Journal of Chongqing Jiaotong University(Natural Science)

Stress Characteristics and Influence Factors of Surface Crack near Fillet Weld in Steel Box Girder

JI Bohai, XIE Shuhui, FU Zhongqiu, YAO Yue

2017, 36(9): 1-5. DOI: 10.3969/j.issn.1674-0696.2017.09.01

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Based on specimen of steel girder bridge local model, the numerical simulation of fillet weld surface crack was carried out. Stress distribution of crack tip and front was analyzed, and stress intensity factor of reference point was calculated based on maximum tangential stress criterion. Additionally, according to actual fatigue crack shape change during propagation, the influence of different crack shapes on stress and stress intensity factor was considered. Analysis results indicate that crack tip appears severe stress concentration phenomena and stress of crack zone decreases obviously. Stress level of crack front is closed to that of cross-section at the same location surface without crack. Under tensile stress, stress intensity factor of type II and type III is approximately equal to zero; and KI decreases gradually with the increase of angles of surface reference points on the whole. Crack tip stress increases linearly with the ratio of minor axis to major axis, and the growth rate slows down when the ratio is larger than 0.6. With the increase of the ratio of minor axis to major axis, the change range of stress intensity factor at front along crack depth is larger than that at crack tip, and comparing with long crack zone, this difference is more obvious in short crack zone.

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Seismic Performance of Prestressed Assembled Bridge Piers with Embedded Steel Tube

DU Qing, GAO Songsong, QING Longbang

2017, 36(9): 6-11. DOI: 10.3969/j.issn.1674-0696.2017.09.02

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A new type of prestressed assembled bridge piers with embedded steel tube (simplified as PEAP model) was proposed. In order to study the seismic behavior of PEAP model, a low cyclic loading test of 3 PEAP models was designed, which analyzed the seismic performances of specimen, such as hysteretic curve, skeleton curve, energy dissipation capacity and ductility. Based on the open source finite element program OpenSEES, the calculation method of numerical simulation of PEAP model was proposed. The numerical simulation of the low cyclic loading test of 3 PEAP models was carried out and the results were compared with the test results. Through comparison, the reliability and rationality of the proposed numerical model is verified, which can provide a reference for the further study of seismic catastrophic behavior of segmental assembly bridge pier.

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Cable Force Measurement of Steel Strand of Stay Cable with HDPE Shell

LIU Dayang, HE Xiaoqin

2017, 36(9): 12-16. DOI: 10.3969/j.issn.1674-0696.2017.09.03

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The reliability and accuracy of cable tension test of steel strand cable with HDPE shell in practical engineering were studied through the simulation analysis of finite element software and the verification of field test data. The analysis of time- history signal of different acquisition and recording points on steel strand and HDPE shell shows that: in cable force measurement test of steel strand of stay cable with HDPE shell, the cable force can be effectively identified by directly installing sensor on HDPE shell which is corresponding to bound-circle of steel strand. The above conclusion is verified by East-Watergate Bridge.

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Calculation of Additional Stress of Metro Tunnel Caused by Adjacent Irregular Foundation Pit Excavation

ZHOU Jie1,2, ZHOU Wen3, CHEN Baiquan4

2017, 36(9): 17-21. DOI: 10.3969/j.issn.1674-0696.2017.09.04

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New buildings often located above the urban metro tunnel in operation, the unload additional stress caused by foundation pit excavation may damage the safety of tunnel. With the help of Mathematica software, firstly, additional stresses of metro tunnel caused by vertical and horizontal unloading of adjacent foundation pit excavation were respectively calculated by Mindlin solutions. Then, the law of factors influencing the additional stress field was analyzed; and the factors were considered including ordination of tunnel, angle between tunnel and foundation pit, excavation depth of foundation pit. Finally, taking the excavation of Chongqing Luobinsen square foundation pit above metro line 1 in operation as an engineering background, the distribution of additional stress along tunnel axis caused by the irregular foundation pit excavation was calculated out. The above research results provide certain basis for further research on the internal forces and deformation of tunnel caused by the irregular foundation pit excavation.

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Research and Practice of Gravel Filling and Grouting Technology of Rail Transit Single Shield TBM

XI Zhendong1, SUN Heming1, LI Jiakun2, ZHANG Zhiwei1, PENG Chaoyang1

2017, 36(9): 22-27. DOI: 10.3969/j.issn.1674- 0696.2017.09.05

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Based on Shangqiao station, Fengming mountain station and their interval tunnel engineering in first-stage project of Chongqing rail transit loop line, the gravel filling and grouting technology of single shield TBM was proposed innovatively. Through PFC3D particle flow simulation test, the indoor test to determine the single and double slurry ratio and the field test, the gravel filling and grouting technology of urban rail transit single shield TBM was obtained. And the proposed technology was successfully applied to Shangqiao station, Fengming mountain station and 6724 m tunneling of their interval tunnel engineering in first-stage project of Chongqing rail transit loop line, which proved that the gravel filling and grouting technology of rail transit single shield TBM is feasible. The proposed technology can be used for reference and promotion of similar TBM projects.

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Analysis Method on Uniformity of Asphalt Pavement Based on Digital Image Processing Technology and Entropy Weight

LIANG Naixing1, DU Zhenyu1, XU Jianping2, HUANG Zhifu3

2017, 36(9): 28-31. DOI: 10.3969/j.issn.1674- 0696.2017.09.06

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In order to evaluate the asphalt pavement segregation simply and rapidly, based on digital image processing technology, the correlation analysis on the uniformity of several asphalt mixture paving images was carried out. After a series of image processing, such as converting the color image into gray image, filtering, de-noising, histogram equalization, image segmentation, morphological processing as well as opening and closing operation, the image was converted into binary image. Secondly, the areas of different file aggregate were extracted, and their weights were calculated by the entropy weight method, which determined the homogeneity evaluation index value. Thirdly, the distribution map of homogeneity evaluation index value was plotted; the obtained homogeneity evaluation index value was compared with the image, the range of homogeneity evaluation index value when the aggregate particles were uniformly distributed in the image was obtained. The research results show that the homogeneity evaluation index value determined by entropy weight can reflect the evenness of asphalt pavement aggregate appropriately.

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Dynamic Stress and Settlement Charateristics of Foundation under Train Load

CHEN Jun

2017, 36(9): 32-38. DOI: 10.3969/j.issn.1674-0696.2017.09.07

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In order to analyze the dynamic stress and settlement charcteristics of the foudation under train load, the dynamic coupling numerical model of rail-embankment-foudation interaction under train load was established, considering the effect of train speed, embankment height and base stiffness. The dynamic stress distribution of the foudation and settlement charcteristics of surface under train load were researched, and the reinforcement effect of different foundation reinforcement forms was discussed. The results show that the dynamic stress of foundation decreases quickly along the horizontal and vertical direction under train load. The vertical dynamic stress of foundation and foundation settlement increase as the train speed increases, while decrease with the increase of the embankment height and base stiffness. The embankment height should not be less than 2 m. The foudation settlement decreases with the increase of the reinforcement depth and stiffness of the reinforced area. The higher train speed, the more obvious effect; and the best foundation reinforcement depth is 3 m.

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Cumulative Damage Calculation of Flexible Pavement Considering Aircraft Operation Characteristics

MA Lukuan, ZHAO Hongduo, DU Zengming, CHEN Zhi’ang

2017, 36(9): 39-43. DOI: 10.3969/j.issn.1674-0696.2017.09.08

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To accurately calculate the accumulated damage at any point of flexible pavement, considering the difference of aircraft weight and taxi speed, the dynamic load calculation method of the single main landing gear when the aircraft was taxiing on the road surface at any cross-section was given. Based on the spatial response analysis of horizontal tensile strain at the bottom of surface and vertical compressive strain on the top of subgrade under dynamic load of the single main landing gear, the frequency influence coefficient of multiple axles was introduced. Considering the rule of lateral wandering and longitudinal distribution of wheel path, the calculation method of load frequency of the single main landing gear at any position in the plane road was obtained. Besides, the number of allowable load applications was also calculated at the corresponding location. Finally, the calculation method to cover the cumulative damage of surface fatigue cracking and rutting of flexible pavement was proposed based on Miner’s linear fatigue damage cumulative theory. The case study shows that the proposed method is feasible, which can provide reference for the theoretical calculation of pavement segment and lateral thinning design.

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Stone Field Planning Based on Expressway Maintenance

ZHANG Zhengqi1, LI Zhuolin1, LI Weiyong2, GUO Hanping3

2017, 36(9): 44-49. DOI: 10.3969/j.issn.1674-0696.2017.09.09

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In order to solve the problems of expressway maintenance management in our country, such as the random layout of the material field, the serious damage to the ecological environment, the bad competition among various small stone fields, the difficulty to ensure the quality of the stone demanded in the maintenance, the relationship between stone fields and maintenance sites was studied, which was based on the distribution and resource characteristics of stone fields in Shaanxi Province. Firstly, the layout of stone field was simplified to the problem of discrete location, and the mixed integer programming model was established. Then to solve the problem, the Dakin branch and bound procedure was used and the principle and influencing factors of stone field layout were expounded. Finally, the plans and layout of the expressway maintenance stone field in the Guanzhong region of Shaanxi province were carried out by the mixed integer programming model and Dakin branch and bound procedure. Research shows that the mixed integer programming model and Dakin branch and bound procedure can be used to obtain the reasonable layout of the stone field.

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Numerical Analysis on Stress and Deformation of Jinfo Mountain Spillway

LIU Liangjun1, ZHANG Hongwei2, ZENG Chao3

2017, 36(9): 50-54. DOI: 10.3969/j.issn.1674-0696.2017.09.10

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In order to study the feasibility of Jinfo mountain spillway building on the thick overburden, Duncan-Chang model was used on the cover layer, and the stress and deformation of cross-section and longitudinal section of spillway in the construction and operation of the sluice were calculated and analyzed, in the case of the tangent elastic modulus coefficient K with the maximum and minimum value. The results show that the max and min principal stress of spillway don’t exceed the standard value. The displacement at the outer slope of foundation transverse groove in the 16-16 section is larger during the operation of the sluice. If the tangent elastic modulus coefficient K increases, the max and min principal stress of spillway structure, the deflection of spillway expansion joint, the settlement of the foundation and the horizontal displacement of transverse groove will decrease. Therefore, the slope stability should be fully demonstrated during the operation of the sluice, and it is suggested the appropriate reinforcement measures should be taken for the thick overburden.

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Analysis and Calculation on Plastic Tube Outside of Plastic Tube Cast-in-Place Concrete Pile

XU Chunhu1, QI Changguang2, ZUO Dianjun3, 4

2017, 36(9): 55-60. DOI: 10.3969/j.issn.1674-0696.2017.09.11

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Plastic tube cast-in-place concrete pile (TC pile) is composed of pre-driven plastic tube filled with concrete. During the period of construction and work of TC piles, the plastic tubes were going to be subjected to the excess pore water pressure, soil compaction pressure and vibration, et al. Therefore, combining with the basic parameters and practical application of the plastic tubes, five calculation schemes were figured out for the mechanical characteristics of plastic tubes by employing the finite element analysis, and the selection of outer corrugated shapes of plastic tubes were also discussed. The analysis results show that the maximum stress of plastic tubes occurs in the early stage of plastic tube extraction; in the case of the same wall thickness, it is optimal for plastic tubes as the wave height divided by wave distance is 0.38; it is suggested that the plastic tubes with circular ripple or big wave angle should not be adopted, whereas the trapezoidal or curved plastic tubes are more feasible.

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Coupling Analysis of Seepage Field and Stress Field of Compressible Skeleton Earth-Rock Dams

WANG Risheng1, 2, ZHAO Mingjie1

2017, 36(9): 61-65. DOI: 10.3969/j.issn.1674-0696.2017.09.12

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In the process of seepage flow of earth-rock dams, the liquid in the pore of soil-stone composite medium would produce pressure change, which acted on the solid skeleton particles of soil-stone composite medium and resulted in a series of changes, such as porosity and deformation of skeleton particle. The porosity and skeleton particle after changes worked on the liquid in the pores in turn and caused the redistribution of its stress field. Hence, the flow regularity of the liquid in the pores and its influence on porosity stress and the coupling effect of stress field and seepage filed must be taken into account in the research of permeability rule for the liquid in soil-stone composite medium. The coupling model of compressible skeleton earth-rock dam was deduced on the basis of related theories. The accuracy and rationality of the proposed model are verified through comparing specific examples, and the verification shows that the relative residuals of coupling results are smaller and closer to actual observation results when the compression of skeleton is taken into account.

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Field Test on Separation Dike Built with Slurry Filled Geotextile Tubes

WU Yuelong 1, TANG Tongzhi2, XU Bo3, ZHANG Hong1, ZHANG Jinliang1

2017, 36(9): 66-72. DOI: 10.3969/j.issn.1674-0696.2017.09.13

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Using geotextile tubes filled with slurry for building separation dike is a kind of new method. At first, the coastal beach silt was filled into appropriate size of woven geotextile tubes by high pressure mud pump, then the dike was formed by the drained tubes and stacked layer by layer, so a large amount of sand and gravel resources was saved. Three different drainage and consolidation types were proposed, including natural drainage, consolidation agent and vacuum preloading. Field tests were carried out and the deformation of dike body, the variation rule of pore water pressure in tubes, the vane shear strength, the physical and mechanical properties of soil under the condition of different drainage forms were studied. At the same time, the model drainage test and hanging bag test provide the technical basis for the selection of geotextile bags and the concentration of filling slurry. Through the comparison of the economy of traditional construction method and building dike method with slurry filled geotextile tubes, it is proved that the proposed method has strong market competitiveness.

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Experiment of Music with Different Loudness Against Driving Fatigue in Monotonous Sound Environment

HU Zhigang, HU Jiabin, QIAO Xianling

2017, 36(9): 73-79. DOI: 10.3969/j.issn.1674- 0696.2017.09.14

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In order to effectively mitigate driving fatigue in monotonous sound environment and reduce traffic accidents, driving simulation experiment was made in different kinds of radio broadcasts environment. Based on the pupil diameter variation coefficients and other indexes, overall evaluation index of driving fatigue was established. The effectiveness of different volume of music as countermeasures against driving fatigue was studied. The result shows that music can be a countermeasure against driving fatigue in monotonous sound environment. In different sound environment, the effectiveness of music against driving fatigue is different. The significance and stability of 75dB and 85dB music are better than those of 65dB, and there are few differences between 75dB and 85dB music.

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Design of Straight-Left Shared Lanes under Single Import Release Mode Based on Utility Theory

WU Zhong, JIANG Yi

2017, 36(9): 80-84. DOI: 10.3969/j.issn.1674- 0696.2017.09.15

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In order to balance the saturation of straight and turn left traffic flow within the same import, and to improve the passable and space-time resource utilization efficiency under single import release mode, the design of the straight-left shared lanes based on utility theory and traffic flow critical model was expounded. According to the field survey of intersection at Wuying Shan road and Huanggang road in Ji’nan of Shandong province, Webster delay model was used to solve the total delay with and without setting straight-left shared lanes under single import release mode. The results show that: the release effect after setting straight-left shared lanes under single import release mode is better.

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Road Network Traffic Flow Allocation Based on Genetic Algorithm

XU Xu, WANG Xinxin

2017, 36(9): 85-90. DOI: 10.3969/j.issn.1674-0696.2017.09.16

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Based on the axial load times, Monte Carlo method was used to calculate pavement structure reliability. Taking pavement structure reliability as road connection reliability, the road network connection reliability was solved by BFS. In order to improve the service level of a road with low service level, the genetic algorithm was used to allocate traffic flow with the target of the highest road network connection reliability. The service level of the whole road network was improved finally. Compared with road network service level and road network connection reliability before and after the traffic flow allocation, manager could acquire some referential advice. The case study shows that genetic algorithm can effectively allocate road network traffic flow.

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Optimization of Public Transport Service Frequency Based on Bus Dynamic Network

ZHANG Weihua, WU Zhenyu, BAI Haijian, WANG Shengping

2017, 36(9): 91-97. DOI: 10.3969/j.issn.1674-0696.2017.09.17

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Taking the bus station as the node of dynamic network, the influence of vehicle distribution and passenger demand for bus stops on the balance of public transport network service was mixed to build the bus dynamic network model, which took the passengers’ total waiting time at stops as its edge weight. Then the corresponding relationship between bus network service and bus dynamic network structure was established. On this basis, the space and time balance of the dynamic network was set as the objective, and the network state recognition mechanism was built. Besides, the temporal and spatial variation rule of bus dynamic network was analyzed under the condition of peak passenger flow and flat peak. Finally, taking the time and space balance of dynamic network as the optimization goal, the ordinary line service frequency optimization model was established. Through the computation of case studies, it is found that the proposed model can obtain the optimal service frequency of ordinary line under the steady state network, which provides a new train of thought for the research of public transport scheduling.

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Calculation and Analysis on Carbon Emission of Road Transport Industry in Fujian Province

CHEN Cheng，HONG Yaling, FANG Lingna, QIU Rongzu

2017, 36(9): 98-103. DOI: 10.3969/j.issn.1674-0696.2017.09.18

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Road transportation is the key industry of energy saving and emission reduction. The reasonable calculation of carbon emission is of great significance to promote the work of energy conservation and emission reduction. The calculation models based on input-output and process analysis method had been applied to the estimation of carbon emission of road transport in Fujian province from 2004 to 2013, and the comparison of carbon emission of road transport between Fujian province and Jiangsu province had been made by using input-output model in terms of total volume, configuration and efficiency of carbon emission. Based on the calculation results of the two models, the characteristics of the two commonly used carbon emission measurement models were analyzed. The results show that: ①The situation of carbon emission of road transport in Fujian province is better than that in Jiangsu province. ②In recent years, the growth of carbon emission of road transport in Fujian province has slowed down, and even began to decline; carbon emission efficiency is increasing yearly. ③Although high emission energy is the main part, the energy consumption structure of road transport industry in Fujian province has improved year by year. ④The calculation results of input-output approach are smaller than those of process analysis approach.

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Modeling of Vortex-Induced Vibrations (VIV) Energy Harvesting and Experimental Validation

YANG Jingdong, LIU Yongzhen, ZHANG Min, ZHANG Hongxin

2017, 36(9): 104-107. DOI: 10.3969/j.issn.1674-0696.2017.09.19

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In order to study vortex-induced vibration of piezoelectric energy harvesting characteristics, a two-dimensional mathematical model about piezoelectric energy harvesting was established based on the theory of piezoelectric and wake oscillator model. An energy harvesting device of a cylinder with double piezoelectric cantilever beam was calculated and analyzed. The results show that the output voltage increases with the increase of load resistance. The maximum output power has an optimum matching resistance. Then the wind tunnel experiment of piezoelectric energy harvesting was conducted. It is demonstrated that the experimental results are consistent with the calculation results and the correctness of the proposed theoretical model is verified. The proposed model provides reference to further design and optimization of vortex-induced vibration energy harvesting system.

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Simulation of Vehicle ACC System Algorithm

XIONG Jian, WANG Xiusheng, LIU Ding

2017, 36(9): 108-114. DOI: 10.3969/j.issn.1674-0696.2017.09.20

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The following characteristics of cruise vehicle and the control of vehicle safety distance are the core of the control system ACC algorithm. ACC algorithm adopted a hierarchical control structure, in which linear quadratic algorithm was taken as the core of the upper controller, and the calculation on the vehicle information measured by sensors was carried out; the expected acceleration and deceleration was obtained through the spacing control strategy and control algorithm; the lower controller was based on inverse dynamics of vehicle, and throttle valve and braking force control model were established on the MATLAB platform. Therefore, the expected throttle valve opening and braking force were obtained, which realized the control of vehicle acceleration and deceleration. Through the combined simulation experiments of MATLAB and CarSim, the comparative simulation research on the spacing strategy among the classical linear quadratic algorithm, the improved linear quadratic algorithm, comprehensive linear quadratic algorithm was carried out. The advantages and disadvantages of the three algorithms were compared and then verified by go-stop condition. The experiment results show that the improved algorithm is more suitable for the characteristics of the vehicle adaptive cruise, with good ride comfort and safety; particularly under emergency braking conditions, parking is steady, which improves occupant’s comfort and safety.

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