Vibration-Based Damage Detection for a Prestressed Concrete Box Girder by Means of Subspace Analysis

Vibration-based damage detection for civil structures has been actively investigated. Many acceleration-based damage detection methods have been developed, among which the subspace-based system identification theory has been well established and has been a popular way to identify the structure's modal parameters, having the advantage of being non-iterative and computationally tractable. Nevertheless, traditional modal parameters, including modal frequencies, mode shapes, and damping ratios, are not always sensitive to damage in actual civil structures. In this paper, a series of static loading tests and nondestructive hammer tests were applied to a prestressed concrete (PC) box girder. After analyzing the structure by the traditional modal analysis method, a technique based on null subspace analysis is proposed to monitor the health state of the PC box girder, and an index reflecting the damage levels is proposed. Compared with traditional modal parameters, the proposed damage index shows higher sensitivity and efficient precision to distinguish different structural damage levels. What is more, the damage caused by fracturing of prestressing tendons, which only slightly affect changes in modal frequencies, can also be obviously observed by this method.