Estimation of Friction Coefficient Using Smart Strand

다국어 초록 (Multilingual 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.

목차 (Table of Contents)

• Abstract
• 1. Introduction
• 2. Friction Coefficients
• 3. Principle of Smart Strand
• 4. Full-Scale Test for Friction Coefficient
• 5. Evaluation of Friction Coefficients
• 6. Conclusions
• References