Time Domain Identification of Linear Structures

Abstract

A time domain system identification program that is able to determine the elements of the structural coefficient matrices in linear mathematical models is presented. A numerical investigation of a five story shear building is used to illustrate that the elements of the stiffness matrix can be correctly determined even when sensors are not placed at every degree of freedom and when single mode free vibration response data are used in the system identification procedure. Results from a laboratory experiment on a two story shear building show that the measured response at each degree of freedom can be matched almost perfectly using the parameters found in the identification process, but that the parameters found from one set of data are not always able to produce a response that matches well the response from another test on the same structure.Information about damaged members can be obtained by studying the changes in the elements of the stiffness matrix. In structures more complicated than shear buildings, it will not usually be possible to define a “complete” model, and an “incomplete” model will have to be used. It is shown here that, when models are formulated using fewer DOFs than the number normally considered appropriate, damaged or modified members in a structure can not be precisely located. If the full set, or a more complete set, of DOFs is used on the other hand then, at least for the structures considered in this study, precise information can be obtained for individual elements of the coefficient matrices.