西南交通大学学报

2019, 54(5): 1-2.

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3D Seismic Vulnerability Analysis of Bridge Structural Components Based on Reliability

SHAN Deshan, GU Xiaoyu, DONG Jun, LI Qiao

2019, 54(5): 885-896. doi: 10.3969/j.issn.0258-2724.20170881

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In order to evaluate the near-field seismic performance of bridge structures, a three-dimensional (3D) seismic vulnerability analysis process for bridge components is established. Based on the reliability theory of engineering structures, 3D failure surfaces of the components are used to characterize the damage status of pier columns and bearing components, and the damage state equation containing multiple independent damage indices is regarded as the damage index for the 3D seismic vulnerability analysis. In light of the existing research on the bending and shearing failure surfaces of piers, damage state equations for piers with bending failure and shear failure and for bearings with relative displacements are built. On this basis, the criteria for 3D seismic damage of pier columns and bearings are established, and quantitative methods for calculating the damage in different damage states are presented. The final calculation and analysis of the 3D seismic vulnerability of bridge components are accomplished in accordance with the bridge seismic design codes in various countries and the reliability theory of engineering structures. A simplified validation of one-dimensional seismic vulnerability shows that the proposed method can be applied to the seismic vulnerability analysis of bridge structures, with a maximum probability deviation of less than 4% from the traditional probabilistic seismic demand analysis (PSDA) method.

Seismic Response Analysis of High-Pier Bridge under Near-Fault Multiple Pulse Record Excitation

ZHENG Shixiong, CHEN Zhiqiang, CHEN Zhiwei, LI Xi

2019, 54(5): 897-907. doi: 10.3969/j.issn.0258-2724.20170725

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The multiple pulse effect of near-fault seismic records on the nonlinear seismic response of high pier railway bridges (HPRB) was investigated. First, three representative groups of seismic records, namely, single pulse record (SPR), multiple pulse record (MPR) and none pulse record (NPR) were selected by visual inspection. Second, pulse characteristics were quantitatively identified using wavelet analysis method (WAM) and energy-based approach (EBA) to investigate if impulse ground motion identification method was applicable to MPR. Finally, a typical HPRB, located in the southern region of China, was adopted as the research object, the non-linear finite element model was established in OpenSees platform, and the non-linear seismic response analysis of the HPRB was carried out. The effects of MPR and SPR on the nonlinear seismic response of the HPRB were compared. The results obtained from the analyses indicate that the WAM and EBA are applicable to ground motions with only one dominant pulse in the velocity history, and are not applicable to multiple pulse ground motions. Near-fault MPRs and SPRs pose the risk of stronger damage to irregular high pier bridges than NPRs. Under MPR excitation, the top displacement of pier 1 and pier 2 is, respectively, 118.9% and 109.6% larger than under NPR excitation. The bending moment and the curvature at the bottom of the pier also increase. Near-fault MPR is found to produce pounding force and pounding times that are, respectively, 3−5 times and 2−3 times greater than those by NPR excitation. In the near field multiple pulse earthquake, the main beam is more likely to cause severe impact damage, and thus, the appropriate anti-collision measures should be adopted in seismic design.

Dynamic Response Influences of Combination Loads of Wind, Wave, and Current on Sea-Crossing Bridges

FANG Chen, LI Yongle, XIANG Huoyue, ZHANG Jingyu

2019, 54(5): 908-914, 922. doi: 10.3969/j.issn.0258-2724.20170716

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To investigate the wind, wave, and current loads and their combination influences on sea-crossing bridge, the joint committee on structural safety (JCSS) combination model was used to combine the wind, wave, and current loads considering the correlations among wind, wave, and current. The Gumbel joint probability model was adopted for the correlation of wind and wave, the combination of current and wind field was achieved by wind current. Taking a sea-crossing bridge as an engineering background, the influences and mechanism of dynamic responses on main beam were analyzed in different combinations, and the influences of secondary load period and different wave fields within load combination on calculation results were discussed. The results show that wind, wave, and current load have great influence on displacement responses of main beam, the displacement responses of the middle span of the JCSS combination with wind as the main load are larger 20%−30% than wave and current as the main load; the random wave and transverse basic mode of bridge are contribute to the lateral responses of the middle span significantly; the displacement responses at different positions of the main beam are affected by the same environmental loads differently, the responses of the middle span are mainly affected by the wind load, the main beam responses at the joint of the tower and beam are mainly affected by the wave load; the wave field simulated by regular wave will underestimate displacement responses of the middle span.

Numerical Simulation of Wind Characteristics at Bridge Sites in Complex Mountainous Terrains

WU Lianhuo, ZHANG Mingjin, LI Yongle, WEI Kei

2019, 54(5): 915-922. doi: 10.3969/j.issn.0258-2724.20180029

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In order to investigate the variation of spatial characteristics of the wind field at bridge sites in complex terrains, a mountainous terrain was built in FLUENT to simulate wind field characteristics. The Lvzhi River Bridge located at a gorge area in the southwest of China was chosen as the engineering background, in which 36 cases with different wind directions were analyzed. Under the influence of the complex terrain, the profiles of average transverse wind velocities along the height direction and bridge axes are quite different. The complex terrain still has an impact on the wind field at 400 m above the peak of the terrain near the bridge site. Affected by large angle bending of the river, the bridge site area forms a terrain similar to the " one-way open slot”. The incoming wind along the river downstream direction is blocked by the mountain, so the wind speed at each bridge is lower than that in the river upstream direction. The average of the velocity differences between these two directions reaches 13.6 m/s. The wind attack angles of all bridges are mainly negative. The suddenly widened gorge results in a part of limited distributary of the wind field and the wind speeds decrease slightly in the widening area. After crossing the widened section, the gorge narrows and the wind speeds remain large.

Mechanical Behavior and Structural Optimization of Steel-Concrete Composite Cable-Pylon Anchor

XIAO Lin, LIU Lifang, WEI Xing, LIU Dejun

2019, 54(5): 923-930, 944. doi: 10.3969/j.issn.0258-2724.20170320

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Full-size model test and nonlinear finite element analysis (FEA) are carried out to investigate the mechanical behavior and optimize the structure design of the steel-concrete composite cable-pylon anchor of Jiayue Bridge, Chongqing. The mechanical performance and load transfer mechanism of the steel-concrete composite cable-pylon anchor are studied first by the model test comparing with the nonlinear FEA. Then, the optimized structural parameters of the composite cable-pylon anchor are analyzed by FEA. Results show that the stresses of components of cable-pylon anchor are on a low level and distribute evenly. The relative slippage between anchor box and concrete pylon is small, and the maximum value is only 0.029 mm. The stiffness of shear connectors has a great impact on the principle stress of concrete pylon. When the stiffness is increased by 5 times, the principle stress of concrete pylon is reduced by 17.3%. The cable-pylon anchor’s structural design of Jiayue Bridge meet the requirement of safety and economics.

3D Shrinkage and Creep Effects of Concrete Under Varying Temperature Environment

YANG Yongqing, LI Shiwei, LI Xiaobin, YU Qu

2019, 54(5): 931-936. doi: 10.3969/j.issn.0258-2724.20170256

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In order to analyze shrinkage and creep effects of concrete exactly, based on the three-dimensional (3D) characteristics of shrinkage and creep, the shrinkage and creep effects of concrete under an ambient temperature environment were analyzed. A 3D shrinkage and creep effects mechanical model for concrete was established for varying temperature environments, and the corresponding calculation process was integrated with finite element analysis software ABAQUS. Then, the feasibility of the method and reliability of the results were verified using two examples. The results demonstrate that the maximum error of the model calculation is 8.2% and –7.1% for long-term deflection and concrete strain, respectively. The model suitably reflects the effect of temperature on creep strain, and the overall trend is consistent with the measured values. The maximum error is –20.5%, and this value decreases with the increase in age, the final error is 6.4%.

Experimental Study on Bonding Performance Between Rebar and Coarse Aggregate Ultra-High Performance Concrete

ZHAO Canhui, LI Haodao, DENG Kailai

2019, 54(5): 937-944. doi: 10.3969/j.issn.0258-2724.20170513

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To investigate the bonding performance between the reinforcement and coarse aggregate UHPC（ultra-high performance concrete）, six sets of pulling out specimens were tested. The effect of reinforcement diameter, cover layer thickness, and anchorage length were quantitatively studied, and further analysis based on the classic thick-cylinder theory and Lame Formula were conducted to obtain the influence of cover layer thickness. The formula for estimating the peak bonding stress was obtained through regression analysis, which was validated with the several physical tests. According to the results, the bonds between the reinforcement and coarse aggregate UHPC have similar failure modes with that of RPC（reactive powder concrete）, including " wipe failure” and " split failure”. The thickness of cover layer in coarse aggregate UHPC is a little larger than that in RPC, while the demand of anchorage length is almost the same. The cover layer thickness and anchorage length have interactive effect on each other, meaning that sufficient anchorage length can reduce the requirement of cover layer thickness. Finally, the suggested anchorage length is presented.

Stress Characteristics and Failure Mechanisms of Plain Concrete Piles of Composite Foundation under Embankment

HUANG Junjie, SHI Xiaona, SU Qian, WANG Wei, WANG Wubin

2019, 54(5): 945-952, 988. doi: 10.3969/j.issn.0258-2724.20180251

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In order to reasonably analyze the stability of embankment supported on composite foundation with plain concrete piles in soft clay area, centrifugal model tests and simulation analyses were conducted to study the stress characteristics of the piles with different spacings under embankment, and a one-by-one exiting method of piles due to rupture breaking was introduced to investigate the failure modes of the piles. The results show that the stress characteristics and failure modes of the piles under embankment self-weight and train load have significant pile spacing effect. While the ratios of the pile spacing to the pile diameter are 4 and 6 respectively, rupture occurs to the first column and the first and second columns of the plain concrete piles close to the embankment toe. With a constant pile spacing, the maximum bending moment and shearing force of the piles increase with an increase in the upper load. When train loads are applied on the embankment surface, piles bear a larger maximum bending moment and shearing force with a closer distance to the embankment toe. When the pile spacing increases from 3 to 6 times the pile diameter, the maximum bending moment of piles increase from 172.9 to 601.0 kN•m, much larger than the ultimate bending moment value calibrated by test; meanwhile, the maximumshearing force of piles increase from 89.4 to 249.1 kN, much less than the ultimate shearing force value. This indicates that the plain concrete piles of composite foundation under embankment in the centrifugal model are governed by bending failure other than shear failure, tension failure or compression failure. Therefore, the piles closest to the embankment toe fail first; then, failure developing towards the embankment center, piles fail one by one in bending failure mode.

Large Shaking Table Test on Seismic Response of Site with Tilted Interlayer

CAO Licong, ZHOU Yuzhe, MA Donghua, LIU Feicheng, ZHANG Jianjing

2019, 54(5): 953-961. doi: 10.3969/j.issn.0258-2724.20170748

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To investigate the dynamic response of a complex site with a tilted interlayer and provide a potential reinforcement for the site, a large-scale shaking table model test was done to study the acceleration, strain and displacement responses of the site. The effects of the interlayer on the stability of the site are discussed based on an analysis of the Fourier spectrum and response spectrum under the El Centro seismic wave. Furthermore, the critical acceleration and stability factor of the site are obtained through a pseudo-static analysis. Experimental results show that the interlayer obviously weakens the peak acceleration of the seismic wave and that the degree of impairing effects intensifies with the seismic peak acceleration increasing. There is a feature of ‘magnitude saturation’ for the acceleration amplification coefficient (AAC) of the position of bedrock. The peak strain of the interlayer is greater than those of the other layers. When the input earthquake amplitude is larger than 0.33g, there is another peak strain in the cover layer which is located at a platform corner and the strain curve presents a form is ‘W’. The interlayer can also weaken to some extent the amplitude of the Fourier spectrum at about 20 Hz. The predominant periods of theresponse spectra measured from different cross sections of the same soil layer are similar, but obviously different between different soil layers. The predominant period of the interlayer (0.31 s) is greater than those of the bedrock layer (0.19 s) and the cover layer (0.21 s). According to the pseudo-static analysis, when the peak acceleration of the seismic wave loaded is 0.33g, the site stability factor is 3.16, and the critical acceleration of the potential slip area is 1.42g.

Analysis of Flow Characteristics of Asymmetric Cam-Rotor Double Stator Pump

WEN Desheng, LIU Chunxiao, WANG Lei, ZHENG Wei, ZHAO Zhengpeng

2019, 54(5): 962-970. doi: 10.3969/j.issn.0258-2724.20170723

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A new type of asymmetric cam-rotor double-stator vane pump was developed to deal with the shortcomings of traditional hydraulic pumps. Two inner and outer stators and one rotor are arranged in the casing of the vane pump, in which the numbers of protrusions inside and outside the rotor are different, so that the vane pump can output multi-stage constant flow, and simultaneously supply oil to multiple systems. The operation principle and characteristics of the vane pump are explained . Through the analysis on the internal structure of the vane pump, the theoretical flow of the inner and outer pumps of the cam rotor at different rotation angles is deduced, and then the instantaneous flow of the vane pump in different working modes is obtained. A test platform for the asymmetric cam-rotor double-stator vane pump was built. The test results show that the flow pulsation of the asymmetric cam-rotor vane pump is 2% less than that of the conventional symmetric vane pump with double convex cams. The test results are basically consistent with the theoretical analysis, which verifies the correctness of the theoretical analysis.

Layout Optimization of Spatial Rigid Frame by Second-Order Effect Analysis

LI Yinqi, CHENG Wenming, LIU Huasen

2019, 54(5): 971-979. doi: 10.3969/j.issn.0258-2724.20170863

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In order to handle three-dimensional spatial frame layout optimization, nonlinear rigidity matrix of the beam-column element with seven degrees of freedom was deduced by second-order elastic theory, while the geometric nonlinearity and restrained torsional warping were considered. An overall second-order analysis for rigid-frame structure was conducted by integrating the nonlinear rigidity matrices of all beam-column elements. A numerical layout optimization model of spatial rigid frame was built, which was able to satisfy the requirements for structural strength, stiffness and stability. In order to solve the numerical model, a two-way control method of reliable topology and guided genetic algorithm (KLGA) was proposed based on the improvement of the genetic algorithm (GA). In one respect, this method enables the separation of the topological variables from the layout design variables, and then integrates them after evaluating the reliable topological variable combinations based on component importance. In addition, the guidance information of structure was added in the algorithm to guide the path of global optimal solution for GA. Finally, two typical examples of rigid frame structure are presented to validate the feasibility and effectiveness of the second-order effect model and optimization method KLGA. For example, in the second-order effect model of example 2, the optimal structural mass acquired by KLGA is 24.5% less than that of GA, and its range of fluctuation promotes from 9.61% to 1.39%, indicating the stability of KLGA.

Site Selection Method of Booster Substations by Integrating Fuzzy Analytic Hierarchy Process with 3D Geographic Information System

ZHU Qing, CHEN Kaizheng, XIE Xiao, ZENG Haowei, ZHANG Yeting, REN Xiaochun

2019, 54(5): 980-988. doi: 10.3969/j.issn.0258-2724.20170887

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In order to overcome the limitations of the traditional selection method of booster substations on wind farms and realize an efficient and low-cost site selection of booster substations, feasibility analyses of candidate sites selected for booster substations are conducted in 3D geographic information system (GIS) based on fuzzy analytic hierarchy process. First, a hierarchical structure of the site selection of booster substations is defined from five aspects: construction cost, disaster index, location factor, obstacle area and adjacent resources. Then, a new siting evaluation model is established by integrating the fuzzy analytic hierarchy process with 3D GIS to realize the evaluation. The model input parameter are obtained by presetting the geometric primary selection rules, and finally the fuzzy evaluation matrix is solved to realize the automatic location selection of the boost substation. Comparing the experimental results of site selection of booster substations on wind farms built in different terrains shows that the calculation time is within 10 min using digital elevation model with 2 m resolution in the fan area. The optimal site score of plain is 0.957 8, which is better than that of the actual built site (0.941 2); the optimal site score of mountain is 0.743 5, which is also better than that of the actual built site (0.706 8). The results show that the method has high accuracy and universal applicability.

Adaptive Web 3D Visualization Method for Diverse Terminals

ZHANG Yunhao, ZHU Jun, LI Weilian, HU Ya, LIU Mingwei

2019, 54(5): 989-996. doi: 10.3969/j.issn.0258-2724.20180399

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With the rapid development of mobile Internet, terminals of 3D GIS (geographic information system) applications have become more and more diverse. The current web visualization methods can hardly meet the requirements of diverse terminals. To solve this problem, an adaptive visualization architecture based on the B/S (browser/server) model was designed. Then some key technologies were explored, such as the diverse organization of 3D data, adaptive quad-tree organization, construction of dynamic index and adaptive scheduling of 3D scene. Finally, a prototype system was developed on the basis of WebGL. The experimental results show that the rendering frame rate of the laptop computer is eventually stable at more than 40 frame per seconds, that of the smartphone and tablet computer is eventually stable at more than 20 frame per seconds, and web visualization on diverse terminals can be ensured with high visual efficiency and effects, thus demonstrating the effectiveness of the proposed method.

Simulation Analysis and Verification on Three-Dimensional Temperature Field of Strain Clamps for Overhead Lines

DONG Xuanchang, QU Fengrui, LI Yanfei, WANG Yiqing

2019, 54(5): 997-1004. doi: 10.3969/j.issn.0258-2724.20180610

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In order to study the temperature distribution of the strain clamps of overhead lines under different conditions, the finite element model based on the simplified structure of the strain clamp was build, and under the conditions of 600 A power frequency alternating current and different contact resistance ratios, the electromagnetic-thermal coupling finite element simulation analysis of the strain clamp was carried out, and the three-dimensional temperature field distribution of the strain clamp was finally obtained. The simulation results show that under normal conditions, the temperature of the conductive plate of the strain clamp is the lowest. When the contact resistance at different parts of the clamp increases, the increase of contact resistance at the conductive plate has the greatest effect on the overall temperature rise of the clamp, whereas the increase of the contact resistance at the crimp connection of the clamp body has the least effect. Meanwhile the temperature of the clamp will also limit the current carrying capacity of overhead lines. Finally the accuracy of the simulation was verified through the clamp resistance test and temperature rise test, and the error is about 2.3%.

Technology for Virtual Reference Station Service with Gradient Information of Spatially Correlated Errors

ZHANG Xi, CHEN Xianchun, FENG Wei, ZHANG Jingjing, BAO Hai

2019, 54(5): 1005-1011. doi: 10.3969/j.issn.0258-2724.20180140

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Traditional virtual reference station (VRS) service usually needs to change VRS frequently and depends on internet communication heavily in long-distance positioning or positioning throughout the area. In order to overcome these deficiencies, a technology was proposed to realize the differential data broadcast throughout the area. Based on the analysis of spatial error model, a computing model of VRS effective service distance was obtained, and the gradient information of spatially correlated errors was appended to differential data. Considering that conventional real-time kinematic (RTK) equipment is compatible with internet and radio, Internet, symbiotic radio and ultra-high frequency (UHF) radio were also combined to broadcast the data. The experimental results show that the virtual single base-station (VSBS) spacing or the distance of VRS changing can reach 5 km in mid-latitude plain areas while the impact of spatially correlated errors is set as 1 cm² in each coordinate component. A signal terminal with less than 2 W transmit power can broadcast the data to a distance of 27 km, which breaks the limits of data exchange needed in VRS service and several kilometers’ distance coverage of VSBS, and meets the application demands of high precision positioning in a distance of tens of kilometers with no internet access.

Efficient Compression Algorithm for Improving Visual Quality ofWeak Targets in High Precision Images

LI Ying, LI Bo, GAO Xinbo

2019, 54(5): 1012-1020. doi: 10.3969/j.issn.0258-2724.20180180

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In order to effectively compress high precision images, and ensure desirable fidelity of weak target area of the reconstructed image, a high precision image compression algorithm based on error optimization coding is proposed to improve the quality of weak target area. First, the JPEG-LS (joint photographic experts group lossless) compression algorithm is used to compress the image data, and the error coding data is selected in an adaptive way during the run-length encoding process. Then, the non-uniform quantization based on visual quality is also carried out, and the quantized values are decomposed to remove the correlation between them. Finally, the entropy coding of the decomposed data is carried out by MQ arithmetic encoder. In the reconstruction, the inverse quantization value is reconstructed according to the quantized interval, and the inverse quantization optimization and filtering optimization are carried out. The performance of this algorithm is also compared with those of JPEG-LS and JPEG2000 (joint photographic experts group 2000) algorithms. The experimental results show that this algorithm can achieve high-efficiency and high-precision compression of image data. This algorithm is low in complexity and easy for hardware implementation. Although the algorithm incorporates error data optimization and coding process, the amount of data encoded is small, and it is equivalent to the JPEG-LS in compression speed. The compression speed of the JPEG2000 algorithm is about 4.47 times higher. At the same time, it effectively reduces the information loss caused by the conventional algorithms. The peak signal-to-noise ratio of the reconstructed image of the proposed algorithm is equivalent to or slightly lower than that of JPEG-LS and JPEG2000, but it has better visual quality and fidelity of the weak target area.

Seismic Collapse-Resistant Performance of Stone Houses in Tibetan and Qiang Autonomous Prefectures of Western Sichuan

XU Hu, DU Ningning, YU Zhixiang, QIAO Yangkai

2019, 54(5): 1021-1029, 1046. doi: 10.3969/j.issn.0258-2724.20180441

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Traditional stone houses in the Tibetan and Qiang autonomous prefectures of Western Sichuan, deserve preservation as indicators of cultural heritage; however many of them have been damaged during earthquakes in recent years. Based on the characteristics of masonry materials and architectural layout, seismic collapse-resistant performance of stone houses was investigated. Unconfined compression tests on three clay specimens and lateral shear tests on a half-scaled clay-brick rubble masonry wall specimen were conducted and also modeled via an explicit dynamic numerical approach. The Holmquist–Johnson–Cook (HJC) constitutive model was applied to the clay and rubble, and a randomly-distributed discrete finite element model was built to show the proportion between clay and brick rubble. Through the comparison of experimental and numerical results, the numerical model was verified and key parameters were calibrated. According to above work, a structural model of a typical two-storey residential stone house with an L-shaped indented platform was built, and its dynamic time-history analysis was conducted. By comparing the calculated seismic damage modes with its real seismic damage, the collapse mechanism was analyzed and the collapse process was simulated. Moreover, the structural fragility of seismic collapse was studied based on the influence of the indented area of the platform. The results indicate that, under rare seismic intensity, when the indented area is increased from 30% to 45%, the probability of structural collapse increases by 16.7%, and the collapse margin ratio decreases by 9%, which has little effect on the fragility curve. However, when the indented area is reduced to 15%, the failure rate of walls on the second floor increases by 18%, leading to the increase of 143% in the probability of structural collapse.

Prestress Loss Identification Method Based on Influence Matrix in Truss Structure

LIU Yanhui, ZHANG Yangyang, LIU Junxiao, REN Peng, ZHUO Biao

2019, 54(5): 1030-1037. doi: 10.3969/j.issn.0258-2724.20180107

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In order to calculate the real-time prestress loss of prestressed strands according to the observed deformation of prestressed truss structure, a prestress loss identification method based on displacement influence matrix is proposed. By finite element analysis, the relationship between the prestress loss and displacement of the observation point on the truss structure is formulated. Moreover, according to the minimum principle, the prestress loss is obtained. The results show that when the unit prestress loss ranges between 30% and 50%, there is minimum error around 1%–2% in calculating prestress loss with displacement influence matrix; the displacement observation point is most sensitive to prestress loss, when it is located at the 1/4 span and 3/4 span of the truss. Finally, by taking an example of the long-span prestressed truss structure near a high-speed railway station on the Qian-Yu line, the accuracy of the method is verified.

Verification of Theoretical Model and Vibration Effect Caused by Blasting in Shallow Buried Tunnel on Mountain Slope

YAN Jian, HE Chuan, ZHANG Jing, SUN Zheng

2019, 54(5): 1038-1046. doi: 10.3969/j.issn.0258-2724.20170839

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Results on the blasting vibration effect and influence range of a mountain tunnel under a slope terrain and shallow buried soil in rock composite stratum conditions are presented. The objective was to verify and obtain an accurate and applicable theoretical model of vibration velocity based on a case study by taking the De-ge tunnel in the project of No.317 national highway that passes below a densely populated county. The 4 usual theoretical models were verified by on-site blasting vibration monitoring and regression analysis. Simultaneously, the vibration velocity, the influence range of vibration and the blasting vibration effect were analyzed through 3-D numerical simulation and comparison with theoretical calculations and field measurement results. The results show that: the degree of fitting of the 4 usual theoretical models is 0.15−0.86, and the theoretical model formulas by Tang, Zhu, and Zhou can complement each other with respective advantages in terms of different blasting horizontal distance and elevation difference. The influence range of blasting vibration obtained by the theoretical model is closer to field measurements than the numerical results. The " hole effect” located on the surface within 28 m of the completed tunnel is clear and the maximum vertical vibration velocity increased from 1.98 cm/s at the initiation point up to 2.23 cm/s at the surface. The " slope effect” is remarkable in 10−20 m from the middle line on the downslope surface. The vertical velocity decreases linearly with the increase of the detonation distance when it reaches 1.83 cm/s. The " elevation amplification effect” on the adverse slope will occur within 5−10 m on the other side of the center line as the elevation increases. In the above range on the ground surface, the protected buildings should be the key points of field monitoring, and the earthquake precautions should be strengthened.

Temperature Field Law in Cold Region Tunnels and Insulation Effect of Air Curtain

GAO Yan, GENG Jiying, JIA Chao, ZHOU Jun, ZHU Yongquan, HE Benguo, ZHONG Yongqiang

2019, 54(5): 1047-1054. doi: 10.3969/j.issn.0258-2724.20170295

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Only laying thermal insulation layer in the tunnel portal section can not completely solve the frost damage problem in cold regions. Therefore, a new air curtain insulation system for cold region tunnels is proposed, a calculation model for temperature field in cold region tunnels subjected to train wind was employed by approaches including superposition principle, separation variable method, and Bessel characteristic function, the distribution law of temperature field in cold region tunnels with different train running speeds and running intervals was studied, the thermal insulation effect of the new air curtain insulation system in cold region tunnels was verified. Only laying thermal insulation layer in the tunnel portal section cannot satisfy the insulation demand for tunnels in cold regions when the ambient temperature is −30 ℃ and the temperature of surrounding rock is 5 ℃, the active thermal insulation measures should be implemented. If the train running speed is more than 200 km/h and the train operation interval is less than 30 min, the whole tunnels need to prevent cold and heat preservation. Finally, it is proved that 50 m air curtain combined with 1050 m insulation layer can meet the thermal insulation requirement of tunnels in cold regions under extreme conditions.

Influence of Vent Location on Efficiency of Smoke Extraction in Tunnel Fire

LIN Peng, WANG Guoyuan, SI Youliang, WANG Zhongkuan, WU Fanyu, GAO Dongli, MEI Xiujuan

2019, 54(5): 1055-1062, 1112. doi: 10.3969/j.issn.0258-2724.20170945

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Abstract:
To study the influence of smoke vent location on smoke extraction efficiency for semi-transversal smoke control system in long tunnel, a 1∶20 reduced-scale tunnel model was built on the basis of Memorial Tunnel. The model has a dimension of 42.7 m × 0.45 m × 0.23 m, with two gradients of 0% and 3.2%. A series of fire experiments were conducted in the tunnel model with the fire source of pool fire (methanol). Meanwhile, three different scenarios were simulated using Fire Dynamics Simulator (FDS 6.0.1), in which two smoke vents are located on the left side, the right side, or both sides of fire source. By comparing the numerical simulation and experimental results, the following conclusions are made: (1) In the horizontal tunnel (0% gradient), the smoke layer distributes symmetrically for the smoke vents symmetrically located on both sides of fire source. Smoke extraction efficiency in this scenario reaches the maximum, with increases of 10.22%–13.58% and 7.66%–16.84% in contrast to the other two cases with smoke vents on the left and right sides respectively. These two cases show no significant difference in smoke extraction efficiency although the length of smoke layer is prolonged; (2) In the tunnel with a gradient of 3.2%, smoke layer asymmetrically distributes on both sides of fire source and more smoke spreads to the uphill side. Smoke extraction efficiency is the lowest for smoke vents on the left side of fire source (downhill side), it increases by 33.9%–39.6% for vents symmetrically located on both sides of fire source, and reaches the maximum for vents on the right side of fire source (uphill side), increasing by 40.5%–51.6% compared with that with the vents on the left side; (3) The influence of smoke vent location on smoke extraction efficiency in the inclined tunnel is more significant than that in horizontal tunnel and the degree of influence reduces with the increase of smoke extraction volume.

Present Situation and Prospect of Evacuated Tube Transportation System

DENG Zigang, ZHANG Yong, WANG Bo, ZHANG Weihua

2019, 54(5): 1063-1072. doi: 10.3969/j.issn.0258-2724.20180204

[Abstract](646)

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Abstract:
As a new type of transit system, the evacuated tube transportation system, combining magnetic levitation train technology and low-air-pressure tube technology, theoretically decreases friction and aerodynamic drag of high-speed trains as much as possible. In order to promote the evacuated tube transportation development, from the point of view of fundamental principles, the feasibility and the key components of vehicle, tube and propulsion were systematically discussed. Meanwhile, its advantages such as fast, convenience, safety, environmental protection and high efficiency were pointed out. The research status of the evacuated tube transportation system was introduced, including the ET3 (America), the Hyperloop (America), the Swiss Super High-speed Metro Swissmetro, and the evacuated tube high temperature superconducting maglev vehicle test platform of Southwest Jiaotong University. Their technical characteristics and advantages in vehicle, tube, propulsion device and cost were compared and analyzed. The key development and research issues which need to be urgently solved were prospected, such as train/track interaction, high-speed linear propulsion, aerodynamics and heat dissipation, tube sealing, in-pipe communication and rescue.

Origin and Solution of Pre-crash Speed Calculation Error

ZHANG Jian, ZHANG Xin, LI Jiang

2019, 54(5): 1073-1078. doi: 10.3969/j.issn.0258-2724.20170562

[Abstract](546)

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Abstract:
In accident analysis vehicle collision model based on the momentum conservation is solved by the inverse algorithm to calculate pre-crash speed accurately. Then post-crash speed is calculated by a kinematics formula with survey data from accident scene, and is used to calculate the pre-crash speed by the model. In this work, the pre-crash speed error emerges when examining the model calculation results by a car crash test. From the model solving and error propagation processes, the origin and solution of the pre-crash speed error was studied by the car crash test to improve the accuracy of traffic accident analysis. Firstly, the matrix theory was applied to study the origin of the pre-crash speed error. Secondly, the inverse iterative algorithm was applied to establish a solution of the pre-crash speed error. Finally, an example was used to verify the solution. Study results and example applications show that the error in post-crash speed calculation with the kinematics formula is the decisive to the pre-crash speed error. Thus, the pre-crash speed error can be eliminated completely by simply correcting the post-crash speed error.

Parameter Matching and Multi-objective Optimization of Fuel Cell Hybrid System

LI Qi, MENG Xiang, CHEN Weirong, ZHANG Guorui

2019, 54(5): 1079-1086. doi: 10.3969/j.issn.0258-2724.20170117

[Abstract](719)

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Abstract:
With the requirements of tram dynamic performance fulfilled, the weight and volume of the fuel cell hybrid system are optimized by the parameter matching method. Firstly, the vehicle dynamic model is built, and three peak powers are obtained, which corresponds three operational modes of trams including startup acceleration, climbing with uniform speeds and maximum speed operation. Secondly, based on the traditional method, the maximum peak power is set as an objective, and the supercapacitor-battery propotion is analyzed. Then, based on the traditional method, the improved particle swarm optimization (IPSO) is used to calculate the multi-objective optimal parameters in terms of the weight and volume of the system. Finally, the traditional method and multi-objective optimization method are compared and analyzed. The results show that both methods can meet the tram power demand. According to the multi-objective optimization method, the fuel cell hybrid tram is configured with two sets of 150 kW fuel cells, 124 supercapacitors (48 V, 165 F) and 337 power batteries (3.7 V, 9 A•h) . The tram can accelerate up to 70 km/h in 32.24 s, the maximum climbing capacity is 85.5‰, and the continuous climbing ability is 732.5 m. Compared with the traditional method, the optimization rate of its weight and volume reaches to 83.075% and 86.696% respectively.

High-Speed Ballasted Railway Track Lateral Resistance Characteristics and Reinforcements

JING Guoqing, JIA Wenli, FU Hao, LU Wei

2019, 54(5): 1087-1092. doi: 10.3969/j.issn.0258-2724.20170480

[Abstract](497)

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Ballast flight commonly occurs in high speed ballasted railway tracks, and the probability of ballast flight increases with the decrease of shoulder height; thus, reduced shoulder heights or flat shoulders are used in some countries, which result in lateral resistance reduction. The influence of shoulder height on lateral resistance was analysed in this study. Further, two polyurethane reinforcement methods were proposed, including crib-ballast reinforcement and shoulder reinforcement, which increased the lateral resistances of flat shoulder ballasted tracks and met the demands of tamping. A series of in-situ lateral resistance tests were carried out in this research. The results show that compared to a shoulder height of 150 mm, a 30% reduction in lateral resistance occurs in flat shoulders. For polyurethane spraying depths of 200 mm and 300 mm, the corresponding changes observed were 31% and 41% increase in crib-ballast reinforcement, 41% and 60% increase in shoulder reinforcement, and 70% and 100% increase in synthetic reinforcement (both crib-ballast and shoulder).

Urban Road Network Design with Balance between Vulnerability and Reliability

LÜ Biao, LIU Yiliu, LIU Haixu

2019, 54(5): 1093-1103. doi: 10.3969/j.issn.0258-2724.20180812

[Abstract](438)

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Abstract:
Under normal events, travelers have route choice behaviors with risk aversion while under abnormal events, their route choice behaviors have a feature of both risk aversion and regret aversion. For this reason, an urban road network design model is constructed. It is a bilevel programming model with two lower level models in which reliability measure depicts road network performance under normal events, and vulnerability measure represents road network performance under abnormal events. The objective of the upper model is to optimize road network vulnerability measure（i.e., maximize road network accessibility measure）while it is subject to a predefined reliability constraint. The lower model include two stochastic user equilibrium models based on the utility theory and on the regret theory respectively. The results of numerical examples show that, compared with the model simply for vulnerability, the proposed model can acquire higher reliability with reduced accessibility to some extent. If investment budget is 0.9 × 10⁷, the average road network accessibility and road network reliability of the proposed model are 0.138 8 and 0.969 6 respectively, whereas as to the model simply for vulnerability, they are 0.140 5 and 0.334 1 respectively. Totally, the accessibility measure decreases by 1.20% and the reliability measure increases by 190.21%. Besides, the neglect of differences in travel decision behaviors may lead to a sub-optimal even false network design.

Vehicle Routing Problem with Pick-up and Delivery under Dynamic Travel Times

LI Manman, LU Jian, ZHANG He

2019, 54(5): 1104-1112. doi: 10.3969/j.issn.0258-2724.20170488

[Abstract](372)

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A two-stage method of optimization and adjustment was applied to solving vehicle routing problem with pick-up and delivery under dynamic travel times in an actual urban network. In optimization stage, according to the recurrent congestion information, a genetic algorithm was used to solve time-dependent vehicle routing problem with pick-up and delivery and arrange the initial delivery routes of vehicles. In adjustment stage, the link travel time is set as the time horizon and the rolling update was adopted to adjust delivery routes and avoid non-recurrent congestion. A series of mix-integer linear programming models were formulated for routing adjustment problem and a 2-opt algorithm hybrid with insertion algorithm was designed to solve the model. According to the shortest paths between customers derived from Dijkstra algorithm, the delivery routes are converted into the ones in an actual urban network. The numerical experiments show that in the rolling update, the time horizon of the link travel time can save 0.24–11.95 min in vehicle travel time compared with the time horizon of the travel time between customers; it can also save 0.08–8.06 min compared with the time horizon of the 24 min, and can decrease 10.02–34.59 in the number of updates compared with the time horizon of 6 min. Therefore, it is difficult to determine the optimal time horizon in the rolling update with a fixed horizon and thus it has a poor practicality. And the solving speed of 2-opt algorithm hybrid with insertion algorithm is 4 times the genetic algorithm.

Temporal Constraint Scheduling Algorithm for Periodic Data of Ethernet-Based Train Communication Network

JIAN Jie, WANG Lide, NIE Xiaobo, SHEN Ping

2019, 54(5): 1113-1120. doi: 10.3969/j.issn.0258-2724.20180006

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Instead of time intervals as the only constraint in message scheduling for industrial Ethernet, a temporal constraint scheduling table generation method for periodic packet data of Ethernet-based train communication network (TCN) is proposed. Firstly, network and message model are modified by time-triggered mechanism. Secondly, a directed graph quantization model for periodic data was proposed according to temporal parameters both from communication equipments and transmitting packets. Finally, a scheduling table generation algorithm based on satisfiability modulo theory was designed. A scenario of unicast and multicast services was scheduled to verify effectiveness of the algorithm. The scheduling performance test and analysis were performed under the actual Ethernet TCN topology. Experimental results show that the proposed scheduling algorithm performs some scheduling tasks that traditional algorithms cannot do, provides a more detailed solution to scheduling requirements for periodic data, and improve scheduling flexibility. In the performance test, the maximum link load exceeds 80%, and its configurable process data traffic reaches 1 000 items.

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2019 Vol. 54, No. 5