Keywords: condition monitoring, damage detection, vibration response, natural frequency, mode shape, neural network, statistical analysis.

Structural health monitoring, or condition monitoring, at a fundamental level refers to the assessment of structures and identification of any damage inherent in the structure. At a higher level, localisation and quantification of specific damage and, further, predicting the impact of this damage on the remaining service life of the structure is the ultimate aim.

The basic premise of vibration-based damage detection is that damage will significantly alter the stiffness, mass or energy dissipation properties of a system, which, in turn, alter the measured dynamic response of that system [1].

Measurement of mode shape changes is more cumbersome than detecting changes in natural frequencies but there is some evidence to suggest that methods based on mode shapes are more robust than those based solely on natural frequencies. The results from modal parameter and model updating methods have been mixed, and require an expert to carry out the testing and interpretation. In many cases, detailed knowledge of the structure in an undamaged state is required, either in the form of experimental data, or an analytical model. However, in order for condition monitoring based on dynamic responses to gain widespread acceptance, a simple and reliable method that is useful without in-depth knowledge of the structure is required [2,3].

This paper presents an overview of some traditional approaches to structural condition monitoring and also reviews some novel developments, which may contribute towards the development of robust methods, which can be applied to large scale civil engineering structures. The methods are broadly grouped into natural frequency based, mode shape based, wavelet based, neural networks and statistical analysis methods and numerical modelling techniques. Many of the methods presented have been tested with limited success on laboratory scale structures. Transferring the approaches proposed to full-scale civil engineering structures such as bridges and commercial buildings represents a challenge for the engineering community, but some recent advances offer potential in this regard.

1

C.R. Farrar, S.W. Doebling, "Damage detection II: field applications to large structures", In: J.M.M. Silva, N.M.M. Maia, (eds.), "Modal Analysis and Testing", Nato Science Series, Kluwer Academic Publishers, Dordrecht, Netherlands, 1999.

2

Y. Lei, A.S. Kiremidjian, K.K. Nair, J.P., Lynch, K.H. Law, T.W. Kenny, E. Carver, A. Kottapalli, "Statistical Damage Detection Using Time Series Analysis on a Structural Health Monitoring Benchmark Problem", Proceedings of the 9th International Conference on Applications of Statistics and Probability in Civil Engineering, San Francisco, California, USA, July 6-9, 2003.

3

S.G. Mattson, S.M. Pandit, "Statistical Moments of Autoregressive Model Residuals for Damage Localisation", Mechanical Systems and Signal Processing, 20, 627-645, 2006. doi:10.1016/j.ymssp.2004.08.005

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