This project was aimed at providing an improvement on the current inspection methods for detecting loose anchor bolts used in highway support structures. A capacitance-based smart washer system was developed and the final prototype was studied in two stages. Stage 1 of the project performed tests in the  laboratory to develop a sensor system prototype with a calibration curve that was able to correlate the capacitance reading and pretension inside the anchor bolts. However, when the system was applied a sign structure specimen, it was found to have severe insulation issues that could lead to failure of capacitance reading. Subsequently, a second prototype was developed using 3D printed PLA attachments to improve insulation. This prototype provided sufficient insulation from steel sign structures and output stable capacitance readings on sign structure specimen. A calibration curve was developed and the relationship between anchor bolt pretension and capacitance readings was finalized. Stage 2 of the project was to monitor the performance of the smart washer system in a long-term manner and in-field situation. It was found that the sensor system was sensitive to environmental factors especially rain that could short circuit system. After applying a simple double-layered plastic waterproof cover on the sensor system, the interruption from humidity was eliminated and stable capacitance readings were recorded again for consecutive 12 months. It is recommended that necessary waterproof protection should be introduced to the sensor system in the field environment to protect the system from environmental issues such as humidity. In conclusion, the concept and prototype of the smart washer system were proven efficient to detect pretension changes inside the anchor bolts. With proper waterproof protections for outdoor use, the smart washer system holds a great potential for improving inspections on loose anchor bolts of highway support structures.

The final report is available.