Strengthening of Steel Plate using Carbon Fiber-Reinforced Polymer with Hybrid Bonded Joint

Abstract

Strengthening steel structures with carbon fiber-reinforced polymer (CFRP) has attracted significant attention in recent decades due to the advantages of the strengthening technology, e.g., lightweight and high resistance to corrosion and severe environments. Typically, epoxy adhesive is used to bond the CFRP material to steel structures during the CFRP installation. Therefore, the effectiveness of the strengthening system depends on the bonding strength in the epoxy layer at the interface between the materials. This paper presents the efficiency improvement of the CFRP strengthening system by using a combination of bolt connection and epoxy adhesive to form a hybrid bonded joint. The effects of the bolted-connection location and clamping force magnitude on the bond strength and tensile behavior of steel plates strengthened with CFRP were investigated. The tensile test of the double-strap joint specimens strengthened with one CFRP layer on each side was carried out with various bolted-connection locations and clamping force levels. The specimens were clamped by applying various torque levels, i.e., 0, 20, 40, 60, and 80 N-m, at the bolt connections. Three different patterns of bolt connection positions were evaluated. The experimental results showed that an increase in the clamping force increased the bonding strength of the epoxy layer and the tensile strength of the reinforcement system. However, when the bolt torque value reached a certain point, the strength in the epoxy layer did not increase any further, even if the torque value increased. The bolt connection location also affected the tensile strength of the strengthening system. The strength effectively increased with the number of bolt connections, particularly for the locations within the effective bond length of the strengthening system.