of ballast particles beneath the sleeper towards both ends. This phenomenon results in the absence of a stabilized inter-particle contact network to support the upper train load, leading to rapid and significant irreversible deformation in the ballasted trackbed.

The synthesis of structural identification with vibration control is cost-effective and beneficial for developing smart building structures. In the past several decades, techniques have been put forward for the combination of structural identification and vibration control. However, it is still a challenging task to synthesize identification and vibration control of time-varying structures under unknown earthquake excitation. First, structural dynamic responses collected by a structural health monitoring (SHM) system are absolute responses under unknown earthquake excitation, so existing identification approaches for unknown external excitations are not applicable for this situation. Moreover, it is essential to have an efficient algorithm for accurately tracking the various scenarios of time-varying structural physical parameters with inexpensive computation to ensure the real-time performance requested by structural vibration control. In this paper, an algorithm is put forward to tackle this challenging problem. It is proposed to treat structural time-varying effect as “virtual unknown inputs” to the corresponding time-invariant structure. A generalized extended Kalman filtering with unknown input (GEKF-UI) is proposed to circumvent the limitations of the existing EKF-UI approaches. The proposed GEKF-UI can simultaneously identify structural system, unknown earthquake excitation, and the “virtual unknown inputs” using only partially measured structural absolute responses. Then, the identified structural state is synthesized in real time with the instantaneous optimal control strategy for optimal semiactive control provided by magnetorheological dampers. Therefore, the proposed algorithm can track various structural time-varying with much less computation, which is more suitable for synthesis with structural control compared with other existing approaches. Some numerical cases of synthesizing identification and vibration control of various type time-varying structures under unknown earthquake motion are adopted to investigate the feasibilities of the proposed algorithm.

Field Test Study on the dynamic response of the cement-improved expansive soil subgrade of a heavy-haul railway

Designing ballastless high-speed railways in frozen regions: A dynamic analysis using three-dimensional numerical modelling

To exactly study the riding comfort of passengers in urban rail transit trains, a coupling vibration model, including passengers, train, and bridge is proposed in this paper. According to the Lagrange Equation, the differential equations of motion of each part are derived, which are coupled with each other through displacement and dynamic interaction forces. A corresponding calculation program is compiled by the Fortran language. A representative steel-concrete composite girder bridge on Beijing Metro Line 5 is selected as the research background, the dynamic responses of passengers and train are simulated in detail, and the dynamic response differences between the passenger and carriage are compared. The passengers’ riding comfort is evaluated according to ISO-2631 Standard based on the simulated data. The result shows that passengers in the middle carriages of the train feel better than those in the head and tail ones. While in the same carriage, passengers on the middle seats feel better than those on both ends of it. If only vibration is considered, passengers will feel better in a fully loaded carriage than those with few passengers. The riding comfort of passengers will be gradually reduced with the increase of the train speed.

Spatio-temporal analysis of carbon footprints for urban public transport systems based on smart card data

Investigation into Impact of Train Speed for Behavior of Ballasted Railway Track Foundations

The high-speed railway (HSR) operates at a high velocity, and the long-wavelength track irregularities can affect its safety and stability. The study was conducted to address control and management issues related to long-wavelength track irregularities on HSRs. It achieved this by establishing a vehicle-track dynamic analysis model based on the multi-rigid-body dynamics theory, aiming to provide recommendations for the development of standards for managing the track irregularities on HSRs. A simulation was conducted to analyze how the train speed, wavelength, and amplitude of track longitudinal irregularities affect the vehicle body’s dynamic response. The variation of the vehicle body’s dynamic response under different working conditions was analyzed, and the most unfavorable wavelength and sensitive wavelength ranges of the track longitudinal irregularities on HSR were studied. The control limits for track longitudinal irregularities measured by a 60 m chord were then determined. The findings indicate that the car body's vertical acceleration gradually decreased with the increase of wavelength but increased linearly with the increase of amplitude. The findings also indicate a gradual increase in the vehicle body’s vertical acceleration as the train speed increases. When the train speed is 250 km/h∼350 km/h, the sensitive wavelength range of long-wavelength track irregularities is 60 m∼110 m. Based on the results, the relationships between the wavelength and the amplitude of track irregularities, train speed, and the vehicle body’s vertical acceleration were acquired by the nonlinear least square method. Finally, a formula for calculating the control limits for track longitudinal irregularities measured by a 60 m chord is proposed.