Analysis On Buffeting Response Of Railway Cable-Stayed Bridges During Erection Stage

With the development of material and construction technology, by using new structural design method the aerodynamic instability of structures could be avoided. But when the span of bridge is becoming longer and longer, the bridge would exhibit some special characteristics such as high flexibility, low structural damping and light in weight; Those characteristics make the structures more susceptible to wind loads and elevate the possibility of wind-induced vibration. Buffeting is a kind of vibration induced by turbulent winds, it can occur at any wind speed. During the construction stage, the whole stiffness of bridge is not large, so excessively large vibration can be excited by buffeting, in this way it is very necessary to study the buffeting response of bridge under construction stage.In this thesis, the buffeting response of the railway bridges under construction is investigated. The main work of this paper is listed as follows:(1) A simplified three-dimensional stochastic wind velocity field model is established in this paper; also the constant amplitude wave superposition is employed to simulate the stochastic wind velocity.(2) As for the calculation of structural natural dynamic behavior, the modeling method for the steel truss stiffened girder is discussed. According to the principle of equivalent rigidity and equivalent mass, a single beam model is built to simulate the whole truss stiffened girder; This simplification is necessary for the analytical process.(3) Based on the buffeting theory proposed by Scanlan, the wind loads which include steady-state wind loads and buffeting loads are converted into time domain description. Then the numerical integration algorithm is used to calculate the equation of motion, so the buffeting response could be obtained. A universal program is developed for buffeting response analysis.(4) A railway bridge under construction is taken as a case study, and the sectional model test and full aeroelastic bridge model wind tunnel test are introduced in details. The buffeting response of the bridge is measured in wind tunnel. Different influences on the buffeting response that take into account aerodynamic admittance function and wind loads acting on the pylon are calculated by using self—developed program.Comparing the results obtained through wind tunnel and the results by theory calculation, some conclusions can be drawn. The wind tunnel results generally comply with the calculation results. The wind tunnel results are smaller than the calculation results when the value of the aerodynamic admittance is set to 1 but are larger than the calculation results when the value of the aerodynamic admittance is replaced by Sears function, so in light of this, for purpose of safety it is necessary to employ the calculation results that are obtained by adopting 1 as aerodynamic admittance to evaluate the buffeting response of cable-stayed bridges. The lateral response of the pylon can be accurately obtained when the loads acting on the pylon are taken into account for calculation. Model for the wind field coherence function, sample of simulated wind speed velocity, calculation accuracy all have significant influence on the accuracy of calculation and analysis.