Assessment and Mitigation of Wind Risk of Suspended-Span Bridges

Within the general framework of risk management, the vulnerability of flexible bridges under wind action is addressed. Particular attention is paid to the risk of aeroelastic instabilities and buffeting oscillations in presence of self-excited phenomena. A computational framework based on semi-empirical cross-sectional models for the wind loading and on the three-dimensional finite-element discretization of the structure is developed. This represents a basic tool for assessing wind risk and it is used to obtain some results in the understanding of bridge behaviour under wind storms and in the comparison of different design solutions. A time-domain model for unsteady wind loading is derived as a development of indicial function load models. Some inaccuracy issues of literature models are solved and the consistency with the quasi-steady limit is ensured. A numerical procedure for identifying the load model coefficients from wind tunnel experimental data in such a way that the reliability of the measured quantities is accounted for is proposed, implemented, and validated. Analyses including structural nonlinearities and damping devices are made possible by the developed time-domain methods. The effects on aeroelastic stability and buffeting response of along-span wind coherence, mean deformations, and load and structural nonlinearities are quantified. Finally, mitigation strategies against aeroelastic instability and excessive buffeting oscillations are discussed. A risk-based comparison of some possible solutions is performed in the special case of a suspension bridge. Crossed hangers, secondary cables with opposed curvature, and tuned mass control devices are considered. The results, rendered in terms of yearly probability of collapse and expected number of days of closure to traffic, easily allow a cost-benefit analysis for deciding among different designs. Interesting results are obtained from the simulation of bridges controlled by tuned mass devices.