Effect of Structural Nonlinearities on Flutter of Cable-Supported Bridges
Abstract
It is well known that cable-supported bridges, like suspension bridges and cable-stayed bridges, are structures that are highly sensitive to wind. This is why there has been an important research effort over the past decades on aeroelastic instability phenomena in bridges like flutter. This has allowed the safe design of long-span bridges with respect to wind effects. Nonetheless, the analysis methods that have become the norm in the field of bridge engineering, such as flutter analysis and wind tunnel tests, rely on some simplifications to facilitate analysis. For example, they assume a linear structural behavior of the bridge structure. Therefore, this research project aims at developing a better understanding of the effect of structural nonlinearities on the wind stability of these bridges. To do so, a new experimental approach able to account for structural nonlinearities of bridges is elaborated for wind tunnel tests. First, a numerical method based on large-displacement finite element analysis is developed to characterize the nonlinear structural behavior of cable-supported bridges. The research focuses on geometric nonlinearities, which are more of a concern for these bridges. It is found that single-span suspension bridges behave more nonlinearly. Secondly, it is shown that the nonlinear behavior obtained from the numerical method can be scaled to be utilized for dynamic section model tests in the wind tunnel that account for the nonlinear structural behavior of the bridge. This led to the development of a springing system able to mechanically reproduce this nonlinear behavior in the wind tunnel. A new experimental apparatus for section model tests was designed and fabricated for this purpose. This section model test rig was utilized at the Boundary Layer Wind Tunnel Laboratory (BLWTL) of the University of Western Ontario. This proved the possibility of accounting for structural nonlinearities when conducting dynamic section model tests. It is demonstrated that structural nonlinearities have an effect on the dynamic response as well as on the critical velocity for flutter. This research project therefore provides to bridge designers an effective tool for the assessment of the influence of structural nonlinearities on the aeroelastic stability of cable-supported bridges.