Empirical-based infill model accounting for in-plane/out-of-plane interaction applied for the seismic assessment of EC8-designed RC frames

In the Mediterranean area, Reinforced Concrete (RC) buildings are usually provided of Unreinforced Masonry (URM) infill wall panels. When subjected to seismic action, these non-structural elements are sensitive to the displacements produced in the In Plane (IP) direction and to the acceleration in the Out Of Plane (OOP) direction. The damage due to IP displacements reduce the OOP capacity and vice-versa: this phenomenon is called IP-OOP interaction. Proposed empirical-based formulations both for predicting infills OOP strength and for modeling the effects of IP displacement demand on OOP behavior and vice versa are illustrated. A new 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. In this paper, the proposed model is described and applied to model the infills of case-study infilled RC frames designed according to Eurocode 8 and different for design PGA at Life Safety Limit State. The results of non-linear time-history analyses are presented and discussed in order to show the effects of taking into account or neglecting the IP-OOP interaction phenomena in assessing the seismic response of the case-study buildings.