Nonlinear analysis of masonry walls based on a damage-plastic formulation

Masonry structures subjected to seismic actions exhibit a complex nonlinear behaviour. To obtain a comprehensive representation of all the occurring nonlinear mechanisms, constitutive models including damage and plasticity are required and nonlinear dynamic analyses are considered the most reliable. Hence, models considering both degrading effects and hereditary nature of restoring forces are needed. Different approaches can be adopted, relying on microscopic, macroscopic, multi-scale and macroelement formulations. The latter are often adopted for real cases, mainly to reduce the computational burden of the analyses. The proposed macroelement accounts for typical flexural and shear in-plane failure mechanisms via two flexural hinges and a shear link, arranged in series with an elastic beam. The hysteretic behaviour is reproduced by a smooth model, in which the introduction of a damage function describes both strength and stiffness degradation effects. The model is used to perform comparisons with experimental results on masonry walls, with the aim of validating the numerical procedure and its capabilities to describe nonlinear masonry response.