Empirical unreinforced masonry infill macro-model accounting for in-plane/out-of-plane interaction

Unreinforced Masonry (URM) infills are widely used in Reinforced Concrete (RC) structures in Mediterranean countries. URM infills are subjected to the seismic action in their plane, i.e. in the In Plane (IP) direction, and in the Out Of Plane (OOP) direction. The IP displacement demand reduce the OOP capacity and vice-versa: this phenomenon is called IP-OOP interaction. A large number of studies has been carried out on the IP behaviour of infills, while their OOP response and the IP-OOP interaction have been less investigated. In this paper, a review of code and literature provisions concerning URM infills OOP behaviour is presented together with a review of the experimental tests carried out to investigate the infills OOP response and the effects of the IP-OOP interaction. An experimental database is collected to assess the effectiveness of literature and code provisions and to propose new empirical formulations both for predicting infills OOP strength, stiffness and displacement capacity and for modelling the effects of IP displacement demand on the OOP behavior and vice versa. A state of art on infills OOP behaviour and IP-OOP interaction modelling is presented. Most of these distributed-plasticity models are not based on experimental evidences and do not allow taking into account the IP and OOP stiffness degradation due to OOP and IP actions, respectively. A lumped-plasticity macro-model based on the proposed empirical formulations and conceived to represent the IP and the OOP behavior taking into account the mutual interaction effects is defined. Part of the proposed modelling strategy is a routine that removes the whole infill panel from the structural model in case of its IP or OOP collapse. The proposed model is used for an example application showing the effects of taking into account or neglecting the IP-OOP interaction phenomena during structural analyses.