Damping ratio identification using attenuation responses extracted by time series semantic segmentation

Abstract

Damping ratio is an essential dynamic characteristic of bridge structures, and its properties have still not been well understood due to the difficulties in accurate calculation with structural health monitoring (SHM) data. It is widely accepted that the exponential attenuation (EA) method using free attenuation responses is a reliable way to calculate damping ratio. To identify the damping ratio from SHM data with EA method, a time series semantic segmentation method is proposed in this paper to extract free attenuation segments from the massive data of monitored acceleration responses. A labeled semantic dataset is firstly constructed based on the long-term monitoring data of the Z24 bridge which is a continuous bridge widely used as a benchmark model for SHM, and the labeling standard is introduced to illustrate the preference of selecting desirable attenuation segments. Then an adapted U-net model is developed and trained with the constructed dataset, and key hyper-parameters including the configuration of convolutional kernel and decision boundary are investigated and determined to meet the requirement of processing time series data of acceleration responses. A large number of attenuation segments have then been extracted by the well-trained model, based on which the damping ratio of the 1st vibration mode in 10 months is obtained with the EA method. The identified damping ratios are found reliable as compared with those identified by the stochastic subspace identification method, thus enabling further investigation of the properties of damping ratio. Finally, the influence of the temperature variation is explored, revealing an obvious correlation relationship between the temperature and the damping ratio. The results of this study not only provide a novel method to calculate damping ratio with SHM data but also could deepen the understanding of damping ratio properties and serve as a reference for more reasonable utilization of the damping ratio in structural dynamic analysis or condition assessment.