A new model describing the response of vertically-spanning unreinforced masonry walls subjected to out-of-plane loading is presented. The model approximates the real behaviour of the walls by a tri-linear force-displacement relationship, which is suitable for engineering practice. Differently from the existing tri-linear models, which are mainly based on experimentally calibrated parameters, the present one relies on principles of mechanics. Its fully analytical formulation provides the potential for using it in the assessment of unreinforced masonry for a wide range of wall configurations and boundary conditions. The comparison of model simulations with experimental results from shake table tests documented in the literature validates the model for cantilever and parapet walls
