Flexural strengthening of reinforced concrete beams using carbon fiber reinforced polymer rope with additional anchorage to limit debonding

The use of CFRP rope as NSM flexural strengthening and at the same time a method of limiting its debonding by anchoring its ends in drilled holes has been described. The work examined the effectiveness of strengthening reinforced concrete beams using NSM CFRP ropes and compared the solution with the traditional one using NSM CFRP strips. The study included 14 elements, including: 3 unstrengthened beams, 5 beams strengthened with NSM CFRP ropes and 6 beams strengthened with NSM CFRP strips. All beams were loaded monotonically until failure with two concentrated forces (four-point loading testing). The measurements were carried out using digital image correlation (DIC). In order to limit the possibility of debonding, in selected beams an anchorage made of CFRP rope glued into previously drilled holes in the beam web at an angle of 90o (6 beams) and in the case of using two CFRP ropes, at an angle of 45o and 90o (2 beams) was used. The analysis included a comparison of: failure modes, load–deflection responses and strain distributions. The obtained value of strengthening efficiency was: with the use of a single rope 25-30%, with the use of two ropes 46 and 49%, for CFRP strip 31-36%. In the case of beams strengthened with CFRP rope, debonding did not occur. In all beams strengthened with CFRP strips, debonding occurred and the additional anchoring did not contribute to the delay of its occurrence. All beams reinforced with CFRP rope achieved higher load-bearing capacity than expected and in no case failed due to debonding, which means that the assumed objectives of the work were met.