Ladder Track Research Articles

Research on Vibration Characteristics of a Flexible Vehicle-Ladder Track System

As a means of vibration reduction, the ladder track has seen broad implementation in urban rail transit. However, issues such as increased vibration noise, rail corrugation, and fastener failure have been observed in certain sections of the ladder track during later operation. To investigate the mechanisms behind these phenomena and provide comprehensive insights into the system's response to various operational conditions, this study employed vehicle-track coupled dynamic theory to establish a three-dimensional finite element model of the flexible vehicle-ladder track system. The vibration transmission and dynamic response characteristics of the vehicle-ladder track system were analyzed. The findings revealed that the vehicle-track resonance and anti-resonance phenomena were more prominent in the medium- to low-frequency range. At specific frequencies, the wheelset exhibited various vibration modes, and the fastener force was found to closely correlate with the ladder vibration mode. Furthermore, the influence of speed on diverse components of the vehicle-ladder track system, in terms of maximum vibration and the dominant vibration frequency range, differed considerably. This study provides a more comprehensive and reasonable exploration of the modeling and dynamic behavior of vehicle-ladder track systems.

Verification of Longitudinal Level Irregularity Suppression Effect at the Structural Boundary by Ballasted Ladder Track

The ladder sleeper, which is a type of longitudinal sleeper with long beams in the longitudinal direction of the rail, was developed for the maintenance-labor saving of ballast tracks. In this study, to quantify the load distribution performance of the ladder sleepers at the structural boundary, full-scale model tests were conducted to quantify the vibration transmission reduction effect of the ladder sleepers. Following that, numerical experiments were carried out using a three-dimensional numerical analysis model and it was revealed that the ladder sleeper can reduce the pressure on the sleeper bottom plane by approximately 70% when compared to conventional prestressed concrete sleepers. Furthermore, when laying the ladder sleeper at the structural boundary, it was shown that laying across the structural boundary may be more effective in reducing the pressure on the sleeper bottom plane than laying it in front of the structural boundary. Finally, ladder sleepers were installed on the commercial line and long-term measurements of the longitudinal level irregularity verified the effect of suppressing the longitudinal level irregularity of the ballasted ladder track.

Numerical investigation on train-induced environmental vibration in floating ladder tracks

Numerical investigation on train-induced environmental vibration in floating ladder tracks

Analysis of the Vibration Mitigation Characteristics of the Ballasted Ladder Track with Elastic Elements

Despite the fact railways are seen as an environmentally friendly and sustainable form of transport, however, the train-induced vibration has been seen as a negative environmental consequence. The ballasted ladder track is one type of ballasted track with longitudinal sleepers. The elastic elements can not only protect the track structure but also control the vibration. To investigate the vibration mitigation effects of ballasted ladder track with elastic elements, a finite element - infinite element (FE-IFE) model was built considering the elastic elements of under-sleeper pads (USPs) and under-ballast mats (UBMs). This model was validated by a laboratory test. Then, the moving train load was obtained based on the multi-body dynamics (MBD)-finite elements method (FEM) analysis. The vibration mitigation effects of the ballasted ladder track with different types of elastic elements were calculated compared with the ballasted tracks without elastic elements. The results indicate that: (1) the ballasted ladder track has the advantage of vibration reduction at low frequencies, with a maximum vibration attenuation of 25.2 dB and an averaged vibration attenuation of 19.0 dB between 5 and 20 Hz through the ballast. (2) The ballasted ladder track with USPs or UBMs can provide better vibration attenuation between 30 and 100 Hz, but it induces a vibration amplification between 5 and 30 Hz. (3) The ballasted ladder track with elastic elements in different cases can provide different vibration mitigation effects. The ballasted ladder track with both USPs and UBMs can provide the best mitigation effect with an average vibration mitigation of approximately 15 dB and a maximum vibration mitigation of 30 dB between 30 and 100 Hz.

Integrating biochemistry into a program serving multiple tracks in medical laboratory science

This Education Case Study addresses two issues: the program-identified need for more biochemistry content in the pre-requisite course, Organic Chemistry I, and its availability to the Medical Laboratory Science Online Career Ladder track students. The underlying principles for resolving the issues are the constraints of the program curriculum and the unavailability of an online organic chemistry course at Georgia Southern University. The first step in addressing the issues involved collaboration between the Medical Laboratory Science and Chemistry faculty members to identify the specific biochemistry topics on which program courses build. Since the Biochemistry I course has the pre-requisites of two semesters of Organic Chemistry and the medical laboratory program of study only had room for one course in this area, a new course was designed to address the program-identified content need. The new course was offered in a face-to-face format but one of the program tracks utilizes entirely online instruction. To allow those students access to the new course, the course instructor obtained e-Faculty status and undertook designing an online version. The process included the expertise of an instructional designer and the resulting online course was rich in content and teaching strategies to provide the social presence necessary for student engagement in that venue. The online course immediately earned Quality Matters Certification and has been offered three times to date. Forty-one students have taken the new course. Of those eligible to apply, 71% entered the Medical Laboratory Science program and 78% of the entrants have graduated or are on track to do so. The average course GPA data for the 5 cohorts reveals that the strong level of student success in the face-to-face course has not been observed in the online course (3.55 and 2.53, respectively) requiring continued efforts to deliver content, engage students, and assess learning in alternative ways.

Integrating Biochemistry Into a Program Serving Multiple Tracks in Medical Laboratory Science

<h3>ABSTRACT</h3> This education case study addresses 2 issues: the program-identified need for more biochemistry content in the prerequisite course, Organic Chemistry I, and its availability to the Medical Laboratory Science Online Career Ladder track students. The underlying principles for resolving the issues are the constraints of the program curriculum and the unavailability of an online organic chemistry course at Georgia Southern University. The first step in addressing the issues involved collaboration between the Medical Laboratory Science and Chemistry faculty members to identify the specific biochemistry topics on which program courses build. Because the Biochemistry I course has the prerequisites of 2 semesters of Organic Chemistry and the medical laboratory program of study only had room for 1 course in this area, a new course was designed to address the program-identified content need. The new course was offered in a face-to-face format, but one of the program tracks utilizes entirely online instruction. To allow those students access to the new course, the course instructor obtained e-Faculty status and undertook designing an online version. The process included the expertise of an instructional designer, and the resulting online course was rich in content and teaching strategies to provide the social presence necessary for student engagement in that venue. The online course immediately earned Quality Matters Certification and has been offered 3 times to date. Forty-one students have taken the new course. Of those eligible to apply, 71% entered the Medical Laboratory Science program, and 78% of the entrants have graduated or are on track to do so. The average course grade point average data for the 5 cohorts reveal that the strong level of student success in the face-to-face course has not been observed in the online course (3.55 and 2.53, respectively), requiring continued efforts to deliver content, engage students, and assess learning in alternative ways.

Numerical and experimental study on noise reduction of concrete LRT bridges

Rolling noise and structure-borne noise radiating from the bridge are two major sources of noise in light rapid transit (LRT) bridges. To control the noise radiation from LRT bridges, an efficient numerical method for noise prediction is needed. In this study, a combined three-dimensional dynamic model and 2.5-dimensional acoustic model were used to investigate noise reduction in a rail and in a U-shaped girder bridge. The effects of three noise mitigation measures on noise control were then compared: installation of a noise barrier, use of a rail pad with a lower stiffness, and use of a floating ladder track. The corresponding noise reduction was investigated using the numerical method. A field test was conducted to validate the noise reduction effects. It was found that the noise barrier was more effective in reducing the rail noise, and the soft rail pad is more effective to control the bridge noise. The floating ladder track can significantly reduce bridge vibration, but the excessive vibration of the ladder track itself became another major noise source. The findings should guide the selection of appropriate mitigation measures for noise reduction in LRT bridges.

Dynamic response of ladder track rested on stochastic foundation under oscillating moving load

The ladder track is a new type of an elastically supported vibration-reduction track system that has been applied to several urban railways. This paper is devoted to the investigation of dynamic behavior of a ladder track under an oscillating moving load. The track is represented by an infinite Timoshenko beam supported by a random elastic foundation. In this regard, equations of motion for the ladder track are developed in a moving frame of reference. In continuation, by employing perturbation theory and contour integration, the response of the ladder track is obtained analytically and its results are verified using the stochastic finite element method. Finally, using the verified model, a series of sensitivity analyses are accomplished on effecting parameters including velocity and load frequency.

Ground Vibration Characteristics of Ballasted Ladder Track

Ballasted ladder tracks are used for some railway lines in Japan. Thus, efforts have been made to reduce ground vibration. To date, no quantitative study has been done on the characteristics of ground vibration reduction. In this study, a three-dimensional dynamic interaction analysis based on a substructure formulation is used for the simulation of a vibration test of a full-scale model. Analytical results are compared to measurements on an existing railway line with train-running loads. A parametric study was conducted to quantify the effects of ground shear wave velocity, surface layer thickness, and train speed. It was verified that the analytical method and model can reproduce the wave propagation in the ground. Furthermore, this study shows that the ballasted ladder track can reduce ground vibrations, especially, on soft ground. This is difficult to achieve by conventional countermeasures.

A Laboratory Test on the Vibration Mitigation Efficiency of Floating Ladder Tracks

With the rapid development of railway systems, increasingly more environmental concerns are focused on railway vibrations. The track solution with the mass-spring-damping principle can be the most effective and economical option to control train-induced ground vibrations. The effect of track vibration mitigation is usually described by insertion loss (IL). IL can typically be obtained by impulse tests in laboratories. To investigate the influences of preloads on IL, a dynamic laboratory experiment was performed on a floating ladder track. Two conditions were considered, a ladder sleeper with and without under sleeper pads (USPs). A modal test was performed, and then, an automatic falling weight system was used for the vibration reduction test. A preloaded car with a deadweight of 2.4 tons was employed. Different concrete masses, with a maximum of 5.4 tons of total weight were applied on the car. Ground vibrations and IL were analysed under these different preloaded weights. The results show that the first natural frequency of the floating ladder track was 33 Hz. When the preload was applied, the ground vibration and IL around the natural frequency were largely influenced. In addition, the values of IL in different frequencies had different sensitivities to the preloads.

An experimental study of vibration reduction of a ballasted ladder track

The ballasted ladder track is a new type of longitudinal track. In this paper, to investigate its vibration reduction effect, both a laboratory test and in situ experiment were conducted. As the vibration sources, a newly designed drop weight impulse setup was employed in the laboratory test, and moving metro trains were employed in the in situ measurement. The vibration reduction effects of the ballasted track with ladder sleepers and regular concrete sleepers were compared. The results show that the ballasted ladder track can effectively decrease the peak value in the time domain and has the potential effect to control the environmental vibration in low frequencies. The shape of the sleeper can induce changes in the vibration field of the ballast.

Optimization of Vibration Reduction Ability of Ladder Tracks by FEM Coupled with ACO

Ladder track, which has drawn increased attention in scientific communities, is an effective method for reducing vibrations from underground railways. In order to optimize the vibration reduction ability of ladder track, a new method, that is, the finite element method (FEM) coupled with ant colony optimization (ACO), has been proposed in this paper. We describe how to build the FEM model verified by the vibration tests in the Track Vibration Abatement and Control Laboratory and how to couple the FEM with ACO. The density and elasticity modulus of the sleeper pad are optimized using this method. After optimization, the vibration acceleration level of the supporting platform in the 1–200 Hz range was reduced from 102.8 dB to 94.4 dB. The optimized density of the sleeper pad is 620 kg/m3, and the optimized elasticity modulus of the sleeper pad is 6.25 × 106 N/m2.

Dynamic analysis of coupled train - ladder track - elevated bridge system

As a new type of vibration reduction, the ladder track system has been successfully used in engineering. In this paper, a numerical model of the train-track-viaduct system is established to study the dynamic responses of an elevated bridge with ladder track. The system is composed of a vehicle submodel, a track submodel and a bridge submodel, with the measured track irregularities as the system self-excitation. The whole time histories of a train running through an elevated bridge with <TEX>$3{\times}27m$</TEX> continuous PC box girders are simulated. The dynamic responses of the bridge such as deflections, lateral and vertical accelerations, and the vehicle responses such as derailment factors, offload factors and car-body accelerations are calculated. The calculated results are partly validated through the comparison with the experimental data. Compared to the common slab track, adapting the ladder sleeper can effectively reduce the accelerations of the bridge girder, and also reduce the car-body accelerations and offload factors of the train vehicle.

NEURONAL CONTROL OF ACCURATE LOCOMOTION

We may associate Olympic gymnasts with extreme precision and coordination, but in nature, precise movements are performed without much notice every day. Complex environments pose as an obstacle to steady locomotion, and yet animals appear to cope with these obstacles effortlessly. This accurate locomotion requires serious neural coordination. How the brain coordinates accuracy during movement is still unclear, but new research suggests the different neurons of the pyramidal tract may be involved.The pyramidal tract consists of nerve fibers connecting the primary motor cortex of the brain with motor neurons in the brain stem and anterior spinal cord. These connections are extremely important, as pyramidal tract neurons control all voluntary motions and damage to the region results in severe motor disability.Scientists have long known two different types of neuron exist in the pyramidal tract: large, fast-conducting neurons and smaller, slow-conducting neurons. Erik Stout and Irina Beloozerova of St Joseph's Hospital and Medical Center, AZ, USA, looked how these two types of neuron might control accurate locomotion. The two researchers trained cats to run on a flat track and on a horizontal ladder track, where the cats had to step precisely on the rungs of a horizontal ladder, and never in the gaps between rungs. Stout and Beloozerova then recorded the activity from slow-conducting and fast-conducting pyramidal tract neurons, to see whether there were differences in their activity patterns between different motions.Both slow and fast pyramidal tract neurons had different activity patterns during flat versus ladder running. Slow-conducting neurons, however, changed their activity in a much more concerted way than fast-conducting neurons. During the late stance and early swing phase of each stride on the ladder, slow-conducting neurons increased their average rate of discharge and decreased their discharge variability. Slow-conducting neurons also increased the magnitude of stride-related frequency modulation during ladder running. While fast-conducting neurons displayed some similar trends in their modulation between different locomotor tasks, the differences were small in magnitude and often insignificant.Because there were very few kinematic differences between flat and ladder running, the changes in slow-conducting neuron activity are probably related to the high accuracy demands of ladder running. This suggests that slow-conducting neurons are more important than fast-conducting neurons for the control of precise movement. The proximate mechanisms by which slow-conducting neurons control precise limb placement are still elusive. Stout and Beloozerova note that while fast-conducting neurons chiefly influence distal musculature, slow-conducting neurons can influence both proximal and distal musculature. They propose that maybe proximal limb musculature plays a greater role in accurate paw placement than previously thought.As technology for instrumenting small slow-conducting neurons improves, perhaps neuroscientists can narrow in on the fine controls of accurate locomotion. Eventually, we may know exactly how slow neurons help us tread carefully.

Optimization of the dynamic properties of the ladder track system to control rail vibration using the multipoint approximation method

The combination model of the vehicle and ladder track system that accounts for the wheel–rail interface has been developed to analyze the wheelset and ladder track vibration characteristics in the frequency and time domains. In the wheel–rail interface, the vertical contact is represented by contact stiffness derived from the Hertz theory of normal elastic contact, and lateral contact is idealized by linear contact used Kalker linear rolling contact theory. The considerable noise and vibration frequency of the ladder track is determined by experimental investigation results. Then the effect of the most significant ladder track parameters on the track vibration is analyzed in time domain using the vehicle–track coupling model. Based on the results of the parametric study, an optimization of the mechanical properties of the ladder track to reduce the track vibrations is performed using the multipoint approximation method. The results of the optimization are presented and discussed.

Optimisation of the dynamic properties of ladder track to minimise the chance of rail corrugation

The ladder track used by the Beijing subway which can be subjected to rail corrugation is considered in this paper. Dynamic models of the vehicle and the ladder track are developed to analyse the track vibration behaviour. Using these models the effect of the most significant ladder track parameters on track vibrations are analysed in the frequency and time domains. Using experimental and numerical results the vibration frequency of the rail that is responsible for rail corrugation is determined. Based on the results of the parametric study, an optimisation of the mechanical properties of the ladder track to reduce or eliminate the track vibrations at the corrugation frequency and ultimately to reduce the chance of rail corrugation is performed using a genetic algorithm-based approach. The results of the optimisation are presented and discussed.

Analysis on Vibration Reduction Characteristics of Ladder Track Structure on Metro Viaduct under Measured Track Irregularities

3D FEM models of ladder track and rail-bearing platform track on metro viaduct were established to analyze the vibration reduction characteristics of ladder track structure. Based on track irregularities measured by track inspection car, time-history vertical accelerations of rail, sleeper, flange and beam bottom were solved to contrast the dynamic characteristics of the two track structure. Results show that the vibration level of rail and sleeper are higher on ladder track than on rail-bearing platform track, and the vibration reducing effect of ladder track for flange and beam bottom mainly embodies in frequency range of 1~40Hz in which average vibration reduction values on flange and beam bottom are 28dB and 22dB, with maximum values 40dB and 33dB. The results can provide reference for design of ladder track as well as its application in metro line.

Modelling the Floating Ladder Track Response to a Moving Load by an Infinite Bernoulli-Euler Beam on Periodic Flexible Supports

Abstract.An infinite Bernoulli-Euler beam (representing the “combined rail” consisting of the rail and longitudinal sleeper) mounted on periodic flexible point supports (representing the railpads) has already proven to be a suitable mathematical model for the floating ladder track (FLT), to define its natural vibrations and its forced response due to a moving load. Adopting deliberately conservative parameters for the existing FLT design, we present further results for the response to a steadily (uniformly) moving load when the periodic supports are assumed to be elastic, and then introduce the mass and viscous damping of the periodic supports. Typical support damping significantly moderates the resulting steady deflexion at any load speed, and in particular substantially reduces the magnitude of the resonant response at the critical speed. The linear mathematical analysis is then extended to include the inertia of the load that otherwise moves uniformly along the beam, generating overstability at supercritical speeds – i.e. at load speeds notably above the critical speed predicted for the resonant response when the load inertia is neglected. Neither the resonance nor the overstability should prevent the safe implementation of the FLT design in modern high speed rail systems.

An Experimental Study of Train-Induced Structural and Environmental Vibrations of a Rail Transit Elevated Bridge with Ladder Tracks

An Experimental Study of Train-Induced Structural and Environmental Vibrations of a Rail Transit Elevated Bridge with Ladder Tracks

Prediction of vibrations from underground trains on Beijing metro line 15

The impact of vibrations due to underground trains on Beijing metro line 15 on sensitive equipment in the Institute of Microelectronics of Tsinghua University was discussed to propose a viable solution to mitigate the vibrations. Using the state-of-the-art three-dimensional coupled periodic finite element-boundary element (FE-BE) method, the dynamic track-tunnel-soil interaction model for metro line 15 was used to predict vibrations in the free field at a train speed of 80 km/h. Three types of tracks (direct fixation fasteners, floating slab track and floating ladder track) on the Beijing metro network were considered in the model. For each track, the acceleration response in the free field was obtained. The numerical results show that the influence of vibrations from underground trains on sensitive equipment depends on the track types. At frequencies above 10 Hz, the floating slab track with a natural frequency of 7 Hz can be effective to attenuate the vibrations.