Mitigation of Motions of Tall Buildings with Specific Examples of ...

low-voltage power sources. In light of these attractive features, semi-active controllable fluid
dampers pose a viable solution to the ongoing problem of structural vibrations.
7.0 Concluding Remarks
A discussion of the various techniques used to mitigate building motion was presented, including
structural and aerodynamic solutions. This paper also addressed a number of passive and active
motion control devices for improving the performance of tall buildings under wind loads for
human comfort considerations, as well as several seismic applications. Detailed examples of practical
applications of such devices to buildings in Australia, Canada, China, Japan, and the United
States were provided.
In light of the wide spectrum
of methods to mitigate
wind-induced motion presented
in this paper, it is perhaps
best to conclude with
an innovative project which
integrates several of these
design approaches. Sir Norman
Foster’s Millennium
Tower concept, proposed
for construction in Japan,
soars 2500 feet skyward
with a base the size of
Tokyo’s Olympic Stadium
(Sudjic 1993). The structure
exploits an aerodynamically
favorable shape through its
circular plan, coupled with
the benefits of tapering with
height, permitting it to perform
efficiently in wind.
The resulting cone shape,
shown in Figure 29a, concentrates
its mass in the
lower floors to additionally
(a) (b) (c)
Figure 29: Design concepts for Millennium Tower: (a) load transfer; (b) aerodynamic
modifications; (c) auxiliary damping scheme (taken from Sudjic 1993).
improve the structure’s resistance to earthquakes. The performance in wind is further supplemented
by the inclusion of a “through-building” opening near the top of the structure, shown in
Figure 29b. Meanwhile, the structural system relies on transfer girders, also shown in Figure 29a,
to distribute gravity loads to the exterior double helix and column system. This exterior helix casing
not only carries the structures load’s but also helps to disrupt the wind flow around the structure,
further improving the vibration performance. In addition to these aerodynamic and structural
modifications, the incorporation of an auxiliary damping system is also planned. As shown in Figure
29c, the systems of water tanks would be located at two levels in the structure and serve as a
hybrid liquid damper system, combining the benefits of passive control at low excitation levels,
Mitigation of Motions of Tall Buildings with Specific Examples of Recent Applications 40