## 1 Introduction  
Wood-wood connections have the potential to make an important contribution to the timber construction industry and at the same time meet all code requirements in terms of load-bearing capacity and dimensional stability. Through the specific application of wood materials, they can also be used as an independent wood-wood fastener. Therefore, they offer an alternative to metal system connectors and contribute to climate protection by reducing CO\({}_{2}\) emissions. The use of such connectors requires more detailed scientific studies and the revision or review of valid calculation approaches. The inclusion of modern wood materials as well as multidimensional geometries, which are precisely manufactured by CNC-milling, must also be considered. The system connector made of wood is an alternative to the common metal system connectors. The wood-wood fastener can be produced in-house or industrially. This adds value to the wood construction industry. The aim is to apply the potential of the findings presented on bar-shaped connections by means of the coupling element \"double dovetail pin\" to surface wall-ceiling connections made of CLT. The structural design of a dovetail connection is based on calculation formulas that distinguish between the failure of a transverse connection of the main girder (mode 1)and a notching failure of the secondary girder (mode 2). The current version of the building authority approval (ABZ) Z-9.1-649 [1] already takes into account the use of glued laminated veneer lumber (LVL) as a material for bar-shaped connections. However, the wood connection is milled into the beams and thus its position depends on the connection placement. In new Eurocode 5 formulas [2], the rounded dovetail connection within bar-shaped connections will be introduced. The calculation formula is given for mode 2--notching failure of the secondary girder--but not for mode 1--transverse tensile failure of the main girder--which can occur even earlier with same-level beam connections. In his work, [PERSON] [3] dealt in depth with the dovetail connection and its beneficial form and also recognized the potential of alternative load transfer paths and multi-step load application. In a topic related publication, [PERSON] et.al. also described experimental and numerical investigations on the rounded dovetail joint (RDJ) in bar-shaped connections [4]. Furthermore, reinforcement measures with self-tapping screws by [PERSON] and [PERSON] [5] and an adhesive layer on beam connections by [PERSON] [6] were investigated. [PERSON] et.al. [7] also investigated experimental geometries of dovetail connections in tests and FE-simulations of bar combinations. [PERSON] and [PERSON] [8] experimented with measures to increase friction within the tenon contact by special shaping of the flanks of RDJ and they also showed the possibilities of multi-step load transfer paths within a stepped connection for truss nodes of timber constructions. Also, the experimental investigations described in [PERSON] et.al. [9] show the potential of CNC-manufactured wood-wood joints with experimental geometries and multi-step load transfer paths. All geometry parameters of the main beam and the secondary beam of a rounded dovetail joint (RDJ) are illustrated in Figure 1.  
The description of the connection failure is based on equivalent formulas of ONORM EN 1995-1-1 [10], introduced by [PERSON] and [PERSON] for the transverse connection [11] and [PERSON] for the notching [12]. An important parameter of the cross connection (mode 1) is the effective connection depth \(t_{\text{eff}}\). Particularly in the case of small pre-timber heights \(h_{\text{VH}}\) below the base of the mortise--as occurs with beam combinations of the same height \(h_{\text{HT}}\) and \(h_{\text{NT}}\)--this mode of failure and thus the parameter \(t_{\text{eff}}\) is decisive. The greater the connection depth \(t_{\text{eff}}\), the higher the load-bearing capacity and, at the same time, the higher the ductility of the connection.