Description of a Mechanical Device for Prestressing of CFRP Sheets -­ Part I

A mechanical device for prestressing carbon fiber-reinforced polymer (CFRP) sheets was developed, and its application for the flexural strengthening of reinforced concrete (RC) beams was investigated in this research program. Significant features of this mechanical device are 1) the CFRP sheets are directly anchored to the device itself; 2) prestressing is easily achieved while the device is not yet attached to the RC beam; 3) the prestressing is applied with a manual torque wrench without the need for power-operated hydraulic jacks; 4) fiber-reinforced polymer (FRP) U-wraps can be easily attached to the end of the prestressed CFRP sheets; and 5) the prestressing transfer is accomplished under slow strain rates. This paper describes in detail the main features and the application procedures for this mechanical device. To investigate the feasibility of using this device for flexural strengthening, the experimental program consisted of testing seven RC beams under a four-point bending test setup. Test results indicate that the device was efficient in applying prestressing to the CFRP sheets and, as predicted, in comparison with the control beams, the flexural capacity and serviceability of the beams were increased after strengthening with the prestressed CFRP sheets. In a second accompanying paper, the experimental and analytical results obtained from the flexural program are discussed in further detail