西南交通大学学报

Lightweight Web Visualization of Massive Road Traffic Data

ZHU Jun, WU Sihao, ZHANG Yunhao, HUANG Huaping, GUO Yukun, CHEN Yidong, LI Weilian

2021, 56(5): 905-912. doi: 10.3969/j.issn.0258-2724.20200107

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In order to further improve the dynamic visualization efficiency of large-scale road traffic data under the network environment, a lightweight visualization method using streaminglight is proposed to express traffic situation under the network environment. The hierarchical organization method of road network that allows road attributes is proposed, and the roads are drawnunder different view heights. The multi-road merging method based on the characteristics of line segment index in WebGL (Web graghics library) technology is presented, and the scene is optimized by combining the visual field elimination and multithreading technology. The animation effects such as gradual change and dynamic streaming light that support the real-time transformation of road congestion state are designed and realized. Finally, the prototype system is developed, and the case experiment and analysis are carried out with the national road network data. Experimental results show that this method can dynamically visualize large-scale road traffic data under the network environment, and its visualization frame rate is stable above 40 frames/s, which is 20−30 frames/s higher than that of the Baidu ECharts GL visualization method.

Influence Mechanism of Bridge Sign Complexity on Cognitive Characteristics of Drivers’ Electroencephalogram

LI Xuewei, ZHAO Xiaohua, HUANG Lihua, RONG Jian

2021, 56(5): 913-920. doi: 10.3969/j.issn.0258-2724.20200109

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Normative documents about design and application of bridge signs are unavailable, while the complex bridge signs affect drivers’ recognition, which further impairs traffic efficiency and traffic safety. In order to clarify the influence of bridge sign complexity on the cognitive processing of drivers, Oddball paradigm is adopted in cognitive electroencephalogram experiments for bridge signs with different complexities. Taking into account the reading behavior and electroencephalogram characteristics of drivers, four main analysis indexes are extracted: the reading time, proportion of seeking correct destination, early attention potential N100 and cognitive potential P300 in event-related potential (ERP). Analysis of variance with repeated measurements is used to quantify the effect of bridge signs complexity on cognitive process and electroencephalogram characteristics of drivers. The results show that with an increase in bridge sign complexity, the drivers’ reading time increases, and the proportion of seeking correct destination decreases. Meanwhile, the migration of N100 average amplitude and peak value shows more negative shift, while the average amplitude of P300 increases positively; that is, to drivers, the early attention distribution increases, the early attention time lags behind, and the cognitive difficulty increases. In addition, the greater the relative difference between the target stimulus and standard stimulus, the shorter the latency of P300, and the easier to distinguish it from the standard stimulus with a low complexity.

Calculation and Evaluation Method of Passenger Flow Distribution under Urban Rail Transit Failure

LIU Fengbo, ZHOU Tingliang, WANG Xiaomin

2021, 56(5): 921-927, 966. doi: 10.3969/j.issn.0258-2724.20200602

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In order to accurately obtain the impact of urban rail transit failures on passenger travel, the interaction states between passenger flow and train are modeled for passengers’ waiting, boarding and alighting processes. A calculation method is established for passenger flow distribution such as waiting passengers on platforms and passengers in carriages. The dynamic passenger flow simulation algorithm and evaluation indexes of passenger service level are designed. Taking an actual rail line under normal operation scenario as the reference, the space-time distribution of passenger flow under urban rail transit failure is computed and evaluated. The effect of waiting time on passenger flow distribution on platforms and in carriages and the effect of waiting time on passenger travel time are analyzed. The case study shows that, passengers wait a little longer on the platform instead of leaving, which will reduce part of travel time under the specific failure. However, the situations of high load rate in carriage and large passenger volume on platform increases, compared with the normal scenario. With the maximum waiting time increasing from 9 min to 15 min, the number of departing passengers decreases by 77.0%, the total travel time with penalty decreases by more than 10.0%, and the passenger retention rate is the same, but the maximum numbers of stranded passengers and waiting passengers increase by 94.1% and 29.6%, respectively.

Evaluation of Activity Location Recognition Using Cellular Signaling Data

YANG Fei, JIANG Haihang, YAO Zhenxing, LIU Haode

2021, 56(5): 928-936. doi: 10.3969/j.issn.0258-2724.20200086

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In order to investigate the recognition results of individuals’ activity locations using cellular signaling data, the field experiment for collecting cellular signaling data was carried out. The GPS trajectory data and the travel logs were collected synchronously as the real data for reference. A three-step method for recognizing activity locations is proposed. Firstly, an equal time interval interpolation method is used to balance the time weight of each trace. Secondly, an agglomerative hierarchical clustering algorithm is applied to merge the traces into different clusters. Finally, a new method of correcting location oscillation is proposed, to solve the problem that clusters in the same activity location oscillate. Results show that the proposed method performs well in term of the accuracy of identifying activity locations, distance error and time error. The average recognition accuracy and distance error is over 84% and within 220 m, respectively. The average errors of departure and arrival time are 7.7 min and 5.3 min, respectively. In the comparison of different travel purposes, the activity locations for work receive the best recognition results, and the results of the locations for shopping is relatively inferior.

Influence of 40.0‰ Maximum Gradient of Metro Main Line on Running Characteristics of Trains

WANG Zhonglin, ZENG Yong, YI Sirong

2021, 56(5): 937-944. doi: 10.3969/j.issn.0258-2724.20200025

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When metro lines cross mountains or rivers, properly increasing the maximum slope standard of the metro main lines will help reduce costs and difficulties of design and construction. In order to study the feasibility of applying the maximum gradient value of 40.0‰ on the metro main line, combined with the vehicle-track system properties of Suzhou Rail Transit Line 8, the influence of the 40.0‰ maximum gradient value on the running characteristics of trains was analyzed from the power of motor car, starting and braking capacity of trains, rescue of failed trains, train running status and dynamic characteristics, and track mechanical characteristics, by using theoretical analysis, train longitudinal dynamics, vehicle-track system dynamics, and finite element method. Results show that the maximum gradient of a metro main line can be 40.0‰ when the B2 type vehicle with 4 motors and 2 trailers is used; when the train passes through the 40.0‰ ramp section, the running safety, stability, starting-braking and fault rescue ability of the train meet the requirements; the maximum stress of the rail is only 37% of the allowable stress, and the maximum longitudinal displacement is only 0.443 mm.

Mechanical Properties of CRTS Ⅱ Slab Ballastless Track on Bridge under Temperature Gradient Loads

ZHANG Pengfei, TU Jian, GUI Hao, LEI Xiaoyan, LIU Linya

2021, 56(5): 945-952. doi: 10.3969/j.issn.0258-2724.20200244

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In order to study the influence of transverse and vertical temperature gradients on the longitudinal mechanical performance of CRTSⅡ slab ballastless track on the bridge, on the basis of the beam-slab-rail interaction principle, a refined spatial finite element model is established for the continuous welded rails (CWRs) of CRTSⅡ slab ballastless track on the long-span bridge. The longitudinal force and displacement of rails and bridge structure on southern and northern surfaces are calculated under the transverse and vertical temperature gradient loads. Analysis results indicate that the vertical temperature gradient of the track slab has little effect on the longitudinal force and displacement of the rail under the same temperature load. When the transverse temperature difference between the southern and northern surface is 10 ℃, the maximum longitudinal force of the rail at the northern side of the continuous beam is 1.4 times that at the southern side, and the maximum longitudinal force of the pier at the northern side of the continuous beam is 3.5 times that at the southern side. Under the action of the transverse temperature gradient, the longitudinal force of the rail is generated by the combined effect of beam dilation and torsion d eformations. The greater transverse temperature gradient leads to the greater maximum longitudinal force and displacement of the rail at the northern side, and the smaller maximum longitudinal force and displacement of the rail at the southern side. The transverse and vertical temperature gradient do no contribute to the safe use of the track and bridge structure. Therefore, in the area of high temperature difference, it is necessary to focus on the stress of the rail, track slab and bridge pier top when designing the east-west of CWRs on long-span bridge, and ensure the transverse stability of the CWR on the bridge.

Representation and Estimation Method for Technical Station Capacity Based on Three-Parameter Interval Gray Numbers

XUE Feng, YUAN Ye, HU Zuoan, BHARAT Pathak

2021, 56(5): 953-959. doi: 10.3969/j.issn.0258-2724.20190982

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Capacity is an important index to measure the production efficiency of railway technical station, in order to reflect capacity scalability and improve measurement accuracy, the applicability of three parameter interval and universal grey number for capacity representation was analyzed. The three parameter interval was used to guarantee the capacity value range of upper and lower bounds, the universal grey number was introduced to reduce the possible interval expansion caused by capacity calculation, and then the concepts of contraction capacity, balance capacity and relaxation capacity were proposed based on the operation state. After comparing various interval estimation methods, Jackknife-after-Bootstrap (JAB) interval estimation method was used to determine the lower and upper limit on capacity. A case of Zhengzhoubei Marshalling Station shows that the interval width determined by the capacity representation and estimation method based on three-parameter interval gray number is smaller, and the interval position is more accurate compared with the original fixed value representation on capacity. The calculated confidence interval is [9.6933, 10.2043], the interval width is 0.511 when the confidence level is 95%; Similarly, when it is 90%, the calculated confidence interval is [9.7358, 10.1653], and the interval width is 0.429. The contraction of carrying capacity in Zhengzhoubei railway station is 0.99, the relaxation is 1.01, and the contraction of resorting capacity is 0.94, the relaxation is 1.07, which indicates that the capacity measurement results show certain relaxation and contraction phenomenon.

Effect of Reflective Thermal Insulation Coatings on Temperature and Stress of Track Slab

JI Lei, WANG Xin, ZHOU Yihang, ZHOU Gan, ZHAO Jincun, CHENG Yonghong, SUN Zhiyuan

2021, 56(5): 960-966. doi: 10.3969/j.issn.0258-2724.20200006

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To reduce the slab temperature and internal stress of ballastless track and alleviate damage caused by ballastless track expansion during high temperature period in summer, a reflective thermal insulation coating for ballastless track was explored with titanium dioxide, glass beads, and other components. The rationality of the dosage of each component was explored, and its cooling performance was tested under infrared light and natural light. The influence of the temperature difference between the surface and the interior of track slab on the internal stress of track slab was analyzed. The results show that the coating can decrease the surface temperature of track slab by up to 16 ℃ during the high temperature period in summer, it can also decrease the temperature difference between the surface and the depth of 180 mm of track slab from 24 ℃ to 12 ℃, with a decrease of about 50%, and effectively decrease the stress of track slab by 0.4 MPa. The coating can effectively reduce the risk of various track diseases caused by temperature stress.

Master-Slave Interpolation Modeling of Compressor Healthy Parameters Based on Kriging Algorithm

ZENG Li, CHEN Renxiang, DONG Shaojiang

2021, 56(5): 967-972. doi: 10.3969/j.issn.0258-2724.20191118

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In order to solve the problem that the accuracy of the model is low due to the lack of compressor flow coefficient in the process of digital modeling of gas turbine compressor, a master-slave interpolation model for flow coefficient is constructed based on the Kriging interpolation algorithm. The distribution characteristics of flow coefficient in high-dimensional space are studied. The mapping relationship among flow coefficient, conversion speed and pressure ratio are explored, and a high-dimensional sample construction method for these three parameters is proposed. A high-precision flow coefficient master-slave interpolation model of gas turbine under transient conditions is established based on the Kriging algorithm. The results show that compared with the traditional Kriging interpolation method and the Newton interpolation method, the calculation result of flow coefficient based on master-slave model is closer to the actual value, and the calculation accuracy is improved by nearly 10%. In addition, the master model can output the estimated vector. Compared with the traditional Kriging model, the interpolation efficiency is improved by nearly 15%.

Fault Detection of Axle Box Bearing Based on Matter-Element and Negative Selection Algorithm

ZHAO Congcong, LIU Yumei, ZHAO Yinghui, BAI Yang

2021, 56(5): 973-980. doi: 10.3969/j.issn.0258-2724.20191103

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In view of the difficulty in obtaining the fault data of high-speed train axle box bearings, a fault detection method combined matter-element model and negative selection algorithm (NSA) was proposed, which did not need prior knowledge. Firstly, detectors of NSA were constructed by means of multi-dimensional matter-element model, and the comprehensive correlation degree (CCD) between detectors and training samples was used as the matching rule. In order to achieve greater coverage of the non-self space by the detector, a control parameter was introduced within the constraint range of CCD. Then, the fitness function was constructed according to the matching rule and the control parameter, and the particle swarm optimization (PSO) algorithm was utilized to generate candidate detectors. The influence of control parameter on detector generation and convergence speed of particle swarm optimization algorithm was analyzed. In order to reduce the redundancy of the candidate detector set, the merging rules of characteristic parameters intervals of candidate detectors were proposed based on the correlation function, and the number of mature detectors was reduced to 18. Various fault signals of axle box bearings were generated by signal simulation method, 100 sets of test samples were established, and 18 mature detectors were used for fault detection. The results show that the mature detectors have good detection performance for different types of bearing fault, and the detector activation rate of normal sample is 1.11%, while its minimum value of fault samples is 96.67%.

Optimization Research on Mixed-Model Multi-manned Assembly Line Balancing Problem of Type I

YANG Wucheng, CHENG Wenming

2021, 56(5): 981-988. doi: 10.3969/j.issn.0258-2724.20191135

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Owing to the incapability of the traditional approaches in solving the mixed-model multi-manned assembly line balancing problem of type I (MMALBP-I), a new mixed integer mathematical model is built to minimize the number of stations/workers and to balance the load between stations by introduce new variants and unequal constraints. What’s more, a modified chicken swarm optimization is also proposed. The algorithm adopts a priority-based coding and in decoding procedure, a worker which the assigned task can start earlier is being selected to reduce the sequence-dependent idle time, and the number of workers is decided by the designed station assignment rules to rude the mean station idle time. Moreover, in order to achieve more systematic and efficient search, the chicken swarm is divided into three groups according to the fitness values of the chickens themselves. The roosters generate new solution by a local search in different range of places based on the fitness value, the hens follow their group-mate roosters or other chickens to search a new solution based on the fitness value, the chicks move around their mother hens to update themselves. The proposed approaches are applied to solve the standard test instances. The results show that compared with the old model, the optimal results of eight more instances are found in the new mode in less time. The performance of the three evaluation indicators obtained using the proposed algorithm are improved by 10.74%, 16.05%, 44.89%, respectively, within the approximate time. Thus, above results verify the effectiveness and superiority of the proposed model and algorithm.

Complexity Measurement Model and Methods of Crowd Intelligence Collaborative Innovation for Design Activities

ZHENG Qing, DING Guofu

2021, 56(5): 989-994, 1010. doi: 10.3969/j.issn.0258-2724.20200238

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Crowd intelligence (CI) innovation has become an important product innovation tool in the environment of Internet as it can amass huge design resources outside the enterprises through online community. It is an important way for enterprises to expand design capabilities, solve design problems, and realize transformation and upgrading. The design activity complexity of crowd intelligence collaborative innovation is difficult to quantitatively describe. As a result, it leads to the absence of a quantitative basis for the release, push, and dynamic adjustment of design activities in the Internet innovation community. To solve these problems, a design activity complexity measurement method based on information entropy theory is put forward. First, the characteristics of the collaborative design process in Internet innovation community, as well as user types and capacity characteristics are analyzed. Second, three dimension including process complexity, problem complexity, and solvability complexity, are proposed to valuate design activities. Then, the quantitative methods are proposed on the basis of information entropy theory. Finally, the suspension design of project LM SF-01 in the Local Motors community is used as an example to calculate its complexity. The complexity in the three dimensions are respectively 318.15, 477.66 bit, and 134.46 bit. According to the characteristics of user participation, the weighted complexity of the design activity is 331.76 bit, which validates the effectiveness and feasibility of the complexity measurement model.

Data Mining Model Based on Neural Network and Its Application on Anti-Climber Device

CHE Quanwei, LEI Cheng, LI Yuru, ZHU Tao, TANG Zhao, YAO Shuguang

2021, 56(5): 995-1001. doi: 10.3969/j.issn.0258-2724.20200266

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Given the low efficiency of traditional finite element analysis method in calculating the crashworthiness of locomotive and vehicle structure, machine learning method is introduced to analyze and predict the crashworthiness and crash safety of vehicle structure on the basis of the existing simulation analysis data. Firstly, the neural network data mining model is established, and according to this model the prediction method for thecollision response of vehicle key structure. Secondly, tests are conducted to validate the finite element model of the anti-climber device, and the collision response data of the finite element model are obtained under different wall thicknesses. Then, the wall thickness of the anti-climber device is used as the model input, and the corresponding displacement, velocity, interfacial force and internal energy are used as the model output. The simulation data are used to train the model, the goodness fit of which is above 0.922. Finally, in order to test and verify the model, the predicted results of the energy absorption device are compared with the finite element simulation results, showing that the average relative errors of velocity, displacement, interfacial force, and internal energy are 7.10%, 4.51%, 6.20%, and 2.50%, respectively. The results indicate that the data mining model based on neural network can well reflect the collision characteristics of the anti-climber device with the precision; meanwhile, its computation time is greatly reduced and thecomputational efficiency is significantly improved.

Masked Face Detection Model Based on Multi-scale Attention-Driven Faster R-CNN

LI Zechen, LI Hengchao, HU Wenshuai, YANG Jinyu, HUA Zexi

2021, 56(5): 1002-1010. doi: 10.3969/j.issn.0258-2724.20210017

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For the purpose of masked face detection, a multi-scale attention-driven faster region-based convolutional neural network (MSAF R-CNN) model is proposed. First, given the Faster R-CNN model architecture and the multi-scale information of the face, Res2Net, a grouped-residual structure, is introduced to model more fine-grained features. Then, inspired by the attention mechanism, a novel spatial-channel attention Res2Net (SCA-Res2Net) module is developed to learn the multi-scale features adaptively. Finally, to further learn the global feature representation and ease the overfitting problem, the weighted spatial pyramid pooling network is embedded on the top of the model, which can segment the feature maps into different groups from finer to coarser scales. Experimental results on the AIZOO and FMDD datasets show that the accuracy of masked face detection with the proposed MSAF R-CNN model can reach 90.37% and 90.11%, respectively, thus verifying the feasibility and effectiveness of the proposed model.

Partial Discharge Process and Feature Extraction of Air Gap in EPR Cable Terminal

GUO Lei, CAO Weidong, BAI Longlei, XING Limeng, XIANG Enxin, ZHOU Lijun

2021, 56(5): 1011-1019, 1028. doi: 10.3969/j.issn.0258-2724.20200157

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Due to the nonstandard manufacturing and installation of the ethylene propylene rubber (EPR) cable terminal for high-speed railways, air gap appears in the terminal, and the partial discharge at the air gap seriously affects the normal operation of high-speed trains. In order to analyze the partial discharge process and characteristics of the 25 kV EPR cable with air-gap defects, a cable sample with air-gap defects was fabricated. The discharge parameters and the development process of phase resolved partial discharge (PRPD) spectrum were measured from the initial discharge to sample breakdown. Based on the Gaussian pyramid and gray-level co-occurrence matrix, the PRPD spectrum of the whole discharge process is extracted. The results show that according to the change of discharge parameters, the whole discharge process can be divided into discharge development stage, discharge duration stage, and near-breakdown stage. Based on the different morphology of PRPD spectrum in each stage, the second-order angular moment, entropy, contrast and the like are extracted by the multi-scale gray-level co-occurrence matrix method and can be used to characterize the discharge stage.

Urbanization Attribute Evaluation for Prefabricated Substation Based on MCD-AHP

WANG Feng, LIU Bofeng, CHAI Shuying, WANG Danlu

2021, 56(5): 1020-1028. doi: 10.3969/j.issn.0258-2724.20200172

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In order to improve the urbanization attribute effect of the prefabricated substation construction for urban rail transits, it is necessary to make an accurate evaluation of its urbanization attribute index. First, an evaluation system of prefabricated substation urbanization attribute indexes is built, including economic attributes, social attributes, and energy-saving attributes, and a quantitative model of the evaluation indexes is presented. Then, the robust analysis method with the minimum covariance determinant (MCD) is used to detect the judgment matrix provided by the expert group in the analytic hierarchy process (AHP) and remove the outlier matrix due to the difference in subjective cognition among the members of the expert group. Finally, the improved MCD-AHP is used to calculate and evaluate the weights of the urbanization attribute indexes for the prefabricated substation. The results show that after removing the outlier matrix samples, the absolute value of the index weight difference calculated by the upper and lower limit matrices ranges from 0 to 0.0103, and the the relative change ratio is from 0 to 9.31%, which is significantly better than the corresponding ranges of 0.0138−0.1355 and 15.99%−106.23% under the full sample state. This method can effectively improve the logical consistency of the judgment matrix and the aggregation of weight values.

Safety Assessment Method of Collector Shoe-Rail Relationship in Urban Rail Transits

JIN Shoujie, LI Kunpeng, ZHAN Dong, WAN Yongsheng, ZHONG Wei, FENG Chao

2021, 56(5): 1029-1034. doi: 10.3969/j.issn.0258-2724.20200075

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In order to realize the safety assessment of the relationship between the collector shoe and contact rail before the initial operation of urban rail transits, the laser imaging, ultraviolet photoelectric sensing, and fiber bragg grating strain sensor are used to measure the dynamic geometric parameters of the contact rail, arcing and dynamic contact force of the collector shoe-rail, and hard spots of the collector shoe. According to the characteristics of each test parameter, their evaluation standards are determined. Four parameters, which are contact rail operation height, contact rail offset, arcing rate and dynamic contact of the collector shoe-rail, are selected to establishe the evaluation function of contact rail quality index through Topsis evaluation method; then based on the above-mentioned evaluation standards and evaluation functions, a set of safety evaluation methods are proposed for the collector shoe-rail relationship before the initial operation of urban rail transits. The inspect device for the collector shoe-rail relationship is used to collect the data of the Zhenlongxi−Yuancun section on Guangzhou Metro Line 21. The results reveal that for the entire line, the deviation between the dynamic geometric parameters and their design values does not exceed ± 5 mm, maximum arcing time lasts 53 ms, maximum arcing rate is 0.025%, maximum and minimum average contact force is 135.6 N and 119.8 N respectively, maximum hard spot is 29.8 g, and the quality index score is bigger than 92.89 points.

Experimental Study on Coefficient Value of Subgrade Reaction in Seismic Analysis of Underground Structures

XU Kunpeng, JING Liping, BIN Jia, CHENG Xinjun, LIANG Haian

2021, 56(5): 1035-1042. doi: 10.3969/j.issn.0258-2724.20191073

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In seismic analysis of underground structures, the precision of the coefficient of subgrade reaction directly determines the accuracy of response displacement method. Considering the deficiencies of relevant research on the coefficient of subgrade reaction, a quasi-static test method was proposed, a large quasi-static model box was developed, and two groups of tests with and without axial load in sandy soil were carried out. On this basis, a correction method for the coefficient of subgrade reaction along depth is proposed and verified by an example. Results indicate that the horizontal coefficient of subgrade reaction decreases with an increase in the pushover level and increases with the soil depth. Moreover, the additional stress has great influence on the coefficient value; using modified coefficient can significantly improve the accuracy of the response displacement method. Compared with the result adopting the coefficient in terms of static finite element method in the code, the maximum bending moment error of the underground structure can be reduced from 16.7% to 9.1%, and the relative displacement error between roof and floor can be reduced from 35.0% to 18.8%. Thus, the feasibility of the new coefficient measuring method and the rationality of the coefficient modified method are validated.

Experimental Investigation of Masonry Shear Strength Under Compression

XIN Ren, WANG Meiyao, WANG Qinglin, WANG Yan

2021, 56(5): 1043-1049. doi: 10.3969/j.issn.0258-2724.20190444

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To avoid the relatively cumbersome strength-testing methods for the existing masonry structures under the combined action of shear and compression, an improved test device substituting uniaxial loading for biaxial is provided to test masonry shear-compression strength under different stress ratios by means of angular rotation of specimen. Comparing the experimental phenomena and numerical analysis results, sliding failure, tensile failure and compression failure of masonry are presented and the failure criterion of shear-compression strength under different stress conditions is established by means of the three-stage shear compression correlation curve with turning points of 0.2 and 0.6, and the stress-strain relationship with turning points of 0.2 under the shear-compression state is proposed. Results show that the improved testing method is simple, efficient and small in error. The mean value of the ratio of theoretical calculation to test result is 1.07, and the coefficient of variation is 0.180. The testing results enrich the constitutive relationship of masonry material, which can provide a theoretical basis for the improvement of masonry failure criterion and the construction of numerical analysis model.

Impact of Sudden Change of Wind Loads on Running Performance of Vehicle on Bridge with Wind Barriers

XU Xinyu, LI Yongle, CHEN Xingyu, ZHENG Xiaolong, LIAO Haili

2021, 56(5): 1050-1055, 1093. doi: 10.3969/j.issn.0258-2724.20191201

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To investigate the impact of sudden change of wind loads on a vehicle passing through the transition section with wind barriers, a multi-span simply-supported beam bridge of high-speed railway was taken as the research object. Aerodynamic characteristics of the vehicle-bridge system were studied by wind tunnel tests under three wind barrier porosities of 100.0%, 43.5% and 0. Based on the dummy body coupling (DBC) method, a wind-vehicle-bridge coupling simulation model was established. Effects of wind barrier porosities and vehicle operation speeds on the vehicle dynamic responses were analyzed with two types of wind barriers setting (continuously and non-continuously). The results show that aerodynamic characteristics of the vehicle change obviously due to the setting of wind barriers. Compared to the 100.0% wind barrier porosity condition, the drag coefficient of vehicle decreases 87% under the condition of 0 wind barrier porosity. The wind barriers set continuously have obvious wind shielding effects. With the decrease of the wind barrier porosities, the vehicle dynamic responses decrease greatly, and the wheel load reduction rate reaches 53%. With the wind barriers set non-continuously, the sudden change of wind loads has great effects on the lateral and vertical accelerations of the vehicle when it enters and leaves the wind barrier section. The lower the porosity of wind barriers is, the more violent the change of the acceleration response is, but the impact on the lateral force of the wheel axle and the wheel load reduction rate is limited. With the vehicle speed increasing, the responses of acceleration generally increase due to the sudden change of wind loads, in an obviously non-linear trend.

Wind-Resistant Safety Analysis of High-Speed Trains Passing Through Bridge-Tunnel Transition

HE Jiajun, XIANG Huoyue, LONG Junting, LI Yongle

2021, 56(5): 1056-1064. doi: 10.3969/j.issn.0258-2724.20190623

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When a train travels from a tunnel to a bridge, it bears a sudden wind load, and the response of the train changes abruptly, which will threaten the travelling safety. Taking a bridge-tunnel transition of a passenger dedicated line as the research background, computational fluid dynamics (CFD) simulation and vehicle-bridge coupling vibration analysis are conducted to calculate the aerodynamic forces and responses of a CRH3 train passing through the bridge-tunnel transition. The aerodynamic forces and vehicle responses of the front train, the middle train and the tail train are compared, the influences of wind attack angle on the aerodynamic force and vehicle response are studied, and the most unfavorable safety index is discussed. Results show that the closer the vehicle body is to the front, the greater the sudden variation in aerodynamic load and vehicle response will be. Compared with the 0° wind attack angle, a positive wind attack angle is relatively favorable to the train running, and the +7° wind attack angle brings a 10% decrease in the drag force and rolling moment of the train; however, a negative wind attack angle will increase the sudden variation effect of aerodynamic load and the running vehicle’s responses, and the −7° wind attack angle brings a 10% increase in the drag force and rolling moment of the train. When the wind speed is below 22.5 m/s, the CRH3 train can safely pass through the transition at a speed of 200 km/h. When the wind speed is 20.0 m/s, the train can safely pass through the transition at a speed of less than 325 km/h. With an increase in the vehicle speed and wind speed, the lateral force of the wheel axle is the first safety index to exceed the limit.

Review of Recent Progress in Durability of Fly Ash Based Geopolymer Concrete

ZHAO Renda, YANG Shiyu, JIA Wentao, ZENG Xianshuai, JIN Hesong, LI Fuhai

2021, 56(5): 1065-1074. doi: 10.3969/j.issn.0258-2724.20190993

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Geopolymer is a new type of chemically activited cementitious material which has been actively investigated across the world for more than 10 years. It may become a green cementitious material to replace cement. In view of the relatively weak durability of alkali activated fly ash (AAFA) geopolymer, recent research progress in AAFA geopolymer based concrete worldwide is systematically reviewed in terms of carbonation resistance, freeze-thaw resistance, chloride ion penetration resistance, acid and sulfate resistance, and weathering resistance. Literature survey results can be summarized as follows: 1) Compared with ordinary Portland concrete (OPC), the anti-carbonization ability of AAFA concrete is weaker, so the carbonized AAFA concrete has an increased porosity and decreased mechanical properties. High temperature curing and addition of Ca(OH)₂, OPC cement, ground granulated blast furnace slag (BFS) and nano-TiO₂ can improve the carbonation resistance of the AAFA concrete. 2) The freeze-thaw resistance of AAFA concrete is generally low. Adding BFS and metakaolin can improve the freeze-thaw resistance of AAFA concrete. 3) Compared with OPC, AAFA concrete has higher Cl^- permeability, and the addition of BFS, lower liquid-solid ratio, high temperature curing, and prolonging curing time can improve the Cl permeability performance of AAFA concrete. 4) AAFA concrete has strong resistance to sulfuric acid, hydrochloric acid, nitric acid, acetic acid and sulfate, and has low water absorption. 5) The efflorescence resistance of AAFA is relatively weak. This is closely related to porosity. Extending the heat curing time, adding aluminum-rich additives, lowering the target sodium to aluminum molar ratio, reducing the water content of the geopolymer, adding nano-SiO₂ and silane surface modification can improve the efflorescence resistance of the AAFA concrete.

A Review on Aseismic Bridges Crossing Fault Rupture Regions

JIA Hongyu, YANG Jian, ZHENG Shixiong, ZHAO Canhui, DU Xiuli

2021, 56(5): 1075-1093. doi: 10.3969/j.issn.0258-2724.20200162

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Abstract:
Under the background of strategy impetus of building a strong transportation country, the construction of bridges across active faults is an inevitable challenge in the development of Chinese highway and railway networks in recent years. This problem is prominent in planning, design and construction of Sichuan-Tibet Railway. At the same time, the contradiction between the regulations of avoiding faults in highway and railway seismic codes and some actual situation where it is impossible to avoid faults in building bridges is becoming increasingly prominent. Under the action of ground motions, the bridges crossing active faults have more complex stress characteristics, failure modes and failure mechanisms than those in far-field regions. The research on bridges crossing faults in China is still in its infancy, and there is a lack of relevant literature, engineering examples and seismic design codes for reference. To guarantee the safety of bridges across faults in the future earthquakes, based on the research status of bridges across fault at home and abroad, this paper reviews the characteristics of active faults, ground motions, damage characteristics of bridges, analysis methods, and conceptual design measures of bridges across faults. In addition, the existing problems and future research prospects in seismic resistance of bridge crossing faults are summarized. It is pointed out that the spatial variability of ground motion of fault earthquakes, failure mechanism of fault-crossing bridges, multiple disaster influence on bridges across faults, rapid repair technology of bridges across faults, and artificial intelligence technology in the application of crossing fault bridges will be the future development directions. This review provides useful references for seismic design, performance evaluation, and code formulation of bridges across faults in the future.

Calculation Methods of Ultimate Tensile Strength for Screw Anchors

CHEN Zhao, WEN Tao, WU Haonan, LI Fuhai

2021, 56(5): 1094-1099. doi: 10.3969/j.issn.0258-2724.20200404

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Abstract:
Screw anchors are a type of post-installed concrete anchors with the advantages of convenient and fast installation and removal, good construction adjustability, and short critical margin distance. Therefore, it has been used more in the field in recent years. To ensure that the requirements of bearing capacity of screw anchors and the safety of the anchored structure, the ultimate tensile strength corresponding to different tensile failure modes should be strictly calculated and designed. However, the research on the bearing capacity of screw anchors is relatively scarce, and that on its tensile failure mechanism is even less. Thus, the designers estimate and design the bearing capacity of screw anchors according to the individual design values provided by manufacturers, and cannot accurately calculate the theoretical ultimate strength. To further understand the tensile failure mechanism and calculation methods for the ultimate tensile strength of screw anchors, the formation mechanisms of the anchor bolt failure, concrete cone failure and combined failure mode for screw anchors under external static tensions are systematically summarized, and the relationship between the failure modes with the ultimate tensile strength and embedment depth is presented. The prediction model of the ultimate tensile strength corresponding to different failure modes is introduced and analyzed in detail. The state of the art on the prediction model of the ultimate tensile strength for the combined failure mode is discussed, and the prospect of further verification and improvement are explored. The current calculation methods of anchor group, spacing, and edge effects are presented, and it is also pointed out that there is a need for studying screw anchors in this regard.

Flexibility Curvature Eigenvalue Method for Debonding Damage Identification of Unit Slab Track

ZHAO Pingrui, XU Tianci, LIU Wenxing, QU Chaoguang, BI Lanxiao, DING Chenxu

2021, 56(5): 1100-1108, 1124. doi: 10.3969/j.issn.0258-2724.20191149

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Abstract:
In order to identify and locate the debondingdamage on the bottom of the CRTS Ⅲ ballastless trackslab, firstly, the flexibility matrix of the track structure is obtained by its modal analysis, and the flexibility curvature eigenvalue matrixis constructed with the use of the noise reduction data processing and Gaussian curvature. According to the accuracy index that can reflect how irregular protrusions in the non-damage area affect the damage location and the effectiveness index that can identify the damage range, the reasonable density of measuring points is obtained. A variety of damage conditions are established to study the scope of applying the indexes for identification.The results show that the flexible curvature eigenvalue of the track slab with the debonding damage has obvious jump in the damaged area; and its peak value corresponds to the center of the damaged area, which can effectively identify the hidden damage at the bottom of the unit plate track plates of CRTS Ⅰ and type Ⅲ of different material properties. Aiming at the debonding damage of the slab bottom larger than 0.4 m × 0.4 m, the measurement point density of 0.2 m is conducive to reducing the impact of noise on damage location and improving damage scope identification. When the side length of the damaged area at the bottom of the track slab is larger than 0.3 m, the flexibility curvature eigenvalue can accurately identify and locate the damage. The maximum absolute value of the flexibility curvature of the track slab increases with the debonding size, and they have a nearly linear relationship. Thus, with the visual graph of the flexibility curvature eigenvalue, the damage area can be identified.

Application Error of Traffic Speed Deflectometer for Asphalt Pavement Structure with Semi-Rigid Base

WU Chaoyang, JIANG Xin

2021, 56(5): 1109-1115. doi: 10.3969/j.issn.0258-2724.20200247

[Abstract](384)

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Abstract:
In order to evaluate the applicability of traffic speed deflectometer (TSD) in asphalt pavement structure with semi-rigid base, the 2.5D finite element method is employed to establish a numerical model subjected to the moving load of TSD. Firstly, the reliability of the 2.5D finite element program is verified with two previous published results. Then, the deflection slope curves of the conventional, full-depth and semi-rigid base asphalt pavement structure are studied and compared with each other, and their characteristics are summarized. Finally, the applicability error of TSD for asphalt pavement structure with semi-rigid base is examined. Results show that there are multiple peak points in the deflection slope curve of asphalt pavement with semi-rigid base. When TSD is applied to typical asphalt pavement structure with semi-rigid base, deflection test error caused by reference sensor error is as high as 87.3% while the reference sensor reading is not 0. In order to achieve accuracy result, the length of rigid beam of TSD is proposed to be extended to 8.0 m.

Calculation Method of Deformation Load of Deep-Buried Tunnel under Influence of Excavation Method

WANG Mingnian, WANG Zhilong, GUI Dengbin, ZHANG Xiao, ZHAO Siguang, TONG Jianjun, LIU Dagang

2021, 56(5): 1116-1124. doi: 10.3969/j.issn.0258-2724.20191124

[Abstract](422)

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Abstract:
In order to study the influence of the excavation method on the deformation load of the surrounding rock, the law of its influence on the deformation load was clarified through theoretical analysis, literature research and field test methods. Considering the influence of surrounding rock grade, tunnel span and excavation method, a quantitative calculation formula for deformation load was established according to the corresponding change law based on the multiple nonlinear regression method. Through the analysis of the deformation load data of 205 monitoring sections in 54 tunnels (108 monitoring sections of large-scale excavation mechanized construction and 97 conventional partial excavation construction monitoring sections). The results show that the surrounding rock after tunnel excavation is stable and the deformation load of surrounding rock is small by adopting large-scale mechanized large-section excavation method. The deformation load of surrounding rock is large when the conventional mechanized subsection excavation method is adopted. In the calculation formula of deformation load of surrounding rock, the value of excavation method influence coefficient k_c ranges from 1.00 to 1.15, the higher the grade of surrounding rock, the greater the k_c value, that is, the worse the surrounding rock, the more obvious the influence of excavation methods on the deformation load of surrounding rock.

Dynamic Characteristics of Silt Considering Time Intermittent Effect

NIE Rusong, DONG Junli, MEI Huihao, LENG Wuming, LI Yafeng, CHENG Longhu

2021, 56(5): 1125-1134. doi: 10.3969/j.issn.0258-2724.20190642

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Abstract:
Train dynamic load is the premise to reveal the real dynamic response characteristics of subgrade. The train load is regarded as a continuous dynamic load in previous cyclic triaxial tests without considering the time intermittent effect. Dynamic triaxial tests of silt under continuous loading and intermittent loading (continuous loading and intermittent alternating circulation) were carried out by using indoor dynamic triaxial apparatus, and the development laws of excess pore water pressure, modulus of resilience and accumulated plastic strain of silt under two loading modes were analyzed. The accumulated excess pore water pressure under continuous dynamic load will dissipate in the intermittent stage, and the axial strain will be restored to a certain extent in the intermittent stage, thus improving the ability of the sample to resist deformation. Ignoring intermittent effect in indoor dynamic triaxial tests will overestimate the cumulative amount of excess pore pressure and plastic strain and the possibility of failure. The permanent deformation behavior of specimens under intermittent loading can be divided into plastic stability, plastic creep, and incremental failure according to stability theory.

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2021 Vol. 56, No. 5