Nondestrutive damage detection by simultaneous identification of stiffness and damping

Abstract

The objective of this study is to develop a nondestructive damage evaluation methodology that can identify simultaneously both stiffness and damping changes in a structure. Two approaches are used to meet the stated objectives. First, a method is developed on the basis of the conservation of total energy; second, the other method utilizes the acceleration-structural parameters (stiffness and damping) sensitivities. The total energy in a system consists of the sum of the kinetic energy, the potential energy, and the dissipated energy. In the second approach, a baseline structure is first identified. A baseline structure is defined to be a structural system having a similar dynamic response to the existing structure with no damage. In this study, natural frequencies and modal damping values are used to identify the baseline structure. The performance of the developed methodology is validated using several numerical experiments; Two classes of structures are considered here: (1) a high-rise building modeled as shear beams and (2) a two-span continuous beam structure. In the shear beam model of the structure, the damping damage is simulated by increasing the Newtonian dash pot constant which models the dissipation at the damaged story. For the two-span continuous beam structure, it is assumed that damping of the undamaged structure can be modeled using a proportional damping matrix. The damping matrix of the damaged structure is modeled as the combination of a proportional damping matrix of the undamaged structure and a stiffness proportional damping matrix of the damaged element. Three damage cases are investigated for each of the two structures considered here. Only one element experiences damping damage for the first damage scenario. In the second damage scenario, both stiffness damage and damping damage are simulated with different severities in one element of the model. In the third damage scenario, two elements are simulated with stiffness damage and damping damage, to verify whether or not the developed methodology works for multi-damage cases. The proposed method is modified to use mode shapes and the modified proposed method is applied to experimental data to identify stiffness damage in a R/C structure.