Keywords: structural health monitoring, non-destructive testing, acoustic emission, source localization, source differentiation, severity assessment.

Bridges are important part of society's infrastructure. Loss of lives and huge financial losses have been caused by bridge failures. Bridges deteriorate with age and early detection of damage helps in prolonging the life. Hence, it is vital that these infrastructures are monitored continuously for symptoms of failure. Structural health monitoring (SHM) refers to the procedure used to assess the condition of structures so that their performance can be monitored and any damage can be detected early, thus increasing reliability, safety and efficiency of the structures.

While global methods of SHM such as vibration analysis can indicate the presence of damage in a structure, local methods are necessary for finding the exact location of the damage and several non-destructive techniques are available for this purpose. Recently acoustic emission (AE) technology is finding an increasing use for SHM of large engineering infrastructures. AE waves are high frequency waves generated from a growing crack and the AE technique involves recording these waves and analysing them to gain information about the damage source. High sensitivity to crack growth, ability to locate source and the possibility of performing real time monitoring are some of the attractive features of the AE technique.

In spite of these advantages, challenges still exist in using the AE technique for monitoring applications, especially in the area of analysis of recorded AE data, because large volumes of data are usually generated during monitoring. The need for effective data analysis can be linked with the three main aims of monitoring: (a) accurately locating the source of the damage; (b) identifying and discriminating signals from different sources of acoustic emission and (c) quantifying the level of damage of the AE source for the severity assessment. This paper presents a study of the important issues in the acoustic emission technique regarding damage source location, source differentiation and quantification of damage size.

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