Steel frames with reinforced concrete infill walls (SRCW) are hybrid systems already introduced in Eurocode 8 where it is specified that such systems should be conceived and designed as reinforced concrete walls by supposing that the energy dissipation takes place at the lateral vertical steel elements and at the vertical reinforcements of the infill wall. In reality, their behaviour might be very different and characterised by a resisting system in which diagonal struts form within the reinforced concrete infills. Hence, such systems may suffer from problems at beam-to-column connections and from crushing of the concrete at a diagonal band. Furthermore, doubts arise about the behaviour in traction of the shear connectors and the anchorage of rebars that, to ensure the behaviour considered by the Eurocode, have to yield at their ends without a transition zone. These issues are strictly related to the lack of a specific capacity design procedure that allows for controlling the formation of a proper dissipating mechanism.

An innovative system is proposed within the RFCS project Inno-Hyco (Innovative hybrid and composite steel-concrete structural solutions for building in seismic areas) and presented in this work. The system is conceived to ensure the formation of diagonal struts in the infill walls by eliminating the connectors of the wall to the vertical columns and by suitably placing stiffeners and bearing plates in the joints. Thus, the hybrid system behaves as a latticed brace instead of a shear wall. The energy dissipation should take place mainly in the vertical steel elements without involving the reinforcements of the infill walls. Detailing of the connection of the dissipating elements allows their replacement and the possible use of buckling restrained elements. A specific capacity design procedure is also presented and the results of numerical simulations to assess the behaviour of the system are finally discussed.