IP-OOP interaction in URM infilled frame structures: A new macro-modelling proposal

Reinforced concrete frame structures with unreinforced masonry (URM) infills represent a common construction practice all over the world. To correctly assess the seismic performance of these structures, prediction of the behaviour of masonry infills under in-plane (IP) and out-of-plane (OOP) loading, as well as their interaction, is of primary importance. Different approaches are available in the literature with different levels of approximation for assessment of the IP-OOP infill response, showing increasing interest in this field. In this context, this paper presents a new macro-element model which can simulate the behaviour of URM infill walls under seismic IP and OOP actions. The model is the evolution of an approach based on a 4-strut configuration characterized by one horizontal strut, one vertical strut and two diagonal struts representing the infill wall. The struts are modelled by fibre-section beam-column elements and their compressive behaviour is defined by empirical strength and strain parameters. The paper also presents some equations to obtain the empirical parameters mentioned, based on the actual mechanical properties of infill walls. In the paper, the validation of the proposed model with the experimental results available in the literature is discussed. Further, the improved capacity to simulate the arching mechanism in infill walls under OOP loads and the better reliability in capturing the interaction between the IP and OOP behaviours are described