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CONTENTS
Volume 3, Number 4, December 2010
 

Abstract
The indirect approach for measuring the bridge frequencies from the dynamic responses of a passing vehicle is a highly potential method. In this study, the effect of road surface roughness on such an approach is studied through finite element simulations. A two-dimensional mathematical model with the vehicle simulated as a moving sprung mass and the bridge as a simply-supported beam is adopted. The dynamic responses of the passing vehicle are solved by the finite element method along with the Newmark B method. Through the numerical examples studied, it is shown that the presence of surface roughness may have negative consequence on the extraction of bridge frequencies from the test vehicle. However, such a shortcoming can be overcome either by introducing multiple moving vehicles on the bridge, besides the test vehicle, or by raising the moving speed of the accompanying vehicles.

Key Words
road surface; roughness; bridge; frequencies; passing vehicle.

Address
K.C. Chang, F.B. Wu and Y.B. Yang: Dept. of Civil Engineering, National Taiwan University, Taipei, Taiwan

Abstract
With taking the geometric nonlinearity of bridge structure into account, a framework is presented for predicting the dynamic responses of a long-span suspension bridge subjected to running train and turbulent wind. The nonlinear dynamic equations of the coupled train-bridge-wind system are established, and solved with the Newmark numerical integration and direct interactive method. The corresponding linear and nonlinear processes for solving the system equation are described, and the corresponding computer codes are written. The proposed framework is then applied to a schemed longspan suspension bridge with the main span of 1120 m. The whole histories of the train passing through the bridge under turbulent wind are simulated, and the dynamic responses of the bridge are obtained. The results demonstrate that the geometric nonlinearity does not influence the variation tendency of the bridge displacement histories, but the maximum responses will be changed obviously; the lateral displacement of bridge are more sensitive to the wind than the vertical ones; compared with wind velocity, train speed affects the vertical maximum responses a little more clearly.

Key Words
geometric nonlinearity; suspension bridge; dynamic response; train; wind.

Address
S.Q. Wang, H. Xia, W.W. Guo and N. Zhang: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China

Abstract
A new technique is proposed for bridge structural damage detection based on spatial wavelet analysis of the time history obtained from vehicle body moving over the bridge, which is different from traditional detection techniques based on the bridge response. A simply-supported Bernoulli-Euler beam subjected to a moving spring-mass unit is established, with the crack in the beam simulated by modeling the cracked section as a rotational spring connecting two undamaged beam segments, and the equations of motion for the system is derived. By using the transfer matrix method, the natural frequencies and mode shapes of the cracked beam are determined. The responses of the beam and the moving spring-mass unit are obtained by modal decomposition theory. The continuous wavelet transform is calculated on the displacement time histories of the sprung-mass. The case study result shows that the damage location can be accurately determined and the method is effective.

Key Words
moving load; beam; dynamic response; damage detection; wavelet transform; Lipschitz exponent.

Address
Ning An, He Xia and Jiawang Zhan: School of Civil Engineering, Beijing Jiaotong University, Beijing 10004, China

Abstract
The Pseudo-Excitation Method (PEM) is applied to study the stochastic space vibration responses of train-bridge coupling system. Each vehicle is modeled as a four-wheel mass-spring-damper system with two layers of suspension system possessing 15 degrees-of- freedom. The bridge is modeled as a spatial beam element, and the track irregularity is assumed to be a uniform random process. The motion equations of the vehicle system are established based on the d\'Alembertian principle, and the motion equations of the bridge system are established based on the Hamilton variational principle. Separate iteration is applied in the solution of equations. Comparisons with the Monte Carlo simulations show the effectiveness and satisfactory accuracy of the proposed method. The PSD of the 3-span simplysupported girder bridge responses, vehicle responses and wheel/rail forces are obtained. Based on the 3

Key Words
train-bridge system; stochastic vibration; FEM; dynamic response.

Address
Xiaozhen Li and Yan Zhu: School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031,China

Abstract
The present paper is concerned with vibrations of an elastic bridge loaded by a moving elastic beam of a finite length, which is an extension of the authors\' previous study where the second beam was modeled as a semi-infinite beam. The second beam, which represents a train, moves with a constant speed along the bridge and is assumed to be connected to the bridge by the limiting case of a rigid interface such that the deflections of the bridge and the train are forced to be equal. The elastic stiffness and the mass of the train are taken into account. The differential equations are developed according to the Bernoulli-Euler theory and formulated in a non-dimensional form. A solution strategy is developed for the flexural vibrations, bending moments and shear forces in the bridge by means of symbolic computation. When the train travels across the bridge, concentrated forces and moments are found to take place at the front and back side of the train.

Key Words
bridge dynamics; moving beam; Euler-Bernoulli theory; rigid interface.

Address
Eugenia C. Cojocaru: Linz Center of Mechtronics GmbH, 4040 Linz, Austria
Hans Irschik: Institute of Technical Mechanics, Johannes-Kepler University, 4040 Linz, Austria

Abstract
Station is an important building in high-speed railway, and its vibration and noise may significantly affect the comfort of waiting passengers. A coupling vibration model for train-structure system is established to analyze and evaluate the vibration level of a typical waiting hall under dynamic train load. The motion of a four-axle vehicle with two suspension system is modeled in multi-body dynamics with linear springs and dampers employed. The station is modeled as a whole finite element structure which is 113 m in longitudinal and 163.5 m in lateral, and the stiffness of the station foundation is considered. According to the assumptions that both wheel and rail are rigid bodies and keep contact to each other in vertical direction, and the wheel/rail interaction and displacement coordination in horizontal direction is defined by the simplified Kalker creep theory, the vehicle spatial vibration model has 27 degrees-of-freedom. An overall analysis procedure is made of the train moving through the station, by which the dynamic responses of the train and the station are calculated. According to the comparison between analysis and test results, the actual connection status between different parts of the station is estimated and the vibration level of the waiting hall is evaluated.

Key Words
high-speed railway; station; moving train; vibration; evaluation.

Address
Mangmang Gao and Jianzhen Xiong: Research & Development Center, China Academy of Railway Sciences, Beijing 100081, China
Zhaojun Xu: Railway Engineering Research Institute, China Academy of Railway Sciences,Beijing 100081, China

Abstract
This study is intended to assess low frequency sound radiated from a viaduct under normal traffic. The bridge comprises steel box girders and wide cantilever decks on which vehicles pass. The low frequency sound and the acceleration response of the bridge under normal traffic are measured to investigate how bridge vibrations affect the low frequency sound observed near the bridge. Observations demonstrate that strong relationships exist between frequency characteristic of bridge

Key Words
field experiment; low frequency sound; sound pressure level; steel box girder bridge; traffic-induced vibration.

Address
M. Kawatani: Dept. of Civil Engineering, Kobe University, Kobe 657-8501, Japan
C.W. Kim: Dept. of Civil and Earth Resources Engineering, Kyoto University, Kyoto 615-8540, Japan
K. Nishitani: Dept. of Civil Engineering, Kobe University, Kobe 657-8501, Japan

Abstract
Based on the Model Coupled Method (MCM), a case study has been carried out on a Concrete-Filled Steel Tubular (CFST) tied arch bridge to investigate the vibration problem. The mathematical model assumed a finite element representation of the bridge together with beam, shell, and link elements, and the vehicle simulation employed a three dimensional linear vehicle model with seven independent degrees-of-freedom. A well-known power spectral density of road pavement profiles defined the road surface roughness for Perfect, Good and Poor roads respectively. In virtue of a home-code program, the dynamic interaction between the bridge and vehicle model was simulated, and the dynamic amplification factors were computed for displacement and internal force. The impact effects of the vehicle on different bridge members and the influencing factors were studied. Meanwhile the acceleration responses of some of the components were analyzed in the frequency domain. From the results some valuable conclusions have been drawn.

Key Words
vibration; tied-arch bridge; vehicle-bridge interaction; amplification; hanger.

Address
Jian-Rong Yang: Faculty of Civil Engineering and Architecture, Kunming University of Science and Technology,
Kunming 650051, China
Jian-Zhong Li: Department of Bridge Engineering, Tongji University, Shanghai 200092, China
Yong-Hong Chen: Kunming Metallurgy College, Kunming 650033, China

Abstract
The performance of full-scale steel and composite bridge safety barriers under vehicle crash is evaluated by using the nonlinear explicit finite element code LS-DYNA. Two types of vehicles used in this study are passenger car and truck, and the performance criteria considered include structural strength and deformation, occupant protection, and post-crash vehicle behavior. It can be concluded that the composite safety barrier satisfies all performance criteria of vehicle crash. Although the steel safety barrier satisfies the performance criteria of occupant protection and post-crash vehicle behavior, it fails to satisfy the performance criterion of deformation. In all performance evaluations, the composite safety barrier exhibits a superior performance in comparing with the steel safety barrier.

Key Words
safety barrier; vehicle crash simulation; finite element modeling; performance evaluation.

Address
Huu-Tai Thai: Dept. of Civil and Environmental Engineering, Sejong University, 98 Kunja Dong, Kwangjin Ku, Seoul 143-747, Republic of Korea


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