ABSTRACT
The strengthening and repair of existing structures using bonded fiber reinforced polymer (FRP), especially carbon fiber reinforced polymer (CFRP), laminates has attracted a great deal of attention in the last three decades. The superior mechanical properties of CFRP laminates, such as high strength, high stiffness, light weight and good fatigue resistance, have made them an effective alternative for steel cover plates used for strengthening and repair of structural steel members. Generally, the purpose of bonding FRP laminates to structural steel members include increasing bending capacity and stiffness, repairing fatigue-cracked elements and increasing fatigue life.
Although the bonding of FRP laminates provides an attractive alternative for upgrading steel members, a comparison between the number of steel structures strengthened using this technique and their concrete counterparts indicates that traditional upgrading methods are still regarded as robust competitors to this technique when it comes to steel structures.
The lack of a code for designing bonded FRP laminates for steel substrates could be blamed as the most important reason. This is naturally not surprising, since there is no established method for designing adhesive joints used to bond composite laminates to structural steel members. The existing knowledge regarding the steel-FRP bonded joints usually comes from the aerospace engineering where the substrate and adhesive materials and the geometry of the joint, e.g. thickness of the adhesive, are different from those used in structural engineering applications.
Study of the literature indicates that new failure criteria based on more realistic assumptions are needed to provide better approximations of joint strength. To establish a suitable failure criterion, it is necessary to obtain a good knowledge of the load-transfer and failure mechanisms in adhesive joints.
The first step towards developing new design models for steel-adhesive joints to be used in structural engineering is to study such adhesive joints and obtain an understanding of the behavior, force transfer mechanism and the failure of the joint.
The purpose of this paper is to provide some information about the behavior of adhesive joints used to bond CFRP laminates to steel substrates using a numerical and experimental approach. An advanced optic measurement system, ARAMIS, was utilized in this study which provided valuable information about some behavioral aspects of adhesive joints which had not previously been investigated. Issues such as the strain distribution along the bond line and the thickness of the adhesive layer, the mode and progression of failure in joints and the effects of material properties on the distribution of strain components are discussed.
