Reinforced concrete flexural strength enhancement due to retro-fitted end anchorage systems and CFRP reinforcement

Abstract

The importance of repair in construction is becoming mandatory in our society with its ever-growing practices in sustainable design. In this respect, carbon fibre has many benefits when compared to steel reinforcement. It is anti-corrosive, has a higher resistance to cyclic and long term loading, a higher tensile strength and it shows great resistance to creep. It is thus highly effective in repair works. This study deals with the strength enhancement of RC beams which can be achieved through the improvement of the end anchorage system implemented in the beam-laminate fastening. The anchorage was first tested separately, and various configurations were tested to make sure that satisfactory load capacities could be reached. The preliminary tests consisted of tension tests applied to simple anchor configurations, which could potentially be installed in a full scale beam system in the event of a repair project. The first set of tests featured CFRP wrap adhered to externally bonded laminate strips. These yielded lower results than expected, and preliminary failure was still predicted in a potential full scale test. A second configuration was established by replacing the CFRP fabric by mild steel sheeting. The tension tests again yielded similarly inefficient results due to failure at the connection. The third anchorage model produced was a mechanical anchor system using holts and milled steel plates which were found to secure the laminate in place highly effectively. The final configuration of the mechanical anchor was established, and full scale four-point bending tests were carried out on various specimens of RC beams sporting this end anchorage system. The results showed ultimate load capacities which were very similar to the predicted values in theory thus proving the anchorage system be sufficiently effective. However, the strength enhancement of the beams in bending was not as high as expected, and intermediate debonding of the laminate occurred between the FRP laminate and the concrete surface. Further tests are required utilizing the same type of anchorage arrangement together with intermediate anchors along the beam span.