西南交通大学学报

Mechanisms and Countermeasures of Out-of-Roundness Wear on Railway Vehicle Wheels

JIN Xuesong, WU Yue, LIANG Shuling, WEN Zefeng

2018, 53(1): 1-14. doi: 10.3969/j.issn.0258-2724.2018.01.001

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Abstract:
The rapid development of high-speed railway in China has significantly improved travel, and thus, people's quality of life. Travel times have been greatly shortened and work efficiency has improved considerably. China's high-speed railway network is becoming a "great artery for the rapid development of national economy". However, the wheel diameter of the high-speed trains in operation continues to decrease due to abrasion and reprofiling. At various stages of diameter reduction, varying degrees of polygonal wear occur. At some stages, polygonal wear is severe and significantly increases the forces between the wheel and rail, resulting in strong vibration and noise in railway vehicles and tracks. This problem affects the quality of the train operation, passenger comfort, and the service life of the vehicle and track components. Serious so-called out-of-roundness wear can even threaten the operational safety of a train. In this paper, the types of out-of-roundness wear are introduced. They are mainly divided into two types:local out-of-roundness wear and out-of-roundness wear along with the entire rolling circle of the wheel. Local out-of-roundness wear includes wheel flats, spalling, shelling, squatting, and other local defects. Polygonal wear, which is commonly observed on the wheels of various recent high-speed trains, is another type of out-of-roundness wear. In the lifecycle of a wheel, its diameter decreases due to wear and reprofiling, and the order (or wavelength) and speed at which polygonal wear occur differ. In this paper, the state of the art of out-of-roundness wear in railway vehicle wheels is reviewed in detail, examining a total of 75 papers. The review analysis shows that research on noncircular wheel abrasion can generally be divided based on the following aspects. (1) The effect of out-of-roundness wear on the dynamic behaviour of the vehicle/track system and vehicle noise:these studies show that the amplitude and wavelength of polygonal wear, vehicle operation speed, and axle weight significantly influence the dynamic behaviour of the coupled vehicle/track system and vehicle noise. (2) The mechanism and development rules of out-of-roundness wear, and detection techniques:to date, there has been no consensus on the mechanisms of polygonal wear in wheels and its development, and further research is pending. However, the likely origin of polygonal wear is the high-frequency flexible resonance of the bogie system, which occurs under fierce excitation of wheel and rail irregularities. High-order polygonal wear develops quickly if the operation speed of the train, excited high-frequency flexible resonance frequency, and wheel circumference satisfy a specific condition. (3) Detection techniques for out-of-roundness wear. Finally, future research in the field is forecasted, including the development of a model of railway vehicle/track rigid-flexible coupling dynamics to reproduce the initiation and development of out-of-roundness wear and further clarify the mechanism of polygonal wear, measures for suppressing out-of-roundness wear through changing commercial operation condition, and building intelligent wheel-roundness modification devices to suppress and remove out-of-roundness wear on wheels.

Field Test on Controlled Grouting Technology for Soft Soil Subgrade of High-Speed Railway

YANG Xin'an, GUO Le, WANG Shujie

2018, 53(1): 15-22. doi: 10.3969/j.issn.0258-2724.2018.01.002

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Abstract:
This study proposes the controlled grouting technology to effectively control the influence of soft soil subgrade grouting on the surface and rail surface deformation of operating high-speed railway. Field tests on grouting uplift for soft soil composite subgrade of high-speed railway, located at the Yangtze River delta, demonstrate potential feasibility and effect of this technology. The effect of different construction control measures on the grouting uplift was studied using data on surface deformation, pore water pressure, and lateral displacement of the soil. Simulations analyzed the influence of the rail deformation on the operational safety of the train at different train speeds. The deformation limit of the rail caused by grouting was determined. The results show that the concept of controlled grouting technology includes grouting, controlling standards, controlling measures, and monitoring. Reasonable grouting parameters, appropriate grouting layer, feasible time interval, and staggered grouting can effectively control the rail deformation. A higher train velocity implies greater deformation of the rail, which leads to a larger derailment factor, axle load shedding rate, and axle lateral force. Therefore, when the train speed is greater than 200 km/h, the overall and differential deformation of the rail surface should not exceed 15 mm; when the train speed reaches 300 km/h, the deformation of the rail surface should be less than 10 mm.

Fatigue Testing of CRTS Ⅲ Ballastless Slab Track Structures under Transverse Bending

LIU Xiaochun, JIN Cheng, YU Zhiwu, HE Chen, YANG Yiyi

2018, 53(1): 23-30. doi: 10.3969/j.issn.0258-2724.2018.01.003

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Abstract:
To investigate the transverse mechanical performance of CRTS Ⅲ slab ballastless track structures under the cyclic action of train loads, a full-scale CRTS Ⅲ slab track structure was fabricated using the same materials and technology as that employed in practical on-site construction applications. Six slab track specimens with one or two sleepers were fabricated from the full-scale slab track structure. Fatigue tests under transverse bending were conducted on these slab track specimens supported on rubber plate-simulated subgrades. The characteristics of stress distribution, deformation distribution, and nature of development of fatigue damage on slab tracks subjected to transverse bending were determined from the fatigue tests. The fatigue test results indicated that longitudinal cracks first appear on the top surface of the track slab in the middle of the slab track specimens with one or two sleepers under fatigue cycles of 15.0-255.0 kN and 42.5-425.0 kN, respectively. Several splitting cracks subsequently developed from the transverse prestressing tendon to the top surface of the track slab on the profile of anchorage end. After cumulative 5 million fatigue cycles, the loads for a composite plate with a track slab-infilling layer under the three-point bending mode corresponding to self-compacting concrete (SCC) cracking and interlayer bond-slip reduced by 20%-30% and more than 25%, respectively. It can be concluded that fatigue damage and interlayer delamination have adverse effects on the cooperative working performance of the track slab and the SCC infilling layer.

Simulation Solution Method for Long and Heavy-Haul Trains Negotiating Elastic Curved Tracks

LIU Pengfei, WANG Kaiyun, ZHAI Wanming

2018, 53(1): 31-37. doi: 10.3969/j.issn.0258-2724.2018.01.004

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To solve the synchronisation simulation problem for long trains and continuous elastic tracks, a representative case employing a train curving negotiation is used. A heavy-haul train-track coupled dynamic model is used to analyse the dynamic performance of the track structure with a 30 t axle-load train, when a coupler compressive force is applied to it. As implified principle is presented to simulate the dynamic interaction between the long heavy-haul train and the track. The general concept behind this method is replacing the large train-track coupled dynamic system by a finite number of three dimensional vehicle models, considering the foundation structure elasticity under the corresponding models. Thus, the motion freedom of the system can be significantly reduced.The results indicate that a long train can be treated as a shorter mixed train, composed of a single-mass vehicle model and a three-dimensional wagon model. As only one wagon is simulated by the detailed dynamics model, with the front and rear connected wagons considered as a single-mass model, conservative results are obtained. As the train negotiates a 400 m radius curve, simultaneously bearing a 2 200 kN coupler force, the lateral and vertical wheel-rail forces in the outer wheel of the wagon are underestimated by about 24% and 4% respectively, relative to the results calculated using a train model composed of several three-dimensional wagons. Correspondingly, the lateral and vertical displacement of outer rail are sequentially underestimated by nearly 20% and 8%. When a single-mass model is used at the ends of the train, and the number of the additional wagons simulated by the three-dimensional dynamic model is 3, both the wheel-rail dynamic interaction of the middle target wagon and the track dynamic behaviour, can be reflected accurately.

Shear Behavior of Mortar Layer in Continuous Slab Track with Different Arrangement Schemes of Embedded Steel Bars

ZHONG Yanglong, GAO Liang, HOU Bowen

2018, 53(1): 38-45, 63. doi: 10.3969/j.issn.0258-2724.2018.01.005

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Abstract:
In order to study the reasonable arrangement scheme of embedded steel bars under different temperatures, a three-dimensional finite element model of continuous slab track was established. In the model, a surface based cohesive zone model (SCZM) was introduced and utilized to simulate the complex interaction between track slab and mortar layer in the process of shear failure, which was bonding-debonding-contact. Nonlinear constraint characteristic of shearing steel bars were also considered. Based on the model validated by the results of longitudinal shear test of slab track, shear behaviors of CA mortar layer were analyzed particularly. The results show that embedded steel bars can significantly improve interlayer shear performance of slab track. The increasing extent of temperature when interlayer is cracking increases from 10.5℃ to 30℃.It is suggested that the 16+8+8 arrangement scheme of embedded steel bars could be used when the temperature rise less than 20℃, and 16+16+16+10+8 is also proposed when the temperature rise at 20~30℃, Over 30℃, other measures should be used.

Deflection Calculation and Analysis of PC Box Girder Bridges with Corrugated Steel Webs

JI Wei, LIN Pengzhen, LIU Shizhong

2018, 53(1): 46-55. doi: 10.3969/j.issn.0258-2724.2018.01.006

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In order to study the effects of shear lag and shear deformation caused by corrugated steel webs on the deflections of prestressed concrete (PC) box girder bridges with corrugated steel webs (CSWs), the deflection calculation for this type of bridge was calculated based on the energy variational method. First, based on the in-plane shear deformation of the flange plates and the distribution law of flexural shear flow, the longitudinal displacement function for this type of bridge was derived. This function can be used to estimate the shear lag effect and the shear deformation of CSWs. Second, based on the obtained longitudinal displacement function, the deflection formulas for a box girder bridge with CSWs were obtained using the variational principle method. The effectiveness of the formulas was verified using model tests and the ANSYS finite element analysis. Finally, variations in the width-span ratio and the heights of CSWs were made, under different types of loads, to study their influences on shear lag and shear deformation, and thereby on the deflections of simply supported and continuous box girder bridges with CSWs. The results show that when the width-span ratio is 0.108-0.650, the shear lag and the shear deformation of CSWs have significant effects on the deflection of continuous box girder bridges with CSWs, when under a concentrated load, which cannot be ignored. When the width-span ratio is 0.108-0.650, the effects of shear deformation of CSWs on the deflection of simply supported and continuous box girder bridges with CSWs, should only be considered under uniform load, while the effect of the shear lag should only be considered under specific span-width ratios and specific heights of CSWs.

Application Study on Grillage Method for Multiple-Cells Box Girder with Transverse Slope

HUANG Zuwei, LEI Junqing, TANG Jishun

2018, 53(1): 56-63. doi: 10.3969/j.issn.0258-2724.2018.01.007

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Mechanical properties of multiple-cells box girder with the transverse slope were analyzed in order to study the factors when using the grillage method. Based on the grillage method, formulas for multiple-cells box girder with tte transverse slope were derived while rationality of considering the transverse slope was discussed. Parameter analysis was done by adopting numerical simulation. Contrastive analysis on mechanical characteristic were done by changing the parameters such as loading positions, width-span ratios of box girder, cross slope angles. The results show that the error in computing characteristic value of grillage section rigidity is decreased up to 12.12% when the transverse slope is considered. The calculated results of grillage model fit the results of solid model, however, distortion cannot be reflect in the grillage model of multiple-cells box girder. The improvement of calculation precision is mainly appear on lateral displacement. Transverse slope would be considered in the grillage model if width-span ratio is greater than 0.8. Vertical displacement of cross section is increased linearly up to 758% when the transverse slope is change from 0 to 2%.

Two-Dimensional Coupled Flutter Method Based on Genetic Hybrid Algorithm

ZHENG Shixiong, ZHU Jinbo, TANG Yu, GUO Junfeng

2018, 53(1): 64-71. doi: 10.3969/j.issn.0258-2724.2018.01.008

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Based on the traditional systematic analysis method of 2d2DOF (two dimensional two degree of freedom), flutter analysis was transformed into a solution to the nonlinear equations of system vibration frequency, innovatively. Several numerical iterative methods for superlinear convergence, such as the quasi-Newton method, were introduced on the basis of numerical analysis theory. Then, the local convergence and initial value dependency of these methods in numerical iteration were studied. To avoid the above-mentioned risks in the flutter analysis, the genetic hybrid algorithm, which has advantages in global searching, was combined with the optimal algorithm "L-M" for local convergence correction, and introduced into the 2d2DOF flutter analysis; a new analysis method was subsequently proposed. The sample numerical analysis showed that in each detected wind node, the calculation errors of the system vibration circle frequency and the system-implicated damping ratio under the two methods were lower than 0.1 per thousand, and the results were almost the same. Thus, the new method is effective, and the corresponding calculation result of the critical wind velocity is consistent with the traditional method; this shows that the new calculation procedure is feasible and the calculation results are accurate. Compared with the traditional method, the proposed method has the advantages of unconditional convergence, wherein initial values do not require artificial selection in each step of the solving process.

Failure Mode of Isolated Beam Bridge by Weighted Rank Sum Ratio Method

ZHANG Yun, TAN Ping, HUANG Jiadong

2018, 53(1): 72-78. doi: 10.3969/j.issn.0258-2724.2018.01.009

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To estimate the failure modes of seismically isolated continuous girder bridges, a practical engineering with six spans was analyzed considering the uncertainty of seismic ground motions. Sixteen ground motion records were selected to be used in IDA method, which could provide sufficient accuracy of seismic analysis demands, and the PGA of these records were distributed in a wide range. Bearings and the bottom of piers were the most vulnerable parts of the bridge, of which failure criteria were estimated by displacement and modified Park-Ang damage theory, respectively. And weighted rank sum ratio method was adopted to analyze evaluation information of the bridge under sixteen ground motion records, then the statistically significant failure modes and the weakest failure mode of the bridge were identified. The results show that the final failure mode of the isolation continuous girder bridge arises at the isolation bearings of the middle piers, at the isolation bearings of the transition piers, and at the bottom of side piers and bearings. The weakest failure mode of this bridge happens with all isolation bearings cease to be effective first, then it comes to the bottom of the side piers and the middle piers, and finally the transitional piers.

Dynamic Response Analysis of Bridge Pier in Deep Water under Combined Loads of Wave, Current and Earthquake

WU Anjie, YANG Wanli, ZHAO Lei

2018, 53(1): 79-87. doi: 10.3969/j.issn.0258-2724.2018.01.010

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The dynamic equation of a structure under the combined loads of wave, current, and earthquake, was presented based on the nonlinear Morison equation, to reveal the coupling mechanism of water and bridge substructure under the combined action of wave-current and earthquake. The dynamic responses of a pile-cap-bridge pier in deep water were calculated by the finite element method, and the influence of the different wave-current elements on the dynamic response of the structure was analysed. The results show that the wave-current and earthquake interact. The influence of the wave-current on seismic response is between -31.6% to 63.5%. Not only does the wave-current change the amplitude of seismic response, but it also changes the time of its occurrence. Moreover, the excitation frequency of the flow field under the combined action of wave-current and earthquake lies between the seismic excitation frequency and the pure wave-current field excitation frequency. Consequently, it is necessary to analyse the combined action of the wave-current and earthquake. With the increase in wave height, the response of the pier structure is significantly affected by the wave flapping on the cap and above. Therefore, it is necessary to select an elevated pile cap for the sea-crossing bridge.

Dynamic Reliability Analysis on Pounding of High-Pier Bridges Subjected to Stochastic Seismic Excitations

JIA Hongyu, DU Xiuli, LUO Nan, ZHANG Jin, ZHENG Shixiong, ZHANG Keyue

2018, 53(1): 88-94. doi: 10.3969/j.issn.0258-2724.2018.01.011

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A dynamic reliability analysis based on the pseudo-excitation method in the frequency domain was proposed to investigate the pounding reliability of high-pier bridges subjected to seismic excitations with different ground motion intensity levels. A high-pier bridge was selected as the numerical example and the pounding reliability of the high-pier bridge was computed for each ground motion intensity level. The horizontal acceleration response spectrum was chosen as the seismic intensity measure and the response spectra for different intensity measures were converted into the corresponding power spectra. Next, the stochastic vibration equation was solved using the pseudo-excitation method to determine the mean and mean square deviation of the structural dynamic responses. The expected values and standard deviation of the structural peak responses were obtained using Davenport's theory. Finally, the pounding reliability between the adjacent beams of the high-pier bridge was determined using the first passage theory. The results indicate that pounding will not occur between the adjacent decks and the pounding reliability is 1.0 when the ground acceleration is less than 0.22g. In addition, there is an obvious decrease in the pounding reliability such that the structure collides under the strong ground motions when the ground acceleration is more than 0.22g.

Influence of Reservoir Water Storage on Wind Characteristics over Bridge Site in Mountainous Area

WANG Yunfei, WANG Bin, LI Yongle

2018, 53(1): 95-101, 145. doi: 10.3969/j.issn.0258-2724.2018.01.012

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In this study, the influence of a hydropower dam built in a mountainous region on the wind characteristics of a bridge site in the reservoir area after storing water was examined.For this purpose, the example of a long-span suspension bridge over a deep-cutting gorge in a complicated mountainous area was considered.The numerical terrain model of the original site and that of the site after the reservoir was filled with water were built by Gambit and ICEM. Numerical simulations for the two models were performed by employing computational fluid dynamics commercial software FLUENT. Different cases were analysed to identify the influence of the reservoir water storage on the distribution of wind velocities along the vertical direction and along the bridge deck, and to identify the influence of water storage on the average velocity of the bridge deck, attack angle, and wind direction angle. The wind velocity at the bridge site clearly increases as compared to the velocity before the reservoir is filled with water, and the velocity amplification factor reaches up to 1.14. However, the velocity amplification factor decreases significantly after the reservoir was filled with water. The average velocity of the bridge deck in most cases decreased to different extents, and the effect of the positive attack angle decreased significantly after reservoir water storage.The variation in the average wind direction angle is consistent with that in the original model. The wind profile shapes exhibit considerable changes in a low altitude range after water storage, but they gradually tend to be the same as the altitude increases.The conclusions of this study provide a basis for the wind-resistant design of bridges.

Numerical Study of Horizontal Wave Load on Composite Pile Foundation in Marine Environment

XIANG Baoshan, WANG Shaohua, CAI Zilong, ZHU Bing, ZHANG Qibo

2018, 53(1): 102-108. doi: 10.3969/j.issn.0258-2724.2018.01.013

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To investigate the effects of pile cap submerged depth and wave obliquity on wave load on a composite pile foundation, a three-dimensional numerical model for wave-structure interaction around the Pingtan Strait railway bridge foundation was established. This model was based on the CFD code FLOW-3D, in which the Reynolds-averaged Navier-Stokes (RANS) equation and k-ε turbulence model are used for wave simulations. After validating by analytical solutions and previous laboratory experiments, the model was used to study the effects of pile cap submerged depth and wave obliquity on wave load on the composite foundation. The numerical results indicate that the pile cap submerged depth can significantly affect the wave load on the composite pile foundation, and the wave load on the pile foundation is maximum when the submerged depth is approximately 1 times the pile cap thickness. In addition, the horizontal wave load on the composite foundation increases with the increment of wave incidence angle when the incidence wave angle is defined as the angle between the long axis of the cap and the wave propagation direction. When the wave incidence angle is 90°, the wave load on the foundation is approximately 1.4 times that with a wave incidence angle of 0°.

Effect of Pounding on Elastic-Plastic Dynamic Response of High Pier Bridge in Mountainous Area

LI Xi, JIA Hongyu, LI Qian, KANG Rui, CHEN Zhiwei

2018, 53(1): 109-118. doi: 10.3969/j.issn.0258-2724.2018.01.014

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To study the effect of pounding on the seismic response of high-pier bridge in mountainous areas, the elastic-plastic dynamic analysis models of two typical bridge structures were established by using the OpenSees framework, based on the prototype of a real high-pier bridge. The variation in stiffness, energy dissipation during the pounding process, and the non-linear behavior of the piers were fully considered in the models. Additionally, the effect of pounding on dynamic responses of a high-pier bridge was analyzed by using the selected natural and artificial ground motions. The results show that pounding can significantly affect the structural responses, especially for poor site conditions, and the maximum change rate is 15.86%. Moreover, the method of connecting the pier and beam further influences the effect of pounding on the pier displacement; A larger difference in dynamic characteristics of adjacent structures corresponds to a larger probability of collision; however, the increasing frequency of pounding may reduce the responses of piers, owing to the restriction effect on the pier deformation. Thus, when selecting the period ratio of adjacent structures, it is necessary to consider its effect on not only the probability of pounding, but also on the degree of effect of pounding. In comparison, beam-abutment pounding is mainly affected by the intensity of ground motions, whereas the beam-beam pounding is influenced by both the intensity of ground motions and the difference in dynamic characteristics of adjacent structures. Therefore, in seismic design, to reduce the pounding of high-pier bridges, it is suggested that different measures should be adopted for different pounding positions.

Construction Parameters Control of Shield Tunnel Underneath Traversing Existing Dual Shield Tunnels

MA Wenhui, PENG Hua, YANG Chengyong

2018, 53(1): 119-127. doi: 10.3969/j.issn.0258-2724.2018.01.015

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In order to investigate reasonable construction parameters of a shield tunnel underneath traversing existing dual shield tunnels, the project that shield tunnel of the East Trunk Canal of the South-to-North Water Diversion Project traversed subway shield tunnels in Beijing was studied as an example. The reason for the difference in settlement between the left and right tunnels was determined by analyzing the numerical simulation and in situ monitoring data of the settlement of existing tunnels and the shield construction parameters. Then, the construction parameters for controlling settlement were given. Moreover, the trends in the variation in settlement of existing tunnels caused by traversing construction was discussed and some measures to counter shield tunnel diseases were proposed and verified. The results show that because of the influences of shield construction with different parameters, the final settlement of the existing left tunnel is 23.9 mm, while that of the right tunnel is only 4.8 mm. Although the settlements of the two tunnels differ significantly, their trends in variation are almost consistent. During the construction, the adjusted range of the working chamber pressure should not be more than 0.005 MPa and the synchronous grouting pressure should be adjusted accurately to be 0.50 MPa. Meanwhile, the secondary grouting pressure should be 0.20-0.35 MPa, and the tunneling speed in the curve section is required to slow down appropriately. Since the maintenance time in a subway is short, chemical grouting is adopted to solve the problem of leakage of water in segment joints and bolt holes while a pressure filling resin is used to repair the cracks in the slab.

Characterization of Vertical and Horizontal Propagations of Double Cracks in Asphalt Pavements under Moving Loads

AI Changfa, XU Cheng, REN Dongya, GUO Yujin, YANG Enhui

2018, 53(1): 128-135. doi: 10.3969/j.issn.0258-2724.2018.01.016

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The purpose of this research is to analyse the evolution of vertical and horizontal propagations of double cracks in asphalt pavements under moving loads using fracture mechanics and finite-element numerical simulations. In this regard, the effects of cracking space and reflective cracking depth on surface top-down cracking and base layer reflective cracking were studied by considering the viscoelastic behaviour of the surface material. Subsequently, crack propagation was characterized and the fatigue lives due to surface top-down cracking under different moving load levels were evaluated. The results indicated that surface top-down cracking mainly occurred in the type Ⅱ mode. Moreover, the cases of single crack and zero crack spacing corresponded to the conditions of most critical and noncritical propagations, respectively. However, crack spacing and the depth of reflective cracking did not have a significant influence on its propagation. For base layer reflective cracking, the most severe type Ⅰ and Ⅱ propagations occurred within a 400 mm cracking space, and the crack propagation level grew with increasing depth. The fatigue lives due to top-down mixed mode cracking under different moving load levels ranked in descending order as high speed, static state, low speed, and braking state. The fatigue life in the braking state was only 20.4% of that in the high-speed state.

Monitoring Video-Based Visibility Detection Method and System for Highways in China

ZHANG Changli, MENG Ying, LI Pengchao, SUN Ting

2018, 53(1): 136-145. doi: 10.3969/j.issn.0258-2724.2018.01.017

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In view of the urgent demands for visibility detection, alarm and emergency disposal on highways in China, a monitoring video-based method for highway visibility detection was proposed. In this method, images of fixed-distance reference objects were first extracted from monitoring camera images, and then candidate visibility values were calculated based on greyscale image distortion analysis on these images. The final visibility result was computed by applying data fusion on the candidate visibility values. Based on this method, a visibility detection, alarm and emergency disposal system was developed. By utilizing the calculated visibility values, this system provides support for intelligent transportation tasks, such as visibility alarm, emergency disposal, traffic control, and information publication, both locally and globally. Experimental results show that the average detection error of this method is 13.4%, thus meeting the accuracy and performance requirements of highway visibility detection. Moreover, this method and the corresponding system can fully reuse the monitoring camera electromechanical systems distributed along the highways; therefore they are suitable for application in operation management and efficiency improvement works on highways in China.

Seismic Vulnerabilitu Models and Simplified Calculation Method for Regular Highway Girder Bridges

CHEN Libo, HUANG Caigui, HUANG Yongbing, LI Huaiguang

2018, 53(1): 146-155. doi: 10.3969/j.issn.0258-2724.2018.01.018

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In order to swiftly assess the probability of a bridge structure reaching a specific damage state, seismic vulnerability models for regular highway girder bridges and a simplified method for their calculation are established, based on the results of a nonlinear dynamic time history analysis. Depending on the type of bridge, column, and design specification, regular highway girder bridges are divided into eight categories, with 80 benchmark bridge samples constructed for each category. Columns and bearings are considered vulnerable components, in which the component limits for different bridge damage states are determined. A finite element model of bridge samples is established using the OpenSees database. By employing an incremental dynamic analysis approach, seismic vulnerability models for regular highway girder bridges are obtained. Based on the analysis results, a new simplified formula for the calculation of median values was fitted and proposed for application to the existing regular highway girder bridge situation in China, along with the recommended values of logarithmic standard deviation. The results indicate that the median value for a double-pier bridge increased by 17% compared to a single-pier type and that of a continuous type increased by 8% compared to a simply supported bridge. Also, the efficiency of the latest design code increase by 7% compared to its former version. The results computed using the proposed simplified formula showed a good correlation with the categorical vulnerability models, with a mean square error and root mean square error of 5.26% and 5.95%, respectively, and a maximum absolute error of 10.58%.

Simulation on Survivability and Cascading Failure Propagation of Urban Subway-Bus Compound Network

SHEN Li, ZHANG Dianye, XIANG Yang, WANG Zhouquan, ZHANG Tong

2018, 53(1): 156-163, 196. doi: 10.3969/j.issn.0258-2724.2018.01.019

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To study the topological characteristics of urban public transit compound network, the validity of urban subway-bus compound network in Chengdu under attack&congestion was analyzed by constructing multimode topology network. Through the complex network theory, firstly, the static invulnerability of urban subway-bus compound network under different attack modes was tested to judge the importance degree of relevant nodes and lines. Then, the propagation of network overload and/or congestion, the cascading failure process under subway emergency were measured, so as to estimate the emergency coordinative performance of the ground public transportation system adjacent to metro lines. The results indicate that compound network has better overall efficiency than single network according to the lower decreasing amplitude and speed droop of the indices of network efficiency under random and intentional attack. In the opinion of the simulation results of cascading failure features of eight metro lines in Chengdu under the emergency episode with&without restrictive capacity, the emergency response capability of the bus lines system along the metro lines can be measured and judged effectively, in order to implementing pointed and efficient strategies&measures to handle the flow overload of the compound network arising from sudden accidents.

Numerical Simulation of Gas-Liquid Two-Phase Flow at Various Inlet Positions in Bubble Column at Low Gas Velocity

WANG Le, SU Junwei, ZHENG Xipeng, YANG Shunsheng

2018, 53(1): 164-172. doi: 10.3969/j.issn.0258-2724.2018.01.020

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In order to examine the law of the gas-liquid two-phase flow at various inlet positions of a bubble column, an Euler-Euler two-fluid model coupled with the population balance model (PBM) was used to simulate the effects of four inlets at various positions in the middle of the bubble column bottom on gas-liquid two-phase flow in the bubble column. We verified the mesh of the computational domain and gas hold-up distribution by comparing with experimental data. This study also investigated dynamic behaviours of gas hold-up, bubble number density, liquid horizontal velocity, etc., which provide instructions and basis for the design of the bubble column. The simulated results using an Euler-Euler two-fluid model with PBM were found to be consistent with the experimental results and better than those calculated using an Euler-Euler two-fluid model with single bubble diameter. Furthermore, the dynamic behaviours of gas hold-up, liquid horizontal velocity, distribution of gas hold-up, and vortex strength were all affected by the inlet position. When the inlet was farther from the middle of the bottom of the bubble column, the gas hold-up had an S-shaped distribution and the vortex strength increased; the gas hold-up and bubble plume oscillation period initially increased and then decreased. The bubble number density was not significantly affected by the inlet positions in the bubble column. Moreover, the group with the bubble diameters of 5.95 mm had the largest bubble number density.

Optimum Sensor Placement Method for Cable-Stayed Bridges Based on Damage Identifiability

LIU Jie, WANG Hailong, ZHANG Zhiguo, ZHANG Ruiyun, CAO Lihui, WANG Guoan

2018, 53(1): 173-181. doi: 10.3969/j.issn.0258-2724.2018.01.021

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Abstract:
In order to make the modal parameters identified by the sensors on cable-stayed bridges that are sufficiently sensitive to structural damage, a damage information index of the node degree of freedom containing the damage information of all elements was proposed and obtained, considering the damage identifiability requirements for optimum sensor placement, and using the method of parameter study and parameter correlation theory. The damage information regarding the degrees of freedom of the nodes could be ordered by ranking the index, i.e. by ranking the damage sensitivity of each degree of freedom. This process did not require the use of any optimization iterative algorithm. Based on this proposal, the first such method for optimum sensor placement, which can avoid defects such as inefficient iterations and optimization, could be analysed. Finally, the location of the sensor, which could provide satisfactory damage identifiability and modal observability, was obtained. The feasibility of the proposed method was demonstrated using a single-tower double-cable-plane cable-stayed bridge. A comparison of the results with those obtained using the EI method (effective independence method) revealed that the total damage information obtained using the proposed method is greater by factors of 589, 582, and 591 for the 3rd, 4th, and 5th orders, respectively.

Novel Scattering Path Recognition Algorithm Based on LPMD

DENG Ping, RUI Yang, DENG Shuifa

2018, 53(1): 182-188. doi: 10.3969/j.issn.0258-2724.2018.01.022

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Abstract:
Non-line-of-sight (NLOS) error is the major source of error in ground wireless localization. In order to recognize single-bound scattering path and multiple-bound scattering paths from all the NLOS scattering paths, we propose a novel recognition algorithm based on line-of-possible-mobile-device (LPMD). This algorithm first utilizes the cross points of all the LPMDs to calculate the coordinate of a reference point. The algorithm then uses part of the cross points far away from the reference point to obtain minus expectation compensation to revise the location of reference point, builds the judgement formula of scatter path type based on the distance between each LPMD and the reference point to make single/multiple bound path judgement. Under normal and special scenery, the simulation tests of scatter path judgement are performed under different parameter conditions; the simulation results show when the distance between the target and the detecting station reaches 4 km. A false alarm probability and a false dismissal probability of the proposed algorithm can be limited to 3%and 9%, respectively. Further, these probabilities can be decreased by about 21% and 8%, respectively, when compared with the original LPMD algorithm..

Intrapulse Feature Evaluation Model of Radar Emitter Signal Based on Differential Evolution, Particle Swarm Optimization and Projection Pursuit Algorithm

ZHU Bin, JIN Weidong, YU Zhibin

2018, 53(1): 189-196. doi: 10.3969/j.issn.0258-2724.2018.01.023

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Abstract:
To address the problems in comprehensive evaluation of radar emitter signal (RES) intrapulse features, such as incomplete evaluation criteria and the lack of objectivity, a new comprehensive evaluation model of RES intrapulse features was proposed based on swarm intelligence. First, the comprehensive evaluation problem of RES intrapulse features was converted into an optimization problem of the conditional multivariate nonlinear objective function through the projection pursuit algorithm. Secondly, the new swarm intelligence algorithm was obtained through the combination of the improved particle swarm optimization algorithm and the differential evolution algorithm. Thirdly, the optimization and solution of the multivariate nonlinear objective function was achieved using the proposed algorithm. The simulation results show that the optimal fitness of the Rosenbrock test function of this new intelligence algorithm is minimal, and the optimal fitness values of the Rastrigrin test function and the Girewank test function are zero, indicating that the calculation accuracy of the proposed algorithm is better than the standard particle swarm optimization algorithm and the differential evolution algorithm. At the same time, the variance of the fitness value of the proposed algorithm is smaller than those of the standard particle swarm optimization algorithm and the differential evolution algorithm, which indicates that the convergence and robustness of the proposed algorithm are better. According to the objective function of the evaluation problem, the results of the proposed algorithm do not fluctuate when comparing the five optimization results with those of the accelerated genetic algorithm, which shows that the intrapulse feature evaluation model based on swarm intelligence can effectively achieve the objective of comprehensive evaluation of RES intrapulse features.

Data Exchange Method of Railway Engineering Information Model for GIS Applications

LI Hao, ZHAO Guotang, FAN Dingyuan, FAN Dengke

2018, 53(1): 197-205. doi: 10.3969/j.issn.0258-2724.2018.01.024

[Abstract](514)

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Abstract:
In order to realize interoperability and information sharing between different platforms, we propose a model data exchange method (called RIMTrans) supporting level of details (LoDs) and scene construction, based on multiple information separation and independent storage. First, parameters describing geometric features were extracted from elements of the Railway Engineering 3D Information Model (RIM), and the Mesh data needed for Geographic Information Systems (GIS) was transformed by fast meshing. Second, the mapping relationship between Industry Foundation Classes (IFC) and RIM semantics was established to ensure the integrity of semantic information during the data exchange process. Third, the attribute definition and description mode specified by IFC were used as the standard exchange format to realize the transmission of attribute information. Finally, RIMs were simplified as mult-level detailed GIS models from the geometric, attribute, and semantic aspects. By selecting a case area of a railway engineering design work station, we adopted the RIMTrans method to carry out the format conversion experiment of the design phase information model. The results show that the data exchange method proposed in this paper is flexible and controllable. The integrity of the railway project semantic information in the 3D model is up to 85%. Compared with the traditional operation mode, the conversion time of the RIM is reduced by 70%, and the accuracy when RIM is integrated into the 3D scene is as high as 100%.

Air Traffic Flow Prediction Model Based on Improved Adding-Weighted One-Rank Local-rejion Method

WANG Chao, ZHU Ming, ZHAO Yuandi

2018, 53(1): 206-213. doi: 10.3969/j.issn.0258-2724.2018.01.025

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Accurate air traffic flow prediction is an important basis for efficient air traffic control and management. Aiming at the inherent chaotic dynamic characteristics of air traffic flow time series, the chaotic traffic-flow time-series prediction model based on improved adding-weight one-rank local-region prediction method was analyzed herein. Firstly, an improved adding-weight one-rank local-region prediction method was proposed, which involved weighing the evolution of adjacent phase points. Further, the prediction results were corrected by construction of error sequences during the prediction process. Secondly, the chaotic characteristics were verified to exist in four groups of air traffic flow time series at different time scales, using the saturation phenomenon of correlation dimension. Finally, a validation experiment for air traffic flow prediction was carried out using the improved method, after phase space reconstruction of air traffic flow time series. The results show that the prediction accuracy of all four groups is improved, wherein the traffic flow time series with time scale of 10 min has the best precision; the relative error in this case reduces by 29.7%.

Modified Constitutive Model and Ductile Fracture Criterion for 5A06 Al-Alloy Sheets at Elevated Temperatures

LIU Kangning, LANG Lihui, XU Qiuyu

2018, 53(1): 214-218. doi: 10.3969/j.issn.0258-2724.2018.01.026

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In order to obtain the formation characteristics of 5A06 aluminium alloy sheets, uniaxial tensile tests were conducted under different conditions. From hot tensile and fracture tests, a modified Misiolek equation was defined that extrapolated the flow stress from the diffuse necking of the metal sheet. By using a radial basis unction (RBF) artificial neural network, a Crockroft-Latham ductile fracture threshold prediction model was also developed. An evaluation of the network compared model results with experimental data. Results show that the material flow stress is very sensitive to temperature and strain rate, and the RBF artificial neural network can predict the ductile fracture threshold with a maximum error of less than 10.6%.

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2018 Vol. 31, No. 1