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Modal strain-based damage identification on a prestressed concrete beam

Book Contribution - Book Chapter Conference Contribution

© 2019 Taylor & Francis Group, London. The development of reliable structural health monitoring (SHM) techniques that can provide valuable information about a structure’s condition is necessary, not only for maintenance purposes but also in a post-earthquake situation. This information is important for making inspections more timely and minimizing the uncertainty associated with post-earthquake damage assessments. Vibration-based Structural Health Monitoring is widely used for monitoring civil infrastructure as it constitutes a non-destructive condition assessment method, dependent on the identification of changes in the dynamic characteristics of a structure that are related to damage. However, the commonly employed dynamic characteristics, i.e. natural frequencies and displacement mode shapes, are relatively insensitive to local damage of moderate severity. Modal strains and curvatures are more sensitive to local damage, but the direct monitoring of these quantities is challenging due to the very small (sub-microstrain) strain levels occurring during ambient, or operational excitation. In the present work, the identification of the modal strains of a pre-stressed concrete beam, subjected to a progressive damage test, is performed. Dynamic measurements are conducted on the beam at the beginning of each loading cycle. The response of the beam is recorded with uniaxial accelerometers and four chains of multiplexed Fiber-optic Bragg Grating (FBG) strain sensors. The evolution of the dynamic characteristics of the beam after each loading cycle is investigated. Changes of the natural frequency values, of the amplitude and the curvature of the strain mode shapes are observed even from an early damaged state, indicating the presence of damage even when the cracks where nearly closed due to the prestressing force. No changes in the displacement mode shapes are observed, which confirms that accurately identified modal strains are much more sensitive to structural damage in prestressed concrete structures than conventional modal displacements.
Book: Proceedings of the 6th International Symposium on Life-Cycle Civil Engineering, IALCCE 2018
Pages: 229 - 236
Publication year:2018