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.
  1. 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.