Monitoring of structural systems by using frequency data

The present work evaluates the possibility of using dynamic data to assess structural integrity. It addresses the problem of understanding when it is sufficient to measure and use only natural frequencies, thus avoiding the n eed to measure modal shapes. The,classic problem of detecting damage in bea ms, or beam assemblies, due to concentrated cracks, or damage spread over a structural member is dealt with. Damage is represented as a decrease in st iffness and linear behaviour before and after the event assumed to have cau sed damage is considered. Damage is restricted to a few unknown sections or elements, so that only the modification of few parameters of the system ne ed to be determined. This study thus rejects assumptions unrelated to the p hysical aspects of the problem, in contrast to many papers on the subject. The amount of data to locate and quantify damage correctly is discussed; ge neral considerations lead to the conclusion that a unique and reliable esti mate of the damage can be obtained using only few additional frequency data with respect to the number of damaged zones. Continuous and discrete (fini te element) models are examined. Finally the paper considers the applicatio ns to both analytical and experimental data of the procedure developed, whi ch takes account of the peculiar characteristics of damage detection proble m. Copyright (C) 1999 John Wiley & Sons, Ltd.