Flutter Analysis Of Long-Span Suspension Bridge During Completed Stage

Flutter is a kind of divergent self-excited vibration, it occurs because the vibrating structure can absorb energy continuously from the airflow, that is greater than the energy consumed by the structural damping. Today, spans of suspension bridges becoming longer and longer, the stiffness and the damping of structures decrease obviously, so the flutter stability has become a very important aspect in the design and construction of long-span suspension bridges.In this thesis, by taking the 4th nanjing suspension bridge over Yangtze river with the main span of 1418m as an example, based on the existing frequency-domain flutter analysis and time-domain flutter analysis, flutter instability of the long-span suspension bridge is studied by theory analysis and wind-tunnel test.The main work of this thesis as follows:First of all, the flutter analysis theory is reviewed. Based on the 2D flutter analysis method and 3D multi-mode flutter analysis method of the bridge, the flutter analysis program is compiled using numerical programming software. One classic example is taken to prove the two programs's correctness and validity. Then the flutter stability of the completion stage is analyzed in frequency-domain.Secondly, how to express the self-excited aerodynamic force in time-domain is discussed. Based on the finite element formulation, the self-excited aerodynamic force has been considered as equivalent aerodynamic stiffness matrix and equivalent aerodynamic damping matrix in order to express the self-excited aerodynamic force in time-domain. A program is developed using the finite element software for 3D flutter analysis in time-domain, and one classic example is taken to prove the program's correctness and validity. Then combined with the the 4th nanjing suspension bridge, analyzing its flutter stability in time-domain.Thirdly, with the 4th nanjing suspension bridge as background, introduce the flutter test of the bridge in wind tunnel and study the flutter characteristic of the girder and determine it's critical wind speed of flutter. At the same time, this thesis uses the formula of Van der Put to estimate the critical wind speed of flutter. Furthermore, the general rules of the flutter stability influenced by the different wind attack angle and structural damping are discussed with flutter derivatives of plate and actual girder using frequency-domain flutter analysis and time-domain flutter analysis. Then the influence is also studied of the flutter derivatives on the the flutter stability of the bridge. At the end, This thesis analyzes the causes and some useful conclusions are drawn.