Detection of Damage Level and Location in Structures using Measured Natural Frequencies

摘要

This research proposes examining changes in natural frequencies of several modes of the monitored structure through a comprehensive screening process to detect damage and identify its location. A data base for all possible damage levels and damage locations can be numerically developed for the structure before being set in service. Such data base contains the dynamic characteristics of the undamaged structure as well as several possible damaged scenarios with different damage levels and locations. The sensitivity of the various natural frequencies to damage level and location are identified and included in the data base. The measured changes in frequencies during the monitoring process are continually correlated to the formed data base where damage location and level can be identified. Two methods are proposed in this research as search engines to identify the damaged element. The first method, the filtration method, relies on comparing the changes in the measured frequencies of the real structure to those contained in the data base in a sequential manner. The second method uses a frequency modal assurance criteria F-MAC factor calculated for all possible damage patterns to indicate the one with the highest correlation. The applicability of the proposed method is experimentally verified through testing a cantilever beam model and a grid system model where damages of different levels are introduced to various locations on the structure.