Field Measurements Of Wind Characteristics In Complex Terrain And Wind-induced Response Of Multi-pylon Cable-stayed Bridge With High Piers

With the further developing of the traffic infrastructures in China, the large-span bridges crossing bays and mountain valleys will be constructed greatly within the period of the next few years. It is difficult to design the large-span bridges over mountain valleys terrain because of the complexity of wind characteristics and the complexity of wind effects on large-span bridges. Therefore, it is one of the focus of the study in the bridge aerodynamics. Field measurement of wind characteristics over the bridge wite with complex terrain and wind-induced vibration responses of the bridge under construction stages were conducted in present thesis taking the Chishi bridge as background, which is a multi-pylon cable-stayed bridge with high piers in Chenzhou, Hunan Province. The parameters of wind characteristics over complex mountainous terrain were obtained, including the average wind speeds, wind direction and wind attack angles, turbulence intensity, gust factors, turbulence integral scale and fluctuating wind power spectrum, etc. Meanwhile, the wind-induced responses of the bridge were analyzed, including the relationship between the root mean square values of acceleration response and the average wind speeds, and the natural frequenies and damping ratios of the bridge which were compared with the numerical results of finite element model of the bridge. The major works of this thesis are as follows:(1) A brief review of the state-of-the-art of field measurement of wind characteristics and wind-induced responses were given. The main research contents of this thesis were presented.(2) The plan of field measurement for wind characteristics and wind-induced responses of Chishi Bridge were given. Also, the measured systems were introduced in detailed. on-site installation was given.(3) The data processing program based on MATLAB software was developed to analysis the wind characteristics on the site of Chishi Bridge. Based on the long-term measured data, firstly, the average wind speeds, wind directions and wind attack angles of the top of the tower and the bridge deck were obtained. The distribution of wind directions and wind attack angles were analyzed. Then the fluctuating wind characteristics were analyzed, including turbulence intensity, gust factors, turbulence integral scales and fluctuating wind power spectrum parameters. Finally, the relationship between turbulence and gust factors, and the measured fluctuating wind power spectrum were given.(4) The wind-induced acceleration responses of the bridge were analyzed based on the measured data. Firstly, the preprosessing of the original data was conducted, including the slimination of wild values, removing tendency and filtering. Secondly, the root mean square values of the acceleration responses of the bridge with 10 min time interval were analyzed. The relationship between the average wind speeds and the root mean square values were analyzed. Finally, the random decrement technique method and the time domain identification method were used to analyze the structural dynamic characteristics, including the natural frequencies and damping ratios. The analytical results were compared the finite element methods results.