PSI - Issue 62

L. Zoccolini et al. / Procedia Structural Integrity 62 (2024) 669–676 L. Zoccolini, E. Bruschi, C. Pettorruso, D. Rossi and V. Quaglini / Structural Integrity Procedia 00 (2019) 000 – 000

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3.1. Application of MR damper on bridges The use of MR dampers on bridges has been studied mainly for the cases of cable-supported bridges (Jung et al., 2003; Ok et al., 2007; M. Yang et al., 2008) , but to the Authors’ knowledge , there is just one documented application on a real structure, and there are only a few experimental studies (Tu et al., 2011). Stay cables are an essential part of cable-stayed bridges, but they have an extremely low inherent damping and are laterally flexible. For these reasons, the cables are vulnerable to various types of excitations, for example, wind and wind-rain induced vibrations (Zhou et al., 2022). These vibrations may cause early fatigue issues, destroy anti corrosion systems, and, in general, are dangerous for the serviceability of bridges. MR dampers can be efficiently used to protect cables from induced vibrations thanks to their characteristic of adapting their response in real-time, since cables may be excited by multi-mode (Z. H. Chen et al., 2016). MR dampers were adopted for the first time as a vibration mitigation system on the Dongting Lake Cable-Stayed Bridge in China (Z. Q. Chen et al., 2003). It is a three-tower cable-stayed bridge characterized by two main spans of 310m and two side spans of 130m (see Fig. 4a). The bridge was built in 1999, and the vibration of the cables was observed during a heavy rain and wind event of the same year. To address this issue, two MR dampers were installed on each of the most extended 156 cables, as can be seen from Fig. 4b. The retrofit of the cable with MR dampers drastically reduced the vibration of the cables and, consequently, the induced vibration on the deck.

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Fig .3. (a) Dongting Lake Cable-Stayed Bridge; (b) MR dampers configuration (Z. Q. Chen et al., 2003).

4. Conclusion Many seismic protection systems are currently available for the protection of bridges, and FVDs are one of them. Indeed, these devices are very effective because they provide resisting forces that are out of phase with respect to the forces induced by external excitations. Moreover, they do not change the fundamental response of the structure and are able to accommodate thermal and traffic induced displacements, guaranteeing the serviceability of the bridge. Among the available FVDs, the passive ones are the most adopted in the seismic protection of bridges thanks to their efficiency in protecting structures from long return period earthquakes and their easy maintenance since they do not require any external equipment to work. Besides the passive devices, there are semi-active ones, such as MR dampers, that provide different responses depending on the external excitations. However, these devices have been mainly adopted to protect stay-cable bridges. Even if the use of MR dampers is limited and still under investigation, these devices may represent a promising technology. The growing research contributions and the increasing body of literature suggest a promising evolution of such technology, overcoming its current limitations.