This paper presents an innovative method of prestressing carbon fibre reinforced polymer (CFRP) plates used as externally bonded reinforcement for flexural strengthening of reinforced concrete (RC) beams. The proposed method aims to achieve self-anchorage of the prestressed CFRP plate and thus eliminate the need for conventional mechanical anchorage at its ends. Experimental tests of RC beams in four-point bending were conducted to investigate the strengthening efficiency of the self-anchored prestressed CFRP plate. The experimental results showed that using the self-anchored prestressed CFRP significantly improved the flexural performance of the strengthened beam in terms of bending stiffness, crack widths, and load-carrying capacity. The utilisation ratio of the prestressed CFRP plate reached 81% at its debonding. Numerical analyses using nonlinear finite element (FE) method were conducted to model the tested specimens. Based on the reliable simulation of flexural cracks and crack-induced CFRP debonding, parametric studies were conducted using FE analyses, in order to investigate the effect of prestressing levels and the CFRP plate's stiffness on the flexural behaviour. Recommendations were then made for selecting a proper prestressing level and the mechanical properties of CFRP plates.

Strengthening of reinforced concrete (RC) structures by externally bonded carbon fiber reinforced polymer (CFRP) laminates has been widely accepted as an effective and cost-efficient method. It is well known that advantages offered by the bonded CFRP laminates can be further increased by prestressing the laminates prior to bonding. Mechanical anchors are essential, in this case, to prevent debonding since interfacial stress at areas close to the ends of the strengthening laminate is several times higher than the strength of the concrete substrate. Common anchorage solutions often consist of bolted metallic plates to clamp the prestressed CFRP laminate. Besides labor-intensive installation operation, the anchor plates are vulnerable to galvanic corrosion, which further complicates the inspection and increases the maintenance costs. There are also doubts about the long-term performance of such anchorage systems as it highly depends on the quality of the adhesive layer between the plate and laminate, and the level of pre-tension in clamping bolts. This paper presents the work conducted at Chalmers University of Technology on the development of an innovative prestressing method and a tool which allow for the application of prestressed CFRP laminates without mechanical anchors. The principles of the novel method and the prestressing system are explained. Experimental and numerical work carried out on an RC beam strengthened with this method is presented. Results indicate that CFRP laminates with high prestressing forces (approximately 30% of CFRP tensile strength) can be safely anchored without the need for mechanical anchors. Numerical results based on finite element analyses show that the proposed prestressing method can reduce the interfacial shear stresses in the CFRP-concrete adhesive joint below the bond strength with a reasonable safety margin.

This paper presents an innovative method for flexural strengthening of reinforced concrete (RC) bridges using pre-stressed carbon fiber reinforced polymer (CFRP) laminates as externally bonded reinforcement (EBR) and glass-fiber reinforced polymer (GFRP) deck panels. The work was a part of an EUfunded project called sustainable refurbishment of existing bridges (SUREBridge). The innovative features of this concept include the tensile reinforcement of the section using self-anchored pre-stressed CFRP laminates and compressive reinforcement of the section using tailor-made GFRP deck panels at the same time. The flexural behavior of RC T-section beams, strengthened using this concept, has been studied experimentally. Four 6-meter-long beams-three strengthened with bonded pre-stressed CFRP laminates in bottom with a pre-stressing force of 100 kN and GFRP deck panels on the top side and one as control beam-were tested in four-point bending configuration. The results indicated a substantial increase of ca. 160% in ultimate load carrying capacity of the strengthened beams as well as considerable improvements in flexural stiffness and cracking loads. The strengthened beams also displayed a ductile behavior after debonding of externally bonded CFRP laminates while maintaining the maximum load level before debonding due to the strong bond between the GFRP decks panels and the concrete beam. It was concluded that the proposed method has the potential to be introduced as a reliable method for strengthening of old concrete bridges.