Static And Dynamic Analysis Of A Long-span Rail-cum-road Cable-stayed Bridge Under Wind And Train Loads

In the region where both roadway and railway bridges are needed,rail-cum-road bridges can share path with both the two ways,save space occupation and construction cost,and are of high economy and efficiency.Wind and train loads are two common and important excitations for long span rail-cum-rod bridges.Hutong rail-cum-road cable-stayed bridge with main span 1092m is considered as engineering background in this dissertation.The nonlinear static and dynamic behavior of the bridge under wind and train loads are analyzed.The running safety performance of trains running on it is also discussed.The main researches can be summarized as followed:(1)In consideration of the development of long-span bridges,especially of long-span rail-cum-road cable-stayed bridges,the current researches about aerostatic stability,wind induc.ed vibration and coupling train-bridge vibration of long-span bridges are reviewed.The significance and necessity of the study on coupled wind-train-bridge system analysis for long-span rail-cum-road bridges is illuminated.(2)An in-situ wind field test is carried out on Hutong Bridge construction site.The averaged and fluctuating wind characteristics are analyzed based on the records obtained from the test.The parameters of wind spectra are gained by curve fitting method.The 3D wind field of Hutong Bridge is simulated by means of spectral representation method based on the fitting parameters.The wind load models of train-bridge system are set up.(3)Based on multi-body theories,a train model with multi DOF is established and the motion function is programed.FE model of Hutong Bridge is built by ANSYS software and the dynamic characteristics of the bridge model is discussed.Geometric nonlinearities including sag effect,beam-column effect and large displacement effect are considered.Based on Inter System Iteration method,the wind-train-bridge system is established.In the system,firstly montion functions of bridge and train are solved separately.Then,bridge and train subsystems are connected by wheel and track relationship.A calculation program is written to realize the iteration between bridge and train subsystems.(4)The analysis method of aerostatic stability for long span bridges is introduced.Procedures of bridge aerostatic stability analysis are programed,in which both bridge geometric nonlinearities and wind load nonlinearity are considered.The whole process and mechanism of aerostatic instability of Hutong Bridge are studied.Influences of different factors are discussed.The results show that the aerostatic instability form of Hutong Bridge is complex spatial bending and torsion.The critical aerostatic instability wind velocity is much larger than the design value,which means the bridge is aerostatic stable.Initial attack angle has a big influence on critical instable wind velocity.With the increase of initial attack angle,the critical wind velocity reduces and gradually approaches to a certain value.The influence of bridge geometric nonlinearities is nonnegligible.With the influence of bridge geometric nonlinearities,the critical wind velocity reduces.(5)The dynamic responses of Hutong Bridge under wind and trains loads and the responses of trains running on the bridges are calculated.The influence of several factors including wind velocities,train velocities,track irregularities,bridge geometric nonlinearities and multi trains on dynamic performance of the bridge and trains are discussed and analyzedThe results show that firstly,the lateral and torsional displacements of the bridge are mainly controlled by wind loads.Vertical reponses are much more affected by trains.But with the increase of wind velocities,the influence of trains reduces.Secondly,larger train velocities cause bigger train responses.Bridge dynamic responses are not sensitive to train velocities.The maximum value of lateral and torsional responses vary with the increase of train velocities.Thirdly,track irregularities have big effect on train responses and small effect on bridge responses.It is considered that track irregularities are the main reason for trains'high frequency vibration.When influences of other factors are analyzed,the deviation caused by track irregularities needs to be erased.Fourthly,in cases when multi trains run through Hutong Bridge together,brige vertical and torsional responses are affected by the number and location of trains.Trains'vibration increase as well.With wind loads effect,dynamic responses of trains on the windward are larger than others.Fifthly,the influence of bridge geometric nonlinerities is nonnegligible.The dynamic responses of both bridge and trains increase in cases considering nonlinear factors.Large displacement nonlinearity has the biggest effect among the three kinds of nonlinearities.Sag effect has great influence on the vertical reponses.The beam-column effect is negligible.Lastly,with one train on bridge,when the instantaneous wind velocity reaches 35m/s and the vehicle velocity is 200km/h,or when the instantaneous wind velocity reaches 30m/s and the vehicle velocity is up to 220km/h,the running safety index of the train is disqualified.With multi trains on the bridge,when the instantaneous wind velocity reaches 30m/s and the vehicle velocity is 200km/h,the running safety index of train on the windward is disqualified.