Analysis of an innovative solution for steel frames with reinforced concrete infill walls

Steel frames with reinforced concrete infill walls (SRCW) are hybrid systems included in Eurocode 8 where their seismic design is based on the assumption that the lateral vertical steel elements and at the vertical reinforcements of the infill wall are the dissipative elements. In reality, the behaviour of such hybrid systems might be very different and characterised by a resisting system in which diagonal struts form within the reinforced concrete infills. As a consequence, such systems might exhibit problems at the beam-to-column connections and concrete crushing at a the diagonal bands. Furthermore, doubts arise about the behaviour in traction of the shear connectors and the anchorage of reinforcements. For these reasons, an innovative hybrid solution is proposed, 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. The energy dissipation is supposed to take place mainly in the vertical steel elements without involving the reinforcements of the infill walls, allowing also their replaceability. Numerical and experimental tests are illustrated and discussed in order to present the capabilities of the proposed steel-concrete hybrid system.