Structural damage localization by combining flexibility and stiffness methods

A damage diagnosis technique based on changes in dynamically measured flexibility and stiffness of structures is presented. The objective is not only to detect the existence of damage, but also to locate it. The covariance-driven subspace identification technique is applied to identify structural modal parameters, and these are then used to assemble the flexibility matrix of dimensions corresponding to the measured degrees of freedom. The corresponding stiffness matrix is obtained by a pseudo-inversion of the flexibility matrix. Damage localization is achieved by a combined assessment of changes in these two measured matrices in moving from the reference state to the damaged state. Since the location of damage is given directly by the position of sensors, no geometrical measurements and finite element models are needed. When using output-only measurement data, an approximate mass-normalization of the mode shapes is adopted and an appropriate correction procedure is proposed. Numerical and experimental applications are considered, in order to examine the efficiency and limitations of the presented method.