The use of the brittle adhesives commonly adopted in construction industry do not provide the best performance for steel structures. CFRP/Steel joint bonded with extremely tough adhesive achieve much higher strength and ductility. However, tough adhesives are not developed for the construction industry and their cost may question the feasibility of this repair solution. This paper presents a new high performance and cost-effective hybrid bi-adhesive CFRP/Steel joint by using an extremely tough adhesive in critical location and the brittle adhesive in the remaining areas of the adhesive layer. The role of the tough adhesive in the proposed joint is fundamentally different from previous bi-adhesive joint proposed in the literature as it contributes mainly in shear. Experimental testing and finite element analysis are conducted. The Digital image correlation (DIC) is used to measure the strain field on the CFRP. The results revealed that the proposed CFRP/Steel hybrid joint achieve higher strength than the joints with brittle adhesive. The use of the tough adhesive in the bi-adhesive joint reduces the concentration of shear stresses significantly. As little quantities of the tough adhesive are required to manufacture the proposed bi-adhesive joint, it deemed to be as cost-effective.

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This paper presents an extensive experimental and numerical study on the behavior of CFRP/Steel adhesively bonded double strap joints (DSJ). A total of 50 DSJ specimens were tested under static tensile loading. The digital image correlation (DIC) was used to measure the backface deformation. A total of six adhesives that feature different stiffness, strength, ductility, and toughness were analyzed. A parametric study including several variants was carried out. The influencing parameters considered are the following: the adhesive type, adhesive thickness, CFRP elastic modulus, CFRP length, surface treatment, and steel thickness. The results revealed that rigid adhesives commonly used in the construction industry do not provide the best performance for the CFRP/steel joints, instead, tough adhesives which combine high strength and ductility are more suitable for strengthening metallic infrastructures. Steel plastic yielding has a significant influence on the strength, behavior, and failure modes of the CFRP/steel adhesive joint. A numerical model validated with experimental data was developed in ABAQUS. The experimental observations including failure modes, joint strengths, and ductility were discussed using the numerical model. The joint strength efficiency is highly recommended as a design criterion for bonded joints.@en