ABSTRACT
The motivation behind this paper is to develop a spectral-based damage identification scheme using output only acceleration response. The method utilizes spectral moment of the response as damage sensitive feature. Spectral moments retrieve information directly from the power spectrum. The major advantages of the method include, first, the method works based on the output only measurement data without demanding any representative model of the structure; second, unlike modal data, the presented method is a broadband approach which implements information from a wide frequency range. The feasibility of the approach in damage identification was validated using real data from the Sydney Harbour Bridge. Currently the bridge carries eight lanes of road traffic and two railway lines. Traffic lane 7 is a dedicated bus and taxi lane on the Eastern side of the bridge. Lane 7 consists of an asphalt road surface on a concrete deck supported by concrete and steel jack arches, Figure 1. There are approximately 800 jack arches over a total distance of 1.2 km. The jack arches are physically very difficult to access and are inspected typically at two yearly intervals according to standard visual inspection practices. For this study, three instrumented jack arches were considered, Joints 1, 4 and 6, Figure 2. These joints are located on the eastern side of the bridge underneath the bus lane near the north pylon. One of the joints had a known crack (Joint 4), along the front face and the crack propagated toward the surface of the deck, while the other joints were intact: one very far from the damaged joint (Joint 1) and the other one very close to the damaged joint (Joint 6). Acceleration data were collected from tri-axial accelerometers mounted on the base of each joint; data were collected before and after repair conducted on the damaged joint. The presented method was applied to see whether the presence of crack in the damaged joint can be identified and to investigate the impact of repair on the damaged joint. It was demonstrated that the proposed method can reliably identify the existing crack in the damaged joint, Figure 3. The presented results illustrated high potential of this approach to identify cracking in concrete structures. Illustration of one of the concrete jack arches underneath the bus lane. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig314_1.jpg"/> Schematic of the evaluated joints. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig314_2.tif"/> Comparison of damage index for Joints 1, 4 and 6. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig314_3.tif"/>
