Input motion extraction and closely-spaced modes recognition through partial system identification: An orthogonality-aided blind source separation approach

Abstract

This research proposes an output-only procedure to extract seismic input motion and identify systems with severe closely-spaced modes incorporating a partial system identification approach. The proposed framework employs new methods to detect free vibration portion of the response histories and clustering the candidate points to find the first mode shape in a blind modal identification (BMI) procedure. The first mode frequency and damping along with mass matrix distribution of the system are calculated then using an orthogonality-based optimization process. The mentioned identified features are utilized next for the input motion extraction without any need to know the higher mode characteristics of the system. Next, higher mode characteristics are detected in succeeding steps considering the removal of each identified mode share from the total response at the end of each step. The perfect performance of the framework was proved against two simulated synthetic structures with mild and severe closely-spaced modes.