Strengthening and repairing of flexural Reinforced Concrete (RC) members with Near-Surface Mounted (NSM) or Externally Bonded (EB) Fibre Reinforced Polymers (FRPs) has shown promising results and gained general acceptance among civil engineers during past decades. Furthermore, the authors of a number of experimental and analytical studies have discussed that using non-prestressed FRPs for strengthening purposes is not completely efficient in terms of exploiting the full capacity of the high-strength FRP materials. Applying prestressing force to the FRP materials not only makes it possible to exploit the full tensile strength of the FRPs but also enhances the serviceability of the flexural member being strengthened by reducing cracks extent/width and by decreasing deflections. A suitable anchorage system that is capable of applying prestressing force to the FRP material in a safe and simple way can increase the efficiency of the strengthening procedure in terms of reducing time and labour costs.
The current study was used to investigate the practicality and effectiveness of two newly developed anchorage systems for post-tensioning FRP material. The developed anchorage systems incorporated the use of SMA bars and proved their capability to act as actuators to post-tension the strengthening material. In the first phase of this study, the first anchorage system was used for both the EB CFRP and the NSM CFRP techniques to strengthen RC beams in flexure. In order to evaluate the efficiency of the first anchorage system, seven RC beams were cast and tested under flexural loading, four of which were strengthened using prestressed CFRP material. Tests results from the beams post-tensioned with this first prestressing system proved the capability of the SMA bars to be used as actuators.
Based on the test results derived from the first system, the second phase of the experimental investigation aimed at simplifying the prestressing procedure. Therefore, the first prestressing system’s design concept was completely revised and an innovative, practical, and simple anchorage system was developed to prestress NSM CFRP strips for flexural strengthening of RC beams. The modified anchorage system was used to strengthen a large-scale, initially cracked RC beam. The results derived from the second anchorage system showed that the system is capable of applying prestressing force in an efficient way while simplifying the prestressing procedure.
To the author’s best knowledge, the study presented in this thesis on using the SMA bars as actuators to prestress FRP materials for flexural strengthening of RC beams is the first of its kind in the world, and the findings suggest a successful transfer of this technology from the research laboratory to application in the field.