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Chen T.,Beijing MTR Construction Administration Corporation | Xu R.,Tsinghua University | Li Q.,Tsinghua University
Acta Mechanica Solida Sinica | Year: 2015

Abstract The effect of strain rate on the tensile strength of defective monocrystalline silicon (Si) nanorods is studied with the molecular dynamics method. The strain rate applied to the nanorods is varied from 107 to 1014 s-1, and the atomic interactions among the Si atoms are described by the Stillinger-Weber (SW) potential functions. The tensile strength of the ideal Si nanorod is shown to be strongly strain rate dependent and increasing with the strain rate. The failure pattern also shows strain rate dependence, indicating that increased strain rates gradually suppress unsuitable relaxation and dissipation mechanisms because of the accompanying larger external loadings. Furthermore, the effects of intrinsic material parameters (i.e., the cutoff radius of SW potential function) and defects (i.e., inevitable surface defects and internal preinstalled defects) are investigated. It is revealed that the effect of strain rate on the tensile strength of Si nanorod is influenced by both the intrinsic physical properties of the material and the distribution of the initial defects, with specific surface defects appearing to be more important to nanostructure design. © 2015 The Chinese Society of Theoretical and Applied Mechanics.

Wang T.,Beijing MTR Construction Administration Corporation | Wang T.,Beijing Jiaotong University | Luo F.-R.,Beijing MTR Construction Administration Corporation | Liu W.-N.,Beijing Jiaotong University | Li X.-G.,Beijing Jiaotong University
Yantu Lixue/Rock and Soil Mechanics | Year: 2011

Drift-pile-beam-arch (Drift-PBA) method has become a major construction method in Beijing metro engineering, which can reduce soil deformation and effect on adjacent structures effectively. Based on the Huangzhuang station project of Beijing metro line No. 10 and the field monitoring data of surface and pipeline settlement, a three-dimensional finite element model of station structure, soil and pipeline is established. The influence of metro station built by drift-PBA method on ground movement is examined; and the response of adjacent rigid-joint pipelines is systematically researched from the aspects of settlement, deformation and pipe-soil interaction. The results show that the ground settlement induced by the two key stages composed of construction of pilot tunnel and center arch region accounts for more than 90 percentage of the total settlement. The settlement and deformation of rigid-joint pipelines, and differential settlement between pipe and soil are closely related to spatial relationship between station and adjacent pipes, and mainly induced by the excavation of soil below the pipelines. The whole body of the rigid-joint pipe bears deformation in common; and the pipeline sustains bending and axial deformation caused by ground movement; therefore, it is suggested that the pipeline strain should be used as deformation criterion.

Li Y.,Beijing Jiaotong University | He P.,Beijing Jiaotong University | Qin D.,Beijing Jiaotong University | Qin D.,Beijing MTR Construction Administration Corporation
Zhongguo Tiedao Kexue/China Railway Science | Year: 2012

Based upon the elastoplastic damage constitutive model of concrete, considering the discontinuity between the assembly block of shield segment and connecting bolts as well as the contact relationship between each assemble block, a 3D discontinuous contact computational model was built. Taking the shield tunnel project of certain metro in Suzhou for example, 3D discontinuous contact computational model was used to simulate the force condition of shield segment. Comparative analysis was conducted between the simulated results and those obtained by routine method model and modified routine method model respectively. Results show that the damage factor of some zones on the K assembly block at the vault in shield segment has exceeded the damage threshold value, and visible cracks thus appear on these zones. Plastic deformation appears on the inner side of shield segment top and bottom subjected to tension. The plastic zone depth of the K assembly block at shield segment top has reached 55% of the section width. The maximum internal force combination of shield segment locates at the joint of the haunch segment on both sides. 3D discontinuous contact computational model can better reflect the influence of segment joint on the internal force as well as the stress and deformation characteristics of concrete material for segment. The setup of the contact element at the joint of shield segment in the model has eliminated the influence on the calculation results by the diversity of the joint stiffness in other model. Both the compressive stiffness and the bending stiffness of shield segment will be affected.

Wang T.,Beijing MTR Construction Administration Corporation | Wang T.,Beijing Jiaotong University | Luo F.,Beijing MTR Construction Administration Corporation | Liu W.,Beijing Jiaotong University | Li X.,Beijing Jiaotong University
Tumu Gongcheng Xuebao/China Civil Engineering Journal | Year: 2012

Using the Huangzhuang metro station project of Beijing metro line 10 as the background, a 3-D finite element model including the station structure, soil and pipeline was established using the field monitoring data. The master-slave contact surface method was adopted to simulate the pipe-soil interaction, and two-node connector element constrain model to simulate the pipe joint deformation. The influence of metro station construction using PBA method on ground movement was examined, and the response of adjacent pipelines was studied concerning the following aspects: settlement, deformation, strain, joint rotation and pullout. The results showed that the ground settlement induced by the construction of the headings and the center arch contributed the most of the total settlement. Pipeline deformation was closely related to the relationship between the station and pipe, and moreover, the response of adjacent pipelines was mainly induced by the excavation of the soil below the pipelines. The pipeline joint born most of the deformation of the flexible joint pipeline, and the pipeline joint rotation and pullout can be used as a deformation criterion. The stages of pipeline joint rotation variation included the initial stage, convex curvature stage, concave curvature stage and stable stage. The joint pullout includes 3 stages: initial variation stage, rapid increase stage and stable stage.

Hu H.,Institute of Geotechnical Engineering | Zhu H.-X.,Beijing MTR Construction Administration Corporation | Jia L.-H.,Institute of Geotechnical Engineering
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2010

By use of numerical methods for the excavation of foundation pits and piles in row by the subway, the separation action of secondary stress at different embedded depths is analyzed, and the rebound of subway foundation by the excavation foundation pit is studied. Based on the software of FLAC3.30, the stress releasing is simulated, the displacement and stress vectorgraphs of subway foundation owing to the pit excavation are analyzed when the model depth of subway is larger or smaller than the excavation dept. The results indicate that the rebound of subway foundation is small when the depth is larger than the pit depth and it is large when the depth is smaller than the pit depth, and satisfactory parameters of piles can be obtained at different depths of the subway foundation.

Han Z.-W.,Beijing MTR Construction Administration Corporation | Dong J.,Beijing Sifang Automation Co | Tu L.-M.,Beijing Sifang Automation Co | Li H.-T.,Beijing Sifang Automation Co
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2012

The deficiency of the metro direct-current feeder protection is mainly attributed to the application of single-ended current as the sole method in the detection and identification of breakdowns, which is time-consuming in case of remote short circuit and is very likely to fail or make mistakes. Therefore, by evaluating the distribution relationship between the side currents and line or load current, this paper proposes a segment domain protection method. Through this method, the protection measurement data at both sides of independent feed segment can be shared synchronously via optical fiber, and brand new protection criteria can be realized after a comprehensive domain processing. This paper presents the composition principles of independent feeder section and consequently proposes the "sum current" protection principle utilizing the sum of two ends' currents, impedance protection principle and double-ended tripping protection principle. In the end, approaches to realizing those protection principles are provided. The method can realize the entire DC feeder quick-action, which improves the speed, sensitivity and reliability of the Metro direct-current feeder protection.

Chen H.,Beijing MTR Construction Administration Corporation | Zhang J.,Bgi Engineering Consultants Ltd.
Journal of Geomatics | Year: 2013

An interval shield tunnel is located in a old town of beijing. It will pass through the old flat tile-roofed house longly. In order to grasp the rules of settlement and provide guidance for the subsequent construction, we choose a part of the area to test. Then the corresponding settlement of the section is carefully measured. We get the settlement data of different shield paramenters. The monitoring data is comprehensively analyzed, then general rules of settlement in the old flat tile-roofed house is summarized. This has important reference value for similar projects in future.

Jia Y.,Beijing Institute of Economics and Management | Liu W.,Beijing Jiaotong University | Li K.,Beijing MTR Construction Administration Corporation
Vibroengineering Procedia | Year: 2015

A novel analytical model of vibration source for metro train based on "coupled vehicle and track basic unit" is established in this paper. The dynamic vehicle-track equations are completed with the displacement compatibility and the force equilibrium, and the model takes into account the infinite track structure, whole vehicle, track irregularity and wheel-rail Hertz contact. The special feature of track structure model is the periodical system of discrete supported sleepers, which converts the infinite integral equation into the combination in the wave number-frequency domain and simplifies the calculation progress. The rail dynamic responses and the wheel-rail contact force can be calculated easily. A complete software package TMCVT is programmed. A calculated example is achieved using the program. Compared the theoretical calculated results and the field tested results ,the coincidence with each other proved the analytical dynamic model for metro train coupled with vehicle and track is correct. © JVE International Ltd.

Qin D.,Beijing Jiaotong University | Qin D.,Beijing MTR Construction Administration Corporation | He P.,Beijing Jiaotong University | Li Y.,Beijing Jiaotong University
Zhongguo Tiedao Kexue/China Railway Science | Year: 2011

One year after the completion of a certain station in Daxing metro line, cracks of different degree have been found on the walls and floors of the building near the station. Based on the test data and statistical data of the building, back analysis is carried out on wall cracks and structural damages of the building to determine whether the structure of the building is still safe by using the displacement method in structural mechanics and ABAQUS finite elements software. The results show that most of the tile crack areas calculated is identical with actual test results. The crack width of tiles calculated is less than 0.1 mm, and the crack width of walls calculated is less than 0.2 mm, both of them are lower than standard requirements. The present cracks on the partial positions of the building walls and floors are non-structural damage cracks caused by the post-construction differential settlement of the metro, and the pressure stress values of the building are all less than the design values of compressive strength. Therefore, the whole building is safe and there will not appear collapse or other dangers.

Ding S.-K.,Beijing MTR Construction Administration Corporation
Jiaotong Yunshu Xitong Gongcheng Yu Xinxi/Journal of Transportation Systems Engineering and Information Technology | Year: 2011

In this paper, the IEEE802.11 series-based WLAN transmission modes are proposed: space free wave and waveguide, which have been widely used in urban rail transit signal system. The engineering characteristics and technical features of these two modes are briefly introduced, and the WLAN radio frequency coverage and communication mechanism are deeply analyzed. Based on the implementation in subway lines Yizhuang and Changping, the wireless coverage of space free wave and waveguide combination transmission are documented, as well as the structure and working mode of train-ground communication system, the performance characteristics and distribution principle of the wireless AP. The calculation of the WLAN free space loss, signal accept strength and link system allowance are also presented. The development direction of WLAN in the signal system is proposed. ©2011 by Science Press.

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