NON-SYNOPTIC WIND-INDUCED EFFECTS ON LONG-SPAN BRIDGES: ANALYTICAL AND NUMERICAL APPROACHES
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Long-span bridges are highly susceptible to wind excitations due to their flexibility and low structural damping. Currently, the analysis framework for examining the synoptic wind-induced effects on long-span bridges is well developed. However, many long-span bridges are located in thunderstorm or tornado-prone areas, and hence may suffer from the non-synoptic wind events during their lifetimes. The primary goal of this dissertation is to develop an effective analysis framework to better investigate non-synoptic wind-induced effects on long-span bridges. A long-span suspension bridge is employed here to demonstrate the effectiveness of the proposed analysis framework and to highlight non-synoptic wind-induced effects on structural response. The work of this dissertation could facility a more appropriate wind design of the flexible horizontal structures subject to the non-synoptic winds.Three approaches with different simulation accuracies and efficiencies have been developed in the proposed analysis framework. In the first approach, both transient wind fields and bridge aerodynamics are simulated using analytical models and are computationally efficient. The newly developed transient aerodynamic model could effectively investigate the change in aerodynamics induced by time-varying transient winds. The simulation results from this analytical approach show that the time-varying mean wind speed of non-synoptic wind event could significantly modify the aerodynamics of wind-bridge interaction system. The second approach is a hybrid approach, where the computational fluid dynamics (CFD) is used to obtain the wind field, the computational structural dynamics (CSD) is employed to capture the structural dynamic response, and the analytical-based transient aerodynamic model is utilized to simulate the aerodynamic and aeroelastic coupling between the winds and the bridge. The results based on this CFD-CSD hybrid approach show that the featured transient mean winds dominate the bridge response while the nonstationary characteristics of wind fluctuations have relatively smaller effects on the bridge dynamics. In the third approach of “strip-theory-based” 3-D fluid-structure interaction (FSI), the bridge is modeled utilizing the 3-D finite element method, the wind field, in which the entire structure is immersed, is discretized into a series of 2-D slices simulated using CFD, and the strongly coupled staggered algorithm for partitioned procedure is adopted to ensure the numerical accuracy and stability of the computation. The numerical results demonstrate the effectiveness and efficiency of the 2-D CFD-3-D CSD FSI analysis framework in the simulation of non-synoptic wind-induced effects on the long-span bridges.