Recovery of the resonance frequency of buildings following strong seismic deformation as a proxy for structural health

Elastic properties of civil engineering structures change when subjected to a dynamic excitation. The modal frequencies show a rapid decrease followed by a relaxation, or slow recovery, that is dependent on the level of damage. In this article, we analyze the slow recovery process applying three relaxation models to fit real earthquake data recorded in a Japanese building that shows variant structural state over 20 years. Despite the differences in conditions, the different scales and the complexity of a real-scale problem, the models originally developed for laboratory experiments are well adapted to real building data. The relaxation parameters (i.e. frequency variation, recovery slope, characteristic times and their amplitudes, and range of relaxation times) are able to characterize the structural state, given their clear connection to the degree of fracturing and mechanical damage to the building. The recovery process following strong seismic deformation, could, therefore, be a suitable proxy to monitor structural health.