Structural health monitoring of time-varying systems by output-only identification

Aim of the paper is the structural health monitoring of bridge structures excited by a massive moving load, whose characteristics, such as the mass and speed, are unknown, considering the presence of a localized damage along the structure. A novel method for the simultaneous identification of both the load characteristics and damage parameters from vibration measurements is proposed: the data processing relies on the Ensemble Empirical Mode Decomposition and the Normalized Hilbert Transform. Neither a priori information about the response of the undamaged structure nor the free decay of the damaged system is required, only a single point measurement is needed. Performances of the technique are studied varying the load characteristics, damage locations and crack depths. Numerical experiments show the identification is rather accurate, results are not very sensitive to the crack location and depth, while they are sensibly affected by the speed of the moving load.