## 1 Introduction  
Offshore wind is a renewable energy technology with an important role in current and future energy systems [1, 2, 3]. At present, offshore wind turbines involve several types of substructures, such as monopiles, gravity-based structures, jackets, tripods, and floating supports [4, 5]. Among them, monopiles are the most suitable type for supporting offshore wind turbines due to their advantages such as simple design, mass fabrication, and an installation approach based on conventional impact driving, relatively low risk, and robustness for most soil conditions. The offshore wind monopile substructure consists of a monopile (MP) and transition piece (TP), and the turbine system refers to the blade, nacelle, hub, and tower. The offshore wind foundation needs to be designed to be durable against various environmental loads for wind turbines to be able to execute the scheduled commercial operation. The grouted connection (GC) serves as the core structure to transfer the load from the turbine system to the foundation. Monopile grouting is a method wherein an MP is inserted into the seabed, the TP is mounted on the outside of the MP, and the two tubular steel members are integrated [6]. In general, a GC consists of components such as one grout annulus and two steel tubes with different dimensions [7]. Moreover, shear keys are generally added to the steel tube surfaces while making contact with the grout material in order to improve the interface shear capacity. As reviewed by [PERSON] et al. [8],shear keys can be used to maximize the grout adhesion between two tubular steel pipe members at the GC. The shear keys are welded to the two tubular walls so that they are in contact with the grout, in which case the shear keys of the inner tube and the outer tube must be arranged to offset each other to form a grout strut. The shear keys can also be divided into horizontal and vertical shear keys, and the GC can be divided into two types, tubular and conical, where, in the conical type, the shear key would not be used. In the case of the horizontal shear key, it resists an axial load, whereas, in the case of the vertical shear key, it resists the torque of the turbine system. In general, GCs have been designed in accordance with the international design standards (i.e., DNVGL-ST-0126 [9] and DIN EN ISO 19902 [10]); however, GC failure has been reported under ultimate load and fatigue load such as (i) the occurrence of contact destruction between tubular steel pipes and grout material due to the generation of an ultimate or cyclic load that exceeds the lateral stiffness of the friction contact, and (ii) the occurrence of material failure along the grout strut or around the shear keys by shear stresses that exceed the shear capacity of the grout [3]. Therefore, to overcome these problems, the design stage of GCs for monopile offshore structures should be specified in the design of the grout thickness, number of shear keys, shear key size, vertical distance of adjacent shear keys, and grout compressive and tensile strength to prevent material and contact failure of the grout against limit states such as the ultimate limit state (ULS) and fatigue limit state (FLS). This paper deals with the three-dimensional finite element (FE) analysis of a monopile GC with elastomeric bearings applied. The introduction of a shear key improves the GC structure response and capacity, but it limits the fatigue strength through stress concentration; hence, it should be addressed through a detailed refined local analysis. Elastomeric bearings are laminated rubber bearings widely used to reduce the response of structures due to their excellent deformability, stable mechanical properties, and low manufacturing cost [11]. If such an elastomeric bearing is installed around the shear keys of the GC, it is expected that the repeated or extreme shear force concentrated on the shear key will be dispersed, thus preventing the failure of the grout material or contact.