This article proposes a continuous relative wavelet entropy-based reference-free damage detection algorithm for truss bridge structures. Advantages of the proposed method are that (1) there is no need to measure dynamic response of pristine structures, in other words, the method is reference-free; (2) it is suitable for highly nonlinear and nonstationary random response data due to the multiresolution signal analysis feature of the continuous wavelet transform; and (3) it is sensitive to slight damage extents (i.e. 5%-10%) for the tested damage type (i.e. loosening of bolts). In order to demonstrate consistency and sensitivity of the proposed method, multiple experimental tests using a laboratory-size truss structure were mainly conducted for various damage scenarios and progressive damage states. The proposed continuous relative wavelet entropy-based reference-free damage detection algorithm showed reliable damage localization capabilities, and it is proven as an effective method compared to other damage detection methods that are dependent on the measurement signals from pristine structures. Due to the generality of the proposed method, applications to identify other types of damage based on different types of signals can be expected.

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In this paper, a new model-based delamination detection methodology is presented for laminated composite plates and its performance is studied both numerically and experimentally. This methodology consists of two main parts: (1) modal analysis of an undamaged baseline finite element (FE) model and experimental modal testing of panels with delamination damage at single or multiple locations and (2) a sensitivity based subset selection technique for single or multiple delamination damage localizations. As an identification model, a higher-order finite element model is combined with a rational micromechanics-based CDM model which defines the delamination damage parameter as a ratio of delaminated area to entire area. The subset selection technique based on sensitivity of the dynamic residual force has been known to be capable of detecting multiple damage locations. However, there has been no experimental study specifically for the applications in laminated composite structures. To implement the methodology, a sensitivity matrix for the laminated composite plate model has been derived. Applications of the proposed methodology to an E-glass/epoxy symmetric composite panel composed of 16 plies [CSM/UM1208/3 layers of C1800] s = [CSM/0/(90/0) 3 ] s with delamination damage are demonstrated both numerically and experimentally. A non-contact scanning laser vibrometer (SLV), a lead zirconate titanate (PZT) actuator and a polyvinylidene fluoride (PVDF) sensor are used to conduct experimental modal testing. From the experimental example, capabilities of the proposed methodology for damage identification are successfully demonstrated for a 2D laminated composite panel. Furthermore, various damage scenarios are considered to show its performance and detailed results are discussed for future improvements.

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