International Journal of Concrete Structures and Materials

Korea Concrete Institute (한국콘크리트학회)
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Estimation of Friction Coefficient Using Smart Strand

  • Jeon, Se-Jin (Department of Civil Systems Engineering, Ajou University) ;
  • Park, Sung Yong (Structural Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology) ;
  • Kim, Sang-Hyun (Department of Civil Systems Engineering, Ajou University) ;
  • Kim, Sung Tae (Structural Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology) ;
  • Park, YoungHwan (Structural Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology)
  • Received : 2015.06.19
  • Accepted : 2015.08.18
  • Published : 2015.09.30
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Abstract

Friction in a post-tensioning system has a significant effect on the distribution of the prestressing force of tendons in prestressed concrete structures. However, attempts to derive friction coefficients using conventional electrical resistance strain gauges do not usually lead to reliable results, mainly due to the damage of sensors and lead wires during the insertion of strands into the sheath and during tensioning. In order to overcome these drawbacks of the existing measurement system, the Smart Strand was developed in this study to accurately measure the strain and prestressing force along the strand. In the Smart Strand, the core wire of a 7-wire strand is replaced with carbon fiber reinforced polymer in which the fiber Bragg grating sensors are embedded. As one of the applications of the Smart Strand, friction coefficients were evaluated using a full-scale test of a 20 m long beam. The test variables were the curvature, diameter, and filling ratio of the sheath. The analysis results showed the average wobble and curvature friction coefficients of 0.0038/m and 0.21/radian, respectively, which correspond to the middle of the range specified in ACI 318-08 in the U.S. and Structural Concrete Design Code in Korea. Also, the accuracy of the coefficients was improved by reducing the effective range specified in these codes by 27-34 %. This study shows the wide range of applicability of the developed Smart Strand system.

Keywords

Acknowledgement

Grant : Development of Smart Prestressing and Monitoring Technologies for Prestressed Concrete Bridges

Supported by : Korea Institute of Civil Engineering and Building Technology

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