Comparison of Wind Tunnel Results for the Development of a New Section Model Test Rig for Bridges

It has been demonstrated by mathematicians using nonlinear simplified models of suspension bridges that a vertical dynamic forcing can cause large torsional vibrations due to geometric nonlinearities of the bridge. Compared to the extensive research that has been conducted on aeroelastic instabilities in cable-supported bridges, the approach used by the mathematicians seems too simplistic, especially in terms of wind load modeling. However, they raise a point that is not considered in the wind design of cable-supported bridges, i.e., an interaction between nonlinear structural coupling and aeroelastic effects. In order to study the effect of structural geometric nonlinearities on the dynamic stability of very long cable-supported bridges, a special wind tunnel procedure was developed. Such procedure requires the development of a new experimental apparatus for section model tests of bridges that allows the representation of geometric nonlinearities and nonlinear structural coupling. Therefore, one of the first steps toward nonlinear section model tests was to design a new bridge rig for dynamic section model tests, which first needed to be validated for standard linear tests. Consequently, this paper will present a comparison of wind tunnel results for a single-box girder bridge model tested in two different wind tunnels, i.e., the main wind tunnel at the Universite de Sherbrooke and the Boundary Layer Wind Tunnel Laboratory (BLWTL) at the University of Western Ontario. At the BLWTL, tests were conducted using the existing bridge rig and the new bridge rig designed for nonlinear tests. At first, the static aerodynamic coefficients and the flutter derivatives are compared. Then, the dynamic responses for smooth and turbulent flows obtained using the different experimental setups are analyzed. This comparison procedure allows the validation of the new bridge rig that will be used in the near future to assess the effect of structural nonlinearities on aeroelastic stability.