Design approaches against wind excitation - Tall Buildings: Structural Systems and Aerodynamic Form - page 167

Because the inherent damping capacity of buildings is often insufficient and difficult
to estimate, auxiliary damping systems - the mechanical design approach - are used
to reduce the effects of wind-induced vibration. These systems, known as “dampers”,
are mechanisms used to slow the lateral movement and reduce its magnitude and
dampen the building sway by influencing the phases of force and displacement.
Auxiliary damping systems can be divided into four groups:
• passive systems
• active systems
• semi-active systems
• hybrid systems.
Passive systems, which are systems that do not need an external power source,
function by counteracting the building sway. These systems can be divided into two
subgroups (Ali and Moon, 2007):
• energy-dissipating material-based damping systems
• auxiliary mass damping systems.
Energy-dissipating material-based damping systems are designed to dampen the
dynamic motion of the building and are generally integrated with the structural
system. Viscoelastic dampers (VEDs) are an example of this kind of system. The “elastic
property” is the ability to return to an earlier state by storing energy, as with a coiled
spring; the “viscous property” is the ability to flow like a thick liquid. The dampers,
which combine elastic and viscous properties, dissipate the energy of the deformation
caused by lateral forces by countering them with their viscoelastic behaviour and
achieve damping by slowing down wind-induced vibration. Viscoelastic dampers
were used in the World Trade Center Twin Towers ( Figure 6.18 ).
Auxiliary mass systems are founded on the principle of creating drift in the opposite
direction to the lateral drift of the building by creating a counteracting inertia force.
Tuned mass dampers (TMDs) are an example of this kind of system. These dampers
basically consist of mechanisms that control the function of a mass producing a
counteracting inertia force and a mechanism to ensure the desired performance
( Figure 6.19 ). The mass, which oscillates against wind-induced vibration, creates the
counteracting inertia force. Generally it is located near the building top to obtain
the best performance. In the Taipei 101, a 730-ton TMD was used near the top of
the building (between the 87th and 92nd floors) ( Figure 6.20 ) . Tuned liquid dampers
(TLDs) are also an example of auxiliary mass damping systems. These dampers consist
of a liquid mass producing a counteracting inertia force and a mechanism to ensure
the desired performance. The “sloshing” of the liquid mass creates an inertia force that
counteracts the wind-induced vibration. Tuned liquid dampers have been considered
for use in the Millennium Tower (proposed) ( Figure 6.21 ).
Active systems, which aim to dampen wind-induced vibration, need an external
energy source and are controlled by feedback from the structural responses. Active
mass dampers (AMDs) are an example of this kind of system. These dampers resemble
TMDs in their appearance, but while TMDs' ability to cope with a range of loads is