Mechanism Of Stiffness Degeneration And Aerostatic Stability Performance Of Long-span Suspension Bridges

In the past, wind-resistant researches of large span suspension bridges mainly focus on the problems about dynamic instability and buffeting response. However, the phenomenon of aerostatic torsional divergence due to the cable stiffness degradation isn’t much concerned about.Wind tunnel tests and studies in recent years have shown that, with the increase of bridge span, the possibility of aerostatic instability of large-span bridges was existed. Therefore, it is necessary to conduct a comprehensive study on aerostatic instability mechanism of long-span suspension bridges.On the foundation of the achievements reported in existed research literature, some work is carried out in this paper. Based on the principle of harmonic synthesis method, cubic uniform spline interpolation method is adopted to realize the fast simulation of three-dimensional turbulent wind fields. The aerostatic instability of a long-span suspension bridge immersed in a turbulent wind field is analysed by the approach of dynamic finite element analysis. The mechanism of torsional stiffness degeneration of cable system and aerostatic torsional divergence of suspension bridges is discussed and improved. The influences of vertical deformation and lateral deformation of main cable on torsional stiffness of cable system are studied. At last, parametric analysis on wind-induced response of large-span suspension bridges is investigated. The major work and conclusions are as follows:(1) The basic concept of aerostatic stability is introduced, a comprehensive review is given to the existed aerostatic stability analysis theories and its solving methods.(2) The harmonic synthesis method and cubic uniform spline interpolation method are used to realize the fast simulation of three-dimensional turbulent wind fields.(3) Respectively, the load incremental double iteration method (static finite element method) and dynamic finite element method are adopted to solve the critical wind speed related to aerostatic instability of a long-span suspension bridge immersed in the uniform flow field, it turns out that the two methods lead to a consistent result.(4) Based on the beam-cable generalized model, the expression of the generalized torsional stiffness of cable system is given, and the generalized equation of motion is established. Moreover, the reasonable critical wind speed related to torsional divergence is defined and the influences of vertical deformation and lateral deformation of main cable on torsional stiffness degeneration of cable system and aerostatic stability performance of suspension bridges are evaluated.(5) The static finite element method is taken to calculate the critical wind speed and critical vertical displacement related to torsional divergence of Xihoumen Suspension Bridge immersed in a uniform flow, then using the dynamic finite element method to calculate the critical wind speed and critical vertical displacement when the bridge immerses in a turbulent wind field. Finally, the theoretical knowledge derived from the fifth chapter is used to explain this calculation results.(6) Parametric analysis on the aerostatic stability of large-span suspension bridge is conducted. The initial angle of wind attack, cable wind load, turbulence intensity, spatial correlation and material nonlinearity are considered to explore and evaluate their impacts on the wind-induced response and aerostatic stability performance of the long-span suspension bridges.