Earthquakes and Structures, Vol. 18, No. 3 (2020) 313-320 DOI: https://doi.org/10.12989/eas.2020.18.3.313 313 Copyright © 2020 Techno-Press, Ltd. http://www.techno-press.org/?journal=eas&subpage=7 ISSN: 2092-7614 (Print), 2092-7622 (Online) 1. Introduction Wind forces cause aerodynamic instability of suspension bridge structures resulting in failures that need to be considered for bridge design and assessment (Andersen and Brandt 2018). Tacoma Narrows in 1940 in Washington, Brighton Chain Pier in 1836 in England, and Wheeling in 1854 in West Virginia are some examples of suspension bridges being destroyed because of the aerodynamic instabilities and uncontrolled oscillations (Arioli et al. 2015, Steinman 2017). Hence, monitoring and controlling of the wind-induced structural motions receive very much attention nowadays because of periodic hurricanes occur in many parts of the world. A wide variety of numerical and mathematical approaches have been used for structural health monitoring (SHM) of bridge structures (Farhangdoust and Mehrabi 2019, Zhou et al. 2018, Soman et al. 2018, Xu 2018, Feng et al. 2018, Saha et al. 2018). In the literature, vortex shedding, flutter, buffeting, and galloping can induce aerodynamic instabilities leading to suspension bridge collapses as a consequence of wind- bridge interaction (Larsen and Larose 2015, Guo et al. 2019, Vaz et al. 2018, Azzi et al. 2018). The dynamic response of Kap Shui Mun Bridge in Hong Kong has been modeled by Zhang et al. (2012) in which vortex shedding, flutter, and buffeting have been addressed as the load excitations. Vortex shedding is recognized as an undesirable aeroelastic phenomenon of the wind-bridge interaction which potentially causes large dynamic oscillations in the Corresponding author, Ph.D Candidate E-mail: sfarh006@fiu.edu suspension bridges (Gazzola 2015, Simiu 2011, Larsen et al. 2000). Vortex shedding results from rolling-up of the separating shear layers of a bluff body alternately on each side of structure gives rise to fluctuating lift forces. A large number of articles have been published on the vortex- induced oscillation of engineering structures (Wang et al. 2018, Munir et al. 2018). The structure will resonate and its oscillations will become self-sustaining if the frequency of vortex shedding matches structure’s fundamental frequency (Li et al. 2011, Fujino and Yoshida 2002). Vibration analysis of suspension bridge deck subjected to the vortex shedding instability has been a concern to engineers because of the associated bridge failure experienced (Laima et al. 2014, Wang et al. 2018). In order to tackle the aerodynamic instability of suspension bridge structures, various teams and researchers have put their concentrations on figuring vortex-induced vibrations out (Zhang et al. 2008). A single-side pounding tuned mass damper was implemented by Wang et al. (2018) to mitigate vortex- induced vibrations of a bridge deck. They experimentally investigated the proposed TMD performance and concluded that the maximum response of their model was reduced by 94% using the TMD with mass ratio of 2%. Due to different given Reynolds numbers, VIV performance has been studied for twin-box bridge sections of Great Belt East Bridge and the Stonecutters Bridge by Zhang et al (2008). Smith (2008) studied dynamic response of Wye Bridge which is a cable stayed box girder bridge with length span of 235 m. They measured the dominant frequencies of wind-induced vibration and studied the effect of vortex shedding excitation on fatigue life of the bridge structure. Field measurements of a twin steel box girder suspension bridge with a center span of 1650 m have been implemented Bistable tuned mass damper for suppressing the vortex induced vibrations in suspension bridges Saman Farhangdoust 1 , Pejman Eghbali 2 and Davood Younesian 2 1 Department of Civil and Environmental Engineering, Florida International University, Miami, FL 33174, USA 2 School of Railway Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran (Received April 24, 2019, Revised January 22, 2020, Accepted February 4, 2020) Abstract. The usage of conventional tuned mass damper (TMD) was proved as an effective method for passive mitigating vortex-induced vibration (VIV) of a bridge deck. Although a variety of linear TMD systems have been so far utilized for vibration control of suspension bridges, a sensitive TMD mechanism to wind spectrum frequency is lacking. Here, we introduce a bistable tuned mass damper (BTMD) mechanism which has an exceptional sensitivity to a broadband input of vortex shedding velocity for suppressing VIV in suspension bridge deck. By use of the Monte Carlo simulation, performance of the nonlinear BTMD is shown to be more efficient than the conventional linear TMD under two different wind load excitations of harmonic (sinusoidal) and broadband input of vortex shedding. Consequently, an appropriate algorithm is proposed to optimize the design parameters of the nonlinear BTMD for Kap Shui Mun Bridge, and then the BTMD system is localized for the interior deck of the suspension bridge. Keywords: bistable tuned mass damper (BTMD); nonlinear vibration control; wind vortex shedding; suspension bridges