Mitigation of Vortex Induced Response in Long Span Bridges

Span length of bridges is ever increasing. With the increase in span, bridges are becoming more slender, making them more prone to wind-induced forces and vibrations. Some bridges show significant wind-induced vibrations after the construction, which were not anticipated during the design. In order to improve the performance of these bridges, two strategies of retrofit are commonly used. First, tuned mass dampers (TMDs) may be added to dissipate the energy. Second, cross-section of the bridge may be retrofitted so that it is aerodynamically more favorable. Both methods are effective in reducing the magnitude of the wind-induced vibration. Among many types of wind-induced vibrations, this thesis deals with vortex-induced vibrations. The various parameters involved in retrofit have conflicting objective. For example if the maximum displacement is required to be reduced the cost involved is more. In such a case of conflicting objectives, multi-objective optimization can be used to find various solutions from the solution space. These solutions are termed as Pareto-optimal solutions. There is no specific solution which can be called as the best solution due to conflicting objectives. Multi-objective optimization gives the various options to choose from, to arrive at a decision for a particular real world problem. In our case, the problem is to decrease the magnitude of vortex-induced vibrations. The conflicting objectives are the cost of the retrofit and the displacement in terms of the performance. In thesis, the multi-objective optimization will be used to obtain various strategies of retrofit under conflicting objectives. The approach is illustrated with an example bridge modeled after Rio-Niterói Bridge.