Enhanced response through supplementary friction damper devices I. Mualla & L. O. Nielsen DampTech Ltd., Technical University of Denmark, Lyngby, Denmark N. Chouw Okayama University, Okayama, Japan B. Belev University of Architechture, Civil Engineering and Geodesy, Sofia, Bulgaria W. I. Liao and C. H. Loh National Centre for Research on Earthquake Enigneering, Taipei, Taiwan A. Agrawal City University of New York, New York, USA ABSTRACT: The paper addresses results of an international effort in further developing a novel friction damper device for a reduction of induced vibrations in structures. A description of the device, results of small-scale experiments and results of full-scale shaking table tests are presented. The result of the investigations shows that the effectiveness of the device is determined not only by the friction material but also by the location as well as the way of its placement. The devices have a stable energy dissipating behaviour. They are flexible in the application, since they only need limited spaces. The device can be installed easily or readjusted after installation. The damping capacity of the device can be easily increased by adding additional friction layers. The friction damper device proves to be an efficient and economical device for a reduction of dynamic response of structures. 1 INTRODUCTION Excessive vibrations of a structure can occur due to accumulation of energy induced by a source in the structure like production activities in a factory. The source can also be outside like a heavy truck or high-speed train that travels in a densely populated area. Even if the vibration is not strong, long-term vibration pollution can severely affect human health. There are many possibilities to reduce the vibration of structures. As an example we consider the Millennium Bridge. The bridge is well known for its original and elegant “blade of light” design (Fig. 1). When it opened on June 10, 2000, the bridge experienced excessive movement due to accumulating loading caused by pedestrians. Their synchronizing footsteps strongly amplified the initially small sway motion of the bridge. In order to control the level of the vibration and to have a desired degree of comfort for the pedestrians, one can stiffen the bridge by adding additional structural members. This will increase the stiffness of the bridge, and move its natural frequencies from the range that will be excited by the pedestrians. One can also increase the damping of the bridge by installing supplementary damper devices to increase the energy absorbing ability of the bridge during its movement. One can reduce the load effect by limiting the number of people or by artificially modifying their walking patterns using flower corners in the path. One can also combine these three possible solutions. The first solution will significantly alter the design, since a much stiffener bridge is required. The third solution will hinder the free flow of the pedestrians. In Figure 1 and 2 the chosen second solution can be seen. Tuned mass dampers are placed below the bridge deck, and viscous dampers at certain locations as shown in Figure 2. While the tuned mass dampers are for controlling the excitation at the bridge frequencies, the viscous dampers are mainly for suppressing the strong lateral movements. Another possible reduction measure is friction device. Because of the high energy dissipation potential and the simplicity in installation and main- Figure 1. The London Millennium Footbridge viewed from the north.