Seismic behaviour of steel Moment Resisting Frames with traditional and innovative connections

In the last decades, increasing efforts have been devoted to developing new types of beam-to-column connections able to accommodate the seismic local ductility demand and dissipate the seismic input energy. Among the proposed strategies, the so-called RBS (Reduced Beam Section) has been widely exploited in the construction market. Nevertheless, new proposals based on the partial-strength philosophy gained approval. Their main advantage is that, in the case of rare seismic events, similarly to RBSs, the connections exhibit wide and stable hysteretic cycles, yet concentrating damage in elements that undergo only minor yielding or are easy to replace. The FREE from DAMage (FREEDAM) and the double split (or X-shaped or hourglass) T-stub connections are promising solutions within this framework. The first strategy includes friction dampers in beam-to-column joints to dissipate the seismic input energy and fix the maximum bending moments transferred to the columns. The second solution differs from the traditional one because the flange of the T-element is appropriately cut according to an hourglass shape. This form replicates the bending moment in the plate part between the stem and the bolts, ensuring a uniform yielding of this part. Even though many research works have already been developed on such innovative connection typologies, experimental results on large-scale structures are still quite limited. Aiming to fill this knowledge gap, an experimental program is currently ongoing at the STRuctural ENGineering Test Hall Laboratory (STRENGTH) of the University of Salerno concerning the pseudo-dynamic testing of a large-scale two-storey steel building equipped with the connection typologies mentioned above. The mock-up has experienced the same sequence of five accelerograms in all the campaigns by the pseudo-dynamic test method. This paper discusses the comparison among the main results obtained so far in the experimental campaigns.