Artificial boundary conditions for model updating and damage detection

The updating of finite-element models commonly makes use of measured modal parameters. The number of modal parameters measured in a typical modal test is small, while the number of model parameters to be adjusted can be large. In this paper, it is shown that the natural frequencies for the structure under a variety of boundary conditions are available from any square, spatially incomplete frequency response function data, without any actual physical alteration of the boundary conditions, hence the term 'artificial boundary conditions'. This approach can provide potentially a large number of additional and distinct mode frequencies from the same modal test. The simplest example of this approach is that the driving-point antiresonance frequencies correspond to the natural frequencies obtained from the structure with the driving-point degree of freedom constrained to ground. This result is developed generally for multiple measured points, and is shown to be related to previous results concerning omitted coordinate systems and spatially incomplete test data. The approach is applied to sensitivity-based model updating and damage detection. (C) 1999 Academic Press.