SUMMARY Vibration‐based damage detection (VBDD) comprises a promising set of techniques for damage detection and health monitoring of civil engineering structures. However, the successful application of these methods to real structures is still a challenging task, due primarily to the large size of such structures and the relatively high levels of variability in their dynamic response under operational load conditions. In this paper, a new methodology is introduced for the application of VBDD techniques, with the goal of enhancing their effectiveness for identifying and locating low damage levels and improving their applicability to the continuous or periodic health monitoring of structures. The basic features of the methodology include the use of a controlled and consistent excitation force, the use of operational deflection shapes (ODSs) at all measured frequency increments rather than only at natural frequencies, the use of a logarithmic scale for representing the ODS amplitudes at each frequency increment and the establishment of a threshold level for damage detection that accounts for experimental variability. The performance of the proposed methodology is verified and demonstrated by applying several Level 1 (damage detection) and Level 2 (damage localization) VBDD techniques using experimental data measured on a steel girder taken from a railway bridge. The proposed approach is shown to perform very well at detecting, locating and monitoring the growth of damage. Copyright © 2011 John Wiley & Sons, Ltd.

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A wavelet-based technique is proposed for structural damage detection and health monitoring. In this technique, characteristics of representative vibration signals under the wavelet transformation are examined for damage identification. The proposed method is based on only the output data without the need for measuring the excitation forces, any modal identification or numerical models. The method is described theoretically and verified both experimentally and numerically using a railway steel bridge. The applicability of utilizing piezoelectric actuators for exciting large structures such as steel bridges is also investigated in this paper. Several damage scenarios were introduced to the test structure by removing bolts from some stiffeners located on the web of the main girder. Similar damage scenarios were introduced to the finite element model of the test structure. The results indicate that the current approach can identify the location of small damage effectively. The proposed method combined with the use of piezoelectric actuators is shown to be very suitable for continuous health monitoring of steel bridges.

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