Abstract

geosynthetic, reinforced, piled embankment is an effective and economic method to solve the problems of possible bearing failure, unacceptable settlement and slope instability for an embankment built over soft soil this has led to its widespread use, especially for high-speed railway embankments. Some design methods have been developed to assess the performance of these reinforced structures, which are mainly based on the results from small-scale models and numerical simulations. However, the reliability of these methods needs to be validated under full-scale field tests. This paper presents a numerical and analytical study for a full-scale field test of the Fengyang high-speed railway embankment. The results were analyzed and discussed in terms of the settlement of subsoil, the stressconcentration ratio (SCR), the axial force and the frictional stress of the pile. They showed that the settlement of the subsoil, from both the finite-element method (FEM) and the analytical method, were in good agreement with the measurement, and thus was a reliable parameter to assess the performance of the piled embankment with reasonable accuracy. The SCR was overestimated by the modified Terzaghi method, with a difference of 25%, while it was underestimated by the FEM, with a difference of approximately 20%. It was also shown that the tensile force in the reinforcement could be effectively assessed using the proposed analytical method, while it was overestimated by the FEM with a difference of 44%. Z geosintetiki ojačan pilotni nasip predstavlja učinkovito in gospodarno metodo za reševanje težav glede nosilnosti temeljnih tal in nesprejemljivih posedkov ter nestabilnosti brežin nasipov zgrajenih na mehkih tleh, kar vodi do široke uporabe, zlasti za nasipe železnic visokih hitrosti. Razvite so bile nekatere metode projektiranja za ocenjevanje uspešnosti teh ojačanih konstrukcij, ki v glavnem temeljijo na rezultatih iz modelov v zmanjšanem merilu in numeričnih simulacij. Zanesljivost teh metod mora biti preverjena s terenskimi preizkusi v naravni velikosti. V članku je predstavljena numerična in analitična študija na terenskem preizkusu v naravni velikosti, in sicer, na nasipu za železnico visokih hitrosti Fengyang. Rezultati so bili analizirani in komentirani za posedke zemljine, razmerje koncentracije napetosti (RKN), osno silo in trenjsko napetost v pilotu. Pokazalo se je, da so rezultati posedkov dobljeni z metodo končnih elementov (MKE) in analitično metodo bili zelo blizu merjenim, in to je bil zanesljiv parameter, da bo ocenitev obnašanja s piloti ojačanega nasipa sprejemljivo natančna. RKN je bil po modificirani Terzaghijevi metodi precenjen za 25%, medtem, ko je bil po MKE podcenjen za približno 20%. Pokazano je bilo tudi, da bi se natezna sila v ojačitvi lahko učinkovito ocenila s predlagano analitično metodo, medtem ko je bila s FEM precenjena za 44%.

Abstract

The increasing need for High-Speed Railway (HSR) to reduce the travelling time requires increasing research within this field. Bridges are main components of any railway network, including HSR networks, and the optimization of their design for this purpose would contribute to a faster and more cost effective development of the HSR network. The initial investment, the running and maintenance costs of the bridges can be decreased through better understanding of the their dynamic behaviour. This thesis studies the dynamic behaviour of end-shield railway bridges under HSR operation. 2D beam analysis is used to study the effect of the distribution of the train’s axle load. Relatively accurate 3D FE-models are developed to study the effect of Soil-Structure Interaction (SSI) and the dynamic response of the bridges. Modelling alternatives are studied to develop an accurate model. A full scale test of a simply supported Bridge with end-shields using load-controlled forced excitation was performed and the results were used to verify the theoretical models. A manual model updating process of the material properties of the 3D FE-model is performed using FRFs from the field measurements. A Simple 2D model is also developed, where a spring/dashpot system is implemented to simplify SSI, and updated to reproduce the field measured responses. The conclusions of the project emphasize the importance of SSI effects in the dynamic analysis of end-shield bridges for predicting their dynamic behaviour. The conclusions also show that the modelling of the surrounding soil and the assumption of the soil material parameters have significant effect on the dynamic response. Even the boundary conditions, bedrock level and the ballast on the railway track affects the response. The results also show that the bridge’s concrete section behaves as uncracked section under the studied dynamic loading. "p"QC 20170403

Abstract

By shortening the transportation time between cities, high-speed rail shortens the spatial distance between cities and exerts a far-reaching influence on urban agglomerations’ spatial structures. In order to explore the influence of high-speed rail on the spatial reconstruction of an urban agglomeration in western China, this paper employs fractal theory to compare and analyze the spatial structure evolution of the Chengdu–Chongqing urban agglomeration in western China before and after the opening of a high-speed railway. The results show that after the completion of the high-speed railway, the intercity accessibility is improved. The Chengdu–Chongqing urban agglomeration’s spatial distribution shows a decreasing density from the central city to the surrounding areas. Furthermore, the urban system presents a trend of an agglomeration distribution. Therefore, strengthening the construction of high-speed rail channels between primary and medium-sized cities, as well as accelerating the construction of intercity railway networks and rapid transportation systems based on high-speed rail cities, would help develop urban agglomerations in western China. Document type: Article

Abstract

Pulse width modulation (PWM) technology is widely used in traction converters for high-speed railways. The harmonic distribution caused by PWM is quite extensive, and increases the possibility of grid–train coupling resonance in the traction power supply system (TPSS). This paper first analyzes the mechanism of resonance, when the characteristic harmonic frequency of a four-quadrant converter (4QC) current that injects into the traction grid matches the resonant frequency of the traction grid, which may result in resonance in the system. To suppress resonance, this paper adopts specific harmonic elimination–pulse width modulation (SHE-PWM) technology combined with a transient direct current control strategy to eliminate the harmonics in the resonant frequency, which may suppress the grid–train coupling resonance. Due to the fact that the SHE-PWM process with multiple switching angles contains complex transcendental equations, the initial value is difficult to provide, and is difficult to solve using ordinary iterative algorithms. In this paper, an active-set secondary optimization method is used to solve the equation. The algorithm has the benefits of low dependence on initial values, fast convergence and high solution accuracy. Finally, the feasibility of the resonant suppression algorithm is verified by means of Matlab simulation. Document type: Article

Abstract

The increasing need for repairs of polygonized wheels on high-speed railways in China is becoming problematic. At high speeds, polygonized wheels cause abnormal vibrations at the wheel-rail interface that can be detected via axle-box accelerations. To investigate the quantitative relationship between axle-box acceleration and wheel polygonization in both the time and frequency domains and under high-speed conditions, a dynamics model was developed to simulate the vehicle-track coupling system and that considers both wheel and track flexibility. The calculated axle-box accelerations were analyzed by using the improved ensemble empirical mode decomposition and Wigner-Ville distribution time-frequency method. The numerical results show that the maximum axle-box accelerations and their frequencies are quantitatively related to the harmonic order and out-of-roundness amplitude of polygonized wheels. In addition, measuring the axle-box acceleration enables both the detection of wheel polygonization and the identification of the degree of damage. Document type: Article

Abstract

The aim of this research is to define a breakage limit for the fastening system of the "Eurobalise" device of the ERTMS/ETCS rail signalling system on the European railways. The widespread presence of the system along the European railway line and the increasing of high-speed lines have led the research to find design solutions able to increase the attack system strength, avoiding its detachment from the sleepers. Mechanical tests on tensile, shear and bending configurations have been carried out to evaluate the jointing systems between Eurobalise and sleepers. Additional full-scale tests allowed the definition of the load actions and of the breaking points. The connection between balise and sleepers is able to react to the train’s aerodynamic actions, confirming the system reliability even for the passage of high-speed trains. Through the experimental approach were defined standard test procedures useful to improve the sheet data of this kind of fastening system.

Abstract

The control and operation of a single-phase 13-level power conditioning system (PCS) for peak power reduction of a high-speed railway substation (HSRS) are proposed. This PCS is a single-phase 3100 V, 2 MVA 13-level H-bridge multi-level inverter structure. It has excellent power quality. It is easy to serialize by voltage. In addition, the DC bus power of each cell inverter is supplied by lithium-ion batteries. The generalized reduction gradient optimization algorithm based on past load pattern is applied to the power management system for peak power reduction of HSRS. The phase detector and power controller for the control of a single-phase PCS based on virtually coordinated axes using an all-pass filter are expected to be robust to external disturbances with fast response characteristics. This study also proposes an adapted select switch (ASS) method that can change the switching depending on the operation state of PCS and the state of charge (SOC) of the battery to minimize battery imbalance by controlling each cell inverter of the H-bridge. The validity of the proposed system was confirmed by PSiM simulation and experiments using a demonstration system of 6 MW PCS and 2.68 MWh batteries at one of Gyeongbu high-speed line substations in Korea. Document type: Article

Abstract

Higher speeds and higher capacity will cause the Swedish rail network to be exposed to disturbing dynamic effects. Higher speeds cause higher vertical acceleration levels of the bridge deck. In this thesis, a numerical analysis of a three span end-frame bridge subjected to train induced vibrations is performed. The aim is to identify which structural components and boundary conditions that affect the dynamic behavior of the bridge. Furthermore, the influence of soil structure interaction (SSI) will be investigated as it may have contribution to the stiffness and damping of the structural system.  In order to capture the dynamic response of the bridge, an analysis in the frequency domain was preformed where frequency response functions (FRF) and acceleration envelopes were obtained. For this purpose, a detailed FE-model in 3D was created. Three different cases were studied, model subjected to ballast, model subjected to soil and model subjected to both ballast and soil in coherence. A high speed load model (HSLM) was used to create simulation of train passages at different speeds and applied to all cases so that the bridge deck accelerations could be studied. A simplified 2D-model with impedance functions representing the soil-structure interaction was created to validate the results from the detailed 3D-model and for practical design purposes.  The result of this numerical analysis showed that the vertical accelerations were within acceptable levels of the maximum allowed limits given in governing publications. Considering the surrounding soil, the results revealed an increase of the dynamic response in the midspan at resonant frequency. However, it was identified that this behavior is not explained by the influence of soil structure interaction but rather the change in boundary conditions of the end-shields. The same dynamic behavior was identified for the simplified 2D-model, with a slight underestimation of the vertical accelerations at resonance.

Abstract

In this thesis, the influence of soil-structure interaction (SSI) of end-frame bridges for high-speed railways was studied. Impedance functions, representing the SSI, was calculated and analyzed. The impedance functions were applied to end-frame bridge models which were analyzed for use in HSR. A new high-speed railway link is currently being planned in Sweden by the Swedish Transport Administration (Trafikverket). \\textit{Ostl\\"{a}nken} is planned to run between the cities of Stockholm and Link\\"{o}ping with a maximum speed limit of 320km/h. As high-speed traffic induces high dynamic impact on bridges, dynamic analysis to ensure safety and passenger comfort is needed according to Eurocode. Thus, there is a demand of dynamically safe bridges that are also cost-effective. One cost-effective bridge is the soil integrated end-frame bridge, however, there are no design advice in Eurocode today on how to take SSI into consideration. The aim of the thesis has therefore been to investigate if the influence of SSI on end-frame bridges for HSR. This thesis was executed using the frequency domain approach to solve dynamic problems in finite element software. Furthermore, impedance functions have been obtained representing the SSI. Impedance functions take dynamic stiffness and dynamic damping into consideration where the damping consists of two parts: material damping and radiation damping due to energy dissipation in the form of elastic waves. To limit the model size, an absorbing region (AR) was used to mitigate waves originating from the source. The accuracy of impedance functions is dependent on several parameters and demands a great computational capacity to reach, mostly governed by the radiation condition. A parameter study of impedance functions was conducted, including parameters such as geometry, modulus of soil and detail levels. The impedance functions were then attached to bridge models on which trains modelled as moving point loads were applied. Envelopes of the acceleration and displacements have been presented and analyzed. Shear strain checks were made in order to verify the assumption of linear-elastic material behavior of the embankment. By using SSI in form of impedance functions attached to bridge models, numerical results show a great reduction of vibrations in models. The study suggests that a large end-frame, either long or high or both, may reduce acceleration as well as displacements. A stiffer embankment material may further reduce vibrations. Shear strain checks confirm that the assumption of linear-elastic soil behavior was true. I det här exjobbet har påverkan av jord-struktur interaktion (soil-structure interaction - SSI) av ändskärmsbroar för höghastighetsbana blivit studerat. Impedansfunktioner som representerar SSI har beräknats och analyserats. Impdansfunktionerna har sedan applicerats på bromodeller och analyserats för höghastighetstrafik. Sveriges första höghastighetsbana håller just nu på att planeras av Trafikverket. Ostlänken kommer att bli den första delen och är planerad att gå från Stockholm till Linköping med en högsta hastighet av 320 km/h. Då höghastighetstrafik introducerar stor dynamisk på verkan på broar behövs dynamisk analys genomföras enligt Eurocode för att kunna säkerställa broarnas säkerhet och komfortkrav. Därför finns idag ett behov av dynamiskt säkra broar som också är kostnadseffektiva. En typ av kostnadseffektiv bro är den med jord integrerade ändskärmsbron. I dagens Eurocode finns dock inga konstruktionsråd vad gäller jord-struktur interaktion av ändskärmarna. Målet med detta examensarbete har därför varit att undersöka påverkan av SSI och besluta huruvida användandet av ändskärmsbron på höghastighetsbanor är legitimerat, eller om den ska undvikas. Det här examensarbetet har utgått från att lösa dynamiska problem i frekvensdomänen med hjälp av FEM. Impedansfunktioner som representerar jord-struktur interaktionen har tagits fram. Impedansfunktioner tar dels hänsyn till dynamisk styvhet och dels dynamisk dämpning. Den dynamiska dämpningen består av två delar; den första är materialdämpning och den andra är vågdämpning där energi dissiperar i vågform. För att begränsa FE modellens storlek har en absorbing region tillämpats för att absorbera vågorna vid randen. Impedansfunktionernas konvergens beror på flertalet parametrar och kräver en hög datakapacitet för att fås, mestadels beroende av radiatorvillkoret. En parameterstudie utfördes för att kunna analysera sensitiviteten hos impedansfunktionerna. Vidare applicerades dessa impedansfunktioner på skal- och balk-bromodeller på vilka HSLM laster påfördes. Skjuvtöjningskontroller gjordes för att verifiera att antagandet om linjärelastiskt materialbeteende var korrekt. Genom att ta hänsyn till SSI i form av impedansfunktioner tyder numeriska resultat på att vibrationer kan reduceras i hög grad. Envelopper visar att en stor ändskärm, antingen lång, hög eller bådadera, kan reducera accelerationer liksom förskjutningar. En styvare bank kan ytterligare reducera vibrationer.