Two-Span Interference Effect On Flutter Stability Of A Long-Span Three-Tower Cable-Stayed Bridge

Compared with the conventional two-tower cable-stayed bridge,the span capacity of three-tower cable-stayed bridge is higher than that of conventional two-tower cable-stayed bridge,and it can effectively reduce the span of single span,and reduce the height of main tower at the same span,so it has better span capacity and economic benefits.With the development of cross-sea projects,the application of the long-span three-tower cable-stayed bridge will be more extensive.Compared with conventional cable-stayed Bridges,three-tower cable-stayed Bridges have one more main span,and the two main spans are closely connected by stay cables,main towers and main girders.The behavior of one main span will cause different response to the other span.In this paper,for a three-tower cable-stayed bridge with two main spans over 1000 meters,the vibration modes and vibration phenomena in the process of time-domain analysis of flutter are studied.And the main work of thesis as follows:First of all,it review the development process of the multi tower cable-stayed bridge,and the wind-induced vibration of the bridge as a general description of the research content.Then it introduces a finite element modeling process of three tower cable-stayed bridge,and get the brief analysis of the vibration mode of,again through the study of the concentrated load of one of the mainspan load,according to the displacement of girder is discussed between across the static interference.Secondly,the main girder segment model is designed and made according to the drawings.Then the three component force coefficients and flutter derivatives of the girder are obtained by wind tunnel test of segmental model.Then,the calculation methods of flutter critical wind speed with one and two degrees of freedom are introduced.According to the flutter derivatives obtained from the tests and the principle of modal combination,the flutter critical wind speeds of various combinations are obtained by using the semi-inverse method.The minimum value of the four combinations is 91.11 m/s.Thirdly,on the basis of the existing time-domain flutter analysis method,I reviewed the calculation process of chattering force and self-excited force,then I writed the ANSYS command stream for the time-domain flutter analysis by myself.And a typical plate flutter case was brought into it to verify its correctness.Then,on the premise of the validity of the calculation results,the truss model of the three-tower cable-stayed bridge is simplified,and the results of the simplified model are compared with the original model.Finally,the critical flutter wind speed of a three-tower cable-stayed bridge is 90.5 m/s,and I get the flutter critical wind speed of this bridge.Based on the wind speed results,the effects of wind speed difference between two main spans,buffeting force loading and the stiffness of the middle tower on the flutter vibration patterns of the structure were investigated.Through calculation,it is found that the vibration patterns of the two main spans tend to be the same with time,and the structure is not prone to flutter when the spatial distribution of wind speed is not uniform.The chattering force does not affect the critical flutter wind speed,but makes the main girder fluctuate irregularly.When the stiffness of the tower decreases,the flutter critical wind speed will decrease,and vice versa,but the effect is small.