On the degrading/hysteretic response of masonry under seismic loads

The seismic assessment of masonry buildings requires the definition of adequate models. Simplified approaches have well known positive outcomes, but the definition of their properties to describe all the complex phenomena in which structural elements are involved, especially when subjected to dynamic loading, is not an easy task. Masonry exhibits a strongly nonlinear behaviour under both static and dynamic loading and hysteretic nature of restoring forces should be considered. This paper presents an innovative smooth hysteretic model (SHM) in which a damage variable is introduced to take into account effects of both strength and stiffness degradation. This model is developed on the basis of the classic Bouc-Wen formulation and used to model the response of masonry in the context of nonlinear analyses with the finite element code FEAP, where a force-based beam finite element with flexural hinges and a shear link reproducing typical failure mechanisms has been implemented.