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

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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In steel structures, a lot of attention is paid to lightweight structures, i.e. reduction of dead load without compromising structural safety, integrity and performance. Thanks to modern steel aluminium foam sandwich panel manufacturing technology a new possibility became available for lightweight structural design. Assessment and understanding of the behaviour of this sandwich panel under in-plane compression or flexure is crucial before its application in steel structures. Column buckling theory is considered and applied to the steel aluminium foam sandwich panel to evaluate its behaviour under in-plane compressive load. In this work, various assumptions are made to generalise Euler's buckling formula. The generalisation requires modification of the buckling stiffness expression to account for sandwich panel composite properties. The modified analytical expression is verified with finite element simulation employing various material models specific to steel face-plates and aluminium foam as well as various geometric imperfections. Based on this study, it can be concluded that Euler's buckling formula can be successfully modified and used in the prediction of the load-carrying capacity of a sandwich panel.

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Nominal stresses have been used for a long time for the assessment of fatigue resistance of welded joints, however, this approach has strong limitations since the definition of the nominal stress may be subjective for complex welded details and/or complex loading. On the other hand, the hot-spot stress approach has been proposed to overcome these limitations considering the structural geometrical discontinuities. However, the hot-spot stress methods also present certain limitations, and the present study aims at evaluating the available numerical and analytical hot-spot stress methods proposed by DNVGL (2016) and IIW (2014). The particular case of an offshore tubular KT joint has been considered herein and discretized in two planes. It has been studied numerically using the ABAQUS software coupled with the hot-spot stress extrapolation methods described in IIW (2014) and DNVGL (2016). The influence of the weld geometry has been considered and evaluated. In addition to the numerical method, the present study has also considered the analytical approach proposed in DNVGL (2016) derived from the combination of Efthymiou solutions for the stress concentration factor with the method of superposition of stresses. The numerical models according to IIW (2014) have been found to be more conservative when compared with the mesh-size methods proposed by DNVGL (2016), both in numerical modelling without the weld or with weld. For the numerical models with weld cord, the mean values of normalized difference index obtained for all braces together, as a result of comparing numerical results with analytical solutions, are lower, when compared with results obtained from the numerical models without weld cord.

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