| With the need of transportation in offshore areas,various kinds of long-span cross-sea bridges have emerged,among which the long-span steel truss cable-stayed bridge with dual-purpose railway and highway is widely used because of its strong spanning capacity and the ability to meet the requirements of highway and railway transportation.Marine environment is usually harsh,and its strong wind and strong waves have a great impact on the long-span and flexible cross-sea bridges.Therefore,it is necessary to study the structural dynamic response of such bridges under wind and wave loads.The frequency of buffeting in wind-induced effect is higher,and the wind speed is lower when it occurs.It is easy to cause fatigue of components.It has adverse effects on the comfort and even safety of bridge driving.Therefore,the buffeting of structure is mainly considered in wind-induced vibration.Taking a long-span steel truss cable-stayed bridge as an example,this paper studies the structural dynamic response law of the bridge structure under the action of single wind,single wave and combined wind and wave.The main research contents include:1.According to the theory and method of calculating wave forces on pier-column structures put forward by scholars at home and abroad,the calculation methods of wave forces on bridge foundation structures caused by regular waves are summarized.Comparing the pier structure with the wavelength,the pier structure can be divided into large-scale structure and small-scale structure.The wave force calculation of small-scale pier-column structure is based on Morison equation based on potential flow theory.The wave force solution can be obtained on the basis of linear wave theory.The wave force calculation of pile-group structure should also consider the effect of pile group.The wave force calculation of large-scale pier-column structure is based on diffraction theory,and the wave force solution of large-scale cylinder can be obtained on the basis of linear wave theory.Wave forces of large-scale rectangular piers can be calculated according to the code.In addition,Jonswap spectrum is used to simulate the time-history wave loads on bridge foundation caused by random waves.2.According to the structural characteristics of long-span cable-stayed bridges and the natural characteristics of fluctuating wind,the three-dimensional spatial fluctuating wind field of long-span cable-stayed bridges is rationally simplified,and the harmonic synthesis method is used to compile the simulation program of the fluctuating wind field,so as to realize the simulation of the three-dimensional spatial fluctuating wind field of long-span cable-stayed bridges.3.The finite element model of cable-stayed bridge is established by finite element software ANSYS and the structural dynamic characteristics are analyzed.The time-history buffeting force of bridge structure is calculated according to quasi-steady aerodynamic theory.Approximately selecting the most unfavorable wave load condition of bridge structure and calculating the time-history wave load under this condition,the time-history wave load and time-history buffeting wind load are loaded by ANSYS,and then the dynamic response of the bridge under the combined action of single wind,single wave(the most unfavorable wave load condition)and corresponding wind-wave load is analyzed and studied.4.According to the characteristics of the wave field at the bridge site,the wave action under different working conditions is selected to analyze the dynamic response of the bridge structure under the action of single wave and the combined action of corresponding wind and wave under different working conditions.The influence of different wave conditions on the dynamic response of bridge structures is studied.The variation of vibration and dynamic response of bridge structures under different wave periods and different wave heights is summarized.In addition,the difference and relationship of structural vibration under combined action of regular wave and random wave and wind are analyzed. |
