Narrow Results

With the urban rail transit construction boom, more and more extradosed cable-stayed bridges have been built and put into service in the urban rail transit lines, due to the advantages of aesthetic appearance and high stiffness. There are distinct dynamic characteristics of the metro train and extradosed cable-stayed bridge system, which have rarely been explored. This paper presents the numerical and experimental investigation of an extradosed cable-stayed bridge under dynamic train load in urban rail transit with the maximum span among its type of bridge in China. Three vehicle modes with different degrees of freedom and two bridge finite element models are adopted to perform the dynamic analysis of the metro train and extradosed cable-stayed bridge system. Moreover, the bridge is instrumented in a comprehensive field measurement campaign including ambient vibration testing, static load testing, and dynamic load testing. The collected modal parameters and static and dynamic responses of the bridge are employed to validate the established numerical models. Dynamic characteristics of the analyzed bridge are subsequently explored. In particular, dynamic effects of the main components including the main girder, pylons, and inclined cables are examined considering a variety of operational conditions. This study provides an effective method for analyzing the dynamic responses and valuable insights into the dynamic performance of large-span extradosed cable-stayed bridges under metro train load in urban rail transit.

The application of long-span steel bridge in urban rail transit is becoming more and more extensive, but the structure-borne noise of steel bridge induced by passing train is also prominent. Research on the structure-borne noise problem of long-span steel bridge in urban rail transit has positive significance in promoting the sustainable development of steel bridge, and improving the quality of sound environment along rail transit. In this work, dynamic receptance principle, finite element method and statistical energy method are combined to establish the structure-borne noise prediction model of the long-span steel bridge, and the rationality and validity of the model are verified based on field measurement results. Based on the prediction model, the noise radiation characteristics of large-span steel truss bridge in urban rail transit are studied, and the following conclusions are drawn: The bridge deck has the strongest acoustic contribution ability, with the contribution rate of 33–44%, followed by the longitudinal web and transverse web, with the contribution rate of 23–30%, followed by the truss chord, with the contribution rate of 5–8%, and the truss web, longitudinal wing and transverse wing have weak contribution ability, with the contribution rate of less than 2%. The acoustic radiation efficiency of steel truss bridge components reaches its peak at the critical frequency, and the critical frequency is determined by the thickness of steel bridge plate components when the material parameters are fixed. Under ordinary track structures, the middle-to-high frequency noise distribution characteristics of large-span steel truss bridge structure are obvious. Damping pad floating slab track can effectively suppress the high-frequency noise of steel bridge, and the overall sound level can be reduced by about 11–14dB.

In noise-sensitive areas of urban rail transit (URT), sound barriers are often used to block the propagation of on-track noise such as the wheel–rail noise. However, the vibrations induced by passing trains can also transmit to the sound barriers. Therefore, it is necessary to study the acoustic radiation characteristics of the sound barrier under moving train loads and to evaluate whether installing sound barriers will affect the overall low-frequency noise radiation from the elevated railway. In this paper, the train–track–bridge dynamic interaction theory is adopted to establish a dynamics model for train–track–bridge-sound barrier coupled system, and the acoustic theory is employed to establish acoustic boundary element models for sound barrier, box girder bridge and sound barrier-box girder bridge coupled system, respectively. These models are then used to systematically analyze the characteristics and mechanism of vibrational noise of the sound barrier due to passing trains. The effects of sound barrier on the acoustic environment are also evaluated. Finally, the influencing mechanism of sound barrier on low-frequency acoustic radiation of elevated railway is investigated, and suggestions for future research on low-frequency acoustic radiation of elevated railway are presented. The research results show that the sound barrier can become a significant low-frequency sound source during the trains passing. Installing sound barriers on elevated railway affects the sound environment around the railway mainly through acoustic effects on the noise propagation. The installation of sound barriers has an effect on the vibration characteristics of the box girder bridge. In order to explore the characteristics of low-frequency sound radiation of elevated railways installed with sound barriers, it is necessary to reanalyze the acoustic generation mechanism of the entire structure of the bridge-sound barriers coupled system and combine it with the propagation mechanism of various sound sources.

Current researches on the network characteristics of metro networks are generally carried out on topology networks without passenger flows running on it, thus more complex features of the networks with ridership loaded on it cannot be captured. In this study, we incorporated the load of metro networks, passenger volume, into the exploration of network features. Thus, the network can be examined in the context of operation, which is the ultimate purpose of the existence of a metro network. To this end, section load was selected as an edge weight to demonstrate the influence of ridership on the network, and a weighted calculation method for complex network indicators and robustness were proposed to capture the unique behaviors of a metro network with passengers flowing in it. The proposed method was applied on Beijing Subway. Firstly, the passenger volume in terms of daily origin and destination matrix was extracted from exhausted transit smart card data. Using the established approach and the matrix as weighting, common indicators of complex network including clustering coefficient, betweenness and degree were calculated, and network robustness were evaluated under potential attacks. The results were further compared to that of unweighted networks, and it suggests indicators of the network with consideration of passenger volumes differ from that without ridership to some extent, and networks tend to be more vulnerable than that without load on it. The significance sequence for the stations can be changed. By introducing passenger flow weighting, actual operation status of the network can be reflected more accurately. It is beneficial to determine the crucial stations and make precautionary measures for the entire network’s operation security.

To quantify the spatiotemporal distribution of passenger flow and the characteristics of an urban rail transit network, we introduce four radius fractal dimensions and two branch fractal dimensions by combining a fractal approach with passenger flow assignment model. These fractal dimensions can numerically describe the complexity of passenger flow in the urban rail transit network and its change characteristics. Based on it, we establish a fractal quantification method to measure the fractal characteristics of passenger follow in the rail transit network. Finally, we validate the reasonability of our proposed method by using the actual data of Beijing subway network. It has been shown that our proposed method can effectively measure the scale-free range of the urban rail transit network, network development and the fractal characteristics of time-varying passenger flow, which further provides a reference for network planning and analysis of passenger flow.

Urban rail transit (URT) system plays a significant role in daily commuting. The main features of URT could be abstracted into two kinds of networks, topological network and transit network. The correlation between topological network and transit network could represent the service level of transportation which is also a main focus to some extent. In this study, static analysis based on one year or single analysis based on one aspect are abundant, the main reason of which is the deficiency of the consistent demand data. In this regard, a comprehensive analysis of the evolution and their correlation of the two network are carried out in this work. We first revisit the topological evolution of rail network on the basis of URT network statistic indicators with a fifty-year time span. Then, based on the traditional node-place model, a correctional node-place model between demand spatial distribution and closeness centrality is established. Pearson correlation coefficient is also employed for a precise analysis. Finally, the application of the model and the corresponding analysis on Beijing Subway System (BSS) examine and evaluate the development level and service level of URT system in Beijing, and some solid evidence for relative decision-making is provided.

The rapid development of new urbanization boosts the pace of urban rail transit (URT) network construction. The new-built lines not only facilitate people’s daily travel, but also change the reliability of the original network. In this paper, based on the complex network theory, the static characteristics of Tianjin URT represented by the current and forward networks are analyzed. The global efficiency is selected as the evaluation index to analyze the evolution characteristics of the network. The results show that Zhigu station and Xiawafang station are more vulnerable in the current network, while Zhangxingzhuang station and Jinzhonghe street station are the key stations in the forward network, and need to be paid more attention. Meanwhile, the lines M9 and Z2 as the key lines in the long-term network and their reliability must be ensured.

Focusing on the time domain optimization problem of an urban rail transit line, this paper constructs a passenger travel network with OD passenger flow data as input, by using a multi-path search algorithm based on dynamic cost to deduce the passenger space-time path. The passenger travel path is restored and the spatial and temporal distribution of passenger flow is calculated. Based on this, considering the influence of passenger flow spatial and temporal distribution on the time domain division, the orderly clustering method is used to optimize the time domain. Factoring in the influence of line capacity constraint, train running sequentially on time domain division and bidirectional time domain, a time domain optimization framework for an urban rail line is proposed in this study to integrate the time domain optimization results and improve the adaptability of optimization method. A practical line is taken as an example to verify the effectiveness of the proposed framework. Compared with the traditional time domain division method, the time domain division result accuracy is significantly improved and lays a foundation for the formulation of train service scheme which accurately matches transport capacity to demand.

Cable-stayed bridges carrying urban rail transit are often equipped with rail expansion devices (REDs) to avoid possible breaking or buckling of the rails. Such devices not only increase construction and maintenance budgets of the track system, but also endanger ride comfort and safety of the trains. Therefore, the maximum expansion length of cable-stayed bridges without the adoption of RED is investigated and presented in this paper. Finite element models of cable-stayed bridges with various lengths are developed based on design parameters of existing bridges with similar lengths. A friction-spring model is utilized to simulate the nonlinear resistance history of fasteners under various loading cases. Track–bridge interactions are then studied by varying the longitudinal restraint conditions for the cable-stayed bridges. The investigation reveals that the admissible overall rail stress allows a maximum expansion length of about 400m for urban rail transit double-tower cable-stayed bridge paved with the ballastless track and WJ-2 small resistance fasteners. This finding provides theoretical bases and practical guidelines for the saving of REDs for many large-span urban rail transit bridges in future design.

This study systematically introduces a floating slab track (FST) with rubber vibration isolator (RVI) and investigates its behavior in urban rail transit. The FEM is used for modal analysis to clarify the modal parameters of the FST system. A vehicle–slab track coupling sub-model and a tunnel–soil coupling sub-model were established and the propagation law was analyzed by calculating the vertical vibration accelerations beneath the shield wall as well as the vertical vibratory acceleration levels of the surrounding soil. A wheel-set drop test was carried out to verify the actual vibration isolation effect compared with the numerical models. The results reveal that the vibratory acceleration levels at the distance of 20m from the tunnel center-line basically meet the requirements for vibration in most areas of a city. The variation trend of the vibratory acceleration level measured in laboratory tests agrees well with the calculated values from the numerical simulation. The attenuation amplitude of the levels reaches 19.33dB with the German high disturbance irregularity and 20.05dB with the short-wave irregularity in the simulation, and the levels are reduced by 45–58dB in laboratory tests which demonstrate the FST with RVI performs well in vibration isolation.

Urban rail transit route laying mode is one of the most important contents in the network planning of urban rail transit. The selection of route laying mode is significant to urban future development. This paper analyzed the influence factors, compared evaluation system that is now used in many cities, established the final evaluation index system of urban rail route laying mode, and then used AHP and Fuzzy evaluation method to quantify the factors of route laying mode. This method can reduce the cost of construction and the influence on the land use etc. Finally, this paper provided reference to the construction of urban rail road.

As a public product, urban rail transit has brought profound influence to the government, society and related companies in the entire process of construction and operation. To correctly understand the advantages and disadvantages of urban rail transit operation, this article combined the goal of urban rail transit enterprises which is to realize the maximization of the comprehensive benefit of social and economic benefits, and used the improved balanced score card method to build the social benefit, economic benefit and service level, internal business, learning and growth of comprehensive performance evaluation index system and paid more attention to the evaluation of social benefits. It used the analytic hierarchy process (AHP) to set evaluation indicators hierarchically and calculated the index weight, finally built comprehensive performance evaluation system of urban rail transit.