Smith and Willford 2007
In this paper, a new philosophy for the design of high-rise buildings with damped outriggers was presented. The dynamic response of a tall building has generally been governed by structure shape, stiffness, mass and damping. The first of three of these inputs are much easier to assess. The effect of shape can be evaluated by wind tunnel testing. Moreover, the mass and stiffness can be predicted the structural designer. However, the available guidance for damping of tall buildings, used primarily to reduce dynamic wind effects, shows huge variance. This is especially compounded by the difficulty of measuring damping experimentally. The authors, therefore, outline design procedures, approaches and a design example for damped outriggers.
System Concept
Viscoelastic dampers were attached between two points on a structure damping response based on the relative motion between the two points. The best location for this device was two points that had significant relative displacement. Dynamic sway induces large relative vertical motion between the perimeter columns and the ends of stiff outrigger elements cantilevering from the core, offering an excellent location for the viscoelastic damper. A damper was inserted across this structural discontinuity, dissipating energy during the cyclic motion, and resulting in an increase in the overall damping of the building. It was necessary for the outrigger element to move vertically relative to the floors at these levels, while the floors bent in double curvature to remain connected to the core and the outer columns.
Results and Discussion
The authors recommend that designers first determine the required stiffness and damping for their structure. Then damping should be estimated, followed by selection of a damping system and optimization of structural stiffness.
This system has economic advantages over conventional damping mechanisms. In addition to significant economic savings, increased damping and stiffness, this system results in a favorable response to cyclic motion. By means of the lateral stiffness of a high-rise structure, the element sizes and material content can be reduced.
Reference
Smith, R.J. and Willford, M.R. (2007). “The Damped outrigger Concept for Tall Buildings,” The Structural Design of Tall and Special Buildings 16, pp. 501–517.