Keywords: damage identification, uniform random load surface, spectral strain energy, power spectral density, modal analysis, plate, bridge.

This study presents the vibration-based uniform random load surface (URLS) response spectral strain energy (SSE) as a parameter for structural damage localization in beam and plate-like structures. In the past, the uniform load surface (ULS) approach has been implemented for structural integrity monitoring based on computations of the modal flexibility [1,2]. Doebling and Farrar [3] reported that modal flexibility (MF) variations obtained from ambient vibration testing are more sensitive to damage than those obtained from forced vibration testing. This indicates that MF is dependent on the location of the loading, measurement points, level of excitation or intensity of loading and randomness of the excitation. This is also indicative that multiple and single excitation may not produce the same level of response spectra.

However, the main argument for the damage identification technique presented in this paper emanates from the comparative studies conducted on the modal flexibility-based ULS application [2]. The authors in [2] reported that the ULS-based damage parameter is less sensitive to both modal truncation error and experimental noise when used for experimental non-destructive damage assessment than the modal flexibility itself. Moreover, the modal strain energy method was reported to be the most damage-sensitive parameter among various parameters investigated, namely mode shapes curvature, modal flexibility, uniform load surface curvature and stiffness methods when applied to damage localization in the I-40 bridge [4]. While these techniques were proven to be powerful, they were based on resonance frequency information and the potential advantages of broadband frequency information were therefore not realised. However, broadband based methods have been reported to be more effective for damage identification than solely resonance frequency based methods. Consequently, the URLS response SSE parameter presented in this paper employs the advantages of both broadband frequency information and the ULS concept for robustness and improved sensitivity enhancement to structural damage than can be realised by other existing methods.

The results obtained in this paper from both numerical simulation and experimental verification studies conducted on plate and beam-like structures demonstrate that the URLS response SSE is more sensitive to damage, less sensitive to measurement noise and modal truncation than the alternative damage identification methods. Moreover, the proposed method is applicable to input-output as well as output-only structural damage identification problems, so is even more versatile than many alternatives.

1

D. Wu, S.S. Law, "Damage localization in plate structures from uniform load surface curvature", Journal of Sound and Vibration, 276, 227-244, 2004. doi:10.1016/j.jsv.2003.07.040

2

Z. Zhang, A.E. Aktan, "Application of modal flexibility and its derivatives in structural identification", Research in Nondestructive Evaluation, 10, 43-61, 1998. doi:10.1007/PL00003899

3

S.W. Doebling, C.R. Farrar, "Computation of structural flexibility for bridge health monitoring using ambient modal data", in "Proceedings of the 11th Conference on Engineering Mechanics Part 2 (of 2)", May 19-22, Fort Lauderdale, FL, USA, 1996.

4

C.R. Farrar, D.V. Jauregui, "Comparative study of damage identification algorithms applied to a bridge: I. Experimental", Smart materials and Structures, 7, 704-719, 1998. doi:10.1088/0964-1726/7/5/013

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