Wireless soft elastomeric capacitor sensor network for long-term fatigue crack monitoring of steel bridges

Long-term monitoring of fatigue cracks in large-scale bridge structures poses unique challenges due to the randomness of crack occurrences, small crack openings that impose negligible impact on global structural responses, slow crack propagation, and environmental impact. In this paper, we describe a recently-created integrated wireless fatigue cracking monitoring system with several unique features aimed at addressing these challenges. These features include: 1) a low cost large-size skin-type capacitive strain sensor to cover large bridge surfaces. A network of such sensors is deployed to capture potential crack initiation and propagation over large fatigue susceptible regions, 2) a novel crack growth index derived from the measured capacitance response, which is robust against long-term signal drift due to environmental impact, 3) a dedicated capacitance sensor board to enable robust wireless data acquisition through the next generation wireless sensing platform Xnode, 4) a novel low-power triggering mechanism to enable autonomous and continuous sensing and data acquisition for long-term monitoring. The integrated monitoring system was deployed in a full-scale steel highway bridge and preliminary field data are presented in this paper.