Longitudinal vibration control strategy for long-span suspension bridges under operational and extreme excitations using eddy current dampers

A full-floating or a semi-floating system is conventionally employed in long-span suspension bridges (LSSBs) to reduce the excessive internal forces of main girders when subjected to various ambient loads/effects. However, such a system may induce appreciable back-and-forth longitudinal displacements of the main girder and result in the deterioration of auxiliary structural components (e.g., expansion joints). In light of this, this paper presents a vibration control strategy for mitigating the longitudinal girder vibrations of LSSBs under primary operational loads (i.e., wind and traffic) and extreme seismic effects using eddy current dampers (ECDs). A general computational framework of the seismic-wind-traffic-bridge system is first developed, whereby the longitudinal girder vibration characteristics of a prototype LSSB with and without ECD installations under various loading scenarios are investigated. Particularly, a novel multi-attribute decision-making (MADM) method is introduced to address a common challenge in developing optimal vibration control designs, i.e., the optimal vibration control design for one objective might adversely affect the others, which is especially critical from a life-cycle bridge management perspective. By using the MADM, typical bridge performance indices under various loading scenarios can be rationally involved in the associated optimization. The results show that different excitations can induce longitudinal girder vibrations with different dominant frequencies, which can be effectively mitigated by the ECD. However, for different bridge performance indices and different loading scenarios, the optimal ECD parameters may vary significantly. The proposed MADM method can help develop a balanced vibration control design that can ensure excellent bridge safety and serviceability simultaneously.