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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1. Introduction Bridges are defined as strategic structures by the Italian Civil Protection. These structures are of critical importance for the maintenance of communication routes, particularly in the aftermath of calamity events, such as earthquakes (Italian Council of Public Works, 2018). Indeed, they play a crucial role during and after seismic events as they may provide essential services, like emergency response and medical care access (Khedmatgozar Dolati et al., 2021). In the last decades, many bridges have been damaged by earthquakes, sometimes up to the collapse. The Wenchuan Earthquake in 2008, magnitude 8 according to CEA, damaged more than 1500 bridges around the Sichuan Province in China (Kawashima et al., 2009). Another earthquake as strong as the Wenchuan one occurred in Chile in 2010; about 100 bridges experienced some damage, and 30 were closed to traffic (Schanack et al., 2012). These events highlighted the urgent need to enhance the seismic resilience of bridges to ensure their uninterrupted operation, even in facing strong seismic activities and their aftermath. Numerous techniques are available for improving the seismic resilience of existing structures and can be utilized to increase the structural capacity and reduce the seismic forces (Anajafi et al., 2020). Among these techniques, energy dissipation devices, such as Fluid Viscous Dampers (FVDs), can improve the performance of the structure, increasing the damping and, therefore, considerably reducing the displacements and the vibrations experienced by the structure. Moreover, these devices have the capacity to dissipate energy without influencing the inherent stiffness of structures (Zoccolini et al., 2023). This behavior is crucial in protecting critical infrastructure, such as bridges, from the devastating effects of dynamic forces such as seismic load because displacements and acceleration of the structure are reduced, but its period does not change (Shen & Kookalani, 2020). However, the dynamic response of bridges is governed by more than just earthquakes, which are events that may happen rarely during the lifetime of the structure. The wind and traffic loads are the most common excitations exerted on a bridge (Liu et al., 2017). They produce almost continuous low-speed motions that are detrimental to the durability of expansion joints and to the other bridge accessories sensitive to the relative movements of structural elements (Zhao et al., 2020). Since their first use on a bridge at the end of the 1980s, FVDs have played a pivotal role in advancing the field of earthquake protection engineering, offering a dynamic solution for both accommodating slow-motion disturbances, such as thermal expansions, and providing robust protection against strong seismic and wind events (Liu et al., 2017; Mavrakis, 2021; Zhao et al., 2020). FVDs are Velocity Dependent Devices (VDDs), and their response is directly connected to the rate of deformation of the bridge. The FVDs dissipate energy in the form of heat whenever an excitation arises. It is possible thanks to the movement of a viscous fluid through a piston characterized by some orifices or a valving system (Ou et al., 2007; Quaglini et al., 2021). This typology of energy dissipation devices is divided into four categories depending on their response: active, passive, semi-active, and adaptive energy dissipation systems (Spencer & Nagarajaiah, 2003; Zoccolini et al., 2023). The active FVDs continuously change their properties to better respond to external excitation. However, this category of energy dissipation system requires sensors, a computerized control system, and a large power supply to work correctly. On the other hand, the passive FVDs do not require any external equipment. They behave according to a fixed force-velocity curve, and their response is triggered directly by the structural deformation (Buckle, 2000). Similarly to active systems, semi-active ones require sensors and control systems to adjust their behavior, but the energy consumption is very low. They need a small external power source, like a battery (Symans & Constantinou, 1999). The presence of external equipment may represent a vulnerability of the energy dissipation systems, but at the same time, the adaptive behavior is desirable. The adaptive FVDs were developed from this idea. Their behavior automatically adapts to external excitations thanks only to unique valving systems or complex geometry (Hazaveh et al., 2017; Javadinasab Hormozabad & Zahrai, 2019). Even if the adaptive FVDs are very promising, they require further developments to be efficiently used in real structures. The most used FVDs in bridge engineering are the passive and semi-active ones. They are used as energy dissipation systems in new bridge designs, but they are equally valuable for retrofitting existing structures, as demonstrated by several examples (Z. H. Chen et al., 2016; Infanti et al., 2004; Klembczyk, 2017). By delving into the historical development and pioneering applications of these dampers, this article aims to provide a comprehensive overview of their key characteristics and to highlight the effectiveness of FVDs in the context of