Many methods for the assessment of structural damage based on vibration-based technique are surveyed for many decades. In this paper, an effective damage detection method by nu-merical evaluation of structural damage is presented based on using an improved sensitivity of modal strain energy. At first, damage localization approach in dynamic systems is formu-lated by fundamental concept of modal strain energy (MSE) to precisely locate the eventual damages. Subsequently, a new optimization function is presented that contain of sensitivity of modal strain energy and error matrix of mode shapes between healthy and damaged struc-tures. Consequently, the optimization function is solved through Thikhonov regularization method to estimate the damage quantification. For verification of the proposed method, a numerical model of portal plane frame is used. Eventually, results show that the modal strain energy indicator can be exactly detected the location of damage. Then, the estimated damage extent indicates that the proposed method based on solution of optimization function by Thi-khonov regularization method can provide the convenient results to predicting the severity of damages.

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