A novel macroelement model for the nonlinear analysis of masonry buildings. Part 1: Axial and flexural behavior

In the numerical modelling of the nonlinear response of masonry buildings by equivalent-frame models based on macroelements representative of the in-plane response of structural members, it is important to correctly capture compressive behavior, lateral stiffness, and strength of the structure. The macroelement model currently implemented in the TREMURI computer program, thanks to the presence of nonlinear interfaces lumped at the element extremities, allows studying the coupled axial and in-plane bending response, with the inherent limitation of approximating the stiffness associated with at least one of these behaviors. The simplified compressive law does not capture the displacement accumulation during cyclic loads; moreover, second-order effects are not modelled. The article presents an improved macroelement model, able to simulate the in-plane cyclic response of masonry walls. The model overcomes some of the limitations of the currently available macroelement. As regards the compressive and flexural behavior, a new compressive law is introduced, together with a methodology to capture the correct flexural stiffness of the panel and to model the second-order effects. The improved model was then implemented in the TREMURI program and validations of the new features are shown, together with a simulation of an experimental test on a single wall characterized by flexural behavior. A companion article presents the shear formulation and shows the ability of the new macroelement of accurately predicting the nonlinear response of masonry structures at the building scale through the simulation of a larger number of experimental tests.