Abstract Summary
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 an automatic 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 Variational Mode Decomposition after a proper tuning procedure and a noise-robust area-based approach is exploited to identify modal damping ratios. The method is preliminarily validated on synthetic multi-modal signals showing excellent results even in case of closely spaced modes. The performance of the proposed approach is also tested for two real existing structures: the first case is the identification of modal parameters for a prestressed concrete girder bridge deck; the results are compared with the ones provided by a finite element model of the structure. The second case-study deals with the dynamic identification of cables in a stay-cabled bridge: modal damping ratios and frequencies are compared to estimates from ambient vibration data analyzed with alternative techniques. The identified frequencies are related to cable stresses and are exploited to critically study the effect of relaxation phenomenon on the cables.
