Figure : Classification of Seismic Protection Systems.
There are five fundamental engineering principles for the current
strategies of seismic protection or structural control for
buildings[6]. These principles are not mutually exclusive. Certain
types of control systems follow multiple principles. The first principle
is to transfer the vibrational energy of the main structural system to
an auxiliary oscillator system. This is based on the energy transfer
philosophy, i.e. the reduction of the motion of the main system is
achieved at the expense of increased motion of the auxiliary oscillator.
The second is to reduce the Now of input excitation energy into the main
structural system. The third is to subject the structure to additional
damping. The fourth is to prevent the building from exhibiting resonance
due to an external excitation. The fifth is to provide a structural
system with computer-controllable forces. The first four of these
principles can be applied to both active and passive control strategies,
while the fifth principle is apparently only for active control
strategy.
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PASSIVE PROTECTION SYSTEM
Passive control system is to increase the energy dissipation capacity of
a structure through localized, discrete energy dissipation devices
located either within a seismic isolation system or over the height of
the structure. Such systems may be referred to as supplemental energy
dissipation systems and have been reviewed by Soong and
Constantinou[7], ATC[8], EERI[9] and Constantinou et
al.[10, 11]. The objective of these systems is to absorb a
significant amount of the seismic input energy, thus reducing the demand
on the structural system. Depending on their construction, these systems
may also increase the stiffness and strength of the structure to which
they are attached. A passive control system does not require an external
power source for operation. Rather, the motion of the structure is
utilized to produce relative motion within the passive control devices
which, in turn, dissipate energy. Supplemental energy dissipation
devices may take many forms and dissipate energy through a variety of
mechanisms including the yielding of mild steel, viscoelastic action in
rubber-like materials, shearing of viscous fluid, movement of fluid
through orifice, and sliding friction.
A passive control system does not require an external power source.
Passive control devices impart forces that are developed in response to
the motion of the structure. The energy in a passively controlled
structural system, including the passive devices, cannot be increased by
the passive control devices.