Non-linear identification of damaged frame members from seismic response data

In structural engineering applications special excitation sources and forms are needed in order to achieve a consistent estimate of non-linear quantities. This condition hardly can be obtained when structures are to be tested in situ. Earthquakes can supply the structure with enough energy to activate a pronounced non-linear behaviour, which can be considered as an indicator of occurrence of damage. Seismic events cause transient structural response and advanced signal processing tools are needed for extracting reliable information from short signals: recently time-frequency analysis has offered some answers when working with transient signal, and its efficacy in non-linear identification may be enhanced by assigning it a role in the classical framework of Volterra series representation. The identification of non-linear stiffness of three dimensional frames with steel members, based on the approximation of system's response on the basis of a truncated Volterra series and the definition of linear modes of vibrations, is presented. The instantaneous estimators of structural dynamic parameters have been determined from the response of the systems to an earthquake loading. A discussion on the results and their reliability completes the paper.