Early damage detection is an important and initial step in structural health monitoring (SHM) that aims to evaluate the global state of a structure and finds whether damage is available throughout the structure. To do this, a new sensitivity function regarding modal strain energy (MSE) is proposed to use as a novel damage-sensitive feature. The sensitivity function is based on proposing a new equation of modal sensitivity and using the presented equation in the global formulation of MSE. In order to apply this sensitivity function as the damagesensitive feature, the matrix of sensitivity of MSE is converted into a vector by the vectorization procedure. A new density-based clustering method named DBSCAN is also presented here to detect early damage using the vector of the sensitivity of MSE. To demonstrate the performance and reliability of the proposed methods, the ASCE benchmark structure (Phase I) is employed as a numerical example. Results show that the proposed sensitivity function is sensitive to damage and can be a reliable damage-sensitive feature in the applications of SHM. Furthermore, numerical results demonstrate that the proposed DBSCAN approach is a robust tool for detecting damage.

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