Study On Buffeting Performance Of A Long-Span Triple-Tower Suspension Bridge And Its Mitigation With MTMD

The triple-tower suspension bridge is a brand new type of structural form that is developed from the double-tower suspension bridge. The addition of a mid-tower makes both the static and dynamic characteristics of the whole bridge system more complicated. With the increase of the bridge span, the wind-induced buffeting response of the triple-tower suspension bridge in strong wind environment becomes more and more prominent. Hence, the refined analysis on buffeting of the long-span triple-tower suspension bridge and its vibration control attract great attentions in engineering area. In this dissertation, the Taizhou Bridge is taken as the engineering background, and the research topics are mainly focused on the wind-induced buffeting of a long-span triple-tower suspension bridge and its vibration control with Multiple Tuned Mass Dampers (MTMD). Based on the measured wind date at Taizhou Bridge site and the commercial finite element package ANSYS, an elaborate research on the buffeting performance of a long-span triple tower suspension bridge and the corresponding buffeting mitigation with MTMD is conducted. The research contents are mainly divided into the following five parts.1. Finite element model establishment of Taizhou Bridge and it dynamic analysis. According to the design parameters of Taizhou Bridge, A three dimensional finite element (FE) model of the long-span triple-tower suspension bridge is established in ANSYS. And the modal parameters are calculated with the subspace iteration method. Based on the measured data acquired in the bridge test and model test, a comparison between the calculated and measured modal parameters is conducted, and the accuracy of the established FE model is verified.2. Field measurement study on the stationary and nonstationary characteristics of a strong typhoon at Taizhou Bridge site. According to the measured wind data of Typhoon Nakri by the anemometer in the structural health monitoring system of Taizhou Bridge, the stationary and nonstationary wind characteristics, including average wind characteristics and turbulent wind characteristics, are studied respectively. Considering the difference between the stationary and nonstationary wind power spectrum model, two measured spectra (stationary spectrum and nonstationary spectrum) are derived from a fitting to the measured spectra accordingly. Hence, two reliable measured spectra are provided for the subsequent simulation of a 3D fluctuating wind field.3. Simplified simulation of a 3D fluctuating wind field for the long-span triple-tower suspension bridge based on interpolation functions. The traditional spectral representation method includes numerous times of Cholesky decomposition during a simulation, so that the computational efficiency is quite restricted. According to the proposed problem, the interpolation function is included to approximate the matrix derived from Cholesky decomposition. Hence, the Cholesky decomposition can be reduced and the computational efficiency is improved. Using the simplified method, the 3D fluctuating wind field of the long-span triple-tower suspension bridge can be fast and efficiently simulated on the premise of enough accuracy.4. Comparative study on the buffeting performance of a long-span triple-tower suspension bridge based on stationary and nonstationary wind spectrum. Considering the difference between stationary and nonstationary wind model, the stationary and nonstationary models of static wind loads, buffeting forces and self-excited forces are respectively derived based on the Davenport quasi-steady theory. Based on the simulated stationary and nonstationary wind field, a comparative study on stationary and nonstationary buffeting performance of a long-span triple-tower suspension bridge is conducted with the established FE model.5. Simulation study on the buffeting mitigation of a long-span triple-tower suspension bridge with MTMD. According to the presented buffeting features of the long-span triple-tower suspension bridge, the design schemes for the MTMD are determined. And then the parameter sensitivity of the design parameters, which includes the number of TMDs, mass ratio, damping ratio, frequency bandwidth, etc., on the control efficiency of MTMD are elaborately studied with the step updating method. Taking into account of both the control efficiency and the robustness, a group of superior parameters is determined for the design of MTMD. And then a comparative study on the buffeting performance of the long-span triple-tower suspension bridge with and without MTMD is further conducted.