Modal Parameters identification in existing bridges based on free vibration tests

The dynamic identification of modal parameters plays a fundamental role in structural health monitoring: mode shapes, frequencies and damping ratios can be exploited to assess the current state of a structure, used for damage detection or in numerical model validation. In recent years, vibration-based methods have become a popular solution for the state of health estimation of strategic civil infrastructures such as bridges: in particular, free vibration tests represent a fast and economic method only requiring the temporary installation of a limited number of sensors on the structure. This contribution presents a procedure for the identification of modal properties of existing bridges exploiting their free decay responses: each mode's contribution is adaptively extracted from free vibration tests data using the Empirical Fourier Decomposition and a noise-robust area-based approach is exploited to identify modal damping ratios. The method is preliminarily validated on a synthetic multi-modal signal showing excellent results even in case of closely spaced modes. The performance of the proposed approach is also tested for a real existing structure: the selected case study deals with the identification of modal parameters for a steel railway bridge deck.