Extraction of Ritz vectors from vibration test data

Modal parameters obtained from modal testing (such as modal vectors, natura l frequencies, and damping ratios) have been used extensively in system ide ntification, finite element model updating, and structural health monitorin g. As an alternative to modal vectors, load-dependent Ritz vectors have bee n shown useful in various areas of structural dynamics such as model reduct ion and damage detection. The applications of Ritz vectors, however, have b een mainly limited in analytic;ll and numerical analyses because of the dif ficulty to identify them from vibration tests. This paper presents a proced ure to extract load-dependent Ritz Vectors using a complete flexibility mat rix constructed from measured vibration test data. The proposed method cann ot only construct the Ritz vectors corresponding to the actual load pattern employed in vibration tests, but also generate Ritz vectors from arbitrary load patterns. Experimental data obtained from the vibration test of a gri d-type bridge structure are employed to validate and illustrate the propose d extraction procedure. (C) 2001 Academic Press.