Experimental and Numerical Characterization of the Dynamic Behaviour of a Historic Suspension Footbridge

This paper investigates the dynamic characteristics and behavior of a historic suspension footbridge through experimental and numerical studies. Ambient vibration tests were performed on the footbridge to extract the modal parameters of the structure such as natural frequencies, damping ratios, and mode shapes. The modal properties were identified from ambient vibration tests adopting the Stochastic Subspace Identification (SSI) technique. The availability of a numerical model reproducing accurately the dynamic characteristics of the footbridge is essential to carry out numerical studies on the footbridge under different dynamic loading scenarios. Due to the lack of the original technical drawings of the footbridge, a geometrical survey was carried out in order to determine the geometric characteristics of the structural elements. Furthermore, the deformed configuration of the main cable under dead load was experimentally measured during the field survey. The results of field vibration tests were used to calibrate and validate the numerical model of the footbridge, e.g., boundary conditions, and initial cable tension. The present study reports the results of the geometrical survey, of the operational modal analysis, and of the numerical modeling of the footbridge. Moreover, the 3-D Finite Element Model of the footbridge and its calibration with respect to ambient vibration tests are reported. After calibration of the finite element model, a good agreement was observed between computed and measured natural frequencies and mode shapes.