Bayesian Operational Modal Analysis of a Pedestrian Bridge Using a Field Test with Multiple Setups

An ambient vibration test was conducted for the pedestrian bridge that links the City University (CityU) of Hong Kong and the adjacent subway station. In this test, 100 locations forming a net of measurement were selected. Due to the limited number of sensors available, 10 setups were designed to cover all the degrees of freedom (dofs) of interest. A recently developed Bayesian method incorporating multiple setups was used to analyze the collected data. Besides the most probable values (MPVs) of modal parameters, the associated posterior uncertainty was also calculated analytically without resorting to the finite difference method. Six modes were identified, including some local modes of specified spans and global modes, and compared with those identified in a previous study. The difficulty encountered in the field test is discussed, along with some interesting features. Practical interpretation of the statistics of modal parameters calculated from frequentist and Bayesian context is also discussed. After the field test, a lift was installed between the ground and the bridge deck, which changed the modal properties of the original structure. This study provides a baseline of the dynamic characteristics of the original structure for future safety assessment.