Viscous-Damper with Motion Amplification Device for High Rise Building Applications

Abstract

Adding damping by the use of various damping devices has become an accepted method to reduce wind-induced vibrations in tall buildings. An interesting example of a 39-storey office tower is presented where large projected accelerations are the result of the vortex shedding off an adjacent existing 52-storey building. Viscous dampers and a motion amplification system are utilized to suppress the anticipated accelerations. A description of the damping system and its analytical complexities are discussed. Non- linear analysis of the tower, with time history forcing functions, derived from the wind tunnel, is presented. The dichotomy of the wind and seismic design requirements on the damping system is discussed. Cost data for the damper system is also presented. This paper presents the results of an investigation of the application of viscous dampers in a high-rise structure located in an urban environment. The structure, a 39-storey steel-tube frame was designed using conventional wind engineering methods of code loadings and deflection limitations and was tested in a wind tunnel at Rowan Williams Davies & Irwin Inc's (RWDI) facilities in Canada. The building is within the immediate proximity of a 52-storey tower in the center of a coastal downtown urban environment. Wind tunnel results indicted that the structure would experience very high acceleration levels caused by winds coming from a northwesterly direction. Detailed investigation into the wind tunnel data indicted that the intense buffeting the tower was experiencing was the result of the vortex shedding from the adjacent 52 storey existing building. The predicted acceleration levels were double the industry standard for office towers. In order to reduce the projected motion levels, several approaches were investigated and evaluated for cost and project impact. Tuned mass dampers and sloshing dampers required valuable office space at the top of the tower and proved to be very expensive (although very effective). Viscoelastic dampers were no longer available from US manufactures. Viscous dampers proved to be the most cost effective and least space intensive on the office tower. An extensive design program was undertaken with various damper configurations vertically in the tower and with many variations on viscous damper specifications. Since the main intent of the damper installation is to reduce wind motions, the viscous dampers need to provide a large force output at very low displacement levels (+1/S). In order to insure reliability at this low movement and to keep the number and cost of the dampers to a minimum, a motion amplification device (MAD) was included in the design. The motion amplification device was used in one direction of the structure, that being the stiffest with the lowest predicted movements. A motion amplification device called a Toggle Brace Damper system (TBD) was tested at the State University of New York in Buffalo (SUNY) by Constaintinou, etc. (1998). Their report demonstrates that the TBD system is a very useful mechanism to amplify inter-story motion. However, the efficiency