In recent years, bonding techniques have received increasing attention in a variety of industrial applications, including aerospace, civil engineering, energy, automotive, and biomedical engineering. Compared with traditional joining methods such as welding and riveting, bonding offers several advantages, including reduced stress concentration, improved resistance to harsh environments, and the ability to join dissimilar materials. However, the long-term reliability of these joints remains a challenge, particularly in terms of their fatigue resistance. This work focuses on the fatigue behaviour of bonded joints subjected to Mode II loading, using double strap joints made of steel and epoxy or polyurethane adhesives. The study includes experimental tests to evaluate the influence of load ratio and frequency on the fatigue life of these joints. Mode II was chosen due to its feasibility for experimental implementation, enabled by the recent introduction of a dedicated bonding procedure for the first non-monotonic cyclic tests [1]. The results are analysed using force-displacement curves, stress-strain responses, and S–N curves to identify the main trends and compare the behaviour of bonded joints under different loading conditions. The aim of this study is to model this behaviour using an imperfect interface model that incorporates the variable damage kinetics observed in the experimental tests [2]. Ultimately, the development of an experimental database and predictive models will support the integration of bonded assemblies into the construction of primary or secondary structures in offshore wind turbines.