The use of welded steel cover plates had been a common design practice to increase beam section capacity in regions of high moment for decades. Many steel girder bridges with cover plates are still in service. Steel girder bridges are subject to cyclic loading, which can initiate crack formation at the toe of the weld and reduce beam capacity. Thus, timely detection of fatigue cracks is of utmost importance in steel girder bridge monitoring. To date, crack monitoring methods using in-house radio frequency identification (RFID)-based sensors have been developed to complement visual inspection and provide quantitative information of damage level. Offering similar properties at a reduced cost, commercial ultra-high frequency (UHF) passive RFID tags have been identified as a more financially viable option for pervasive crack monitoring using a dense array of sensors. This paper presents a study on damage sensitivity of low-cost commercial UHF RFID tags for crack detection and monitoring on metallic structures. Using backscatter power as a parameter for damage identification, a crack sensing system has been developed for single and multiple tag configurations for increased sensing pervasiveness. The effect on backscatter power of the existence and stage of crack propagation has been successfully characterized. For further automation of crack detection, a damage index based on the variation of backscatter power has also been established. The tested commercial RFID-based crack sensor contributes to the usage of this technology on steel girder bridges.
The detection and localization of damage in a timely manner is critical in order to avoid the failure of structures. When a structure is subjected to an unscheduled impulsive force, the resulting damage can lead to failure in a very short period of time. As such, a monitoring strategy that can adapt to variability in the environment and that anticipates changes in physical processes has the potential of detecting, locating and mitigating damage. These requirements can be met by a Structural Control (SC) system that is capable of measuring and analyzing dynamic responses in real time. Such a system requires an effective damage identification method capable of locating and quantifying damage. The Eigenparameter Decomposition (ED) of Structural Flexibility Change method is validated with real data and can be used in the computational core of this system. The condition screening is implemented on a damaged structure and compared to an original baseline calculation, hence providing a supervised learning environment. A laboratory-scale experimental study on a 5-story shear building with different damage conditions subjected to an impulsive force has been chosen to validate the effectiveness of the proposed method. The effectiveness of the ED method to locate damage is compared to that of the Damage Index method. The ED method has also been modified to be able to locate and quantify damage. The experimental study shows the effectiveness of the modified method.
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