Current seismic codes (e.g. the NTC08 Italian code and the EC8 European code) adopt a performance-based approach for both design of new buildings and assessment of existing ones. Different limit states are considered by verifying structural members as well as non structural elements and facilities. Therefore, seismic performances depend on all components of buildings, including non structural elements and facilities which, even if represent the greater share of the whole building cost, are generally neglected in the practice.

The key role of non structural elements on building performances are confirmed by recent earthquakes (e.g. L’Aquila 2009, Emilia 2012) where, due to the extensive damage suffered by infills, partitions and ceilings, a lot of private and public buildings were unusable, determining heavy socio-economic effects. Further, the collapse of infill panels, particularly in the case of out-of-plane failure, represented a heavy source of risk to life safety.

Therefore, an integrated approach taking into account all buildings components is needed in design of new building and assessment of existing ones.

In this paper a first attempt to assess seismic performances of existing buildings taking into account both structural and non structural elements (infills) and their mutual interaction is shown. For this purpose, some building types with RC framed structure designed only to vertical loads and representative of typical Italian buildings are studied.

Non linear static analyses according to NTC08 are carried out on 3D models defined adopting a macro-modelling based on lumped plasticity. At both ends of each structural member a bending moment–rotation relation is defined through a bi-linear curve, which is appropriately modified in case of brittle failure.

Masonry infill panels are modelled by using an equivalent diagonal strut; plastic hinges at the ends of each strut are defined to act only under compression load and are modified to take into account the effects of the in plane response on the out-of-plane capacity.

Results show that seismic performances of the analysed buildings are mainly influenced by the brittle failure of structural elements. On the contrary, in case of bending failure (ductile), the values of peak ground acceleration related to the out-of-plane failure are generally lower than those relevant to the structural members' collapse. Nevertheless, as a consequence of the premature out-of-plane collapse of infill panels, no soft story mechanism of structures is predicted.