There are many situations in real life when a structure is subjected to vibrations caused by dynamic loads due to machines, road traffic, rail traffic or air traffic, wind, earthquake, blast loading, sea waves, or tsunami. The movement of pedestrians may cause vibrations in a floor of a building and in a suspension bridge. The term dynamic loads include any loading which varies with time. The manner in which a structure responds to a given dynamic excitation depends upon the nature of excitation and the dynamic characteristics of the structure, that is, the manner in which it stores and dissipates energy. The energy is stored in the form of potential energy and is dissipated in the form of kinetic energy through vibrations. Some of these loads could lead to catastrophic loss to lives and properties in a very short span of time while others cause irritation to the users of the facility.