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Wavelet based technique for multi crack detection of a beam-like structure using the vibration data measured directly from a moving vehicle

In this paper an idea for crack detection of a multi-cracked beam-like structure by analyzing the vibration measured directly from the vehicle is presented. The crack model is adopted from fracture mechanics. The dynamic response of the bridgevehicle system is measured directly from the moving vehicle. When the vehicle moves along the structure, the dynamic response of the vehicle is distorted by the cracks at their locations. | Vietnam Journal of Mechanics, VAST, Vol. 32, No. 4 (2010), pp. 222 – 234 WAVELET BASED TECHNIQUE FOR MULTI-CRACK DETECTION OF A BEAM-LIKE STRUCTURE USING THE VIBRATION DATA MEASURED DIRECTLY FROM A MOVING VEHICLE Nguyen Viet Khoa and Tran Thanh Hai Institute of Mechanics, Vietnam Abstract. In this paper an idea for crack detection of a multi-cracked beam-like structure by analyzing the vibration measured directly from the vehicle is presented. The crack model is adopted from fracture mechanics. The dynamic response of the bridgevehicle system is measured directly from the moving vehicle. When the vehicle moves along the structure, the dynamic response of the vehicle is distorted by the cracks at their locations. These distortions are generally small and difficult to be detected visually. In order to detect the cracks, Wavelet Transform - an effective method of detecting such small distortions was adopted. The existence of the cracks can be revealed by large values (peaks) in the wavelet transform. Locations of the cracks can be determined by positions of the peaks and the vehicle speed. Numerical results show that the method can detect cracks as small as 10 % of the beam height with noise level up to 5%. The proposed method is applicable for low velocity-movements while high velocity-movements are not recommended. 1. INTRODUCTION The detection of cracks in mechanical systems and civil engineering structures has attracted many researchers in the last two decades as reviewed by Doebling et al. (1998). There are a large number of nondestructive methods for crack detection that are based on the changes in the dynamic properties of the structure (frequencies, mode shapes, transfer functions). Pandey et al (1991) proposed the application of mode shape curvature in detecting damage. The reduction in cross section caused by the damage tends to increase the curvature of the mode shapes in the vicinity of the damage. Verboven et al (2002, 2003) presented autonomous damage