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2012 Vol.20 Issue.1,Published 2012-03-30

Articles
 
Articles
1 Experimental investigation of damage identification for continuous railway bridges
Deshan SHAN, Chunyu FU, Qiao LI
Considering the issue of misjudgment in railway bridge damage identification, a method combining the step-by-step damage detection method with the statistical pattern recognition is proposed to detect the structural damage of a railway continuous girder bridge. The whole process of damage identification is divided into three identification sub-steps, namely, damage early warning, damage location, and damage extent identification. The multi-class pattern classification algorithm of C-support vector machine and the regression algorithm of ε-support vector machine are engaged to identify the damage location and damage extent, respectively. For verifying the proposed method, both of the proposed method and the optimization method are used to deal with the measured data obtained from a specific railway continuous girder model bridge. The results show that the proposed method can not only identify the damage location correctly, but also obtain the damage extent which is consistent with the experimental results accurately. By uncoupling finite element analysis and damage identification, normalizing the index, and seeking the separation hyper plane with maximum margin, the proposed method has more favorable advantages in generalization and anti-noise. As a result, it has the ability to identify the damage location and extent, and can be applied to the damage identification in real bridge structures.
2012 Vol. 20 (1): 1-9 [Abstract] ( 6749 ) [HTML 1KB] [ PDF 237KB] ( 1364 )
10 Characteristics of wheel-rail vibration of the vertical section in high-speed railways
Jiuchuan YANG, Kaiyun WANG1, Hongyu CHEN
In order to analyze the characteristics of wheel-rail vibration of the vertical section in a high-speed railway, a vehicle-line dynamics model is established using the dynamics software SIMPACK. Through this model, the paper analyzes the influence of vertical section parameters, including vertical section slope and vertical curve radius, on wheel-rail dynamics interaction and the acting region of wheel-rail vibration. In addition, the characteristics of wheel-rail vibration of the vertical section under different velocities are investigated. The results show that the variation of wheel load is not sensitive to the vertical section slope but is greatly affected by the vertical curve radius. It was also observed that the smaller the vertical curve radius is, the more severe the interaction between the wheel and rail becomes. Furthermore, the acting region of wheel-rail vibration expands with the vertical curve radius increasing. On another note, it is necessary to match the slope and vertical curve radius reasonably, on account of the influence of operation speed on the characteristics of wheel-rail vibration. This is especially important at the design stage of vertical sections for lines of different grades.
2012 Vol. 20 (1): 10-15 [Abstract] ( 5575 ) [HTML 1KB] [ PDF 294KB] ( 1508 )
16 Effects of vibration in desert area caused by moving trains
Jabbar-Ali ZAKERI, Morteza ESMAEILI, Seyedali MOSAYEBI, Rauf ABBASI
The ballast layer, filled with fine particles like blown sand, is one of the important problems of ballasted railway tracks in desert areas. Blown sand, as a contaminator of ballast layer, increases track stiffness and may cause serious damage to sleepers, pads, rails, and vehicles. In this paper, the effects of increasing track stiffness due to windy sands in the ballast layer and the train induced vibrations due to this phenomenon were studied. Based on field studies in a desert area in Iran, a two-dimensional finite/infinite element model for a railway track with plane strain condition was analyzed using the software ABAQUS, and the track vibrations were examined by changing the values of stiffness of ballast layer. Vibrations caused by the load of train at different distances from the cross-section of track were investigated, and the values of vertical vibration displacement, velocity, and acceleration were calculated. Results show that acceleration values of vertical vibration increase with the increasing of ballast layer stiffness caused by the filling of sand, while the vertical vibration velocity of track and the induced ground displacement decrease. The farther the distance from the source of vibration, the less the displacement, velocity, and acceleration. In addition, the methods for reducing train-induced vibrations were introduced
2012 Vol. 20 (1): 16-23 [Abstract] ( 6669 ) [HTML 1KB] [ PDF 583KB] ( 2099 )
24 Unsymmetrical load effect of geologically inclined bedding strata on tunnels of passenger dedicated lines
Benguo HE, Zhiqiang ZHANG, Yu CHEN
In order to study the unsymmetrical load effect in geological bedding strata for the Muzhailing tunnel on the Lanzhou-Chongqing passenger dedicated line in China, we investigated the deformation, mechanical response and pressure of the surrounding rock and the mechanical characteristics of bolts of the tunnel. The results suggest that open zones appear at arch and invert where joints open up, when layered stratum is horizontal, or when the dip angle of inclined bedding is small. Open zones occur perpendicular to a joint. The failure mode is bending disjunction at the arch. What’s more, with the dip angle increasing, tunnel excavating would induce shear zones where joints experience a certain shear displacement, and lead to obvious geological bedding unsymmetrical load. The failure mode is shear damage. For the joint dip angle in the range of 75–90°, the failure mode is flexural crushing at the wall and vertical shear rupture above the arch. The restraining effect of two sides weakens for vertical dip. On the whole, shear failure instability trend would occur and the tunnel collapses evenly. When the angle between the bolt and structure plane is greater than 23°, bolts can enhance the shearing stiffness of joint plane. Unfortunately, in the general purpose graph of tunnel for 250 km/h of passenger dedicated lines, the bolts have equal length and spacing. The rationale behind this is worthy of further study. For inclined bedding, the surrounding rock pressure at the left wall is more than that at the right wall. In addition, lining is likely to be damaged at left shoulder and side wall. With the dip angle increasing, the unsymmetrical load gradually achieves symmetry. Asymmetry design for support is recommended to reduce the unsymmetrical load on lining disturbed by excavation.
2012 Vol. 20 (1): 24-30 [Abstract] ( 4977 ) [HTML 1KB] [ PDF 1577KB] ( 1245 )
31 Characteristic analysis of air pressure wave generated by high-speed trains traveling through a tunnel
Chuanhui WU, Xiangling GAO, Pinxian GAO
It is a complicated dynamic phenomenon when a transient pressure pulse is triggered by two high-speed trains passing each other in a tunnel. The air pressure pulse is a transient excitation to side wall of the car body. It can stimulate almost all vibration modes of the car body and the correlated assemblies, cause serious aerodynamic noise, and have important impacts on car body distortion, train noise, and operation safety. This article analyzes the time-frequency characteristics and main parameters of field-measured the air pressure wave, and its relationship with the train velocity as well as the vibration of the car body. Cepstrum analysis concludes that in the process of the meeting, the air pressure wave in tunnel crossing is a multiplying pressure wave instead of a superposed wave. The pressure pulse during the meeting is non-symmetrical one featured with a sharp front, large amplitude, fluctuating central section, and less sharp tail. The pulse width is inversely proportional to the train speed. As the speed increases, the impulse amplitude is amplified, and the speed of pulse front is advanced.
2012 Vol. 20 (1): 31-35 [Abstract] ( 5323 ) [HTML 1KB] [ PDF 315KB] ( 1223 )
36 Aerodynamic performances and vehicle dynamic response of high-speed trains passing each other
Yinghui ZHAO, Jiye ZHANG, Tian LI, Weihua ZHANG
Based on the aerodynamics and vehicle dynamics, the aerodynamic performances and vehicle dynamic characteristics of two high-speed trains passing each other on the ground, embankment and bridge are studied. Firstly, a train aerodynamic model and a vehicle dynamic model are established. Through the simulation of the two models, the pressure waves, aerodynamic forces, and vehicle dynamic responses are obtained. Then, the pressure waves and aerodynamic forces on different foundations are compared. The results show that the variation trends of pressure wave and aerodynamic forces of trains passing each other on different foundations are almost similar. The peak-to-peak differences in pressure wave and aerodynamic force are below 4% and 3% in three cases in open air. Besides, the differences of security indexes, including coefficient of derailment, wheel unloading rate, the wheelset lateral force, and the wheel-rail vertical force, are below 2% among the three cases; the differences of comfort indexes, including the lateral acceleration and the vertical acceleration, are also below 2%. It is concluded that the dynamic performances of trains passing each other are influenced little by different foundations in open air.
2012 Vol. 20 (1): 36-43 [Abstract] ( 6173 ) [HTML 1KB] [ PDF 466KB] ( 1589 )
44 Numerical simulation and analysis of aerodynamic drag on a subsonic train in evacuated tube transportation
Yaoping ZHANG
The aerodynamic drag on a train running in an evacuated tube varies with tube air pressure, train speed and shape, as well as blockage ratio. This paper uses numerical simulations to study the effects of different factors on the aerodynamic drag of a train running at subsonic speed in an evacuated tube. Firstly, we present the assumption of a steady state, two dimensional, incompressible viscous flow with lubricity wall conditions. Subsequently, based on the Navier-Stokes equation and the k-? turbulent models, we calculate the aerodynamic drag imposed on the column train with a 3-meter diameter running under different pressure and blockage ratio conditions in an evacuated tube transportation (ETT) system. The simulation is performed with FLUENT 6.3 software package. An analyses of the simulation results suggest that the blockage ratio for ETT should be in the range of 0.25–0.7, and the tube internal diameter in the range of 2–4 m, with the feasible vacuum pressure in the range of 1–10 000 Pa for the future subsonic ETT trains.
2012 Vol. 20 (1): 44-48 [Abstract] ( 6679 ) [HTML 1KB] [ PDF 108KB] ( 1650 )
49 Evaluation of floating car technologies for travel time estimation
Xiaobo LIU, Steven CHIEN, Kitae KIM
Travel times have been traditionally estimated from data collected by roadway sensors. Recently, new technologies, such as cell phone tracking, license plate matching, automatic vehicle identifications and video detection, are employed for this purpose. In this study, the data collected by TRANSMIT readers, Bluetooth sensors, and INRIX are assessed by comparing each to the “ground truth” travel times collected by probe vehicles carrying GPS-based navigation devices. Travel times of probe vehicles traveling on the study segment of I-287 in New Jersey were collected in 2009. Statistical measures, such as standard deviation, average absolute speed error, and speed error bias, were used to make an in-depth analysis. The accuracy of each travel time estimation method is analyzed. The data collected by Bluetooth sensors and the TRANSMIT readers seem more consistent with the ground true data, and slightly outperform the data reported by INRIX. This study established a procedure for analyzing the accuracy of floating car data (FCD) collected by different technologies.
2012 Vol. 20 (1): 49-56 [Abstract] ( 5162 ) [HTML 1KB] [ PDF 366KB] ( 1483 )
57 Reliability analysis of stochastic park-and-ride network
Wenbo FAN
Park-and-ride (P&R) facilities can alleviate the traffic burden in central urban areas by enabling car drivers to park at the perimeter of congested areas and continue their journeys with public transportation (e.g., metro and bus rapid transit). Whether a P&R scheme is successful depends on its attractiveness to car users. This paper presents an evaluation method for the reliability analysis of P&R mode. Two indices, P&R reliability and mode reliability, are introduced to represent the reliabilities of a transfer point and an entire trip, respectively. Then, a systematic reliability analysis is conducted for a stochastic P&R network, where travelers can complete their journeys via two options: auto mode or P&R mode. A variational inequality (VI) model is proposed and solved by a heuristic solution algorithm. Numerical results show that the P&R facility reliability is significantly influenced by the capacity of parking facilities, the dispatching frequency of the connecting metro, and the metro fare. In addition, a higher level of total demand in the network has significant negative impacts on P&R mode’s attractiveness compared to auto mode
2012 Vol. 20 (1): 57-64 [Abstract] ( 4689 ) [HTML 1KB] [ PDF 304KB] ( 1054 )
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