Control of Interfacial Stresses in Beams Strengthened with Prestressed CFRP Laminates

Paper in proceeding, 2007

The outstanding mechanical properties of Carbon Fiber Reinforced Polymers (CFRP), such as high strength-to-weight ratio, high modulus of elasticity, high corrosion resistance and durability have made them suitable for strengthening applications. High capacity of CFRP laminates may not be completely used due to weakness of the adhesive joint used to bond the laminate to the structure. To use CFRP laminates more efficiently, prestressing might be applied to the laminate before bonding. Although prestressing has several advantages and improves the structural behavior of the strengthened member, a major problem with this strengthening scheme is the very high interfacial stresses which are built up at the end of the laminate. One way to deal with the problem is to clamp the laminate using mechanical anchors which often are made of steel plates. There are, however, couple of problems involved in using mechanical anchors such as high cost of manufacturing, installation and inspection, corrosion risk and durability and making fatigue prone points in steel structures due to drilling. Increasing demands on strengthening technique incorporating prestressing necessitate new techniques for controlling the interfacial stresses in the bonded joint without using mechanical anchors. In this paper, possible techniques to reduce the magnitude of the interfacial stresses along the bond line have been investigated. The methods include changing the geometric and mechanical properties of the strengthening components and modifying the distribution of interfacial stresses along the bond line. FE-analysis has been used to examine the effectiveness of each technique. It has been shown that using step prestressing method is the most effective one and by that interfacial stresses might be reduced by a factor of ten, which in many cases allows using high initial presressing forces in the laminate without the need to use mechanical anchors.