The Research On Wind-resistant Capability Of Composite Girder Suspension Bridges

The composite girder is typical open deck cross section, which is widely appliedin cable-stayed bridges due to its economy and convenience in construction. Whenused in suspension bridge systems, they may suffer from severe vortex-inducedvibrations and even catastrophic flutter instability at low wind velocity as a result ofcombined effect of low torsional stiffness and unfavorable aerodynamic performance.In order to increase the wind-resistant capability of composite girder suspensionbridges, it is desirable to investigate the aerodynamic characteristics of the opencomposite girder suspension bridges. In this study, by taking Yichang MiaozuiYangtze River Bridge with a main span of838m as background, the vortex-inducedvibrations and flutter characteristics of the bridge are investigated by wind tunnel testand analytical analysis. The main contents of the thesis are summarized as follows:(1)The basic concept and theory of wind-induced vibrations, the influencingfactors of aerodynamic performance and aerodynamic measures are summarized. Themain contents of the present study are given.(2) The effect of the location and number of wind barriers beneath the deck onthe vortex-induced vibration and flutter instability is investigated. A total of fivegroups of typical position of wind barrier are tested and analyzed. It is shown that thevortex-induced vibration of the open composite girder with different position of windbarriers is different, especially for the torsional vibration. The performance ofvortex-induced vibration and flutter of the girder with two wind barriers is increasedsignificantly.(3) The flutter of the composite girder suspension bridge is analyzed by using thefinite-element-based flutter analysis method, and the variation of frequency anddamping ratio for each complex mode with wind velocity is portrayed. Additionally,the variation of the eigenvalue in the flutter analysis is theoretically explained byusing the perturbation technique of complex eigenvalue problems. The resultsindicates thatâ‘ the critical flutter velocity obtained with the finite-element-basedflutter analysis is quite close to, and slightly larger than, the experimental valuesobtained from the sectional model tests, which may be caused by the di fferentcriterions used in assessing the flutter threshold between analysis and wind tunnelexperiments,â‘¡the decrement of modal frequency for the torsional mode is mutually contributed by the presence of aerodynamic stiffness and the non-classicalaerodynamic damping.(4) A comparison is made of the three empirical modes for vortex-inducedvibrations. Based on the VIV test in wind tunnel, the model parameters for eachempirical model are identified. It is shown that the different empirical modes yieldalmost the same fluctuating lift force and the all the three models well reproduce theexperimental data of VIV.