Innovative prestressing method for externally bonded CFRP laminates without mechanical anchorage

Abstract

Strengthening of reinforced concrete (RC) structures by externally bonded carbon fiber reinforced polymer (CFRP) laminates has been widely accepted as an effective and costefficient 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 reasonable safety margin.

A Practical Finite Element Modeling Strategy to Capture Cracking and Crushing Behavior of Reinforced Concrete Structures

“…A two-component epoxy adhesive (StoPox SK41, StoCretec GmbH, Kriftel, Germany) was applied to bond the CFRP plate; whose layer design thickness was 1 mm. Mechanical properties of the above-mentioned materials used for the FE analyses are listed in Table 1: the elastic modulus E c , compressive strength f c , and tensile strength f ct of concrete C35/45 at the age of 287 days were estimated according to Eurocode 2 [36]; the Poisson's ratio of concrete ν c was defined according to Model Code 2010 [15]; the elastic modulus E s , yield strength f sy , ultimate strength f su , and ultimate strain ε su of steel reinforcement were measured by laboratory tests on bars with a diameter of 16 mm (Φ16) according to ASTM A615 [37]; the elastic modulus E f and ultimate tensile strain ε fu of the CFRP plate were measured according to standard tensile tests as reported in [38]; the elastic modulus E a , tensile strength f a , and Poisson's ratio ν a of the epoxy adhesive were reported in [39].…”

Experimental study on flexural behaviour of reinforced concrete beams strengthened with passive and active CFRP strips using a novel anchorage system

“…Some of these systems have already been implemented on-site and now they are used in practical applications, like the first system which uses anchoring steel plates and small tensioning device developed in Germany [16], the system with composite anchoring head [17] or the first Swiss system [18]. There are also novel systems without typical anchorages, which uses thermal [19] or mechanical [20] gradual reduction of the prestressing force. Lots of other solutions are still in the development phase like systems tested by Woo et al [21] or Yang et al [22].…”

Heuristic Optimization of a New Type of Prestressed Arched Truss

“…In [12][13][14], an innovative approach is presented by which the load capacity and serviceability characteristics of cold-formed prestressed steel beams were improved using prestressing methods. Yang et al [15] used polymer laminates reinforced with carbon fiber to strengthen the reinforced concrete structures. This method effectively reduced the cost of the system.…”