Figure : Classification of Seismic Protection Systems.
  1. METALLIC YIELD DAMPER
One of the effective mechanisms available for the dissipation of energy input to a structure from an earthquake is through inelastic deformation of metals. Many of these devices use mild steel plates with triangular or X shapes so that yielding is spread almost uniformly throughout the material. A typical X-shaped plate damper or ADAS (added damping and stiffness) device is shown in Fig. 3. Other configurations of steel yielding devices, used mostly in Japan, include bending type of honeycomb and slit dampers and shear panel type. Other materials, such as lead and shape-memory alloys, have also been evaluated [16]. Some particularly desirable features of these devices are their stable hysteretic behavior, low-cycle fatigue property, long term reliability, and relative insensitivity to environmental temperature. Hence, numerous analytical and experimental investigations have been conducted to determine these characteristics of individual devices.
  1. FRICTION DAMPER
Friction dampers utilize the mechanism of solid friction that develops between two solid bodies sliding relative to one another to provide the desired energy dissipation. Several types of friction dampers have been developed for the purpose of improving seismic response of structures. An example of such a device is depicted in Fig. 6. During cyclic loading, the mechanism enforces slippage in both tensile and compressive directions. Generally, friction devices generate rectangular hysteretic loops similar to the characteristics of Coulomb friction. After a hysteretic restoring force model has been validated for a particular device, it can be readily incorporated into an overall structural analysis [17].
  1. VISCO-ELASTIC DAMPER
Viscoelastic (VE) materials used in structural applications are usually copolymers or glassy substances that dissipate energy through shear deformation. A typical VE damper, which consists of VE layers bonded with steel plates, is shown in Fig. 7. When mounted in a structure, shear deformation and hence energy dissipation takes place when structural vibration induces relative motion between the outer steel flanges and the center plates. Significant advances in research and development of VE dampers, particularly for seismic applications, have been made in recent years through analyses and experimental tests [18, 19].
  1. FLUID VISCOUS DAMPER
Fluids can also be used to dissipate energy and numerous device configurations and materials have been proposed. One class involves the use of a cylindrical piston immersed in a viscoelastic fluid. Such a system has been studied both experimentally and analytically by Makris et al. (1993). Another proposed device involves the concept of a viscous damping wall, again using a viscoelastic fluid (Arima et al. 1988; Miyazaki and Mitsuaka 1992). Viscous fluid dampers, widely used in aerospace and military applications, have recently been adapted for structural applications (Constantinou et al. 1993). Characteristics of these devices which are ofprimary interest in structural applications, are the linear viscous response achieved over a broad frequency range, insensitivity to temperature, and compactness in comparison to stroke and output force. The viscous nature of the device is obtained through the use of specially configured orifices, and is responsible for generating damper forces that are out of phase with displacement.
A viscous fluid damper generally consists of a piston in the damper housing filled with a compound of silicone or oil (Makris and Constantinou 1990; Constantinou and Symans 1992). A typical damper of this type is schematically shown in Fig. 7. It dissipates energy through movement of the piston in the highly viscous fluid. If the fluid is purely viscous (for instance, Newtonian), then the output force of the damper is directly proportional to the velocity of the piston. Over a large frequency range, the damper exhibits viscoelastic fluid behavior.
  1. TUNED MASS DAMPER
Early applications of tuned mass dampers (TMDs) have been directed toward mitigation of wind induced excitations. Recently, numerical and experimental studies have been carried out to examine the effectiveness of TMDs in reducing seismic response of structures. It is noted that a passive TMD can only be tuned to a single structural frequency. While the first-mode response of a MDOF structure with TMD can be substantially reduced, the higher mode response may in fact increase as the number of stories increases. For earthquake-type excitations, the response reduction is large for resonant ground motions and diminishes as the dominant frequency of the ground motion gets further away from the structure’s natural frequency to which the TMD is tuned. There has been numerous application of TMDs over the world throughout the years [20].