The out of plane seismic demand of infill walls in the nonlinear field

Field observations after seismic events evidenced that, in many cases, the damage of infill walls is due to out-of-plane actions that pose a risk to human life (falling of heavy parts). The out-of-plane behaviour of the infill walls depends on many factors including the type of infill wall, the in-plane damage and the efficiency of their connection to the RC frame. The evaluation of the performance of the out-of-plane infill walls requires the evaluation of both seismic demand (i.e. seismic action on the infill) and capacity (strength). The main aim of this paper is to study the effect of the nonlinear behaviour of the structure on the out-of-plane seismic demand of the infill walls, also taking in account their nonlinearity and flexibility. In particular, 3D RC frames are studied considering a lumped plasticity model for the RC elements and adopting a recent nonlinear model that implements the in-plane and out-of-plane interaction behaviour for the infill walls. The analyses highlight that the nonlinear behaviour of the infill wall influences the variation of acceleration along the height of the wall; this effect is amplified when also the nonlinearity of the RC structure is considered. Moreover, the effect of the infill nonlinearities varies along the height of the building.