Modelling of the Cyclic Response of an Unreinforced Masonry Wall through a Force Based Beam Element

The seismic assessment of existing masonry buildings is based on the prediction of their nonlinear response under lateral loading. This requires a reliable estimation of the force and displacement demand. For this purpose, modelling strategies using structural component elements are widely applied both in research and in engineering practice, since they can provide a satisfactory description of the cyclic behaviour of a masonry building with a limited computational cost. One of such modelling strategies are equivalent frame models, in which beam elements describe the response of piers and spandrels. This paper proposes the use of two-node, force-based beam elements with distributed inelasticity to model the in-plane response of modern unreinforced brick masonry panels. The nonlinearity of the response is described through the use of numerically integrated fibre sections and a suitable material model, implemented for this scope in the open-source platform “OpenSees”, describing a coupling at the local level between axial and shear response. Experimental results from a shear and compression test are used to validate the approach and justify some details of the proposed modelling strategy. Since the experimental data included also local displacement measures, the comparison of the numerical and experimental results is extended to curvatures and shear strains. The good agreement between numerical and experimental response confirms the applicability of the proposed approach for modelling the cyclic response of unreinforced brick masonry walls.