西南交通大学学报

2019, 54(6): 1-2.

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Evolutionary Game Model of Traffic Violations among Taxi Drivers

JIANG Xinguo, ZHOU Yue, XIA Liang, FU Chuanyun

2019, 54(6): 1121-1128. doi: 10.3969/j.issn.0258-2724.20180531

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In order to investigate the mechanism of violation costs on taxi drivers’ traffic violation behavior, the composition and cumulation of traffic violation costs over time are explored with a demerit point system. To be specific, the taxi driver’s license status were classified into two categories by setting warning score, i.e., ordinary driver and critical driver. An evolutionary game model was introduced to analyze the strategies adopted by taxi drivers and traffic policemen. Simulations were conducted to reveal the evolutionary outcomes of violation strategies under different enforcement and license management conditions. The results show that the violation costs, which impact the strategy equilibrium, is predominately determined by the level of law enforcement and deducted penalty points; for the numerical example, the administrative costsfor critical drivers are lower than those of the ordinary ones, revealing that police could use about 30% lower enforcement possibility to obtain the similar effectiveness; the violation probability of critical drivers is far lower as opposed to that of the ordinary drivers under the same enforcement; If there is equal number of drivers who daily reset their licenses, they would have 10% penalties than that of the driver whose licenses never reset in one cycle (1 a). Moreover, the penalty difference become much remarkable with time. The results demonstrate that turning the taxi driver’s license qualification from ordinary into critical state through adjustable enforcement strategy will help to constrain the traffic violations and reduce the enforcement costs.

Field Tests on Lateral Operational Characteristics of Passenger Cars on Helical Ramps (Bridges)

XU Jin, LI Jianxing, LIN Wei, CUI Qiang, WU Guoxiong, YANG Kui

2019, 54(6): 1129-1138. doi: 10.3969/j.issn.0258-2724.20170824

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Helical ramps and helical bridges are widely used in recent years, however the driving patterns and dynamic characteristics of vehicles running on them are still unclear. Therefore, to obtain the driving pattern of passenger cars on helical ramps (bridge), driving tests using real cars were carried out on Fuling Yangtze River Bridge, Second Fuling Wujiang River Bridge, Rongqiao Helical Bridge and Jinkai Helical Bridge in Chongqing. Trajectory and lateral acceleration speed of cars under drivers’ naturalistic driving were continuously collected, as well as environment information. Based on naturalistic driving data, the variation, amplitude and influencing factors of speed and lateral acceleration were obtained, together with lane usage pattern. It was found that diversified lateral acceleration patterns on helical ramps were observed, such as stabilized, increasing, deceasing, and drum-typed. Larger lateral acceleration were recorded on ramps along the inner ring than on ramps along the outer ring. Lateral acceleration measured on some one-way ramps are significantly higher than the recommended valve in highway design guidelines and even exceeding the unbearable threshold, which cause passengers discomfort in side direction. Ramp radius and driving space greatly affect lateral acceleration, lateral acceleration drops as ramp radius increases if driving space holds constant, and the smallest lateral acceleration was measured on mixed two-way helical ramp. For one-way helical ramps with two lanes, regardless of on upward ramp or downward ramp, driving on inside lane accounted for a major proportion of driving patterns.

Light-Duty Vehicles Driving Cycle Construction Based on Urban Roads

ZHANG Hong, YAO Yangang, YANG Xiaoqin

2019, 54(6): 1139-1146, 1154. doi: 10.3969/j.issn.0258-2724.20180224

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In order to regulate vehicle energy consumption, calibrate vehicle emission and optimize vehicle performance, the driving cycles of light-duty vehicles on the urban roads of Hohhot is analyzed. Firstly, the 74 sample data of driving cycles were collected through special data acquisition equipments of CATC (China automotive test cycle). These samples cover tall types of roads, light-duty vehicles and drivers. Secondly, weights were assigned to different vehicles to set vehicle type proportion. The sample data are processed by principal component analysis and clustering analysis and the short segment rules are formulated. Finally the kinematic segments are clipped and their characteristics values are classified. Thus, the operating conditions of light-duty vehicles on urban roads are constructed. The results show that the average speed of CATC is 25.87 km/h, average running speed is 33.92 km/h, uniform speed ratio is 20.59%, idling ratio is 23.72%, acceleration ratio is 28.56% and deceleration ratio is 27.13%. Compared to the European Union (EU) cycle test condition, the average speed, average running speed and uniform speed ratio are lower than those of the EU standard, while the acceleration ratio, deceleration ratio and idling ratio are higher.

Nonlinear Fractal Characteristics of Air Traffic Flow

WANG Fei

2019, 54(6): 1147-1154. doi: 10.3969/j.issn.0258-2724.20180328

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To provide scientific evidence for traffic flow modeling and prediction, the nonlinear characteristics of air traffic flow were studied based on fractal. First, 4 time series were constructed, and their nonlinearities were tested by the surrogate data method, and the 5-minute-scale time series was determined as the subsequent research object. Then, the wavelet decomposition method was used to study the self-similarity of time series. The global and local Hurst exponents were calculated by R/S method to study the long-range correlation characteristics. Next, scale-free ranges of time series were calculated using second-order difference of correlation integral. Then, the multi-fractal characteristics of time series were studied by multi-fractal spectrum method. Finally, the correlation dimensions of time series were calculated by Grassbeger-Procaccia method. The results show that the probability of the nonlinearity of 5-min-scale time series is 99.2%, and the nonlinearities of the other 3 time series are not clear. It is qualitatively observed that the time series has strong self-similarity. The global Hurst exponent is 0.756 5, and the local Hurst exponents are all more than 0.5, which indicate that the time series has a long-range correlation. The second-order difference of the correlation integral can effectively identify scale-free ranges, which shows that the time series has scale-free property and the scale-free ranges are different corresponding to different embedding dimensions. The bell-shaped multi-fractal spectrum shows the time series has multi-fractal characteristics. The correlation dimension is 6.89, indicating that at least 7 variables are needed to clearly describe the corresponding air traffic flow.

Effect of Transverse Deflection on Force State of Prestressed Concrete Trough Girders with Asymmetric Cross-Section

ZHU Liming, TANG Jun, XING Shiling

2019, 54(6): 1155-1161. doi: 10.3969/j.issn.0258-2724.20170683

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This work aims to study the influence of transverse deflection of a beam body on pushing construction of an prestressed concrete (PC) open thin-walled beam with asymmetric cross-section and provide a reasonable deviation correction threshold for the incremental launching technique. Taking as a prototype the world’s first case of an asymmetrical cross-section trough girder—Tianjin Second Avenue Cross-Jinshan Railway Interchange Project, an actual bridge model was built using the finite element software ANSYS to study the stress state of the trough girder under the most unfavourable conditions. On this basis, using the maximum deviation distance that meets safety requirements for girder placement as the deviation limit, the influence of different transverse deflection modes on the force of the beam body was analysed. Results show that the cross-section force of the trough girder is not balanced when the deflection does not occur; however, the force imbalance is aggravated by translation to the right. When the most unfavourable transverse deflection occurs in the beam with a displacement of 96 mm, the internal force change of the trough girder is small. Therefore, it is suggested that the transverse deviation correction threshold could be relaxed to 96 mm in jacking construction.

Design of Half-Through Cable-Arch Bridge with 700 m Main Span

XIE Xiaoli, FU Yuanjie, DENG Nianchun

2019, 54(6): 1162-1168, 1176. doi: 10.3969/j.issn.0258-2724.20170565

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As the span of arch bridges increases, the stability problem of the arch rib is becoming severe and the huge horizontal thrust needs to be balanced with tie rods or foundation; meanwhile, large anchors of a long-span suspension bridge costs a lot. Aiming at the two problems above, a new type of bridge structure, half-through cable-arch bridge, was proposed based on mechanical properties of arches and cables. The specific structure and force mechanism of this new type bridge are elaborated. First, arch rings are added to both the main span and side span of a suspension bridge. Then, its anchors are removed and main cables are anchored to the side arch feet. Finally, by choosing appropriate parameters such as sag-to-span ratio, rise-to-span ratio and arch-axis coefficient, the tension of main cable, the thrust of main arch and the thrust of side arch can be basically equal in value under dead load, so that the structure is in a state of no thrust and thus structural mechanical properties can be improved. Taking a half-through cable-arch bridge with a 700 m main span as an example, the design of its structural layout and components are described in details and a sequence of construction steps is suggested. Finite element analysis shows that the arch and cable of half-through cable-arch bridge share the load of bridge deck; compared with the continuous arch bridge under the same conditions, the half-through cable-arch bridge can increase the strength bearing by nearly 25% and increase the stable bearing capacity nearly by 70%. In addition, the horizontal force generated by the structure is nearly zero under dead load, which lays a solid foundation for breaking through the span limit of arch bridges.

Overloaded Truck Models and Their Load Effects on Multiple-One Lane for Highway Bridges

LIU Lang, CHEN Dongjun, REN Qingyang

2019, 54(6): 1169-1176. doi: 10.3969/j.issn.0258-2724.20170468

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To analyze characteristics of typical parameters of overloaded trucks as well as their models, weight-in-motion (WIM) data was collected over three years from California, U.S., and the permit truck issued by California Department of Transportation (Caltrans) was selected as a reference to extract overloaded truck data, then, the characteristics and configurations of these overloaded trucks were analyzed to build typical overloaded truck models with mean and standard deviation calculated. In addition, load effects induced by trucks moving on multiple lanes and single lane were calculated respectively, and the two load effects were compared with the specifications issued by the Ministry of Transport of China (JTG D60−2015) and American Association of State Highway and Transportation Officials (AASHTO) respectively. The results show, superposed load effects on multiple lanes were significantly greater than those loading on one lane and the codified values in specifications, whereas, the load effects on one lane are close to or a little higher than the specified values. For effect ratios of multiple lanes to one lane, the largest one is 2.05 for both moment and shear, and the average value is 1.65 and 1.70 for the two, respectively.

Smoke Exhaust Technology of Different Opening State of Smoke Vent in Mawan Tunnel

ZENG Yanhua, LI Jie, ZHANG Xianfu, HAN Tong, DING Maorui, ZHANG Song

2019, 54(6): 1177-1186. doi: 10.3969/j.issn.0258-2724.20170452

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In order to study the effect of the tunnel smoke exhaust mode and the opening state of the smoke Vent on the smoke exhaust efficiency during the fire, the smoke exhaust characteristics and smoke exhaust efficiency of the Mawan underwater shield tunnel were analyzed. Firstly, through the theoretical analysis and fire dynamics simulator FDS, the critical wind speed of the longitudinal ventilation and smoke exhaust mode and the optimal smoke exhausting amount of the key ventilation and smoke exhaust mode are calculated. Secondly, a variety of working conditions are set based on different opening state of the smoke Vent. And the smoke height, spread length, visibility at the height of the human eye, CO volume concentration, wind speed at the exhaust port and smoke exhaust efficiency were studied. The results show that: (1) the critical wind speed of the Mawan Underwater Shield Tunnel is 4.5 m/s. When the key smoke evacuation method is adopted, the optimal air volume of smoke exhaust for opening the upstream and downstream exhaust vents is 290 m³/s, and the value for opening the downstream exhaust vents is 410 m³/s. (2) When the upstream and downstream exhaust vents are opened, timely opening the exhaust vents directly above the fire source can ensure that the visibility of the human eye is higher than 10 m, and the CO concentration exceeds the human tolerance limit only in the range of 200 m upstream and downstream of the fire source, and the maximum value is only 450 ppm. The smoke height rises within the range of nearly 100 m in the upstream direction of the fire source, the smoke spread distance is shortened. (3) When the upstream and downstream exhaust vents are opened, and the exhaust vents at the top of the fire point are opened in time, the overall exhaust efficiency is higher than when the exhaust vents at the top of the fire point are not opened. When only the downstream exhaust vents are opened, the opposite is true. (4) In combination with the personnel escape index, when a fire occurs, the key smoke evacuation method should be adopted, the upstream and downstream exhaust vents should be opened, and the nearest exhaust vent of the fire point should be opened in time.

Study on Design Model of Quasi-Rectangular Shield Tunnel Linings

YE Yuhang, LIU Xian, LIU Zhen, ZHANG Weixi, YANG Zhihao, ZHU Yaohong

2019, 54(6): 1187-1195. doi: 10.3969/j.issn.0258-2724.20170553

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In order to obtain a design model for quasi-rectangular shield tunnel linings, a full-scale ring test was conducted to acquire the deformation and internal forces of the linings with loads simulated according to the actual ones in normal operation conditions. The test results were then analyzed in comparison with the numerical results based on the equivalent stiffness model and the beam-spring model, to determine parameters of the design model of quasi-rectangular tunnel linings. Results show that using the equivalent stiffness model to design of the quasi-rectangular shield tunnel linings, the segment stiffness reduction factor that can account for the deformation along both the long and short axes could not be obtained. While applying the beam-spring model, the computed structural responses and the influence of longitudinal joints on moment distribution both agree well with the experimental results. Therefore, it is more reasonable to use the beam-spring model as the design model of quasi-rectangular shield tunnel linings. For the quasi-rectangular shield tunnel linings under study, input parameters for the design model, including the shearing rigidity, negative-moment bending rigidity, and positive-moment bending rigidity of segment joints, are recommended as 341 × 10⁶ − 368 × 10⁶ N/m, 114 × 10⁶ − 491 × 10⁶ N•m/rad, and 85 × 10⁶ − 177 × 10⁶ N•m/rad, respectively

Temperature Field Characteristics of High-Speed Railway Subgrade Surface with Asphalt Concrete Layer in Cold Regions

CHEN Xianhua, MA Lili, YANG Guotao, CAI Degou

2019, 54(6): 1196-1202. doi: 10.3969/j.issn.0258-2724.20170490

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In order to gain better insight on the temperature field characteristics of the subgrade surface with asphalt concrete layer in cold regions, the transient thermal finite element analysis is adopted to study the temperature field spatial-temporal distribution of ballastless tracks in cold regions and the influence of asphalt concrete layer. Firstly, numerical models based on the CRTS system (ballastless track) of Haerbin-Qiqihaer passenger line were developed. The numerical model was then verified with the field test results. Finally, the temperature field characteristics of the subgrade surface with asphalt concrete layer and the time-varying law of the temperature characteristics for typical cross sections and typical points in the ballastless tracks are evaluated through comparison.. The results show that the temperature field of track slab system in cold regions have a non-uniform distribution and show a double U-shaped distribution horizontally. The temperature gradient is non-linear, and the averaged monthly temperature gradient alternate between positive and negative. The subgrade depth, of which the temperature is affected by the ballastless track structure in northeastern China, can reach 0.4 m in a day, 2.5 m in a month and about 4.0 m in a year. It is concluded that the thin asphalt concrete layer over the subgrade surface has the function of heat preservation and prompts 1−7 ℃ increase in the daily average temperature of subgrade surface whereas it makes no significant change to the temperature field distribution of the ballastless track subgrade in cold regions.

Band Gap Characteristics of Vibration Isolators of Phononic Crystals under Floating Slab

NONG Xingzhong, LI Xiang, LIU Tanghui, SHENG Xi, WANG Ping, ZHAO Caiyou

2019, 54(6): 1203-1209, 1276. doi: 10.3969/j.issn.0258-2724.20180849

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In order to improve the vibration damping effect of the floating slab track and hinder the propagation of the vertical vibration energy of the floating slab to the rail base, a vibration isolator for the floating slab track based on the local resonance mechanism of phononic crystals is developed. The band gap characteristics of phononic crystals with local resonance for the isolator are studied by the finite element method, and its vibration damping effect in the band gap frequency range is verified. The vertical stiffness of the isolator is calculated, and the finite element model of the three-dimensional floating slab track with these isolators is established. The force transmissibility and the base acceleration response of the whole structure are calculated, and then compared with the results of the traditional steel spring floating slab. The results of this work show that the isolators have a band gap of phononic crystals with local resonance, which suppresses the vibration in the frequency band of 50−150 Hz. The vertical static stiffness of the isolators are similar to that of the traditional steel springs, i.e., 6.0 kN/mm. It retains the vibration isolation performance of the steel spring floating slab track in low natural frequency, and has band gap suppression characteristics in the frequency band of 50−120 Hz. The force transmissibility is reduced by about 10 dB at around 51 Hz. The base acceleration response in the 51−150 Hz is significantly smaller than that of the normal steel spring floating slab track, and the base acceleration response in the 51−60 Hz is reduced by about 30% compared to the steel spring floating slab track. Therefore, the developed isolator is able to improve the vibration damping performance of the floating slab track.

Influence of Train Load on Mechanical Property of Prefabricated Slab Track

REN Juanjuan, DENG Shijie, YAN Yafei, DU Wei, NI Yuefeng

2019, 54(6): 1210-1218. doi: 10.3969/j.issn.0258-2724.20170642

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To study the influence of passenger and freight trains on the mechanical deterioration of concrete for slab track, the indoor cyclic loading test was conducted and described by using the damage variables based on damage mechanics. First, the FE model consisting of the rail, fastening, slab, CA mortar, roadbed, and subgrade was established. In this model, the reasonable load combination was determined contemplating the equivalent stress levels for the test specimens, as well as the loading frequencies for passing trains. Next, a cyclic loading test for concrete specimens was performed using a MTS loading system. Besides, the dynamic elastic module and the flexural strength for concretes at various loading cycles were calculated with the help of nondestructive testing system. Finally, taking the dynamic elastic modulus and the flexural strength as damage variables, the influences of different stress levels and loading frequencies on the deterioration of mechanical properties for the track slab were obtained. The results reveal that: under passenger or freight train load, the damage of dynamic modulus is about twice that of flexural strength at 2 million loading cycles. Keeping the stress level constant, the damage of dynamic modulus and flexural strength for concrete are greater with the lower loading frequency, especially between 10 Hz and 15 Hz. At a constant loading frequency, the damage of dynamic elastic modulus and flexural strength of concrete accelerates as the stress level increases. Concrete with a stress level of 0.7 is broken after about 1 000 loading cycles. Trains running at a lower speed would fasten the damage accumulation at the beginning of the deterioration process, while trains running at a higher speed would aggravate the consequential damage development.

Theoretical Calculation of Crack Performance in Continuous Track Slab in Severe Cold Area

WEI Youxin, YANG Bin, ZHAO Yanxi, CAI Xiaopei, HUANG Cheng

2019, 54(6): 1219-1226. doi: 10.3969/j.issn.0258-2724.20180557

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In order to study the crack performance and its influencing factors in the continuous track slab in severe cold area, previous assumptions and mechanical models for the calculation of cracks in continuous track slab were modified according to their actual working states in severe cold area. Based on theoretical derivation and experimental verification, a methodology for calculating the crack performance in continuous track slab in different working conditions was proposed; the cracking law of the continuous track slab and the development trend of cracks with temperature drop were summarized. Results show that the crack performance in continuous track slab is closely related to the temperature drop amplitude and the spacing between adjacent cracks. The continuous track slab undergoes a primary cracking phase in a concentrated manner at a temperature drop of about 5 ℃. As the temperature drops further, the fixed zone length of the track slab will decrease to 0, and a secondary cracking phase occurs to the track slab in a single and sporadic manner; what’s more, the smaller the spacing between adjacent cracks is, the larger the temperature drop magnitude to initiate the secondary cracking of the track slab is. Tests show that when the spacing between adjacent cracks is smaller than 3.25 m, the track slab will not cause the secondary cracking at a temperature drop less than 37 ℃. The generation of a single crack only affects the mechanical properties of the track structure in the range of its left and right sliding zones, and if the sliding areas of the new and old cracks partially overlap, the new crack will cause a sudden decrease in the reinforcement stress and crack width amplitude of the adjacent existing cracks.

Optimization Design for Internal Structure of Embedded Rail Trough

BI Lanxiao, LIU Weixing, XING Mengting, ZHAO Pingrui, LIU Xueyi

2019, 54(6): 1227-1234. doi: 10.3969/j.issn.0258-2724.20170734

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Embedded ballastless tracks are stable, low maintenance, and good at shock absorption and noise reduction, such that it accommodates the requirements of urban rail transit operation, and has been widely used in the construction of modern tram lines. Owning to the structural characteristics of embedded tracks, its optimization focuses on the trough structure and the polymer composite covering the rail. In this work, the static and dynamic behaviors of embedded ballastless tracks are analyzed by using the finite element software ANSYS. On the basis of topology optimization, given the requirements of cost, safety, noise, and vibration on the urban rail transit, the structure of embedded rail trough is optimized. The results indicate that less composite material at the junction of embedded rail waist and bottom saves the cost while guaranteeing track stiffness. Instead of being lowered in height, polymer composite material should cover the rail completely to decrease the noise and vibration. The width of the bearing slot should range between 200 and 220 mm at normal parts. Increasing the width of the bearing slot is the most effective measure to reduce the vibration in the areas subject to strict vibration requirement. The elastic modulus of the composite material should be chosen to ensure the track transverse stiffness and reduce the stress level of concrete track slab.

Mechanical Properties and Water Holding Characteristics of Initially Isotropic Soils and Transversely Isotropic Soils

GUO Nan, CHEN Zhenghan, YANG Xiaohui, GUO Jianfeng, SUN Shuguo

2019, 54(6): 1235-1243. doi: 10.3969/j.issn.0258-2724.20180065

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In order to investigate the difference between the mechanical properties and water quantity variation of unsaturated loess under different initial conditions, a method for preparing isotropic and transversely isotropic specimens was suggested. An improved triaxial apparatus for unsaturated soils was used to carry out 72 consolidated drained triaxial tests on prepared isotropic, transversely isotropic and regular specimens. Isotropic samples with different cutting angles were studied experimentally and found to be approximately isotropic. For three different initial states, the failure stress of the isotropic unsaturated specimen is the largest, followed by that of the transversely isotropic unsaturated specimen; the initial tangent modulus of the transversely isotropic specimen is the largest at the shear stage, while those of the other two groups are smaller and approximately equal. Both the isotropic and transversely isotropic specimens have slight dilatancy at the initial stage of shear, while all ordinary remoulded specimens are in the state of shear contraction. Under different initial conditions, the change of the suction of unsaturated samples has little effect on the drainage, the absolute slope value of the deviator stress-water content curve of the transversely isotropic sample is the lowest, and those of the other two groups are almost the same. The mechanical properties and water holding characteristics of the isotropic, transversely isotropic and ordinary remoulded specimens are different. The research results obtained may provide a useful reference for the establishment of different models of soil under different initial conditions and for various engineering applications.

Semi-analytical Analysis of One-Dimensional Nonlinear Consolidation of Multi-layered Structured Soft Clay

XIA Changqing, HU Anfeng, FU Peng, CUI Jun, XIE Kanghe, ZHOU Yushan

2019, 54(6): 1244-1251. doi: 10.3969/j.issn.0258-2724.20170612

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To study the impact of structural properties on the consolidation behavior of multi-layered soft clay under time-dependent loading, the problem of nonlinear consolidation of structured soft clay was addressed by analyzing the nonlinear variable permeability and compressibility of structured soft clay and the variation of the yield stress with depth. First, the consolidation process in different drainage situations was analyzed in detail using the structured soft clay trilinear compression model and e-lg k_v permeability model. Then, one-dimensional consolidation equations were established by semi-analytical method. A calculation procedure was developed to solve the problem, and the effectiveness of the proposed method was verified by comparison with the existing nonlinear consolidation results. Finally, in the engineering background of a four-layer soft clay ground, influences of time-dependent loading and structural properties on the consolidation behavior of multi-layered soft clay were investigated. The results show that when the ultimate load is fixed while loading rates are varying, the degree of consolidation defined in terms of effective stress (U_p) is larger than that defined in terms of settlement (U_s) at the early stage, but the opposite will occur at the late stage. On the other hand, when the loading rate is fixed but the ultimate loads are different, with the ultimate load increasing, the values of U_s and U_p decrease at the early stage but increse at the late stage. At the early stage of cosolidation, the U_p obtained by the nonlinear consolidation analysis considering structural properties is significantly larger than that without considering structural properties, but the discrepancy decreases gradually as the consolidation proceeds.

Corrosion Prediction of Coated Steel in Magnesium Cement Concrete Based on Wiener Degradation

QIAO Hongxia, WANG Penghui, LI Yuanke, GUO Xiangke, GONG Wei

2019, 54(6): 1252-1257. doi: 10.3969/j.issn.0258-2724.20170388

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The corrosion of magnesium cement concrete on steel bars limits its widespread application. To solve this problem, coating is proposed to alleviate the corrosion of steel bars and ensure that magnesium cement-reinforced concrete buildings meet the design requirements over their service life. Based on the natural environment of the Western saline soil area, a rapid corrosion test of magnesium oxychloride-coated reinforced concrete was performed using the solution immersion accelerated corrosion test method. Electrochemical tests of magnesium oxychloride-coated reinforced concrete were periodically conducted using an electrochemical workstation. The electrochemical parameter of corrosion current density, which characterises the corrosion of a coated steel bar, was used as the degradation index; then, a reliability model was built on the basis of the Wiener degradation process, and the corrosion of a coated steel bar was predicted. The results show that the corrosion reliability function of a steel bar coated with magnesium cement-reinforced concrete can be obtained by using the corrosion current density as a durability degradation index, and the coated steel bar reaches moderate corrosion at approximately 30 000 d.

Seismic Performance of Multi-storey Masonry Wall Repaired by Carbon Fiber Reinforced Polymer Grids

TAO Yi, GU Jinben, XIN Ren, YAO Jitao

2019, 54(6): 1258-1267. doi: 10.3969/j.issn.0258-2724.20170491

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To study the failure mechanism and repair effect of plain masonry structure repaired by carbon fiber reinforced polymer (CFRP) grids, firstly, a three-storey masonry wall with openings was destroyed under the pseudo-static action, then, the areas where the cracks intensively occurred in destroyed masonry wall were repaired by CFRP grids, at last, the pseudo-static action was retested. The seismic performances of the masonry wall prior to and after repair were compared according to the lower limit of repair requirements, and the repairing suggestions were proposed. The results show that CFRP grids can effectively retard or prevent the occurrence of masonry shear diagonal cracks, and then the seismic resistance of masonry walls is developed. The lower limit of repair area is 22% when the shear bearing capacity fully restored is the indicator. The failure modes of the walls after repaired are related to the repair positions, the CFRP grids debonding and piers failure are the majority failure modes of the test. The failures initiate layer by layer from low to high, and develop from the unrepaired to the repaired zones on the same floor. The piers failure is most likely to cause the structure failure or even collapse, therefore, CFRP grids need to be preferentially applied to the piers where the shear stress is relative large, the additional strengthening measures are also essential.

Micromechanical Analysis of Steel Fiber Corrosion in Ultra-high Performance Concrete

SHU Gang, ZHANG Qinghua, HUANG Yun, BU Yizhi

2019, 54(6): 1268-1276. doi: 10.3969/j.issn.0258-2724.20170453

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In order to study the influence of the volume content and corrosion degree of the steel fiber on the strength and deformation of the structure, the large-volume randomization of the steel fiber in ultra-high performance concrete (UHPC) matrix was realized by the ABAQUS software redeveloped by self-compiling Python script file. Based on this, the UHPC defect corrosion simulation method was developed and the equivalent method of the steel fiber corrosion was explored. Finally, the UHPC beam four-point bending test was taked as an example to verify the UHPC micromechanics analysis method, corrosion simulation method, and equivalent means. The results show that when the fiber volume content is 2%, the UHPC beam has the best bending resistance; corrosion weakens the cross-section of fibers, stress concentration near the corrosion pits and the destroyed interfacial bonding are the key factors affecting the corrosion effect. The random material property distribution method is limited to simulate the macroscopic deformation of UHPC beams, and can’t accurately simulate the distribution of stress field.

Load Characteristics of Anti-rolling Torsion Bar of High-Speed Train

WANG Wengjing, ZHANG Zhipeng, LI Guangquan, SONG Chunyuan

2019, 54(6): 1277-1282, 1348. doi: 10.3969/j.issn.0258-2724.20180060

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In order to obtain the load characteristics of the anti-rolling torsion bar during the high-speed train operation, first, the change rules of the load with the train speed, curve radius, and curve superelevation were studied by combining the gyroscope and the speed signal. Second, the maximum loads of the anti-rolling torsion bar at different speed levels were obtained, and the load spectrum, trend load spectrum, and dynamic load spectrum were compiled to calculate the damage ratio of the trend load to dynamic load in the whole test load. The results show that the dynamic load amplitude of the anti-rolling torsion bar increases with the increasing of the train running speed under straight running condition. When the speed increases from 250 km/h to 350 km/h, the maximum load amplitude increases by 30%. At a given surplus superelevation condition, the maximum trend load amplitude of the anti-roll torsion bar decreases with the decreasing of the curve radius, which is from 6.61 kN to 3.54 kN at the operation speed of 240 km/h. For the same curve radius, the trend load amplitude increases with the increasing of the curve superelevation and the maximum load amplitude increases from 3.36 kN to 5.80 kN at the operation speed of 240 km/h.

Wear Predication of Tunnel Boring Machine Cutters Based on In-situ Measured Data

YANG Jihua, YAN Changbin

2019, 54(6): 1283-1292. doi: 10.3969/j.issn.0258-2724.20170677

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Abstract:
To reasonably predict the influence of geological conditions, tunneling parameters, and cutter ring characteristics on the wear of disc cutter rings during tunnel boring machine (TBM) construction, the rock breaking mechanism and cutter ring wear mechanism were studied. The concept of comprehensive wear coefficient was put forward according to tribology theory by considering the in-situ measured data such as tunneling thrust, penetration, wear rate, disc cutter radius, disc cutter installation radius, and disc cutter ring sizes. The wear prediction model of disc cutter ring was finally established with consideration of the interaction of various factors, such wear prediction model of disc cutter ring can predict the effective tunneling length of every disc cutters. The wear prediction model was applied in the hard rock tunneling of water conveyance tunnel by double shield TBM in Lanzhou water source construction project, and its validity was also verified by comparing with other prediction models. The results show that the comprehensive wear coefficient decrease with the installation radius of disc cutters increasing and increases with the disc cutter installation angle increasing. The comprehensive wear coefficient has the similar rule as that of other comparing models. The predicted effective tunneling length is consistent with the actual tunneling length with error of less than 10%, which illustrates that the disc cutter wear prediction model based on comprehensive wear coefficient is reliable.

Design and Experiment of Comprehensive Alternating Pressure Testing Machine

GAN Rong, HAO Luoliang, WANG Shuai, ZHANG Jianshuang, LIU Sha

2019, 54(6): 1293-1297. doi: 10.3969/j.issn.0258-2724.20190264

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Abstract:
At present, the piston reciprocating alternating testing machine can not be used in the alternating tests for gas medium pressure instruments, vacuum instruments, positive and negative pressure gauges and differential pressure instruments under a static pressure environment. A comprehensive alternating pressure testing machine was designed to operate under this environment. Firstly, according to the upper and lower limits of the alternating test requirements for general pressure gauges, precision pressure gauges and digital pressure gauges, frequency and times parameters are analyzed. Secondly, the sinusoidal pressure pulse generator is selected, the sinusoidal frequency is collected by a counter, and the inlet solenoid valve is controlled to automatically stop testing within the preset alternating times. The experimental results of the designed prototype show that the upper limit, lower limit and frequency range of the pressure sine wave produced by the controllable inlet and outlet solenoid valves fall in the range of the evaluation program, and the control error between upper and lower limited data is limited as 0.3%.The alternating frequency error by the controllable inlet and outlet flow valves shall be no more than ± 5 times/min, which meets the requirement of the evaluation program. The number recorded by the counter is consistent with the number of actual tests.

Overriding Behavior in Train Collisions Based on Moving Vehicle-Track Coupled Model

YANG Chao, LI Qiang, WANG Xi, WANG Mingmeng

2019, 54(6): 1298-1304. doi: 10.3969/j.issn.0258-2724.20170948

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Abstract:
In order to reveal how vehicle parameters affect the overriding behavior in train collisions, the vehicle model and the moving track model were developed in view of the basic ideas of vehicle-track interaction. The nonlinear wheel-rail contact model was applied in coupling both models. A nonlinear coupler model was used to connect two adjacent vehicle models. Then the head-on collision of two identical trains was simulated at low speeds. The dynamic responses of vehicles and tracks were obtained with different parameters. Finally, the wheel lift was taken as the vehicle-collision overriding index. The sensitivity and the relative sensitivity were analyzed in terms of wheel lift to impact speed, to height of car body mass center and to vertical stiffness of secondary suspensions. The results indicate that when other conditions remain unchanged, the wheel lift rapidly increases to 36.5 mm if the impact speed increases to 27 km/h. The wheel lift increases by 41% when the height of mass center increases by 20%. However, it decreases by 16.6% if the vertical stiffness of secondary suspension increases by 20%. In other words, the wheel lift increases with the impact speed and height of mass center, and decreases with the vertical stiffness. The sensitivity of wheel lift to impact speed is nonlinear. The relative sensitivities of wheel lift to height of mass center and vertical stiffness are 205% and −83%, respectively.

Structural Dynamic Characteristics of Force-Measurement System for Impulse Wind Tunnel

LÜ Jinzhou, ZHANG Xiaoqing, ZHAO Xiaonan, CHEN Guangxiong, WU Yingchuan

2019, 54(6): 1305-1313. doi: 10.3969/j.issn.0258-2724.20170737

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Abstract:
During testing in impulse wind tunnel, vibrations of the force-measurement system (FMS) caused by airflow will greatly tamper measurement results. To solve this issue, firstly the dynamic model of the FMS was constructed according to its structural characteristics. Then, the virtual calibration and modal analysis were carried out. Thirdly, the transient analysis and inertia compensation were processed to obtain the response of the FMS. Finally, the force measurement tests was conducted in the impulse wind tunnel, and both the elastic and inertia outputs were obtained in tests. Results show that after inertia compensation, the mean measurement accuracy were improved, and the transient measurement accuracy were improved significantly. When there was resonance, the lowest transient measurement accuracy was 87.4% after inertia compensation. In the other cases, the transient measurement accuracy exceeded 91%. Vibrations on the output curves of the FMS were virtually smoothed after inertia compensation, demonstrating that inertia compensation can eliminate the disturbance in the outputs.

Static Recrystallization Behavior of Nitrogen Alloyed HRB500E Steel

WU Shangwen, WU Guangliang, ZHANG Yongji, MENG Zhengbing

2019, 54(6): 1314-1322. doi: 10.3969/j.issn.0258-2724.20170918

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In order to provide necessary theoretical basis for hot rolling process, the static recrystallization behavior of nitrogen alloyed HRB500E steel was studied by using stress relaxation method. The effects of various strain capacity, strain temperature and strain rate on the static recrystallization of samples were analyzed with Gleeble-1500D thermal simulation machine. Besides, the results were compared with those of vanadium microalloyed HRB500E steel. Based on the experimental results and Avrami equation, the kinetic models of static recrystallization were established in terms of two kinds of experimental steels, and the static recrystallization fraction curve was compared with the predicted one of the model. The results show that when the strain is increased in the range of 0.4−1.0, the strain temperature in the range of 950−1 100 ℃, and the strain rate in the range of 0.1−1.0 s⁻¹, t_0.5 (time for 50% recrystallization) decreases and the recrystallization speed increases. In particular, the static recrystallization of the experimental steels is more notably affected by strain capacity and strain temperature than strain rate. Under the same strain conditions, the static recrystallization process of the nitrogen alloyed HRB500E steel lags behind that of the vanadium microalloyed HRB500E steel. The verification results show that the prediction results of the kinetic models were in good agreement with the experimental results.

Balanced Current Control Method for Virtual Synchronous Generator in Electro-Hydrogen Multi-Energy Complementary Microgrid

CHEN Weirong, YU Jin, LI Qi, PU Yuchen, YANG Hanqing, HAN Ying

2019, 54(6): 1323-1331. doi: 10.3969/j.issn.0258-2724.20180860

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Abstract:
The multi-energy complementary microgrid concentrates multiple complementary energy sources in the same grid-connected system, which can effectively improve energy utilization efficiency and power supply reliability of the microgrid. Virtual synchronous generator (VSG) technology enables friendly networking of distributed power supplies. However, in the case of non-ideal operation, the traditional VSG control does not have the ability to suppress the negative sequence current when the grid voltage is unbalanced, which will lead to the imbalance of the three-phase grid-connected current of the microgrid. To solve this problem, a VSG balanced current control method based on electro-hydrogen multi-energy complementary microgrid is proposed. This work builds a power system model including photovoltaic and energy storage systems, and a hydrogen energy system model including an electrolytic cell-hydrogen storage-fuel cell system. Then, the basic principle of VSG is analyzed, and through the analysis of the VSG grid-connected small-signal model, the system parameters and control parameters are designed to improve system stability margin. The causes of the unbalanced current are shown in a way of quantitative analysis. In addition, by improving the current command calculation method in the dq coordinate system, it is able to suppress the negative sequence current and ensure the power quality of the electro-hydrogen multi-complementary microgrid. Finally, the energy management strategy of multi-energy complementary microgrid is verified to be effective by simulation. The simulation results show that the VSG balanced current control method can achieve the three-phase balance of the grid-connected current in the case of voltage imbalance and the inrush current is suppressed from 52 A to 27 A. Furthermore, it significantly reduces power fluctuations.

Suppression Solutions to Transient Traction Current Interference in Neutral Zone for Track Circuit

YANG Shiwu, CHEN Bingjun, CHEN Haikang, CUI Yong, TANG Qiankun

2019, 54(6): 1332-1341. doi: 10.3969/j.issn.0258-2724.20180692

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When an electric locomotive or an EMU (electric multiple unit) passes neutral zone in a track section, transient traction current is very likely to cause harmonic interference to track circuit, which may produce failure. To guarantee stable performance of track circuit under the influence of harmonic interference, the suppression methods of transient traction current are studied. Based on the European standards, the windowed FFT (fast Fourier transformation) method is adopted to design the procedure of harmonic data processing, and the analysis results of field test data are utilized to illustrate the interference mechanism for track circuit. Then, taking an example with a 1 700 Hz signal carrier and 1 750 Hz harmonic frequency, the solution and simulation results of FPGA (field-programmable gate array)-based FIR (finite impulse response) digital filter are briefly discussed from the point of direct suppression to harmonic interference. Due to the tiny difference between signal frequency and interference harmonic, the solution has to run at the cost of long response time and high order. Lastly, based on the current source feature of harmonic interference and project feasibility, the collaborative optimization scheme for the transmitter and attenuator of track circuit is proposed. Namely, by optimizing the transmitting level and attenuator step, the suppression to harmonic inference can be improved with an increase of 6 dB in signal-to-interference ratio while the operation states of track circuit are ensured including its clearance, occupancy and cab signaling.

Evaluation Method of Seat Comfort for High-Speed Trains Based on Seat Ergonomic Parameters

WANG Jin, ZHI Jinyi, XIANG Zerui, LI Ran, XU Xiaofei, YAN Lei, XU Gang

2019, 54(6): 1342-1348. doi: 10.3969/j.issn.0258-2724.20180499

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To reduce the cost in the comfort evaluation of high-speed trains and avoid strenuous questionnaire investigation and statistical analysis, the static comfort evaluation method of high speed train seats is studied. Firstly, the seat comfort calculation method is derived by determining the comfort evaluation index and index weight for high-speed train seats. Secondly, the BP neural network is used to construct a static seat comfort evaluation model, which takes the 8 ergonomic parameters of the high-speed train seat as the input and the seat comfort evaluation as the output. Finally, a case study is carried out to train and verify the constructed neural network evaluation model, and the weights and thresholds of the neural network are extracted to construct a mathematical expression of the neural network. The results show that when the neural network has one hidden layer and 13 nodes, the training achieves the desirable results with the mean error of 2.13×10⁻³ and mean square error of 6.091×10⁻⁶, and there is no over fitting. The network is verified by the real ergonomic data of the first-class and second-class seats in CHR2 and the corresponding comfort evaluations. The error of first-class seats between the predicted value of neural network and the actual one is 3.07%, and the error of second-class seats is 1.42%, demonstrating that the network model has high prediction accuracy and is superior to the multiple regression model.

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2019 Vol. 54, No. 6