Modified Bouc-Wen model with damage and flexibility increase for the dynamic analysis of masonry walls

The purpose of this study is to present a force-based macroelement for the static and dynamic analysis of the in-plane response of masonry panels. The nonlinear behaviour of masonry is described by a constitutive model based on the Bouc-Wen hysteretic formulation modified with the introduction of damage and flexibility increase by means of two scalar variables that regulate the rate and type of degradation. Damage is considered as a reduction of the hysteretic force, while flexibility increase is modelled through an amplification of the elastic displacement, both depending on the dissipated energy. The aim is to give a more accurate representation of the strength and stiffness decay masonry walls undergo when subjected to cyclic loadings and to better represent the loading and unloading branches of the response curves. To investigate the effect of the degradation in the dynamic field, the behaviour a slender wall is analysed under harmonic excitations.