Chapter 2 Long-Term Performance of Specialized Fluid Dampers Under Continuous Vibration on a Pedestrian Bridge Alan R. Klembczyk Abstract In 2001, Taylor Devices Inc. developed special Viscous Dampers for use on the Millennium Bridge in London, England. These dampers were specified and designed to be used for mitigating the dynamic response of the bridge due to pedestrian traffic. Prior to the integration of the dampers, the bridge had experienced unacceptable movements, especially during periods when larger crowds of people were on the bridge. The result was that the bridge had to be closed until a solution was found. Much research was done and several papers were published about the nature of that problem and the ensuing solution. After successful component level testing and the installation of 37 Taylor Viscous Dampers, the bridge was re-opened to the public in February, 2002. Tests with approximately 2000 people demonstrated a much improved dynamic response. Since that time, the dampers have been subjected to almost constant dynamic input, some more than others. Due to the location of the bridge in central London, there has been nearly constant pedestrian traffic on the bridge each day and even throughout the night. However, because of the specialized nature of the damper design, no degradation in damper performance or in the dynamic response of the bridge itself has been experienced. This paper will outline the specifics in quantifying the continued damper performance through an intermediate inspection after 7 years, followed by a successful comprehensive inspection after 11 years. This included the removal, dynamic testing, and re-installation of three selected dampers. Keywords Millennium Bridge • Bridge damper test results • Fluid viscous dampers • Continuous vibration • Vibration damper 2.1 Introduction The unique design and the resulting unacceptable response of the Millennium Bridge in central London (see Fig. 2.1) have been well publicized and documented. The specifics of this dynamic response and the resulting solution will not be reiterated within the context of this paper. However, in order to provide a necessary background, a short summary is presented here. In June 2000, the bridge was first opened to the public. Shortly thereafter, with substantial pedestrian traffic present, the bridge began to sway in a lateral motion to the discomfort of many of the pedestrians. The bridge was subsequently shut down and significant studies were performed to provide solutions to stop the excessive swaying. Since the response frequency was near the frequency of human footfalls during walking, it was determined that stiffening of the structure was not a practical solution. The unique design and its aesthetic appearance would have been sacrificed if structural modifications were made to keep the various modal frequencies away from walking frequencies. A more acceptable solution was determined to substantially increase the damping level of the bridge over all input conditions in order to prevent pedestrian traffic from exciting the bridge. The required amount of added damping was determined to be nearly 20% critical, a value that is effectively unachievable with typical solutions, such as tuned mass dampers, frictional elements, or structural modifications. Many challenges became immediately apparent when proposing a damping solution for this unique structure. One of the most significant was the fact that the owner of the bridge required a permanent and maintenance-free solution that would last throughout the life of the bridge; this being in excess of 50 years. Since the expected pedestrian traffic was such that the dampers would cycle nearly continuously at 1.3 Hz, it was necessary to specify a cycle life of 2 109 cycles minimum. Due to this stringent requirement, Taylor Devices proposed the use of specialized Fluid Dampers that employed the use of flexing metal bellows seals, rather than traditional sliding seals that are elastomeric in nature and therefore subject to wear and degradation over long-term environmental and cyclic conditions. A.R. Klembczyk ( ) Taylor Devices, Inc., 90 Taylor Drive, North Tonawanda, NY, 14120-0748, USA e-mail: alanklembczyk@taylordevices.com © The Society for Experimental Mechanics, Inc. 2017 J. Caicedo, S. Pakzad (eds.), Dynamics of Civil Structures, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-54777-0_2 11
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