Friction characteristics between the strands and the duct have a significant effect on the distribution of prestressing force and can be incorporated by the curvature and wobble friction coefficients in the design of prestressed concrete structures. However, the recommended friction coefficients show a wide range of variation, which can cause the inaccurate estimation of prestressing force. In this study, the friction coefficients were evaluated based on the strains of tendons measured by Smart Strands using optical fiber sensors in a full-scale test specimen and two actual long-span girder bridges. The test specimen was investigated to determine how the duct shapes and other factors affect the friction coefficients. Simultaneous equations method and least squares method for obtaining friction coefficients were employed and the results were compared in the actual bridges. This study shows one of the applications of the developed Smart Strand system that can overcome several drawbacks of the existing measurement system.
This research was supported by a grant from a Strategic Research Project (Smart Monitoring System for Concrete Structures Using FRP Nerve Sensor) funded by the Korea Institute of Civil Engineering and Building Technology. The efforts of Sung Tae Kim in the Korea Institute of Civil Engineering and Building Technology for preparing and monitoring the Smart Strands are also greatly appreciated.
