07-04-2009, 10:45 PM
Many structures have their fundamental frequencies of vibration within the range
of frequencies where the energy of most of the earthquake ground motions is a maximum. In such cases a structure will amplify the ground vibrations and produce accelerations, which increases from the base of the structure to its top. Besides producing undesirable levels of acceleration in the structure, these amplified structural motions can cause large stresses in structural elements and large relative displacements between different parts of the structure. This can result in permanent damage to parts of the structure or even to catastrophic collapse. The amplified accelerations throughout the structure act on the occupants and contents of the structure and can cause harm and damage to occupants and contents even when no structural damage occurs.
The use of seismic isolations bearings permits the structure to be less strong than
would be required if the structure were to have it base fixed to the ground. This results in a lower cost and lower weight of structure. It is an exceptionally effective method for the practical and economical retrofitting of structures that to do not meet current seismic
standards, or for which a higher degree of safety is desired. Especially, for retrofit of those structure that cannot afford to stop functioning, this method found to be very useful. This would be especially important for such structures as hospitals, emergency centers, communication centers, disaster response center, power stations etc. Proper isolation of structures such as nuclear power plants, oil refineries, chemical plants and processing plants can also prevent potentially catastrophic secondary harm from occurring due to damage of such systems as a consequence of an earthquake. For many industries and businesses, the most significant benefit deriving from seismic isolation can be the prevention of loss of operation during and after a major earthquake. However, for effective functioning of seismic isolation, it is necessary to have isolation devices that can fulfill the essential requirements as well as be durable, less expensive and require minimum maintenance during the lifetime of structure.
