西南交通大学学报

A Review of Vulnerable Line Identification in Power Systems

LIU Zhigang, ZHANG Qiao, HE Xiaofeng, FAN Wenli

2021, 56(4): 673-688. doi: 10.3969/j.issn.0258-2724.20200717

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Abstract:
With the further interconnection of the power grid, the scope of blackouts have become more extensive. Identification of vulnerable lines has important theoretical and practical significance for preventing cascading failures and ensuring the safety and stable operation of the system. The current research methods of vulnerable lines identification are summarized. The related research results in recent years are divided into two categories. The first category is based on power system status analysis, concentrating on power flow calculation and power grid dynamic characteristics. The application of entropy theory, cascading fault simulation method, risk assessment theory, energy function theory and reinforcement learning theory in the identification of vulnerable lines is introduced. The second category takes the complex network theory as the background. The application of the improved betweenness method, maximum flow theory method and dual graph method in the identification of vulnerable lines is summarized. According to the analysis, the existing methods favorably take into account the system structure and status, and the static and dynamic characteristics of the system, but exclude the uncertainty of the source and load; i.e., they only consider the vulnerability of a single line. Finally, given the development and demands of power systems, the main research interests in the future are illustrated as new energy grid integration, mobile shock load access, data-driven based and composite vulnerable lines identification.

Continuous Power Supply Scheme and Power Flow Algorithm of Traction Cables for Urban Railways

LIU Wei, LIU Xueqing, WANG Hui, LI Qunzhan, LIU Tongtong, PAN Weiguo

2021, 56(4): 689-697. doi: 10.3969/j.issn.0258-2724.20200066

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Continuous power supply scheme of traction cables is explored for urban railways, in which the power runs through the whole line, and two main substations are set with the same phase power supply devices, one for primary use and one for standby. The feeding section distance is modeled and solved in the cases of the unilateral and bilateral continuous power supply. The model takes the voltage loss as a constraint condition, and the maximum number of trains that the feeding section can supply is obtained by solving the model in a way of gradual increase in the number of trains. Further, the allowable value of the feeding section distance is calculated, which provides a reference for the position setting and checking of the traction transformer. To develop a layered power flow algorithm with interactive iteration, the line-based traction power supply system is modeled, and the traction power supply system is divided into the cable layer and traction layer. In this algorithm, the power flow is solved within the layer, and the variable values are modified between the layers to realize interactive iteration and obtain the final calculation results. This algorithm has the merits of reducing matrix order and increasing computational efficiency. The case analysis shows that in contrast to the traditional power supply scheme, the continuous power supply scheme can increase the utilization rate of regenerative braking energy by 99.15%, and reduce the annual electricity cost by 29.55 million yuan with the use of regenerative braking energy, and the non-recurring investment by 136.72 million yuan.

Analysis on Extreme Distance of Power Supply for Urban Rail AC Power Supply System

ZHANG Liyan, YANG Lianghui, HAN Dushuo

2021, 56(4): 698-705. doi: 10.3969/j.issn.0258-2724.20200059

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The power supply distance is an important indicator to measure the power supply capacity of a traction system, and has a practical impact on the stability and economic operation of the system. The urban rail AC power supply system uses the cable structure of the traction network, which has the outstanding characteristics of stable and large-capacity transmission. Therefore, it is of great significance to quantitatively study the power supply distance of the system. In this work, the extreme distance of power supply is analyzed theoretically. According to the circuit topology characteristics of the system, the traction network impedance as well as traction network voltage loss and rail potential are deduced for a single vehicle and multiple vehicles. First, by the natural power comparison between the overhead line and the cable in the traction network, the extreme distance of power supply is calculated in the cases of different cable cross-sectional areas. Secondly, the extreme distance of power supply is analyzed with the constraint of the voltage loss at the peak operating of the system. Finally the rail potential values prescribed in existing electrified railway standards are used as constraints to analyze the maximum short loop length of the system. In simulation, the maximum single-section power supply length of the urban rail AC power supply system can reach 9.31 km. When the main substation is located in the middle of the line, the extreme power-supply distance can reach 84.22 km.

Visual Simultaneous Localization and Mapping Algorithm Based on Convolutional Neural Network to Optimize Loop Detection

GUO Lie, GE Pingshu, WANG Xiao, WANG Dongxing

2021, 56(4): 706-712, 768. doi: 10.3969/j.issn.0258-2724.20190723

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Traditional visual SLAM (simultaneous localization and mapping) without loop detection may lead to error accumulation. Even if there exits loop detection, it is unable to be applied to the lightweight applications because of its low accuracy and efficiency. Thus, a visual SLAM with loop detection optimization is studied. In the front-end estimation, ORB (oriented fast and rotated brief) feature points were abstracted and matched. PnP (perspective-n-point) was solved for the successful matched point to estimate the camera motion and screen out the key frame images. In the back-end optimization, SqueezeNet convolution neural network (CNN) was used to extract the feature vectors. The cosine similarities were calculated to determine whether there were loops or not. If there was a loop, the corresponding constraint was added to the posture graph. Then the global posture was optimized by using the graph optimization theory. Finally, tests and comparisons were conducted on the data sets produced by our research group and the public data sets of TUM. The results show that the proposed algorithm can detect loops successfully and add constraints to global trajectory optimization compared with the non-loop detection algorithm. Compared with the traditional word bag method, the recall rate of this method can be increased by 21% and the calculation time can be reduced by 74% under the same loop detection accuracy. Compared with RGB-D SLAM algorithm, the error of this method can be reduced by 29%.

Comparison of AOA Localization in Ultrashort Wave under Various Azimuth Calculation Methods

MA Fangli, XU Yang, XU Peng

2021, 56(4): 713-719. doi: 10.3969/j.issn.0258-2724.20200014

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Given that azimuth calculation is fundamental to angle-of-arrival (AOA) localization, the spherical approximation method and normal cylindrical projection-plane method for azimuth calculation on geodetic coordinates are proposed firstly. Furthermore, the AOA localization equations based on spherical accuracy calculation, spherical approximation calculation, and normal cylindrical projection-rectangle are established respectively. Finally, the unconstrained nonlinear programming method is used to establish the three optimization AOA localization models on geodetic coordinates, which correspond to the above equations respectively, and the models are verified by the point-by-point grid search method. The numerical results show without considering the direction-finding error, the spherical accuracy AOA localization model has the highest precision, which is independent of latitude, but its positioning operation time is the longest. As for the spherical approximation AOA localization model and the normal cylindrical projection-rectangle AOA localization model, both have a high precision, the positioning error of the latter is slightly higher than that of the former, and its positioning operation time is also longer than that of the former. The positioning accuracy of AOA localization network can be improved by increasing either the direction finding accuracy of each site or the number of direction finding sites. The appropriate AOA localization model is selected according to the overall positioning requirements of the timeliness and precision.

Method of Motor Starting Current Control Based on Hydraulic Pump/Motor Reverse Drive

LIU Huanlong, LI Shun, XIE Chixin

2021, 56(4): 720-729. doi: 10.3969/j.issn.0258-2724.20190727

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Aiming at the short cruising range of the battery rail engineering vehicles (BREVs) and the large starting current of the permanent magnet synchronous motor (PMSM), a new method of controlling the starting current of the PMSM driven by the hydraulic pump/motor was proposed based on the characteristics of the reverse transmission of the energy of the hydraulic pump/motor. By making the hydraulic pump/motor work in the motor mode, the PMSM was driven to a certain initial speed and then the power was turned on to realize the start of the PMSM with initial speed, which can suppress or weaken the starting current of PMSM. The PMSM was started at initial speed by adopting the positionless vector control method, combined with the short-circuit current vector method, the rotor speed and position at the starting time of the motor were calculated, and the joint simulation was carried out by AMESim and MATLAB/Simulink.The results show that the proposed new method of starting current control of PMSM can reduce the starting peak current of the PMSM by about 70%. The starting current is related to the initial speed when the PMSM is switched on and starting. The closer the initial speed of PMSM is to the required speed, the smaller the starting current is. After the speed of PMSM is stable, the current is only related to the PMSM load. The greater the working displacement of the hydraulic pump/motor or the charging pressure of the accumulator, the faster the speed response of motor during reverse drive.

Residual Life Prediction of Mechanical Equipment Based on Feature Learning in Big Data Background

GUO Liang, LI Changgen, GAO Hongli, DONG Xun, XIANG Shoubing

2021, 56(4): 730-735, 768. doi: 10.3969/j.issn.0258-2724.20190528

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For the traditional data-driven methods of remaining useful life prediction, health indicators are generally built with some hand-crafted feature extraction methods. However, in the big data era, hand-crafted feature extraction methods require specific expert knowledge and time-costing. In order to solve this problem, a feature learning based method (adaptive feature learning based remaining useful life prediction, AFLRULP) was proposed to predict remaining useful life of the mechanical equipment. Firstly, a window data matrix was constructed to solve the data fluctuation problem. Then, a one-dimensional convolutional neural network with multi-layers was built to map the data matrix to the health conditions of the mechanical equipment. Finally, the remaining useful life was predicted with a failure threshold. In order to verify the effectiveness of the proposed method, it is validated by a bearing life-cycle dataset. Additionally, the proposed method was compared with some manual feature extraction based methods. The results show that the proposed method (AFLRULP) does not need to manually extract features, it can map the original monitoring data to the performance status and remaining life of mechanical equipment. Additionally, compared with the existing life prediction methods based on manual feature extraction, the proposed method improves the cumulative relative accuracy of bearing life prediction by an average of 0.20.

Maintenance Scheduling Model for Road Networks Considering Payment Modes

MAO Xinhua, WANG Jianwei, YUAN Changwei

2021, 56(4): 736-743. doi: 10.3969/j.issn.0258-2724.20200192

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To ensure that the maintenance contractor obtains the maximum present value of revenue, the road network maintenance scheduling problem was explored under different payment modes of the client. First, three payment modes, i.e., time-based payment mode, progress-based payment mode and maintenance-cost-based payment mode were defined. Second, a mixed integer nonlinear programming model for maintenance scheduling was built with the goal of maximizing the present value of the contractor ’s revenue, and a tabu search algorithm was used to solve the model. Finally, the proposed model and algorithm were validated by a case study. Research results show that three different payment modes have large differences in terms of the road segments assigned to each maintenance crew and the maintenance sequence of each road segment. When the contractor’s advanced capital reaches a certain level, the continual rise of advance-fund capability may not be able to result in a better maintenance scheduling solution and cannot produce more present value of revenue. The relationship between the client’s payment ratio and the present value of revenue is close to monotonically increasingwhereas there is a negative exponential relationship between the discount rate and the present value of revenue. Increasing the number of maintenance crews can have more present value of revenue, but its marginal benefits are gradually reduced. Only when the contractor’s advance-fund capability and the number of maintenance crews increase synchronously, can more present value of revenue be obtained.

Collaborative Optimization for Overnight Train Operation and Maintenance Window Setting of High-Speed Railways

XU Chang’an, LI Shengdong, LI Sihan, NI Shaoquan

2021, 56(4): 744-751. doi: 10.3969/j.issn.0258-2724.20191205

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There is a coupling relationship between overnight train operation and maintenance window setting of high-speed railways. Their collaborative optimization contributes to meeting passenger travel demands at night and improves the allocation of railway transportation resources. Taking the corridor-type high-speed railways as the object, the analysis of the dynamic relationship between overnight train operation and maintenance window setting is performed, with the goal of minimizing the total travel time of all overnight trains and the impact of overnight train operation on the existing train timetable. A nonlinear mixed integer programming model is established to realize the collaborative optimization of overnight train operation and maintenance window in the condition of the undetermined train operation mode. Given the complexity of the problem, dimension reduction strategies such as dual-objective transformation and constraint linearization are proposed; then a heuristic algorithm based on the adaptive large neighborhood search is designed to solve the problem. Finally, a case study of Beijing−Guangzhou railway corridors was conducted to verify the method. The results show that the algorithm can converge to the optimal solution after about 40 iterations at a cost of 784 s.

Deflection Calculation of New Type Composite Box Girder with Corrugated Steel Webs Based on Reddy Theory

WANG Li, LIU Shizhong, LU Wei, NIU Sisheng, MAO Yana

2021, 56(4): 752-759. doi: 10.3969/j.issn.0258-2724.20200377

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In order to accurately calculate the deflection of a new type of composite box girder with corrugated steel webs (CSWs), Reddy high-order theory is used to analyze the slip deformation of the steel-concrete interface and the high-order shear deformation effect of the whole section; the isoparametric finite element determinant of the new-pattern composite box girder with CSWs is derived by the principle of minimum potential energy, using the shape function as the interpolation function of height variation in the element. Taking an 8.0 m long new-pattern simply supported composite box girder with CSWs as an example, the corresponding calculation program is compiled by the proposed methodology and applied to calculate vertical deflections of the beam under concentrated and uniform load. Results of the finite element simulation are then compared with those of model tests to verify the reliability of the analytical calculation method. Finally, influences of the shear stiffness of shear key, type of corrugated web, height ratio of sub-beams, and height-span ratio on the deflection of the new type of composite box girder with CSWs are analyzed. The results show that after taking into consideration the full-section shear deformation effect of the new type of composite box girder with CSWs, its deflection is increased by about 10% compared with the theoretical value of the elementary beam, and increased by about 1.87% compared with Timoshenko ’s theoretical value. As the span-to-height ratio increases gradually, the contribution of the full-section shear deformation effect to the deflection gradually decreases. With a smaller span-to-height ratio, a smaller shear stiffness of shear key, or a larger height ratio of sub-beams, shear deformation displays more significant effect on the vertical deflection of the structure, while the CSW type has little effect on the box deflection.

Lateral Displacement Restrainer of Beam Based on Elastic Deviation Prevention and Plastic Unloading Mechanism

ZHAO Chenggong, ZHAO Renda, JIA Yi, WANG Yongbao, LI Fuhai

2021, 56(4): 760-768. doi: 10.3969/j.issn.0258-2724.20190741

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In order to alleviate the lateral deflection or overturning of the beam under various factors, and improve the rigid blocking defect of the existing anti-offset equipment, a lateral-movement limiting device of beam body based on the elastic anti-deflection and plastic unloading concept is designed by referring to the mechanical shock absorption and isolation device. In this device, spring parameters (for elastic deviation prevention under normal conditions) are selected according to the reduced data of bending strength of the pier bottom and the maximum allowable transverse displacement of the beam, and the number of anchoring bolts in the weak layer (for unloading pier protection under large loads) is calculated using the reduced data of support reaction force. Taking a curved continuous girder bridge in Shaanxi Province as an example, the displacement and stress increments of the bridge with and without equipment of the device under static and dynamic actions are simulated using the finite element analysis software Midas Civil. Data comparison shows that the radial displacement restriction effect of the equipment under various static loads is remarkable (the average displacement limit rate is more than 70%, and the main displacement inducement limit rate is more than 80%); in most time-histories of the El Centro Site waves, the displacement and stress increments of the beam with equipment are smaller than those without equipment, and the peak displacement (the reduction rate is above 90%) and the peak stress (the average reduction rate is about 50%) are significantly reduced after installing the equipment. This shows that the equipment can effectively reduce the dynamic displacement increment of the beam without stress concentration and has good seismic deviation prevention effect.

Effect of Turbulence Integral Scale on Fluctuating Wind Pressure and Its Distribution Characteristics on Rectangular Upwind Surface

DU Shubi, LI Mingshui, YANG Xiongwei

2021, 56(4): 769-776. doi: 10.3969/j.issn.0258-2724.20190677

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In order to study the influence of turbulence integral scale on the fluctuating wind pressure and its distribution characteristics on the rectangular windward surface of a high-rise building, rectangular models with 2∶1 and 1∶2 width-depth ratios were put in a wind tunnel to obtain statistical features of wind pressure in turbulent flow fields with different integral scales for comparative analysis, including the mean wind pressure coefficient, root mean square coefficient, correlation coefficient and coherence function, and power spectrum of fluctuating wind pressure. Results are as follows: At the same height of the rectangular model in different turbulence flow fields, the wind pressure power spectrum is dominated by a quasi-steady effect in low-frequency regions, but it increases as the integral scale increases in high-frequency regions. The correlation and coherence of wind pressure increases with the integral scale increasing, and wind pressure is always more correlated than the turbulence flow. However, as the integral scale increases, the correlation width of wind pressure decreases, and the root mean square coefficient of fluctuating wind pressure increases. On the other hand, at different heights of the rectangular model in the same turbulence flow field, the farther away from the stagnation point, the smaller the wind pressure correlation function and coherence function, and the larger the root mean square coefficient of fluctuating wind pressure. In addition, the mean wind pressure coefficient is rarely affected by turbulence integral scale.

Spatial Distribution Characteristics of Dynamic Displacement of Heavy-Haul Railway Subgrade System under Launching Impact Load

YIN Zihong, ZHU Renzheng, QIU Hongtao, WANG Qingsong

2021, 56(4): 777-784. doi: 10.3969/j.issn.0258-2724.20191106

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To study the spatial distribution characteristics of dynamic response of military heavy-haul railway subgrade, using highly nonlinear analysis program ANSYS/LS-DYNA3D, a 3D explicit dynamic model of a track-subgrade-foundation system was established with the 3D consistent viscous-spring artificial boundary. The trapezoidal impulse load was used to simulate the launching impact load, and spatial distribution characteristics of the dynamic displacement of the subgrade system under loads of different amplitudes (150−600 kN) were discussed. The model reliability was then verified by Boussinesq elastic theory and Lin Xiuxian ’s multi-layer system equivalent theory. The results indicated that the vertical dynamic displacement of the subgrade system reaches the maximum value when the launching impact load on the track starts to unload. At the end of unloading, there is a certain amount of residual deformation in the top surface of the ballast bed, and the residual deformation increases linearly with an increase in load amplitude, and the growth rate is about 0.6 × 10⁻² mm/kN. Under different load amplitudes, the dynamic displacement of the subgrade system is distributed symmetrically both laterally and longitudinally along the line, it decays linearly along the vertical direction, and the decaying rate increases with the increase of the load amplitude. The larger the load amplitude is, the more significant the wheelset effect of dynamic displacement and the contribution of ballast bed and subgrade bed to rail dynamic force are; the peak dynamic displacement of subgrade system is approximately linear with the load amplitude. With the increase of the load amplitude, the peak dynamic displacement of the ballast bed surface grows at the fastest rate of about 1.27 × 10⁻² mm/kN, followed by the peak value of the subgrade bed surface and the subgrade bed bottom at growth rates of about 1.23 × 10⁻² and 1.20 × 10⁻² mm/kN, respectively, and the peak value of the subgrade body grow at the slowest rate of about 1.10 × 10⁻² mm/kN.

Extension Evaluation on Excavation Safety of Deep Foundation Pit in Sandy Cobble Stratum Based on Entropy Method

WANG Wei, LIU Danna, PENG Di

2021, 56(4): 785-791, 838. doi: 10.3969/j.issn.0258-2724.20200333

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In order to objectively evaluate the safety and stability of deep foundation pit excavation in watery sandy pebble stratum, eight evaluation indexes, such as ground settlement, building settlement and groundwater level, are selected to evaluate the excavation safety according to the structural deformation, stress, groundwater and surrounding environment. A deep foundation pit project of a metro station in Chengdu is used as an example, and according to the measured data within the four months of foundation pit excavation, the entropy method is employed to assign the selected evaluation indexes. Based on the correlation function between the matterelement theory and extension set, the extension evaluation model of excavation safety for the deep foundation pitis established. Comparing the evaluation results with those of fuzzy comprehensive evaluation, it is concludedthat the axial force of concrete support, pile top settlement and the horizontal displacement of support structure are the most important three indexes in the entropy weight calculation of this case, which have the greatest impact on the safety evaluation. For the safety evaluation of ground settlement and pipeline settlement, the extension evaluation result is one grade higher than the fuzzy comprehensive evaluation result, which is consistent with actual monitoring data and is conducive to the prevention and control of potential risks in the construction process. The extension evaluation model based on entropy weight can accurately improve the safety of the foundation pit excavation through single factor analysis and comprehensive analysis, and the extension evaluation model can be applied in the safety evaluation of foundation pits in watery sandy cobble strata in Chengdu.

Rock Burst Intensity Classification of Lhasa−Linzhi Railway Based on Stress Criterion

WU Fangyin, HE Chuan, WANG Bo, ZHANG Junbo, MENG Wei, LIU Jinsong

2021, 56(4): 792-800. doi: 10.3969/j.issn.0258-2724.20191167

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The rockburst prediction results of a tunnel in the Lhasa−Linzhi railway cannot meet the actual situation on site by applying the existing criteria directly. In order to formulate the rockburst intensity classification scheme and stress criterion for the whole line of the Lhasa−Linzhi railway, the measurement of the wall stress after tunnel excavation, point load test on rock samples and the excavation simulation based two-stage back analysis of initial geostress field were carried out based on the in-situ rockburst development characteristics and rules, rockburst failure trace in Sangzhuling tunnel of the Lhasa−Linzhi railway and kNN (k-nearest neighbor classification) algorithm, and then the rockburst intensity classification scheme and stress criterion for the Lhasa−Linzhi railway were proposed. After the verification of the prediction accuracy of rockburst in the Sangzhuling tunnel, the criterion was applied to the rockburst prediction of typical rock burst tunnels (the Zhulagang tunnel, the Dagala tunnel and the Gangmula tunnel) of the Lhasa−Linzhi railway, and the results are compared with the existing ones. The results show that for the Lhasa−Linzhi railway, the Russenes rockburst criterion will underestimate the occurrence of slight rockburst, but it is better to judge moderate rockburst. The rock burst grade judged by the Wang Lansheng criterion mainly focuses on slight rockburst, and the actual moderate and strong rockburst grades are not correctly judged, which indicates that it is easy to underestimate the actual rockburst grade. The rockburst grade judged by the Guanbaoshu criterion mainly focuses on strong rockburst, and it is easy to overestimate the actual rockburst grade because it basically does not correctly judge the actual slight and moderate rockburst grade. The rockburst criterion of the Lhasa−Linzhi railway is equal to the Lu Sen criterion in judging moderate rock burst grade, and its accuracy rate of rockburst prediction results is higher than other criteria, which is more in line with the actual situation of the Lhasa−Linzhi railway.

Random Search Method of Fracture Surface for Seismic Stability of Reinforced Retaining Wall

LI Qian, LING Tianqing, HAN Linfeng, ZHANG Ruigang

2021, 56(4): 801-808. doi: 10.3969/j.issn.0258-2724.20200320

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In order to determine the fracture surface location of the reinforced retaining wall, a polyline fracture surfaceform was proposed based on the horizontal slice method. The fracture surface of the reinforced retaining wall is viewed to be composed of several line segments, one connected with another in a plane at different lengths and angles. According to the mechanical equilibrium of horizontal soil strip under seismic action, the calculation formula of reinforcement forces related to fracture surface parameters is derived. The total force of the reinforcement is taken as the objective function, and the calculation is run in a way of a two-layer cycle. The outer layer is a cycle of the fracture point position of the horizontal filling behind the wall, and the inner layer is a random angular cycle. By comparing the total forces of reinforcement calculated in each outer cycle, the fracture surface corresponding to the maximum value is the critical fracture surface of the reinforced retaining wall. A calculation example is used to verify the calculation method of the polyline fracture surface, and the influential factors on the stability of the reinforced retaining wall are analyzed. The results show that the calculation method in which the polyline fracture surface is generated by the random angular method can obtain reasonable results without mathematical optimization, and the fracture surface location of the reinforced retaining wall is closer to the free face than the logarithmic spiral fracture surface. The increase in the internal friction angle of the fill reduces the total tensile force and the length of the reinforcement, which can enhance the internal stability of the reinforced retaining wall.

Shear Properties of Paleosol Containing Calcareous ConcretionsBased on Ring Shear Tests

JIANG Chengcheng, FAN Wen, YUAN Weina

2021, 56(4): 809-817. doi: 10.3969/j.issn.0258-2724.20190951

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Paleosol containing calcareous concretion is widely distributed in the shear zone of loess landslides and affects the shear failure characteristics of landslides. Based on ring shear tests, the shear characteristics of paleosol with different contents of calcareous concretions under different normal stresses were discussed, and the test results were analyzed from macro-and micro-aspects. The results indicate that under low axial (normal) stress, the stress-displacement curves are of softening type and have obvious residual strength characteristics. With the increase of calcium nodule content, the strain softening characteristics become weak. Under high axial (normal) stress, the stress-displacement curves show strain hardening. Calcareous nodule particles can increase the shear strength and peak friction angle of soil and reduce the cohesion. The thickness of shear band is positively correlated with the content of calcareous concretions and negatively correlated with D50. Particle crushing occurred under the larger deformation. According to the particle size distribution analysis before and after shearing, the breakage of calcareous concretions mainly occurred to particles in the size range of 3−5 mm, with a breakage percentage of 19.5%−55.5%, and the paleosol was broken from 0.01−0.05 mm into smaller particles of 0.002−0.010 mm. Based on macroscopic observation and mechanical analysis of shear failure surfaces, all samples can be divided into two groups with “—” and “U” failure surface patterns, respectively, and three failure modes, including sliding shear mode, turbulent and transitional shear mode.

Spatial Development Characteristics of Post-Fire Debris Flow in Bajiaolou Town

YANG Ying, HU Xiewen, WANG Yan, JIN Tao, CAO Xichao, HAN Mei

2021, 56(4): 818-827. doi: 10.3969/j.issn.0258-2724.20200015

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As a special type of debris flows closely relevant to forest fire, the generation of post-fire debris flow often shows a spatial variation. It is of great significance to analyze the spatial development characteristics and its influencing factors for hazard mitigation and reduction. By means of field investigation, in-situ and laboratory tests, and remote sensing interpretation, multi-factor analysis was conducted on the 15 channels in the burned area in Bajiaolou town of Yajiang county in terms of their spatial development characteristics, topography, forest fire, vegetation and rainfall conditions. The results show that the higher the fire intensity, the stronger the soil water repellency and the lower the permeability; moreover, the physical and mechanical properties of soil deteriorate more seriously, which contribute to the generation of post-fire debris flow. The occurrence frequency of post-fire debris flow rises when the burned area become larger and the vegetation cover coefficient lower. In contrast to the large basins, the smaller basins show more vulnerability to post-fire debris flow for their short channel lengths and high longitudinal slopes. Besides, the recurrence time of the triggering rainfall intensity that corresponds to four of five debris-flow events in the study areas is less than 5 years, and the triggering rainfall intensity also increases with time.

State of the Art in Connection of Vertically Distributed Reinforcements for Precast Shear Wall

ZHANG Shiqian, CHEN Yueshi, LIU Yanan, MA Xinxu, LIAO Xiandong, XIAO Xuwen

2021, 56(4): 828-838. doi: 10.3969/j.issn.0258-2724.20191064

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Precast concrete shear wall structure is one of the most common structures for China ’s high-rise residential buildings. Reliable vertical connection is critical for the structure to ensure safety. According to the number of vertically distribution reinforcement connections or lap joints (connection degree) on the floor, the vertical connection for precast shear wall can be divided into three forms: full connection, partial connection and no connection. Based on relevant research, for three kinds of connection degrees of precast shear wall, the connection form of vertically distributed reinforcements, structural characteristics and mechanical properties are systematically summarized. Then the influence of the vertically distributed reinforcement connection on the seismic performance of the shear wall and the deficiencies of the current research are analyzed. Further, based on the principle of equivalent bending and shear resistance, a new shear wall structure with non-connected vertical distribution reinforcement is proposed, and its design calculation method is presented. Finally, the new connection technology and nondestructive testing technology for precast shear wall are predicted, and it is pointed out that the precast shear wall structure with non-connected vertically distributed reinforcements is more promising in the future.

Moisture Susceptibility of SBS and Coarse Crumb Rubber Composite Modified Asphalt Permeable Mixture

XIAO Feipeng, ZONG Qidi, WANG Jingang, CHEN Jun, LIU Ji

2021, 56(4): 839-846. doi: 10.3969/j.issn.0258-2724.20191116

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Permeable asphalt concrete (PAC) possesses good capacity of drainage and noise reduction due to its large porosity. Nevertheless, it is prone to suffer water damage. Coarse crumb rubber (CCR) and styrene-butadiene-styrene block copolymer (SBS) were used to prepare composite modified asphalt. Freeze-thaw splitting tensile strength ratio (TSR) was employed to evaluate the moisture susceptibility of PAC. The influences of the contents of SBS, coarse crumb rubber, asphalt binder, and hydrated lime as well as the nominal maximum particle size (NMPS) and passing percentage of key sieve sizes on the moisture susceptibility of PAC were explored to reveal the moisture damage resistance mechanism of SBS and CCR composite modified asphalt (SBS/CRMA) mixture. The results indicate that the increases in SBS content, the NMPS of aggregates, and the addition of slaked lime can effectively increase the TSR value. To optimize moisture susceptibility and cost efficiency, it is recommended that the favorable contents of SBS and CCR are 6% and 10%, respectively. Moreover, through grey relational analysis, the key sieve sizes that affect the moisture susceptibility of permeable asphalt mixtures with various NMPS were presented as well.

Strain Rate Sensitivity of Porous Cotton-Phenolic Bearing Retainer

ZHANG Yafeng, ZHANG Shaohua, ZHOU Gang, ZHANG Jiyang, QING Tao, ZHOU Ningning

2021, 56(4): 847-852, 863. doi: 10.3969/j.issn.0258-2724.20190457

[Abstract](474)

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Abstract:
In order to study the strain rate sensitivity of porous cotton cloth-phenolic bearing retainer, the hardness and elastic modulus of the porous cotton cloth-phenolic bearing retainer were measured by nanoindenter when the strain rate ranged from 0.01 s⁻¹ to 0.05 s⁻¹. And then the viscoelastic properties of the materials were analyzed by Kelvin-Voigt model. The strain hardening effect and strain local softening effect of the material under different strain rates were studied. The results show that with the increase of strain rate, the hardness and elastic modulus of porous cotton cloth-phenolic material first increase and then decrease. When the strain rate increases from 0.01 s⁻¹ to 0.05 s⁻¹, the increase of hardness and elastic modulus of porous cotton cloth-phenolic material is related to the strain hardening phenomenon of the material. When the strain rate increases from 0.05 s⁻¹ to 0.30 s⁻¹, the creep displacement increases significantly, the contact stiffness decreases rapidly, the deformation is consumed in the contact interface between the indenter and the material in the form of heat, the material in the contact area of the indenter changes from viscoelasticity to viscosity, the local material viscosity decreases, and the hardness and elastic modulus decrease rapidly. The change of hardness and elastic modulus of porous cotton cloth-phenolic aldehyde with strain rate is the result of the competition between strain hardening effect and strain local softening effect.

Experimental Study on Deformation Behavior of Polypropylene Fiber Reinforced Concrete Beams

LI Fuhai, HE Xiaoyunfeng, WU Haonan, JIANG Yilin, WANG Yibin, HU Dinghan

2021, 56(4): 853-863. doi: 10.3969/j.issn.0258-2724.20190959

[Abstract](534)

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Abstract:
In order to explore the difference in deformation behaviors of polypropylene engineered cementitious composite (PP-ECC) beam and reinforced concrete (RC) beam, bending resistance tests were performed on four PP-ECC beams and four RC beams using two loading systems, i.e., step loading and cyclic loading. Meanwhile, based on the effective moment of inertia method, the maximum deformation calculation formula applicable to the PP-ECC beams under short-term loads was derived. The results show that the PP-ECC beam undergoes a more obvious plastic deformation stage under successive loading. Compared with the RC beam, the deformation curve of the PP-ECC beam after 5 cycles of cyclic loading fits better with the original curve. During cyclic loading, the growth rates of the loading and unloading deformation of PP-ECC beams under the reference load are both lower than those of RC beams with the same reinforcement ratio, showing better damage resistance and deformation recovery ability. In general, the calculated results of deformation correction model based on the effective moment of inertia method fit well with the test results, and the proposed method can be applied to the calculation of maximum deformation of PP-ECC beams under short-term load in practical engineering.

Simulation of Ⅰ - Ⅱ Mixed Mode Cracking Behavior of Ultra-Dense Asphalt Concrete

DU Jianhuan, REN Dongya, HUANG Yangquan, AI Changfa, QIU Yanjun

2021, 56(4): 864-871. doi: 10.3969/j.issn.0258-2724.20190988

[Abstract](513)

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Abstract:
This work aims to study the propagation behavior of Ⅰ - Ⅱ mixed mode micro-cracks in the ultra-dense asphalt concrete in cold regions. Based on the Eshelby equivalent inclusion theory and the maximum circumferential stress fracture criterion, the relationship between the declination angle β and the stress field is established for the composite cracks propagating in unstable mode, and whereby the crack propagation direction is determined. Then, a two-dimensional mesoscopic discrete element model of asphalt concrete is built; taking the viscoelasticity of asphalt concrete into consideration, the model is used to simulate the mixed mode micromechanical fracture behavior of the ultra-dense asphalt concrete. The influence of declination angle β on the unstable crack growth is analyzed. Results are obtained as follows: For the two-dimensional plane problems, the change of declination angle β mainly causes the change of crack distribution in asphalt concrete, greatly reducing the effective modulus and shear modulus of asphalt concrete in the time domain. Under the action of constant load, the increase of declination angle β shortens the process of crack initiation and propagation in the ultra-dense asphalt concrete, causing the fracture mode gradually transformed from type Ⅰ cracking into type Ⅱ cracking. Meanwhile, the increase of declination angle β not only causes a certain deflection of the stress field near the crack tip, but also leads to a decrease of the stress field and failure zone in the crack tip region.

Influence of Wheelset Installation Deflection Angle on Dynamic Characteristics of High-Speed Vehicles Crossing Switch

CHEN Rong, WANG Xuetong, CHEN Jiayin, DING Ye, XU Jingmang

2021, 56(4): 872-882. doi: 10.3969/j.issn.0258-2724.20190535

[Abstract](497)

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Abstract:
The initial deflection angle of high-speed trains caused by inaccurate positioning sharply can aggravate wheel-rail contact relationships and affect traffic safety, especially when passing through weak areas such as turnouts. In order to study the dynamic performance of vehicles passing through high-speed turnouts at initial installation deflection angle, a vehicle-turnout coupling dynamic model with initial deflection angle was established with No.18 turnouts as the research object. Four working conditions, namely front wheel pair deflection, rear wheel pair deflection, front and rear wheel pair deflection in the same direction and front and rear wheel pair deflection in the opposite direction, were simulated. The effects of different deflection angles on the vehicle's fork entry posture and straight and reverse crossing performance were analyzed by combining theoretical derivation and numerical simulation. The results indicate that the initial deflection angle deflecting to switch rail will cause the advance of wheel-rail transition position, and even the rim contact will be caused. The influence of initial installation deflection angle on wheel-rail vertical force is mainly related to deflection form and deflection angle. When the deflection angle exceeds a certain limit, the inherent irregularity in turnout area further aggravates vertical wheel-rail impact. The wheel-rail transverse force is mainly controlled by the superposition of the main contact point direction and the transverse impact direction of the turnout area. When the front and rear wheelsets deflect reversely, the wheel-rail contact relationship deteriorates. When the deflection angle is from −2.0 to −3.0 mrad, the derailment coefficient exceeds the limit, which affects the driving safety.

Calculation Method of Hertz Normal Contact Stiffness

GUAN Qinghua, ZHAO Xin, WEN Zefeng, JIN Xuesong

2021, 56(4): 883-888. doi: 10.3969/j.issn.0258-2724.20210015

[Abstract](824)

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Abstract:
Elastic contact deformation between the wheel and rail is pivotal in the computation of the wheel-rail contact force in the vehicle-track coupled dynamics. Based on the Hertz contact theory, the nonlinear contact stiffness is used to depict the relation of the wheel-rail normal contact force and their relative compression. The current empirical formulas of the Hertz contact stiffness for the wheel-rail contact are based on the work of British Railway in 1970 s, and are classified into two categories, i.e., coned profile and worn profile. However, they are restricted to specific wheel radii and rail profiles. In this work, based on Hertz contact theory, the general formulas of the elastic normal contact stiffness are deduced, which can satisfy the Hertz contact conditions. According to the characteristics of the wheel-rail geometry, the dimension of wheel-rail contact spots and contact stiffness parameters are tabulated and determined. Finally, an example of LM wheel profile and CN60 rail profile is used to compare the results of the empirical formulas and those of the proposed formulas. The results show that the Hertz contact parameter table formed by the proposed contact formula makes up the absence of the contact stiffness in the current ones, and can be used directly in elastic contact calculation. When the circle around the nominal center of the wheel profile and the central circle of the rail head are in contact, the results calculated by empirical formulas have less error in the contact stiffness deviation of the worn tread, which varies in 0.40% − 0.44%. Otherwise, there is a significant difference between the results of empirical formulas and those of the proposed formulas, the range of which is −25.97% −131.42%.

Mechanical Properties of Tension-Torsion Coupling in Aluminum Conductor Steel Reinforced

ZHANG Long, HUANG Jue, ZHONG Yongli, YAN Zhitao

2021, 56(4): 889-896, 904. doi: 10.3969/j.issn.0258-2724.20200076

[Abstract](536)

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Abstract:
The torsion parameter of the conductor is one of its basic mechanical properties. Moreover, the tension-torsioncoupling effect of iced transmission lines will greatly affect the accuracy of galloping analysis. To analyze this effect, the torsional test was carried out for the typical 7-strand aluminum conductor steel reinforced (ACSR) LGJ/JL/G1A-70/10, and the modeling and numerical analysis of the corresponding components are carried out by using the finite element simulation software ANSYS, the results ofwhich is compared with those calculated by the 4 theories based on the tension-torsioncoupling theory of wire rope. The results of numerical analysis are in good agreement with those of the torsion test. Thetwist factor values fluctuate greatly, which will lead to significant errors. Under the normal stress state, the conductor tension will produce a large torsion effect, and the section torsion of the conductor will also lead to a slight tension change. The tension-torsion coupling coefficient is not equal to the torsion-tension one. The theories based on steel wire rope do not consider the slip deformation and coordinate update of sub strand conductors, which overestimates the axial stiffness and the coupling effect of tension and torsion to a certain extent.

Evaluation of Train Passenger Interface Design Based on Analytic Hierarchy Process with Independent Weight Method

HE Sijun, ZHI Jinyi

2021, 56(4): 897-904. doi: 10.3969/j.issn.0258-2724.20190586

[Abstract](465)

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Abstract:
In order to overcome the limitations of the existing evaluation model of high-speed train passenger interface, such as single index, subjective randomness of weighting method and lack of quantitative analysis. Firstly, a satisfaction survey was conducted on the new type double deck high-speed test sample train. On this basis, starting from the comprehensiveness, systematicness and hierarchy of the evaluation indicators, a hierarchical index system is constructed, which consists of five evaluation criteria and 36 specific indexes, including facility scale, safety design, function use, space environment, and aesthetic design. Secondly, a fuzzy comprehensive evaluation model is proposed, which combines the analytic hierarchy process (AHP) method with independent weight method, it retains the subjective opinions of experts and objective information in the passenger experience survey data. Finally, the weights of each level of the passenger interface evaluation index system are solved based on expert judgment data and survey score data, and the evaluation grades of the new prototype and the existing train are calculated. The results show that the comment grade of the new prototype is satisfactory with the membership degree of 0.3977, and the comment grade of the existing train is very satisfactory with the membership degree of 0.4422. According to the weight calculation, the design improvement sequence of passenger interface should be facility scale, functional operation, space environment, safety design, and aesthetic design. In the evaluation criteria, the man-machine surface of the seat, the rounded corners of the facility, the adjustability of the seat, the air quality and the color coordination are the factors that have the greatest impact on passenger satisfaction.

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2021 Vol. 56, No. 4