The Safety Of Road Vehicles Driven On Bridge Deck Under Crosswind And Its Windproof Precautions

Strong winds not only intensify the vibration of bridges, reduce the fatigue life and durability of the structure, but also threaten the safety and comfort of vehicles traveling on the bridge. To lessenthe number of wind-induced traffic accidents occurred on bridgesin windy weather,the universal practice is to install wind barriers along the bridge decks, which has become one of the effectivecountermeasures to guarantee the vehicle safety. Based on the coupling vibration theory of the wind-vehicle-bridge system, this paper focuses on the issues of the sheltering efficiency of wind barriers,and the safety and comfort of vehicles traveling onbridges.Main research works are as follows:(1) A simulation algorithm of one-dimensionmultivariate stochastic wind velocity field is proposed based on inverse fast Fourier transform (IFFT). Since the phase of the IFFT for a conjugate-symmetric sequence is zero, a conjugate-symmetric series can be created in the frequency-domain. The fluctuating wind velocity for one point can be generated by just one execution of IFFT, which not only releases the computational work from enormous superposition of trigonometric operation but also decreases the executions of IFFT. So, the algorithm is very efficient. Mathematical analysis shows that the ergodic property of the mean value and the auto-correlation function of the simulated sample are satisfied, and the ergodicity of the cross-correlation function can also be satisfied as long as the period of the sample is long enough.(2) The coupling vibration model of the wind-road vehicle-bridge system is established. According on the typical types of road vehicles, the dynamic analysis models, a two-axle vehicle with 13 degrees of freedom and a four-axle trailing truck with 24 independent degrees of freedom, are set up. The effects of the deflection characteristics of tires on the dynamics equations of vehicle are disscussed. The principle of the interaction between vehicles and bridges is clarified. In consideration of the coherence functionmodel of the stochastic road surface excitation, a simulation method of the road roughness samples in the time-domain is presentedbased on the IFFTtechnique. Considering the moving property of the vehicle and the influences of the horizontal and vertical turbulence wind on the transient yaw angle and attack angle of the moving vehicle, the expressions of aerodynamic forces on road vehicles are deduced, which can correctly reflect the wind loads acting on the moving road vehicles. On the basis of the above discussions, the analytical equations of the coupling vibration of the wind-road vehicle-bridge system are established.(3) An analysis program of wind-road vehicle-bridge system is compiled. Based on the programming framework of MFC and the 3D display technology of OpenGL, the coupling vibration analysis program of wind-road vehicle-bridge system, named as WVBANSYS, is compiled on the platform of Visual Studio 9.0. The calculation functions of the program, including the coupling analysis of vehicle-bridge system, the time-domain flutter analysis of bridge and the time-domain buffeting analysis of bridge, are verified respectively.(4) The affecting factors and the variation rules of the dynamic response of the wind-road vehicle-bridge the coupling vibration system are investigated. Based on the response characteristics of vehicles, the judging criteria for the wind-induced sideslip and roll-over accidents are improved.The evaluation criteria of vehicle ride comfort on the basis of theISO 2631 specification is also disscussed. To focus on the issues of the safety and comfort of the driving vehicles under crosswind, some conclusions are drawn:Thederivative of the aerodynamic yaw angle dC/dy/decreases the safety and comfort of the driving vehicles, and it is in favor of the evaluation of the comfort of vehicles taken into account the effects of the deflection characteristics of tires; the differences between the coherence functions of road roughness lead to remarkable differences of the dynamic responses of vehicles; The unfavorable factors, including high wind velocity and vehicle speed, the location of the vehicle in the windward side and poor road conditions, could decrease the safety and comfort indicatorvalues of road vehicles.(5) The effects of wind barriers on the local wind environment of the bridge deck and the driving safety of vehicles are studied. In the wind tunnel, the ventilation ratios of wind barrier on the distribution characteristics of the mean wind velocity and turbulence intensity above the bridge deck are investigated. The influences of the ventilation ratios of wind barrier on the aerodynamic characteristics ofvarious road vehicles are also investigated. Results show that wind barriers decrease the mean velocity and the turbulence intensity of the bridge deck and obviously reduce the magnitudes of the aerodynamic forces acting on vehicles. The critical wind velocity for the safety of vehicles under crosswind is presented by means of the simplified static analysis and the coupling vibration analysis method.Results show that the large container truck is more prone to roll-over accidents in the absence of wind barriers; wind barriers significantly improve the critical wind speed of vehicles; the critical wind speed of vehicles increases with the decreasing of the ventilation ratios of wind barriers.