## 1 Introduction  
A quite common architectural layout for large single-storey RC frames, typically housing industrial plants, warehouses, gyms, and logistics centers, provides the presence of \"drift-sensitive\" masonry infills and glazed curtain walls. The last usually form an upper band providing natural light to the interior spaces (see Figure 1). The Italian building stock contains plenty of these buildings, most of them raised more than forty years ago based on outdated technical standards and often designed to withstand gravitational loads only. The seismic retrofitting of these building entails challenges due to the usual poor detailing (and/or inadequacy) of RC elements' cross-sections and the vulnerability of both masonry infills and windows to lateral drifts. In addition to more conventional interventions (e.g., through shear walls), substandard RC structures can be retrofitted through a relatively low number of dissipative braces deployed in specific locations of the frame. With respect to technologically more sophisticated viscous dampers, steel hysteretic dampers (SHD) provide supplemental energy dissipation and stiffening with greater affordability and less onerous maintenance. The response of SHDs is not (or only slightly) affected by velocity; indeed, their force-displacement characteristic is conventionally expressed by means of bilinear hysteretic models. These devices are usually inserted along diagonal braces to undergo large plastic deformation within sacrificial mild steel components during severe earthquakes. This allows most of the earthquake-induced energy to be absorbed, reducing the damages to the main frame. The first SHDs were introduced in the 1970s [1]. Subsequently, SHDs exploiting plastic deformations induced by axial loads [2], shear loads [3], bending [4,5], and torsion [6] have been developed. In recent years, the number of worldwide applications for the seismic retrofit of public buildings such as schools [7, 8, 9] and hospitals [10] has been rapidly increasing. Frontier studies have focused on the assessment of the actual cyclic engagement (i.e., low cycle fatigue) of the dampers [11] and on their suitability for the protection of acceleration-sensitive non-structural components during minor seismic events [12]. Indeed, according to the most common design practice [13,14], SHDs are designed to exceed the plastic threshold only under severe ultimate limit state earthquakes. Otherwise, during weak serviceability events, they offer a negligible energy dissipation (i.e., damping) and a high stiffening effect, as they are engaged in their elastic range. In certain cases, this stiffening effect can have unfavourable results, i.e., higher storey accelerations; however, this drawback can be effectively addressed through the employment of dampers featuring adaptive (i.e., multi-step) yielding thresholds that are progressively activated based on the intensity of the earthquake [15]. With respect to the protection level of the main frame, design procedures for braed frames can be grouped into two categories: (1) methods that aim to keep the main structure within its elastic range; and (2) methods that envisage controlled plastic excursions. Within the first category, [PERSON] and [PERSON] (1988) [16] proposed a procedure based on minimizing the discrepancy between the input seismic energy and the energy dissipated by the hysteretic braces (\"Vibrating Energy Surface\"). In later refinements [17], the same authors introduced a \"Relative Performance Index\" relating the energy dissipated within the braces and that stored in the indefinitely-elastic bare frame. A larger number of design procedures belong to the second category, involving acceptance of a certain degree of plasticization of the main structure. For instance, [PERSON] and [PERSON] (1993) [18] proposed a criterion for the distribution of hysteretic braces at different levels of the lateral stiffness and yield strength in order to control the amplitude of plastic excursion of the main structure.