Multimode Vibration Control Strategies of Long-Span Bridges Subjected to Multi-hazard: A Case Study of the Runyang Suspension Bridge.

Purpose: This study is an attempt to illustrate and discuss multi-hazard interactions in vibration control of long-span bridges subjected to wind and seismic loads. Such bridges, being flexible structures, are inherently vulnerable to wind loads. However, some response parameters of such bridges, for example, tower and deck acceleration, can be significant during large earthquakes which produce ground motions with low-frequency content. Methods: To illustrate this problem, a case study of the Runyang Suspension Bridge (RSB) is used. A finite element model of the bridge is created and verified against published literature. A set of ground motions from large worldwide earthquakes and spatially varying wind velocity time series, simulated as a realization of a random field, are used to evaluate the bridge's dynamic response with and without control devices. The control devices applied in this study are passive-tuned mass dampers (TMDs). Careful investigation of the uncontrolled response of the bridge shows that while wind load is mainly important for the displacement of the bridge deck, seismic loads can induce significant acceleration of the tower and the deck. Since the response of the tower and the deck are coupled at some higher modes of vibration, seismic action, although most critical for the tower, is also relevant for deck acceleration. These observations indicate the need for a multi-performance-based control strategy. Results: It is found that TMDs optimal for reducing seismic-induced deck acceleration can lead to amplification of wind-induced deck displacement. At the same time, TMDs optimal for reducing wind-induced displacement response are, in some cases, harmful to seismic-induced deck acceleration. These results clearly show multi-hazard interaction in control performance. Conclusions: To account for this problem, a control strategy for the deck and tower's seismic and wind responses is investigated. This consists of TMDs placed at the top of each tower and 4 TMDs placed on the deck. By tuning the TMDs to different vibration modes of the bridge, the system is shown to be effective for both seismic and wind actions. [ABSTRACT FROM AUTHOR]