Updating local physical and global generalized parameters of coupled substructure models

The idea behind model based damage detection techniques is to identify structural parameters from experimental modal data obtained before and after the damage has happened. Of course, the underlying model and its parameters must be capable to describe the damage. For damage diagnosis of complex structures the modeling uncertainties may not only be restricted to the assumed damage area but may he present everywhere, for example, due to insufficient mesh refinement (discretization errors), unsuitable element types ( i.e. missing shear deformation capability) or unsuitable boundary conditions and material laws. These uncertainties may detoriate the accuracy and will generally lead to non-unique results for the damage parameters. In the paper we will describe a method allowing to split the uncertain parameters into two groups: the first group contains the local physical parameters related to the assumed damage area ( the main structure) whereas the second group contains some global generalized parameters related to the remaining structure (the residual structure). These global parameters are represented by the modal stiffnesses and masses of the residual structure with unconstrained interface degrees of freedom. This approach allows to restrict the measurement of the mode shapes to those critical areas where structural modifications are expected either due to damage or due to intended design changes. One application will describe the identification of the local stiffness and mass modification of a beam type frame structure due to a damaged bolted joint. The joint parameters are defined within the main structure only whereas the global parameters are defined to account for the modeling uncertainties of the remaining structure.