Steel and concrete hybrid structures: recent advancements and their implications for seismic design

The optimum combination of steel and concrete elements to constitute hybrid steel-concrete seismic-resistant structural systems should exploit the stiffness of concrete and the ductility and dissipative capacity of steel. If the seismic damage is limited to some, easy to replace, steel components only and the residual deformations are limited, the structural system can be quickly repaired and go back to the full functionality even in the aftermath of major earthquakes. This design strategy allows obtaining structural resilient systems. In this context, the present work aims at reviewing the recent outcomes of a European research project where two hybrid structural systems were numerically and experimentally investigated. A proposal for design recommendations consistent with the framework of the Eurocodes is also presented. The first hybrid system considered is a steel frame with reinforced concrete infill walls designed as a truss structure where seismic damage is concentrated in the vertical steel components with reduced sections undergoing yielding in tension. All other steel elements as well as the reinforced concrete infill walls are designed to work within their elastic range. The second hybrid system considered is a reinforced concrete wall coupled to two steel columns by means of steel links. Both columns and the wall are designed to work in their elastic range while the yielding of the coupling links allows dissipating the seismic energy. Design criteria aiming at activating all links along the building height and the effect of the coupling ratio are discussed.