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Monitoring Concrete Strength Using Strain Energy Based Structural Health Monitoring Technique: Hypothetical Case Study of a Gravity Dam



Identifying the variation in Modulus of Elasticity (MoE) of concrete is essential to comprehend the state of functionality of the concrete structural system. At different stages of service life, from construction to the demolition or restoration, the structure needs to be monitored so that any anomaly in the strength of the structure, whether due to strength gain, inappropriate construction or due to damage, can be identified readily. A very small deviation in the strength may need an appropriate and robust identification parameter to detect the anomaly. The current research article considers four modal parameters namely Eigenfrequency, Displacement Mode Shape (DMS), Curvature Mode Shape (CMS) and Strain Energy Mode Shape (SEMS) in order to comprehend the strength reduction. Vibration-based health monitoring technique is employed to the 2D numerical model of a concrete gravity dam known as Koyna dam, as a hypothetical case study. The model is validated through the two-step process using available data and random excitation. In this process, the simulated acceleration response of the structure is analyzed to extract modal information. Upon validation, the model is used to study the strength variation during its strength gaining phase and initial service life. Results show that although Eigen frequency, DMS and CMS can be sensitive to the large strength incongruity, none of them is suitable for identifying and representing the minute change in MoE, especially during the strength gaining phase of concrete. While on the other hand, SEMS is found to be sensitive enough to be able to differentiate between the very small variation in the governing strength parameter. Therefore, it is concluded that SEMS can represent the modal response of a concrete structure quite precisely at different times of its service life and can differentiate between the variation of Eigenfrequency due to a large amount of damage at a small location and a small strength variation in the overall structure. This property indicates that SEMS is the most appropriate parameter for identifying the system of a mass concrete structure like a gravity dam.


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