## 1 Introduction  
The evolution of seismic design strategies for steel structures has increasingly focused on minimizing post-earthquake damage while ensuring structural integrity [1; 2; 3; 4]. Modern seismic codes are mainly based on the application of the capacity design principles, i.e., distinguishing dissipative and non-dissipative zones. Dissipative zones are expected to undergo plastic deformations during earthquakes and are devoted to dissipating the energy, whereas non-dissipative zones must remain elastic to avoid brittle failure mechanisms. Such strategies, while effective in absorbing seismic energy, often result in structural damage that is economically and functionally debilitating. Innovations in seismic design have led to the development and application of additional energy dissipation mechanisms, like friction dampers [5]. Steel beam-to-column joints equipped with friction devices dissipate seismic energy effectively and limit plastic deformations into replaceable elements. This approach aligns with the modern trend towards low-damage structures, which are increasingly preferred for their resilience and cost-effectiveness in seismic regions [6]. Friction dampers are characterized by their stable and predictable response and the localization of demand into easily replaceable parts, minimizing post-earthquake damage. This adaptability allows their integration into various structural configurations, making them one of the most promising solutions for seismic design. The effectiveness of these dampers has been validated through numerous studies and applications across seismic-prone regions, including Europe and Japan. Notably, European studies have focused on symmetric friction mechanisms [7, 8] in contrast to the asymmetric friction mechanisms explored in New Zealand [9, 10, 11, 12, 13, 14, 15]. The design of moment-resisting frames (MRFs) with friction dampers offers significant advantages. It allows for decoupling the stiffness and the resistance of the joints, thus enabling full-rigid and partial-strength behavior in accordance with [16]. A pivotal advancement in seismic supplementary dissipation strategies is embodied in the FREEDAM (acronym of \"free from damage\") devices (Figure 1), which are conceived to ensure that beam-to-column connections elastically behave even after severe seismic events, thereby preserving the structural integrity of buildings provided that the limit of the device stroke is not overcome. The FREEDAM device is located under the lower beam flange and accommodates large slippage that allows a relative rotation between the beam and the column by enforcing a center of rotation in the stem of the upper T-Stub connecting the upper beam flange to the column. The slippage of the damper develops through vertical slotted holes located in the friction shims and horizontal slotted holes located in a haunch stiffener that is directly connected to the beam. The local details of the damper may affect the rotation capacity of the beam-to-column assembly. In particular, the configuration of the slotted holes plays a key role in accommodating the slippage and in transferring the shear force to the connected members. Therefore, the study described in this paper aims to investigate the ultimate flexural behavior of FREEDAM connections, varying the details of the slotted holes, namely, the configuration with single slotted holes for a row of bolts is compared with a modified device with multiple slotted holes corresponding to the number of bolts. This second type of configuration has been designed to promote the bearing resistance of all bolts in the damper when its stroke is reached, and other secondary mechanisms may occur, e.g., the yielding of the beam [17], at the end of the haunch or local instability mechanisms in the web of the beam near the bolted haunch.