The Nonlinear Vibration Research On Large-span Bridge Structure Under Turbulent Wind

Along with the renewal and improvement of various modern technology, the bridge structure is developing in the direction of the long span. The main span about 1 km has begun to appear in the world on cable-stayed bridges and suspension bridges, such as the main span 1088 m—Su Tong Bridge, 1018 m—Stonecutters Bridge, 1104m—Russian Island Bridge, etc...In the past, when researchers studied the wind-induced vibration response of long-span bridges, especially the bridge flutter, most of them had considered only the standard segment model of the main beam structure and had a wind tunnel tests on it, meantime, they reduced the wind into mean wind. However due to the factors which are geometric nonlinear of the main span and parameter nonlinear in turbulence wind load, will cause highly nonlinear behavior on large span bridge, these nonlinear behaviors will lead to some different motion states which the structure in the section model test on mean wind can’t behave at the process of vibration. Therefore, this paper will extended the research object from the traditional standard of segment model test to the main span of the whole bridge structure, combined with some mature theory to study the long-span bridges’ critical flutter state and its influencing factors and the structure of the nonlinear vibration behavior under turbulent wind, to provide some ideas and suggestions in practical engineering of solving flutter critical wind speed design and vibration control about large span bridge.The main research contents in this paper are shown as followings:To simplify the long span bridge main span prototype into a three dimensional rectangular plate structure, with the Von Karman plate theory of large deformation, the slender body theory and low-speed aerodynamics theory as the theoretical basis, using Hamilton principle and Lighthill aerodynamic model to establish three dimension motion differential equation of the large span bridge. Nondimensionalized the obtained differential equations, using Galerkin method to discrete the dimensionless equation and obtained the dynamic equations of the structure.Based on the dynamic equation, to study the sensitivity to the flutter amplitude of the structure of the modal function, initial condition, structural damping and other parameters. In the 1:1:2 ratio of turbulent wind’s frequency with the main and the second frequency of the bridge, to analyse the differential equation of the threedimesional motion of the main span of the bridge by using the method of multiple scales,then gain the average equation of the motorial structure. Based on the accurate numerical, by using Poincare section drawings, bifurcation diagram, phase trajectory diagram and other tools to study the motion state of the large span bridge structure and the nonlinear response behavior, such as cycle, bifurcation and chaotic motion.Through the simplification and the Galerkin discretization of the dynamic equations of the long-span bridges, a simplified equation for solving the critical flutter wind speed of the main span structure is obtained. Based on this equation, to gain the method(L-V) for solving the bridge main span flutter critical wind speed. Compared the flutter critical wind speed calculated by L-V method with the section model wind tunnel test results which have studied by the previous scholars, verify the feasible of L-V method. On the basis of it, analysis the influence of the width span ratio, the thickness span ratio, the angle of the wind and the turbulence components on the flutter critical wind speed of the long-span bridges.