Physical redundancy is a common approach in applications with safety-critical systems. But that is not always possible in some structural health monitoring (SHM) applications whether for economic, spatial, or safety reasons. Many SHM sensor validating applications only rely on analytical redundancy. In such circumstances, sensor faults and structural damage need to be assuredly discriminated. A self-diagnosis strain sensor operating in a continuous online SHM scenario is considered. The sensor is based on a full electric resistance strain gauge Wheatstone bridge. The state of the art shows that such a sensorhas not yet been developed. The loop current step response (LCSR) is a wellknown method to detect strain gauge debonding. However, applying the LCSR method to a full strain gauge Wheatstone bridge has some limitations analyzed in this paper. Two new methods for detecting strain gauge debonding are proposed and evaluated. These methods are based on consistency checking of the strain gauges grids temperature measurements-employing an array of (a) digital contact temperature sensors or (b) quasi-contact microelectromechanical system thermopile sensors. The experimental results reveal that both methods are suitable for application in an SHM self-diagnosis sensor scenario. However, the quasi-contact measuring method showed to be more sensitive to the strain gauge grid debonding fault though.KEYWORDS loop current step response (LCSR) method, self-diagnosis sensor, strain measurement, temperature measurement, thermal sensors

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SUMMARY Structural health monitoring is an emergent powerful diagnostic tool that can be used to identify and to prevent possible failures of the various components that comprise an infrastructure. In a suspension bridge, the measurement of the vertical and transversal displacements plays an important role for its safety evaluation. Considering the restrictions usually found on these structures, an enhanced solution comprises a non‐contact vision‐based measurement system with dynamic response, accuracy and amplitude range well suited to the physical phenomenon to measure. A methodology to perform the vision system calibration is described, which can be carried out in situ, while the deck is moving, requiring little effort and a minimum set of information. The key idea is to use the factorization method to get an initial estimation of the object shape and camera's parameters, and to incorporate the knowledge about the distances between the calibration targets in a non‐linear optimization process to achieve a metric shape reconstruction and optimize the camera's parameters estimation. Results obtained by numerical simulation experiments are reported, showing the negligible influence of noisy calibration data in the calibration performance and also the robustness of the calibration process on the camera's parameters estimation. Tests carried out to assess the calibration and tracking of the bridge deck motion showed that, even in an environmental severely affected by noise, it is possible to measure the vertical and transversal displacements of the bridge deck with excellent levels of accuracy. Copyright © 2011 John Wiley & Sons, Ltd.

Structural Health Monitoring is an emergent powerful diagnostic tool that can be used to identify and to prevent possible failures of the various components that comprise an infrastructure. In the particular case of a suspension bridge, the measurement of the vertical and transversal displacements plays an important role for its safety evaluation. Taking into account the restrictions usually found on these structures, an enhanced solution comprises a non‐contact vision‐based measurement system with dynamic response, accuracy and amplitude range well suited to the physical phenomenon to measure. The paper describes a methodology to perform the vision system calibration that can be carried out in‐situ, while the deck is moving, requiring little effort and a minimum set of information. Specifically, only a set of active targets fixed on the deck and the knowledge about the distances between them is required. Results related to the performance evaluation, obtained by numerical simulation and by real experiments with a reduced structure model, are presented and they show that, even in an environment severely affected by disturbance noise, it is possible to measure the vertical and transversal displacements with a standard accuracy better than 10 mm.

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