<p>The seismic vulnerability of traditionally constructed masonry infilled frames has been repeatedly highlighted in post-event surveys, as well as by experimental and numerical studies. Infill walls with sliding joints can improve the seismic response of these structures. The paper describes some design equations derived from a parametric numerical analysis focusing on the interaction between the RC frame and the masonry infill with sliding joints. A previously proposed analytical model, able to predict the lateral strength contribution and the column shear overload due to the infill-frame interaction, is here extended to widen its field of application to walls with column-to-infill contact material characterized by and elastic response instead of an elastic-plastic one. A previously validated finite element modelling method is used to conduct a parametric study examining the role of the key design parameters of ductile masonry infill walls that implement sliding joints. The main model parameters are calibrated using data obtained from a previous comprehensive experimental campaign. A comparison of numerical and experimental results is also reported. The influence of different infill-frame contact material stiffnesses is analysed together with other design parameters, such as the bay length, the masonry properties, the layout of sliding and contact joints.</p>