Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

El Damatty, Ashraf

2nd Supervisor

King, J. Peter C.

Co-Supervisor

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.

Summary for Lay Audience

Cable-supported bridges, such as suspension bridges and cable-stayed bridges, are commonly used in our modern road networks for the crossing of major obstacles. These structures can be very long, and it is not uncommon to have bridges spanning distances over 1 km. These bridges are therefore very flexible, what makes them vulnerable to wind actions. In order to ensure the safety of such long bridges, engineers utilize techniques that can be either run on a computer using a numerical representation of a bridge or performed in a wind tunnel using scale models of bridges. The stability of bridges when subjected to wind is one of the main concerns for which engineers have utilized these methods. The approaches rely on some simplifications that ease their utilization, especially pertaining to how the bridge structure behaves. Consequently, this project aims at developing a new approach for studying the stability of bridges for which the structural behavior is modeled accurately. At first, a numerical approach is elaborated to characterize with good accuracy the behavior of cable-supported bridges. Then, the results of this new numerical techniques were utilized for the development of a new method for testing bridges in the wind tunnel. By comparing it to typical wind tunnel tests for bridges, this new innovative wind tunnel test approach is utilized to demonstrate the effect of accounting for an accurate bridge structural behavior on the stability of bridges. It is believed that this research will eventually lead to safer bridge designs against wind.

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