Control For Wind-induced Vibration Responses Of Long-span Bridge

To be important transporting facilities and lifeline infrastructures, long-span bridges have been widely investigated and constructed across the world in recent years. Owing to their light and flexible properties, long-span bridges may vibrate excessively subjected to intensive external excitations. Therefore, it is essential to abate their strong dynamic responses for their safety, applicability and durability during long term service, which is also an actual issue for common civil engineers and researchers. As far as the vibration control of bridges is concerned, most attentions are paid to the dynamic responses subjected to wind loads or seismic excitations.The control for wind-induced vibration of long-span bridges was studied in this thesis.Control measures for wind-induced vibration have mainly aerodynamic measures, structural measures and mechanical measures. After the collapse of Tacoma Bridge which was caused by wind-induced vibration instability in 1940, much attention has been put on the research of improving the aerodynamic stability of bridge by means of control measures. Considering the factors of economic, convenience and aesthetic, aerodynamic control measures which were installed on the girder becomes the focal point in vibration control research. Simulation of stochastic wind velocity field is prerequisite to flutter or buffeting analysis of long-span bridges in time-domain. The spectral method and the filtering method are the two traditional simulation methods, which are most widely used. Wavelet analysis method is the development and extension of Fourier analysis, which can quickly and accurately extract the local spectral density characteristics of sample.So wavelet analysis method is the main content to stimulate stochastic wind velocity field.Tianxingzhou Yangtze River Bridge is the first bridge with four railway lines and is the longest span highway and railway combined cabled-stayed bridge in the world. This floating system of bridge, however, may result in large lateral dynamic responses in decks subjected to strong wind. Furthermore, it may substantially affect bridge safety and common functions. Therefore, how to use economical and effective measures to reduce wind induced finite vibration becomes one of the primary problems of bridge engineering. The domestic and foreign researchers have done plenty of research about the vertical buffeting vibration of long-span bridges. But to the lateral vibration, little research has been done. Lateral dynamic response control for long span bridge subjected to wind induced lateral buffeting has been systematically investigated in this thesis based on Tianxingzhou Bridge. The work of this thesis mainly includes the several parts as follows:(1) We first described the domestic and foreign research status of wind-induced-vibration of long-span bridges, introduced several typical methods of wind-induced-vibration control of long-span bridges, and generalized several effective aerodynamic control measures to main beam cross-section. The effectiveness of aerodynamic control measure to buffeting was proved.(2) The main girder section of Sutong Yangtze River Bridge were analysised by means of CFD method. We got coefficients of tri-component from different angles and compared the results with tunnel experimental results and explored the reasons for the changes of coefficients of tri-component through analysising fluid velocity filed.(3) A comprehensive analysis has been done about different girder sections how to affect coefficients of tri-component. On that basis, 46 main girder sections were designed which have different width guide vane, different width fairing, different central slot width, different width-depth ratio and different ventilation ratio of parapets. We have analysised the affections of guide vane width, fairing width, central slot width, width-depth ratio and ventilation ratio of parapets to coefficients of tri-component by means of CFD method. Through the comparison analysis of various sections, we generalized the influences of aerodynamic control measures to the static wind load of long-span bridges, and gave the most suitable sections which were designed in this thesis.(4) Wavelet method was applied to the simulation of the stochastic wind field, performing the effective simulation of spatial stochastic wind field. According to the idea of multi-resolution analysis and orthonormal wavelets, relationship between wavelet coefficient s and PSD(power spectral density)function is deduced , then the wavelet coefficients on each and every scale are obtained from the given PSD function,the intermittency was introduced into wavelet coefficients while at the same time preserves the target spectral characters. As a result, the inverse wavelet transform is applied to generating stationary wind velocity history through the given wavelet coefficients.(5) The three dimensional finite element model of Tianxingzhou cable-stayed Bridge is established and its dynamic characteristics are numerically investigated. Based on this, hybrid control for lateral buffeting responses in decks of floating system cable-stayed bridge installed MR dampers and fluid dampers are investigated. Hybrid control approach is developed and thereby applied for mitigating lateral dynamic responses of Tianxingzhou cable-stayed bridge in decks subjected to buffeting based on fuzzy semi-active control strategy.