Damage assessment by stiffness identification for a full-scale three-story steel moment resisting frame building subjected to a sequence of earthquake excitations

This research experimentally investigates a practical hysteresis loop analysis method for damage assessment through stiffness identification using a full scale three-story steel moment resistant frame structure subjected to a sequence of 6 shake table tests with different magnitudes of 3D excitations. The effective elastic stiffness, k (e) , is calculated based on the analysis of the experimentally measured and reconstructed hysteresis loops. Structural degradation is then evaluated by tracking changes in identified stiffness over time and across different earthquake events. Finally, the fundamental frequency of the building is calculated using the identified stiffness to compare with the experimental frequency from experimental transfer functions. Results show average differences between the final stiffness of one event and the initial stiffness of the following event are less than 5% in both horizontal directions, indicating a good continuity and accuracy of the identification over events. The average difference between the experimental and calculated fundamental frequency are less than 0.1 Hz in both directions over all events. The overall results clearly delineate the capability of the method to accurately and consistently quantify and localize structural damage that may not be detected by external visual detection over several earthquake events of different magnitude, indicating its ability to be used in long term monitoring.