The effect of infill panels on the response of RC frames subjected to seismic action is widely recognised and has been subject of numerous experimental investigations, while several attempts to model it analytically have been reported. In this paper, the implementation, within a fibre-based Finite Elements program, of an advanced double-strut nonlinear cyclic model for masonry panels is described. The accuracy of the model is first assessed through comparison with experimental results obtained from pseudo-dynamic tests of large or full-scale frame models. This is followed by a sensitivity study whereby the relative importance of each parameter necessary to calibrate the model is evaluated, so that guidance on the general employment of the latter can be given. Furthermore, a representative range of values for the geometrical and material properties of the infill panels has been also defined. 1.