A comparative assessment of modal parameters and flutter derivatives using multiple output-only system identification methods

The wind tunnel tests including the bridge profile test, and the scaled-down bridge model test are crucial for analyzing bridge stability and modifying the design profile. It can provide critical information regarding the aerodynamic behavior of the bridge through investigating the flutter derivatives. In recent years, research in wind engineering has commonly utilized the Modified Ibrahim Time Domain Method (MITD) to determine flutter derivatives through free vibration tests. It can deliver the buffeting force effects through an iteration method within a smooth flow. This paper adopts the output-only Stochastic Subsystem Identification (SSI) methods to identify the flutter derivatives. These methods consider the buffeting force as a random force that can be incorporated into the stochastic state space equation. The advantage of SSI is that it can identify the flutter derivatives through the random vibration data of the bridge under various wind speeds. Furthermore, the SSI can be divided into two different methods: the Covariant-driven Stochastic Subsystem Identification method (SSI-COV) and the Data driven Stochastic Subsystem Identification method (SSI-DATA). This paper will present the results obtained under various wind speeds using three distinct system identification methods to investigate the originally proposed bridge section and the enhanced one. The accuracy of the results obtained through multiple output-only system identification methods will be demonstrated and the modal parameters can also be identified. It can be seen that the identified frequencies are consistent with the designed frequencies. The results validate the applicability and precision of the adopted Stochastic Subspace Identification methods for bridge aerodynamics analysis.