|Title:||Dynamic analysis of coupled road vehicle and long span cable-stayed bridge systems under cross winds|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Bridges, Cable-stayed -- Aerodynamics
Motor vehicles -- Aerodynamics
|Department:||Department of Civil and Structural Engineering|
|Pages:||1 v. (various pagings) : ill. (some col.) ; 30 cm|
|Abstract:||This thesis mainly focuses on the development of a framework for performing dynamic analysis of coupled road vehicle and long span cable-stayed bridge systems under cross winds and the evaluation of the safety and ride comfort of road vehicles running on a long span cable-stayed bridge under cross winds. First, a fully computerised approach for assembling the equations of motion of any types of coupled road vehicle and long span cable-stayed bridge systems and for investigating vehicle-bridge interaction problem is developed. The main features of this approach include: (a) the mass matrix, damping matrix, and stiffness matrix of the bridge alone are established using the conventional finite element method; (b) the rigid body element, spring element, and damping device element are used to model any configuration of the vehicle; and (c) the equations of motion of the bridge can be automatically expanded to the equations of motion of the coupled vehicle and bridge system by the computer program with road surface roughness included. When the type of vehicle is changed, only a little input information on the vehicle needs to be revised. The accuracy and applicability of the fully computerised approach and the associated computer program are demonstrated through a case study using a long span cable-stayed bridge with a group of moving heavy vehicle. The case study considers the dynamic response of the coupled five high-sided road vehicles arranged in line at interval of 10 meters and one triple-tower long span cable-stayed bridge having an overall length of 1,177m. The case study also investigates the ride comfort of the high-sided vehicles running on the long span bridge in the vertical direction. The effects of road condition and vehicle speed on the dynamic response of the vehicle-bridge system are assessed. The road condition and vehicle speed affect the bridge response slightly but influence the vehicle response and the contact forces significantly. The ride comfort of the concerned vehicle running on the bridge meets the ride comfort criteria stipulated in the document issued by the International Standard Organisation (ISO). Compared with the dynamic response of the vehicle running on the ground, the vibration of the bridge is a dominant factor causing the vertical acceleration response of the vehicle under a very good road condition. On the other hand, the vertical road surface roughness is a dominant factor for the vertical acceleration response of the vehicle under the average road condition. The time-domain buffeting analysis of the triple-tower long span cable-stayed bridge is then performed to explore aeroelstic effects under different mean wind speeds and to facilitate the investigation on the coupled road vehicle-long span bridge systems under cross winds. The most up-to-date information and technique on the simulation of buffeting forces and self-excited forces in the time domain are adopted. A comparison of dynamic response of the bridge induced by cross winds with that by moving vehicles is conducted to find the differences in the bridge response due to two types of excitations. A more realistic model of high-sided road vehicles subjected to cross winds with both vertical and lateral motions included is then presented to investigate the safety and the ride comfort of the vehicle running on the ground in cross winds and the effects of road surface roughness and vehicle suspension system. The road surface roughness can considerably affect the vertical displacement response and the contact forces of the vehicle, but has no effect on the lateral and rotational responses of the vehicle. The vehicle suspension affects not only the vertical response and the contact forces but also the lateral and rotational responses of the vehicle. Vehicle accident speeds of the high-sided road vehicle running on the ground due to a sudden crosswind gust are given for a series of mean wind speeds and road conditions. The ride comfort of the concerned vehicle satisfies the specified comfort criteria when the vehicle speed and mean wind are 80km/h and 15.0m/s, respectively. A framework for dynamic analysis of coupled road vehicle and cable-stayed bridge systems under cross winds is then developed in the time domain. The most up-to-date information in the areas of both vehicle-bridge interaction and wind-bridge interaction is taken into consideration. The wind forces acting on the road vehicles are, however, assumed to be steady wind forces because of the lack of relevant test data. Different from the conventional investigation of vehicle-bridge interaction, a special damper, of which the damping coefficient is dependent on unknown motion of the vehicle and the bridge, is introduced to consider the possible sideslip of the vehicle tire relative to the bridge deck in the lateral direction. The turbulent wind velocity used in the calculation of wind forces on the vehicle is kept compatibility with those used in the calculation of wind forces on the bridge. The equations of motion of the coupled road vehicle-bridge system with the special dampers under cross winds are assembled using the fully computerised approach. The associated computer programs are accordingly developed and then used to predict the dynamic response of coupled road vehicle-bridge systems under cross winds. A case study on the safety and ride comfort of high-sided road vehicles running over a long span cable-stayed bridge under cross winds is finally performed, and the effects of road surface roughness, mean wind velocity, and vehicle speed are investigated. The accident vehicle speeds due to a sudden crosswind gust are obtained from a great deal of computation work, which provide a reference to traffic control of the cable-stayed bridge during windy periods. The oscillation of the cable-stayed bridge affects the accident vehicle speed considerably under higher mean wind velocity after a comparison of the safety of the vehicle running on the bridge and the ground under a sudden crosswind gust. The vertical and lateral ride comfort of the concerned road vehicle running on the bridge subjected to cross winds can meet the specified comfort criteria when the vehicle speed and mean wind are 80km/h and 15.0m/s, respectively.|
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