Figure : Friction controllable bearing tested by Feng.
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HYBRID MASS DAMPER
The hybrid mass damper (HMD) is the most common control device employed
in full-scale civil engineering applications. The HMD is a combination
of a TMD and an active control actuator. The ability of this device to
reduce structural responses relies mainly on the natural motion of the
TMD. The forces from the control actuator are employed to increase the
efficiency of the HMD and to increase its robustness to changes in the
dynamic characteristics of the structure. The energy and forces required
to operate a typical HMD are far less than those associated with a fully
active mass driver system of comparable performance.
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HYBRID BASE ISOLATION
Another class of hybrid control systems that has been investigated by a
number of researchers is found in the active base-isolation system,
consisting of a passive base-isolation system combined with a control
actuator to supplement the effects of the base-isolation system.
Base-isolation systems have been implemented on civil engineering
structures worldwide for a number of years because of their simplicity,
reliability, and effectiveness. Excellent review articles of
base-isolation systems are presented by Kelly (1981, 1986), Buckle and
Mayes (1990), and Soong and Constantinou (1994). However, base-isolation
systems are passive systems and are limited in their ability to adapt to
changing demands for structural response reduction. With the addition of
an active control device to a base-isolated structure, a higher level of
performance can be potentially achieved without a substantial increase
in the cost (Reinhorn et al. 1987), which is very appealing from a
practical viewpoint. Since base isolation by itself can reduce the
inter-story drift and the absolute acceleration of the structure at the
expense of large absolute base displacement, the combination with active
control is able to achieve both low inter-story drift and, at the same
time, limit the maximum base displacement with a single set of control
forces. A robust control for uncertain linear base-isolated structures
was proposed by Kelly et al. (1987), and more recently by Schmitendorf
et al. (1994) and Yoshida et al. (1994).
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LOCK UP DEVICES
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COMMONLY USED SEISMIC PROTECTION SYSTEMS IN BANGLADESH
Chapter 3