Moving Train Loads Research Articles

Numerical Investigations on Track-substructure System Considering the Effect of Different Train Speeds

Quasi-static and dynamic loads from train-traffic are applied to the entire track system: super-structure, substructure and subsoil. Due to lack of maintenance of the track bed, the dynamic loads on the track system causes an accumulation of excess pore water pressure within the sub-structure. Furthermore, a pumping effect exerted on the track system, which depends on the axle load and velocity of the vehicle, may cause in mud hole formation, rising of the underlying soil, ballast contamination and the clogging of gravel bed pores. Consequently, the subgrade resistance is reduced and hence the system loading capacity. The main objective is to detect mud holes as early as possible by non-invasive, non-destructive measurements to avoid costly interim or long term treatments. The present publication focuses on the comparison of vertical velocities due to a moving train load in the absence of water, thus eliminating any complexities arising from any variation in the pore pressure. Due to the large velocity of the trains, elastic and plastic deformations might develop in the vicinity of the track-subgrade system. In the current publication, a simplified numerical simulation of one axle of an ICE train traversing along the rail track with various speeds have been simulated.

A study on the deformation characteristics of ballasted track at structural transition zone by multi-actuator moving loading test apparatus

At a structural transition zone between concrete structure and embankment, settlements of ballasted tracks generally become larger than those in a general section. To investigate the deformation characteristics of ballasted track at the transition zone, scale model tests using multi-actuator moving loading test apparatus were carried out. This test apparatus is equipped with sixteen electric–hydraulic actuators to simulate a moving train load traveling on the rails. In the test case without any buffering structure at the transition zone, large local settlement appeared even under the condition of constant moving load without any dynamic wheel load change. Conversely, by installing an approach block (wedge-shaped backfill with well graded and well compacted crushed stone) at the transition zone, local large settlement did not appear. Similarly by installing an approach slab (reinforced concrete slab) or a resilient mat (resilient polyurethane mat installed on the concrete structure), settlement at the transition zone became less than that in the case without any buffering structure.

Numerical prediction of ground vibrations induced by high-speed trains including wheel–rail–soil coupled effects

A simplified analytical model including the coupled effects of the wheel–rail–soil system and geometric irregularities of the track is proposed for evaluation of the moving train load. The wheel–rail–soil system is simulated as a series of moving point loads on an Euler–Bernoulli beam resting on a visco-elastic half-space, and the wave-number transform is adopted to derive the 2.5D finite element formulation. The numerical model is validated by published data in the literature. Numerical predictions of ground vibrations by using the proposed method are conducted at a site on the Qin-Shen Line in China.

Moving train loads and parameters identification on a steel truss girder model

This paper presents a new system for moving train loads and its parameters identification. A model of simply supported truss girder is constructed according to a side span of Poyang Lake continuous steel truss girder. The moving train loads are simulated by a model train with three coaches. In this system, time history displacements of measurement stations on bridge are simultaneously measured by using displacement image monitoring system when the model train moves across the bridge. Basic parameters of the model train, including moving speed, axle numbers and axle spacing, are identified with a parameter acquisition system. Finally moving train loads are identified by using multi-axle moving loads identification system. A series of experiments have been conducted. Effects of a few main parameters on the proposed system are investigated. The result shows that this system is a feasible and accurate method for the identification and makes preparations for the practical practice in engineering.

Dynamic analysis of slab track on multi-layered transversely isotropic saturated soils subjected to train loads

The dynamic responses of a slab track on transversely isotropic saturated soils subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to simulate the rails and a lower Euler beam to model the slab. Rail pads between the rails and slab are represented by a continuous layer of springs and dashpots. A series of point loads are formulated to describe the moving train loads. The governing equations of track-ground systems are solved using the double Fourier transform, and the dynamic responses in the time domain are obtained by the inverse Fourier transform. The results show that a train load with high velocity will generate a larger response in transversely isotropic saturated soil than the lower velocity load, and special attention should be paid on the pore pressure in the vicinity of the ground surface. The anisotropic parameters of a surface soil layer will have greater influence on the displacement and excess pore water pressure than those of the subsoil layer. The traditional design method taking ground soil as homogeneous isotropic soil is unsafe for the case of RE < 1 and RG < 1, so a transversely isotropic foundation model is of great significance to the design for high train velocities.

Vibration Analysis of Bridge Structure under Moving Train Load and Earthquake Action

In this paper, vibration of a steel truss bridge under moving train and earthquake action is analyzed. The following conclusions are drawn by modal analysis and time-history analysis. 1) Lateral dynamic response of this structure is more obvious under earthquake action and lateral dynamic effect of train running load; 2) seismic response in the directions different from train load is small, and dynamic response becomes larger obviously when they are considered together.

열차 증속에 따른 콘크리트 궤도 노반의 동적 응력 변화

보다 빠른 교통 수단에 대한 사회적 관심이 현재 운영 중인 KTX의 운행속도인 350km/h을 넘어서는 고속 열차의 운행을 요구하고 있다. 본 연구에서는 콘크리트 궤도 구조물에서 열차 속도 변화에 따른 노반 변위의 변화양상을 추적하고 비선형적인 노반 응력 변화를 살펴보기 위해 유한요소해석을 실시하였다. 궤도-차량 상호작용을 간단한 형태로 고려하기 위해 이동 하중의 질점 시스템을 개발하였다. 열차 하중의 이동 속도를 100km/h에서 700km/h까지 변화시켜 결과를 얻었다. 열차 속도 증가에 따라 레일과 노반 변위는 비선형적으로 증가하였으나 뚜렷한 임계 속도 효과는 나타나지 않았다. 낮은 열차 속도 대역에서는 열차 속도보다 노반에서 에너지를 전달하는 탄성파 속도가 빠르다. 하지만 400km/h 이상의 열차 속도 대역에서는 열차 속도와 에너지 전달 속도가 거의 일치하였다. 열차 속도 증가에 따라 노반 응력 이력이 크게 변하며 경로 의존적인 토질 재료에서 상당한 크기의 소성 변형률이 예상된다. Societal interest on a faster transportation demands an increase of the train speed exceeding current operation speed of 350 km/h. To trace the pattern of variations in displacements and subsoil stresses in the concrete slab track system, finite element simulations were conducted. For a simple track-vehicle modeling, a mass-point system representing the moving train load was developed. Dynamic responses with various train speeds from 100 to 700 km/h were investigated. As train speeds increase the displacement at rail and subsoil increases nonlinearly, whereas significant dynamic amplification at the critical velocity has not been found. At low train speed, the velocity of elastic wave carrying elastic energy is faster than the train speed. At high train speed exceeding 400 km/h, however, the train speed is approximately identical to the elastic wave velocity. Nonlinearity in the stress history in subsoil is amplified with increasing train speeds, which may cause significant plastic strains in path-dependent subsoil materials.

Vibration Resonance and Cancellation of Simply Supported Bridges under Moving Train Loads

Based on the theoretical solution for vibrations of simply supported bridges under moving train loads, resonance and cancellation conditions are derived. The results reveal two types of vibration cancellations for simply supported bridges under moving train loads: the first is related to a single moving load, which is independent of the number and the composition of the train, while the second is related to the interval between a pair of moving loads. When cancellation occurs, the free vibrations induced by the moving loads cancel to null, and the bridge response is determined by the loads still on it. A resonance disappearance effect occurs when train speed meets both the resonance and cancellation conditions, while the cancellation plays a predominant role. Bridge damping has an influence on the cancellation effect: the higher the damping and the longer the interval between the loads, the lower is the cancellation efficiency. In a case study, dynamic responses of a bridge under high-speed train loads are analyzed and the mechanisms of resonance and cancellation are explained to support the theoretical solution.

파일슬래브구조가 적용된 고속철도 토공노반에서의 진동 전파

콘크리트궤도가 도입됨에 따라 토공노반에서의 잔류침하 억제가 중요한 사안으로 대두되고 있다. 파일슬래브구조는 침하억제공법으로서 슬래브는 성토하중을 분산하고 파일은 분산된 하중을 지지층까지 직접 전달시켜 충분히 지지력을 확보하여 침하를 방지한다. 철도노반에 적용시 하중전달특성은 매우 우수하지만, 주행하중에 대한 진동전달 및 상호작용에 대한 특성이 규명되지 않았다. 구조적 특성상 이동하는 열차하중에 의해 발생한 진동은 슬래브를 반사층으로 하여 상부성토체 내에서 다중반사되어 전파할 가능성이 있는데 이는 열차의 주행안정성과 승차감에 영향을 미칠 수 있다. 본 논문에서는 파일슬래브가 설치된 철도노반에서 열차 주행에 의해 발생되는 진동에너지의 전파특성을 평가하기 위하여 인공적인 충격하중과 고속열차의 실측하중을 사용하여 노반구조별 진동전파특성을 시간영역 및 주파수 영역에서 해석하였다. 검토 결과, 파일슬래브 구조에서의 진동 반사효과를 확인하였으며, 적정 성토고가 확보되는 경우에는 진동에 안정적이지만 성토고가 낮은 경우에는 저주파 영역의 진동에너지가 증가하는 것으로 나타났다. The suppression of residual settlement is required on earthwork sections as concrete track is introduced. Use of pile-slab structure is one of the settlement restraining methods applied on soft ground. The slab distributes the upper embankment load and piles transfer the load from the slab to the stiff ground. While this method is very effective in terms of load transfer, it has not yet been established for dealing with the vibration transfer effects and interaction characteristics between a structure and the ground. It is possible that vibration caused by a moving train load is propagated in the upper embankment, because the slab acts as a reflection layer and waves are multi-reflected. In this present paper, wave propagation generated by a moving train load is evaluated in the time and frequency domains to consider a roadbed structure using an artificial impact load and field measured train load. The results confirmed the wave reflection effect on the pile-slab structure, if the embankment height is sufficient, vibration propagation can be stably restrained, whereas if the height is not sufficient, the vibration amplitude is increased.

Multi-Axle Moving Train Loads Identification on Continuous Bridge from Bridge Displacement Responses

A new method for multi-axle moving train loads identification on continuous bridge is presented in this paper. In order to improve the accuracy and efficiency for moving loads identification, both cubic spline interpolation technique and dynamic displacement influence line technique were employed. The time history displacements of the measurement stations under unit force were calculated with cubic spline interpolation technique based on the finite element model of the bridge. The dynamic displacement influence line was obtained to be used for identifying the moving train loads with simulated annealing genetic algorithm by minimizing the errors between the measured displacements and the reconstructed displacements from the moving train loads. A series of comparative studies were carried out to investigate effects of different span numbers with the same length, different length with the same span number and measurement noise on the proposed method. The result shows that the proposed method is an accurate and efficient method for multi-axle moving train loads identification on continuous bridge.

Numerical study on moving train parameter identification system through a simply supported bridge

This paper presents a new experimental system for moving train parameter identification on bridge. The numerical method is adopted to simulate the experimental system and to investigate the effect of the system on identification of the moving train parameters. Displacement responses are obtained by solving the equation of motion of a simply supported bridge model. Basic parameters of the train (i.e., moving speed, wheel axle numbers, and axle spacing) are recognized with a self-designed parameter recognition system. Axle load values on bridge are identified with a load identification system based on simulated annealing genetic algorithm and by minimizing the errors between measured and reconstructed displacements from the moving train loads at each time step. Measured data are simulated by adding artificial noise to the calculated data. A series of numerical simulations is performed to analyze the effect of the system under various train situations. The results show that the experimental system is feasible and valid for identification of moving train parameters, thereby providing effective preparation for practice.

Numerical Investigation of Stress Concentration Phenomenon in Piled Embankment under Moving Train Loads

A numerical study is performed to investigate the stress concentration phenomenon in a piled embankment during high-speed train passage. In the numerical simulation, the loading of a moving train is first represented in the model as a series of time-varying equivalent concentrated forces vertically acting on the ballast surface, and the explicit finite element method (FEM) is then used to analyze the ballast-embankment-ground system subjected to the equivalent forces. The study shows that owing to the very high stiffness of the piles relative to the soft soil, a majority of the wave energy, which is generated by the passage of wheel axles, is concentrated to the improving piles and transferred down to the stiff soil stratum. By this stress concentration phenomenon, the soft soil surrounding the piles is subjected to less stress, and thus preventing undesirable dynamic effects that could be induced in the soft soil.

이동열차하중에 대한 강봉으로 보강된 프리캐스트 프리스트레스트 옹벽의 동적 안정성 평가

프리캐스트 콘크리트제품은 빠른 시공, 노동력 절감, 높은 품질확보의 장점을 가지고 있어 옹벽구조물 분야에도 많이 적용하고 있다. 본 논문에서는 철도에 적용되는 프리캐스트 프리스트레스트로 제작된 옹벽의 동적안정성을 평가하기 위하여 이동열차 하중 재하상태에서의 수치해석을 수행하였다. 해석에는 2차원 유한요소 해석이 적용되었다. 궤도에 작용하는 이동열차하중은 이동하중에 대한 충격력을 대표하는 조도성분의 위상각 자료와 열차자중을 대표하는 준정적 하중을 조합하여 사용하였다. 해석에는 노반과 옹벽구조물의 시간영역 변위, 응력, 가속도 결과값을 이용하여 옹벽의 동적안정성을 평가하였으며, 평가결과 충분한 적용성을 확인하였다. The precast production has many advantages by fast construction period, labor-saving and high quality. In recent years, the application of the precast product has been increased in the earth retaining wall field. This paper presents the results of the numerical analysis that was carried out to evaluate the dynamic stability of precast and prestressed earth retaining wall under moving train load. The two-dimensional FEM analysis was used to the numerical analyses. The train load to act on trackbed is combined by the real measured roughness phase angle and quasi-static load. The dynamic stability is analysed by the displacement, acceleration and stress under moving train load at each specified location. The results of the analysis show that the precast and prestressed retaining wall has very stable capability for the railway.

Fatigue Damage Analysis of Monolithic Joint of Steel Truss Bridge Considering Welding Residual Stresses

This investigation firstly performs a thermal elasto-plastic analysis using finite element techniques to evaluate residual stresses in monolithic joint weldments, then develops an effective procedure by combining the welding residual stress and dynamic responses by moving train loads , finally calculates the stress history of hot spots in local weldments .The results showed that the stresses of some hot spots in weldments had exceeded the yield stress of steel , so the fatigue of these spots should be categorized into low cycle fatigue; the load application on the welded bridge produces a reassessment of the stress field in the weldments and, in particular, a relaxation of the maximum stress.

Assessment Spectra for Structures Subject to Passing Underground Trains

Underground trains passing below structures may produce vibrations harming occupants and nonstructural elements, though they do not usually result in structural damage. This is a problem of more importance when assessing buildings such as libraries, hospitals, laboratories, museums, etc. To prepare simple tools to fulfill design needs, in this paper assessment spectra for various underground trains moving with different velocities are calculated. Using these spectra, without resorting to the time consuming and costly analysis of a tunnel-soil system under moving loads, the maximum structural responses can be calculated rapidly. To make this end, the soil-tunnel interaction is modeled using a 3D finite difference scheme under the standard moving train loads. The dynamic analysis of such a system results in the ground surface vibration time histories at different distances from the tunnel axis. Then the maximum values of velocity responses are calculated for an SDF dynamical system. The above calculations are accomplished for different train velocities, tunnel depths, distances from tunnel, and soil types, and are presented as assessment velocity spectra.

Moving train loads identification on a continuous steel truss girder by using dynamic displacement influence line method

This paper presents a dynamic displacement influence line method for moving load identification on bridge. The finite element model of Poyang Lake continuous truss bridge-train systems is established and the dispersed modal shapes are acquired by modal analysis. Multi-axle moving train loads are identified with simulated annealing genetic algorithm by minimizing the errors between the measured displacements and the reconstructed displacements from the identified moving loads. In the identification process, the dynamic displacement influence line technique is used to calculate the time history displacement responses of the bridge to avoid solving equations of motion of the bridge repetitively. Several important parameters of the bridge-train system are discussed to investigate their effects on the proposed method. The results demonstrate that the proposed method is an accurate and efficient method for moving train load identification on complex bridges.

MULTI-AXLE MOVING TRAIN LOADS IDENTIFICATION ON SIMPLY SUPPORTED BRIDGE BY USING SIMULATED ANNEALING GENETIC ALGORITHM

Identification of multi-axle moving train loads is very important for the bridge design, construction, and maintenance. This paper presents an optimization method for identification of multi-axle moving train loads on bridges, which minimizes differences between the measured deflections and the deflections reconstructed from the identified moving loads and has the merits of both the global searching properties of genetic algorithms and the local searching properties of simulated annealing algorithms. Effects of algorithm parameters and of bridge-train system parameters on the robustness and accuracy of the proposed method are investigated. The results show that the method is feasible, accurate, and effective for multi-axle moving train loads identification.

Strengthening of a steel railway bridge and its impact on the dynamic response to passing trains

Two different strengthening methods for a through-girder steel railway bridge are investigated. The studied structure is the Söderström Bridge, located in the city of Stockholm, Sweden. Due to fatigue problems, it is in need of assessment and strengthening. In one of the methods, arches are added under the bridge modifying the structural system and lowering the stress ranges for all structural members. The other method consists of prestressing the floor beams. This increases their stiffness and transforms the mean stress in the lower flanges from tension to compression. A 3D finite element model is created and verified with measurements. The different strengthening methods are tested in the model by dynamic analysis with moving train loads. The strengthening methods show some positive effect concerning the fatigue life. Changes in vertical bridge deck acceleration for high speed traffic are also presented. A comparison between the European code and the Swedish code regarding vertical bridge deck acceleration levels for high speed traffic shows large differences for the bridge.

Dynamic Response of a New Railway Emergency Steel Truss Girder under the Moving Train Loads

In China, a new railway middle-span emergency steel truss girder, which can adapt to the technical requirements about quickly repairing the damaged railway bridges, is developed under the new situation. The old emergency steel truss girder for the railway bridges can not adapt to the current technical requirements. So, the new railway middle-span emergency steel truss girder (hereinafter referred to as the new girder) is developed after hard work. The great changes on the structure, the connections, the structural details and the multi-purpose have taken place on it compared to the existing old similar girder. In this paper, the structure and technical characteristics of the new girder are introduced. In order to improve the new girder’s design, the dynamic responses of the new girder are calculated using the train-bridge coupling vibration theory. In the paper, the 32m-span girder are the main object of study. The vibration-related laws are revealed versus the different train speeds, and the proposals about the largest traffic safety speed are given.

Experimental Study on Moving Train Loads Identification from Bridge Responses

This paper describes a method for multi-axle moving train loads identification based on simulated annealing genetic algorithm by minimizing the errors between the measured displacements and the reconstructed displacements from the identified moving loads. Experimental studies were carried out to investigate the effect of the proposed method on moving loads identification. A simply supported steel beam model and a model train with three carriages were constructed in laboratory. A series of comparative researches for moving loads identification have been conducted. Effects of moving speed and measurement station numbers on the accuracy of the proposed method are investigated. The results show that the proposed method is accurate and feasible for multi-axle moving train loads identification.