Vibration-based condition monitoring of smart prefabricated concrete elements

The University of Trento is promoting a research effort aimed at developing an innovative distributed construction system based on smart prefabricated concrete elements that can allow real-time assessment of the condition of bridge structures. So far, two reduced-scale prototypes have been produced, each consisting of a 0.2×0.3×5.6m RC beam specifically designed for permanent instrumentation with 8 long-gauge Fiber Optics Sensors (FOS) at the lower edge. The sensors employed are FBG-based and can measure finite displacements both in statics and dynamics. The acquisition module uses a single commercial interrogation unit and a software-controlled optical switch, allowing acquisition of dynamic multi-channel signals from FBG-FOS, with a sample frequency of 625 Hz per channel. The performance of the system is undergoing validation in the laboratory. The scope of the experiment is to correlate changes in the dynamic response of the beams with different damage scenarios, using a direct modal strain approach. Each specimen is dynamically characterized in the undamaged state and in different condition states, simulating different cracking levels. The location and the extent of damage are evaluated through the calculation of damage indices which take into account changes in frequency and in strain-mode-shapes. This paper presents in detail the results of the experiment as conducted on one of these prototypes and demonstrates how the damage distribution detected by the system is fully compatible with the damage extent appraised by inspection.