Preliminary Evaluation of Wind Instability for Long Span Bridges

Long span and wind critical structures often require a wind tunnel study for determining the critical wind speeds which could potentially cause instabilities in the structure. This wind tunnel test is often cumbersome and expensive and therefore should only be used for the final design stage. In this study, consideration is primarily focused on numerically determining the fluttering effect. The critical flutter wind speed of a bridge superstructure is computed through the use of computational fluid dynamics in conjunction with finite element analysis of the full bridge model. Upon evaluation of discrete vortex method, flutter derivatives are determined which are then used to describe the full dynamic equation. The quadratic complex eigenvalue solution of this response equation is solved to find the critical wind speed of the given cross section. This critical wind speed allows the engineer to have a preliminary justification of whether the chosen shape is within a reasonable aeroelastic response given wind design speeds at the project site. This is especially important because, for large bridge projects, the industry is trending towards design-build projects where it is beneficial to fast-track the design process. This study is focused on the Abraham Lincoln cable stay bridge in Louisville, Kentucky, with comparison to wind tunnel results done on the structure.