Detection of local damage in complex nonlinear structures based on substructural approach

In this paper, the technique recently proposed by the authors for the detection of structural local damage in large size linear structures is extended to explore the detection of local damage in some complex nonlinear structures. The technique is based on substructural approach in which a complex nonlinear structure is decomposed into substructures Interaction effect between adjacent substructures is accounted by considering the interaction forces at substructural interfaces as the 'unknown inputs' to the substructures. An algorithm utilizing the classical Kalman extended estimator and the recursive least squares estimation for the unknown inputs is proposed to identify structural parameters at element level and the 'unknown inputs' to the substructure. Two cases that measurements at the substructure interfaces are available or not available are considered. Structural local damage is estimated from the change of structural parameters, such as the degradation of the stiffness, at element level. The technique enables distributed identification of local damage in complex nonlinear structures utilizing only a limited number of measured acceleration responses. Performance of proposed technique is illustrated by a numerical example of detecting local damage in a multi-story hysteretic building. It is shown that the proposed technique can be used for detecting structural local damage in some complex nonlinear structures.