Series of Full-Scale Field Vibration Tests and Bayesian Modal Identification of a Pedestrian Bridge

Many spectacular pedestrian bridges were designed and constructed recently. Owing to their special shapes, it is expected that various types and a wide range of vibration frequency components will be induced by pedestrians. To avoid accidents and reduce risk, the vibration characteristics of pedestrian bridges during their service life must be carefully assessed. The most direct and reliable way to study the vibration characteristics of a structural system is through field vibration tests. In this paper, a series of full-scale field vibration tests (including ambient, forced, and free vibration tests) were carried out on a pedestrian bridge at City University of Hong Kong (CityU). The difficulties encountered in the field tests are reported. The recently developed Bayesian methods were utilized to determine the modal parameters of the bridge based on measurements from all three kinds of tests. In addition to the most probable values (MPVs) of modal parameters, the associated posterior uncertainties were also analytically calculated. Four modes were identified, including three vertical bending modes and one torsional mode. The accuracy of the identified modal parameters was assessed through the posterior uncertainty. Because the amplitudes of the vibration in the three kinds of tests were different, the modal parameters determined from these kinds of tests were compared and discussed. Suggestions related to the proper use and potential vibration problems during the lifecycle of pedestrian bridges were provided based on the analysis results.