Experimental study on crack propagation of CFRP-strengthened RC beams subjected to torsion

This paper presents an experimental study into the torsional behaviour and crack propagation of 28 reinforced concrete (RC) beams comprising of 6 unstrengthened beams and 22 beams strengthened using near surface-mounted (NSM) carbon-fibre-reinforced polymers (CFRP). The strengthened beams were designed to capture the influence of: FRP spacing, full wrapping vs U-jacketing and the use of discontinuous CFRP laminates vs continuous FRP sheets within the grooves. A photogrammetry technique was used to determine the three-dimensional displacement of targets placed on the north and south faces of the beams at selected load levels up to failure. The aim of this study was to measure the torsional crack width propagation for each beam. The torsional deformations of the beams were evaluated and verified using photogrammetry measurements and the differences in the width of the large torsional cracks across the tested beams were examined. It was observed that the width of the torsional cracks for the strengthened beams was smaller than that of the control beams under the same load. In addition, the results also indicate that the crack widths of the beams using mortar as the FRP bonding agent showed clear differences from the beams strengthened using epoxy bonding.