Techno Press
Tp_Editing System.E (TES.E)
Login Search


was
 
CONTENTS
Volume 20, Number 2, February 2015
 

Abstract
.

Key Words
.

Address
.

Abstract
The performance of bridges under strong wind and traffic is of great importance to set the traveling speed limit or to make operational decisions for severe weather, such as controlling traffic or even closing the bridge. Meanwhile, the vehicle\'s safety is highly concerned when it is running on bridges or highways under strong wind. During the past two decades, researchers have made significant contributions to the simulation of the wind-vehicle-bridge system and their interactive effects. This paper aims to provide a comprehensive review of the overall performance of the bridge and traffic system under strong wind, including bridge structures and vehicles, and the associated mitigation efforts.

Key Words
vehicle aerodynamics; bridge aerodynamics; strong wind; traffic; bridge

Address
C.S. Cai, Jiexuan Hu and Xuan Kong: Department of Civil and Environmental Engineering, Louisiana State University,
Baton Rouge, LA 70803, USA
Suren Chen: Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO 80523, USA
Yan Han: School of Civil Engineering and Architecture, Changsha University of Science & Technology,
Changsha, Hunan, China, 410004
Wei Zhang: Department of Civil and Environmental Engineering, University of Connecticut, Storrs,
Connecticut 06269, USA


Abstract
A numerical model for analyzing airtraintrack interaction is proposed to investigate the dynamic behavior of a high-speed train running on a track in crosswinds. The model is composed of a traintrack interaction model and a trainair interaction model. The traintrack interaction model is built on the basis of the vehicletrack coupled dynamics theory. The trainair interaction model is developed based on the train aerodynamics, in which the Arbitrary LagrangianEulerian (ALE) method is employed to deal with the dynamic boundary between the train and the air. Based on the airtraintrack model, characteristics of flow structure around a high-speed train are described and the dynamic behavior of the high-speed train running on track in crosswinds is investigated. Results show that the dynamic indices of the head car are larger than those of other cars in crosswinds. From the viewpoint of dynamic safety evaluation, the running safety of the train in crosswinds is basically controlled by the head car. Compared with the generally used assessment indices of running safety such as the derailment coefficient and the wheel-load reduction ratio, the overturning coefficient will overestimate the running safety of a train on a track under crosswind condition. It is suggested to use the wheel-load reduction ratio and the lateral wheelrail force as the dominant safety assessment indices when high-speed trains run in crosswinds.

Key Words
high-speed train; dynamic safety; crosswind; aerodynamics; vehicletrack coupled dynamics; Arbitrary LagrangianEulerian method

Address
Wanming Zhai and Zhen Li: Train and Track Research Institute, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, P.R. China
Jizhong Yang: China Railway Eryuan Engineering Group Co. Ltd., No. 3 Tongjin Road, Chengdu 610031, P.R. China
Haiyan Han: Beijing Urban Construction Design and Development Group Co. Ltd, Beijing, P.R. China

Abstract
To investigate the effects of \"sudden change\" of wind fluctuations on vehicle running performance, which is caused by the artificial discrete simulation of wind field, a three-dimensional vehicle model is set up with multi-body dynamics theory and the vehicle dynamic responses in crosswind conditions are obtained in time domain. Based on Hilbert Huang Transform, the effects of simulation separations on time-frequency characteristics of wind field are discussed. In addition, the probability density distribution of \"sudden change\" of wind fluctuations is displayed, addressing the effects of simulation separation, mean wind speed and vehicle speed on the \"sudden change\" of wind fluctuations. The \"sudden change\" of vehicle dynamic responses, which is due to the discontinuity of wind fluctuations on moving vehicle, is also analyzed. With Principal Component Analysis, the comprehensive evaluation of vehicle running performance in crosswind conditions at different simulation separations of wind field is investigated. The results demonstrate that the artificial discrete simulation of wind field often causes \"sudden change\" in the wind fluctuations and the corresponding vehicle dynamic responses are noticeably affected. It provides a theoretical foundation for the choice of a suitable simulation separation of wind field in engineering application.

Key Words
artificial discrete simulation; sudden change; wind simulation separation; multibody dynamics; Hilbert Huang Transform; Principal Component Analysis

Address
Mengxue Wu, Yongle Li and Ning Chen: Department of Bridge Engineering, Southwest Jiaotong University, 610031 Chengdu, Sichuan, P.R. China

Abstract
Several frameworks for the dynamic analysis of wind-vehicle-bridge systems were presented in the past decade to study the safety or ride comfort of road vehicles as they pass through bridges under crosswinds. The wind loads on the vehicles were generally formed based on the aerodynamic parameters of the stationary vehicles on the ground, and the wind loads for the pure bridge decks without the effects of road vehicles. And very few studies were carried out to explore the dynamic effects of the aerodynamic interference between road vehicles and bridge decks, particularly for the moving road vehicles. In this study, the aerodynamic parameters for both the moving road vehicle and the deck considering the mutually-affected aerodynamic effects are formulized firstly. And the corresponding wind loads on the road vehicle-bridge system are obtained. Then a refined analytical framework of the WVB system incorporating the resultant wind loads, a driver model, and the road roughness in plane to fully consider the lateral motion of the road vehicle under crosswinds is proposed. It is shown that obvious lateral and yaw motions of the road vehicle occur. For the selected single road vehicle passing a long span bridge, slight effects are caused by the aerodynamic interference between the moving vehicle and deck on the dynamic responses of the system.

Key Words
wind-vehicle-bridge system; aerodynamic parameter; interference; moving vehicle

Address
Bin Wang: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu, China;
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University,
Hong Kong, China;
Key Laboratory of High-speed Railway Engineering (Southwest Jiaotong University), Ministry of Education, Chengdu, Sichuan 610031, China
You-Lin Xu: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University,
Hong Kong, China
Yongle Li: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu, China;
Key Laboratory of High-speed Railway Engineering (Southwest Jiaotong University), Ministry of Education, Chengdu, Sichuan 610031, China

Abstract
For high-speed railways (HSR) in wind prone regions, wind barriers are often installed on bridges to ensure the running safety of trains. This paper analyzes the effect of wind barriers on the running safety of a high-speed train to cross winds when it passes on a bridge. Two simply-supported (S-S) PC bridges in China, one with 32 m box beams and the other with 16 m trough beams, are selected to perform the dynamic analyses. The bridges are modeled by 3-D finite elements and each vehicle in a train by a multi-rigid-body system connected with suspension springs and dashpots. The wind excitations on the train vehicles and the bridges are numerically simulated, using the static tri-component coefficients obtained from a wind tunnel test, taking into account the effects of wind barriers, train speed and the spatial correlation with wind forces on the deck. The whole histories of a train passing over the two bridges under strong cross winds are simulated and compared, considering variations of wind velocities, train speeds and without or with wind barriers. The threshold curves of wind velocity for train running safety on the two bridges are compared, from which the windbreak effect of the wind barrier are evaluated, based on which a beam structure with better performance is recommended.

Key Words
high-speed railway; cross winds; dynamic analysis; simply-supported beam bridge; wind barrier; windbreak effect; running safety

Address
Weiwei Guo: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;
Beijing Key Laboratory of Structural Wind Engineering and Urban Wind Environment, Beijing 100044, China;
Division of Structural Engineering and Bridges, KTH Royal Institute of Technology, SE-10044, Sweden
He Xia: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;
Beijing Key Laboratory of Structural Wind Engineering and Urban Wind Environment, Beijing 100044, China
Raid Karoumi: Division of Structural Engineering and Bridges, KTH Royal Institute of Technology, SE-10044, Sweden
Tian Zhang: Institute of Road and Bridge Engineering, Dalian Maritime University, Dalian116026, China
Xiaozhen Li: School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China

Abstract
Wind tunnel experiments are used to investigate the aerodynamic interactions between vehicles and wind barriers on a railway bridge. Wind barriers with four different heights (1.72 m, 2.05 m, 2.5 m and 2.95 m, full-scale) and three different porosities (0%, 30% and 40%) are studied to yield the aerodynamic coefficients of the vehicle and the wind barriers. The effects of the wind barriers on the aerodynamic coefficients of the vehicle are analyzed as well as the effects of the vehicle on the aerodynamic coefficients of the wind barriers. Finally, the relationship between the drag forces on the wind barriers and the aerodynamic coefficients of the vehicle are discussed. The results show that the wind barriers can significantly reduce the drag coefficients of the vehicle, but that porous wind barriers increase the lift forces on the vehicle. The windward vehicle will significantly reduce the drag coefficients of the porous wind barriers, but the windward and leeward vehicle will increase the drag coefficients of the solid wind barrier. The overturning moment coefficient is a linear function of the drag forces on the wind barriers if the full-scale height of the wind barriers h<2.5 m and the overturning moment coefficients CO>0.

Key Words
wind barrier; aerodynamic effect; crosswinds; wind tunnel test; vehicle; railway bridge

Address
Xiang Huoyue, Li Yongle and Wang Bin: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, China;
Key Laboratory of High-speed Railway Engineering (Southwest Jiaotong University), Ministry of Education, Chengdu, Sichuan 610031, China


Abstract
Long-span cable-stayed bridges exhibit some features which are more critical than typical long span bridges such as geometric and aerodynamic nonlinearities, higher probability of the presence of multiple vehicles on the bridge, and more significant influence of wind loads acting on the ultra high pylon and super long cables. A three-dimensional nonlinear fully-coupled analytical model is developed in this study to improve the dynamic performance prediction of long cable-stayed bridges under combined traffic and wind loads. The modified spectral representation method is introduced to simulate the fluctuating wind field of all the components of the whole bridge simultaneously with high accuracy and efficiency. Then, the aerostatic and aerodynamic wind forces acting on the whole bridge including the bridge deck, pylon, cables and even piers are all derived. The cellular automation method is applied to simulate the stochastic traffic flow which can reflect the real traffic properties on the long span bridge such as lane changing, acceleration, or deceleration. The dynamic interaction between vehicles and the bridge depends on both the geometrical and mechanical relationships between the wheels of vehicles and the contact points on the bridge deck. Nonlinear properties such as geometric nonlinearity and aerodynamic nonlinearity are fully considered. The equations of motion of the coupled wind-traffic-bridge system are derived and solved with a nonlinear separate iteration method which can considerably improve the calculation efficiency. A long cable-stayed bridge, Sutong Bridge across the Yangze River in China, is selected as a numerical example to demonstrate the dynamic interaction of the coupled system. The influences of the whole bridge wind field as well as the geometric and aerodynamic nonlinearities on the responses of the wind-traffic-bridge system are discussed.

Key Words
bridges; long span; traffic; geometric nonlinearity, aerodynamic nonlinearity; wind field; nonlinear iteration method

Address
Wanshui Han and Jun Wu: Highway College Chang\'an University, Xi\'an, Shaanxi, 710064, China
Lin Ma: Department of Civil and Environmental Engineering, Hohai University, Nanjing, Jiangsu 210098, China
C.S. Cai: Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803. USA
Suren Chen: Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO 80523, USA


Abstract
The presence of traffic on a slender long-span bridge deck will modify the cross-section profile of the bridge, which may influence the flutter derivatives and in turn, the critical flutter wind velocity of the bridge. Studies on the influence of vehicles on the flutter derivatives and the critical flutter wind velocity of bridges are rather rare as compared to the investigations on the coupled buffeting vibration of the wind-vehicle-bridge system. A typical streamlined cross-section for long-span bridges is adopted for both experimental and analytical studies. The scaled bridge section model with vehicle models distributed on the bridge deck considering different traffic flow scenarios has been tested in the wind tunnel. The flutter derivatives of the modified bridge cross section have been identified using forced vibration method and the results suggest that the influence of vehicles on the flutter derivatives of the typical streamlined cross-section cannot be ignored. Based on the identified flutter derivatives, the influence of vehicles on the flutter stability of the bridge is investigated. The results show that the effect of vehicles on the flutter wind velocity is obvious.

Key Words
long-span suspension bridges; flutter stability; influence of vehicles; finite element (FE) model; ANSYS

Address
Yan Han, Shuqian Liu and Jianren Zhang: School of Civil Engineering and Architecture, Changsha University of Science & Technology, Changsha, China, 410004
C.S. Cai: Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge,
USA, LA 70803
Suren Chen: Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, USA, Co 80523
Xuhui He: School of Civil Engineering, Central South University, Changsha, China, 410075

Abstract
In this paper, wireless monitoring of typhoon-induced variation of dynamic characteristics of a cable-stayed bridge is presented. Firstly, cable-stayed bridge with the wireless monitoring system is described. Wireless vibration sensor nodes are utilized to measure accelerations from bridge deck and stay cables. Also, modal analysis methods are selected to extract dynamic characteristics. Secondly, dynamic responses of the cable-stayed bridge under the attack of two typhoons are analyzed by estimating relationships between wind velocity and dynamic characteristics. Wind-induced variations of deck and cable vibration responses are examined based on the field measurements under the two consecutive typhoons, Bolaven and Tembin. Finally, time-varying analyses are performed to investigate non-stationary random properties of the dynamic responses under the typhoons.

Key Words
wireless monitoring; typhoon-induced variation; dynamic characteristics; cable-stayed bridge

Address
Jae-Hyung Park, Thanh-Canh Huynh and Jeong-Tae Kim: Department of Ocean Engineering, Pukyong National University, 45 Yongso-ro, Nam-gu, Busan 608-737, Republic of Korea


Abstract
To overcome the drawbacks of the traditional contact-type sensor for structural displacement measurement, the vision-based technology with the aid of the digital image processing algorithm has received increasing concerns from the community of structural health monitoring (SHM). The advanced vision-based system has been widely used to measure the structural displacement of civil engineering structures due to its overwhelming merits of non-contact, long-distance, and high-resolution. However, seldom currently-available vision-based systems are capable of realizing the synchronous structural displacement measurement for multiple points on the investigated structure. In this paper, the method for vision-based multi-point structural displacement measurement is presented. A series of moving loading experiments on a scale arch bridge model are carried out to validate the accuracy and reliability of the vision-based system for multi-point structural displacement measurement. The structural displacements of five points on the bridge deck are measured by the vision-based system and compared with those obtained by the linear variable differential transformer (LVDT). The comparative study demonstrates that the vision-based system is deemed to be an effective and reliable means for multi-point structural displacement measurement.

Key Words
structural health monitoring; dynamic displacement; vision-based system; digital image processing technique; pattern matching algorithm

Address
X.W. Ye, C.Z. Dong and T. Liu: Department of Civil Engineering, Zhejiang University, Hangzhou 310058, China
Ting-Hua Yi: School of Civil Engineering, Dalian University of Technology, Dalian 116023, China
H. Bai: Tangram Electronic Engineering Co. Ltd., Beijing 100088, China

Abstract
This paper investigates the effects of Reynolds number (Re) on the aerodynamic characteristics of a twin-deck bridge. A 1:36 scale sectional model of a twin girder bridge was tested using the Wall of Wind (WOW) open jet wind tunnel facility at Florida International University (FIU). Static tests were performed on the model, instrumented with pressure taps and load cells, at high wind speeds with Re ranging from 1.3X10 to 6.1X10 based on the section width. Results show that the section was almost insensitive to Re when pitched to negative angles of attack. However, mean and fluctuating pressure distributions changed noticeably for zero and positive wind angles of attack while testing at different Re regimes. The pressure results suggested that with the Re increase, a larger separation bubble formed on the bottom surface of the upstream girder accompanied with a narrower wake region. As a result, drag coefficient decreased mildly and negative lift coefficient increased. Flow modification due to the Re increase also helped in distributing forces more equally between the two girders. The bare deck section was found to be prone to vortex shedding with limited dependence on the Re. Based on the observations, vortex mitigation devices attached to the bottom surface were effective in inhibiting vortex shedding, particularly at lower Re regime.

Key Words
Reynolds number effect; twin box girder bridge; vortex shedding; force and moment coefficient; pressure distribution; aerodynamic response

Address
Ramtin Kargarmoakhar, Arindam G. Chowdhuryand Peter A. Irwin: Department of Civil and Environmental Engineering and International Hurricane Research Center, Florida International University, Miami, FL, USA

Abstract
Higher-mode vertical vortex-induced vibrations (VIV) have been observed on several steel box-girder suspension bridges where different vertical modes are selectively excited in turn with wind velocity in accordance with the Strouhal law. Understanding the relationship of VIV amplitudes for different modes of vibration is very important for wind-resistant design of long-span box-girder suspension bridges. In this study, the basic rectangular cross-section with side ratio of B/D=6 is used to investigate the effect of different modes on VIV amplitudes by section model tests. The section model is flexibly mounted in wind tunnel with a variety of spring constants for simulating different modes of vibration and the non-dimensional vertical amplitudes are determined as a function of reduced velocity U/fD. Two \'lock-in\' ranges are observed at the same onset reduced velocities of approximately 4.8 and 9.4 for all cases. The second \'lock-in\' range, which is induced by the conventional vortex shedding, consistently gives larger responses than the first one and the Sc-normalized maximum non-dimensional responses are almost the same for different spring constants. The first \'lock-in\' range where the vibration frequency is approximately two times the vortex shedding frequency is probably a result of super-harmonic resonance or the \"frequency demultiplication\". The main conclusion drawn from the section model study, central to the higher-mode VIV of suspension bridges, is that the VIV amplitude for different modes is the same provided that the Sc number for these modes is identical.

Key Words
suspension bridges; bridge deck; vortex-induced vibrations; wind tunnel tests; section model tests

Address
X.G. Hua, Z.Q. Chen, W. Chen, H.W. Niu and Z.W. Huang: Wind Engineering Research Center, Key Laboratory for Wind and Bridge Engineering of Hunan Province, College of Civil Engineering, Hunan University, Changsha 410082, China


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com