Strengthening RC T-beams in flexure and shear using new mechanically-anchored FRP and dry fibre systems

摘要

Current conventional strengthening of reinforced concrete (RC) beams using epoxy-bonded fibre-reinforced polymer (FRP) technique requires difficult surface preparation and is susceptible to a brittle form of failure due to peel-off or debonding of the FRP laminate from the beam. This research presents two new mechanically-anchored FRP and dry fibre strengthening systems that can be used to improve the performance of RC beams in flexure and shear, respectively. Unlike conventional FRP-strengthening methods, the proposed systems require less surface preparation and adhesive application, and eliminate peel-off and debonding of FRP sheets. In order to experimentally evaluate the effectiveness of the new strengthening systems, a total of seven half-scale RC T-beams were tested under four-point loading system up to failure. Three RC T-beams were tested to evaluate the increase in shear capacity using a new FRP strengthening system. One beam was tested as a control beam. One beam was strengthened by using a U-shaped carbon FRP (CFRP) sheet that was externally bonded to the web of the beam. One beam was strengthened by using new anchored U-shaped dry carbon fibre (CF) sheet method. In this method, dry CF sheets are wrapped around and bonded to two steel rods. Then the rods are anchored to the corners of the web-flange intersection of the T-beam with mechanical bolts. The new method relies on utilizing the full mechanical contribution of the dry CF sheets, which will be activated upon development of strain in the RC web, and transferring them through a longitudinal steel rod to the core of the compression web-flange zone by means of mechanical anchors. Four RC T-beams were tested to evaluate the increase in flexural capacity and ductility using a new FRP strengthening system. One beam was tested as a control beam. One beam was strengthened with conventional epoxy-bonding method. Two beams were strengthened with the new hybrid FRP sheet / ductile anchor system (one with unbonded CFRP, while the other with bonded CFRP). The proposed system leads to a ductile failure mode by triggering the yield in the steel anchor system (steel links) while avoiding peel- off or debonding of FRP sheets, which is sudden in nature. The tested beams where modeled to analytically evaluate their performance. The experimental and analytical results indicate that the proposed new retrofitting methods are structurally efficient in enhancing the shear and flexure strengths and ductility of RC T-beams compared to conventional epoxy-bonding methods