Simplified modeling of masonry infill walls with horizontal sliding joints

The vulnerability of masonry infilled frame structures has been demonstrated by many recent earthquakes and research studies and it is often triggered by the in-plane interaction between the flexible frame and the masonry infill (characterized by an inherent higher stiffness). Among the different solutions studied to mitigate such issue, a deformable infill typology with horizontal sliding joints has been proposed and tested by the authors in previous studies, capable of reducing the infill-frame interaction and of limiting the damage in the masonry, so that also the out of plane infill stability is maintained. This paper proposes a simplified approach to assess the seismic performance of this innovative masonry infill typology. Analytical formulations, based on geometrical and mechanical properties, are proposed to describe the in-plane response of the infill and its interaction with the bounding frame. Thanks to these formulations, a simplified numerical model for the infill, adopting an equivalent strut approach, is calibrated to be used in the non-linear analysis of infilled frame structures, accounting for their cyclic response. The reliability of the method is validated trough the comparison of the estimated infill resistance and shear demand on the column with those obtained from an extensive experimental campaign and numerical study based on refined finite element models. The results show the efficiency of the proposed simplified model in estimating the response of the infilled RC frame, in particular the shear action in the frame columns, which are the critical element of the structure.