Nonlinear seismic analysis of innovative steel frames with infill walls

This paper deals with seismic resistant systems constituted by steel frames with reinforced concrete infill walls. Some innovations to overcome major drawbacks of classical systems, basically conceived like reinforced concrete shear walls, are introduced. The new system is configured to control the formation of diagonal struts in the infill walls; the energy dissipation takes place only in the vertical elements of the steel frame subjected mainly to axial forces without involving the reinforcements of the infill walls. A tailored procedure for the capacity design of the system is outlined. A numerical model for the nonlinear analysis, obtained with beam element and nonlinear links, is thus presented. The comparison of results with those obtained with refined finite element models, in which the reinforced concrete wall and the steel members are modelled with shell finite elements, is carried out. The proposed model is able to capture the sequence of wall cracking and yielding of ductile side elements. Finally, the procedure is applied to a six-storey building in order to demonstrate the capability of the innovative system to develop the dissipative mechanism