Rytter [1993] has broadly categorized damage identification into four levels"

• determination of presence of damage in the structure
• determination of geometric location of the damage
• quantification of the severity of the damage; and
• prediction of remaining service life of the structure.

It is important to detect the incipient damage at the first available signal to take necessary steps for the well being of the structure. It is necessary to keep track of the changes in the stiffness and other significant mechanical properties of the critical members in a structure in real time as damage beyond a certain level becomes a safety hazard and may invite downgrading of its use or even abandoning of the structure.