Figure : Working Process of Active Protection
System[12].
-
ACTIVE TUNED MASS DAMPER
One of the earliest approaches to active control of vibrations in
structures has been Active Tuned Mass Damper (ATMD) systems. This system
is also known as an Active Mass Driver (AMD). In an ATMD system, an
actuator placed between the structure and the TMD system applies a
computed force in real time. The tuned mass damper has been suggested to
be connected to electrohydraulic servomechanisms to form an active mass
damper. Both the active control forces and the inertia forces resulting
from motions of the mass damper can be used beneficially for reducing
the dynamic response of a structures. Such a control system has been
shown to be very efficient for tall buildings under strong earthquake
loads. Out of these, active mass/tuned mass dampers have been
implemented for the response reduction of tall buildings in controlling
wind-induced vibrations. Yamamoto et al. [35] present the
performance results of ATMD systems installed in four actual steel-frame
high-rise buildings in Japan, ranging in height from 58.0 to 189.7 m
(11–34 stories). The ATMD systems for three of the buildings utilized
existing masses, such as ice thermal storage tanks (used for air
conditioning) and a heliport as the controlling masses. To verify the
control systems, they carried out forced vibration tests on each
building before completion, using the ATMD system itself to shake the
building. After the ATMD system shook the building for a period of 10 s,
it was activated to suppress the response of the building. The authors
also monitored the response of the completed buildings under minor
seismic events and wind loading. Their results showed that the installed
ATMDs were effective at controlling the response of the buildings. The
majority of research published on TMD systems is limited to a single
ATMD. A few researchers have advocated the use of multiple ATMDs in a
given structure. Li et al. [40] advocate the use of multiple ATMDs
for control of vibrations due to ground motions and show that several
smaller ATMDs perform better than a single large ATMD. Ikeda et al.
[39] discuss the performance of an ATMD system actually installed in
a ten-story, steel-frame building in Tokyo in 1989. The system utilizes
two AMTDs to control both lateral and torsional vibrations and the LQR
control algorithm. Since its installation, the building has been
subjected to actual earthquake and typhoon wind loadings, with 26% and
11% reductions in lateral and torsional vibrations during earthquakes,
and a 33% reduction in peak response due to wind loadings.