Conceptual study of an innovative friction damper for the seismic retrofit of precast RC structures with poor connections

Precast RC structures have been widely used in industrial and commercial buildings since the 60 s in the most developed areas. However, during those decades of economic growth, most buildings were constructed without seismic design criteria, accounting for gravity loads only. For this reason, this structural typology often faces a significant seismic risk in earthquake-prone areas due to the lack of effective connection between structural elements. As a result, the seismic retrofit of precast RC structures is essential to prolong their service life and mitigate seismic losses. The present work shows the conceptualisation study of an innovative seismic protection device called Bidirectional Rotational Friction Damper (BRFD) for precast RC structures that behave simultaneously as a beam-to-column joint and damper. This device unifies the concepts of rotational friction dampers and a movable plate system, producing a damping effect along two main directions. Furthermore, the device's ability to dissipate energy through friction enables it to remain undamaged during multiple seismic events while maintaining its damping capacity. After defining a simplified analytical model, to evaluate the influence of the BRFD on a structure's behaviour during a seismic event, a case study was conducted on a single-story, single-bay precast reinforced concrete structure made of plane parallel frames, i.e. that lacks secondary frames. Quasi-static and nonlinear time history analyses were performed to evaluate the BRFD efficacy in reducing seismic forces and displacements, and an importance analysis was carried out using a multi-criteria decision-making (MCDM) approach to identify the optimal configuration of the BRFD for the case study. The main results highlight that introducing the BRFD positively influences the dynamic performance of the structure, producing a significant reduction of interstorey drift and total base shear and preventing structural and non-structural damage.