Free from damage beam-to-column joints: Testing and design of DST connections with friction pads

Dealing with the seismic behavior of steel MRFs, in last decade, the adoption of dissipative partialstrength beam-to-column joints has started to be considered an effective alternative to the traditional design approach which, aiming to dissipate the seismic input energy at beam ends, suggests the use of full-strength joints. On the base of past experimental results, the use of dissipative Double Split Tee (DST) connections can be considered a promising solution from the technological standpoint, because they can be easily replaced after the occurrence of a seismic event. Nevertheless, their dissipation supply under cyclic loads has been demonstrated to be characterized by significant pinching and strength degradation which undermine the energy dissipation capacity. The need to overcome these drawbacks to gain competitive technological solutions has suggested an innovative approach based on the integration of beam-to-column joints by means of friction dampers located at the beam flange level. Therefore, the use of partial strength DST joints equipped with friction pads is proposed. Aiming to the assessment of the cyclic rotational response of such innovative connections, two experimental programs have been undertaken. The first one has been aimed at characterizing the dissipative performances of five frictional interfaces to be employed as dampers. The second one is aimed at the application of the same materials to DST joints specifically designed for dissipating the seismic input energy in a couple of friction dampers located at the beam flanges level. The results of the experimental analysis carried out at the Materials and Structures Laboratory of Salerno University are herein presented, showing the potential of the proposed damage-free beam-to-column joints.