A comparison between a FEM/DEM and a FEM-based couple-stress multiscale model for the in-plane failure analysis of masonry walls

Lorenzo Leonetti;Emanuele Reccia;Patrizia Trovalusci;Antonella Cecchi

2017-01-01

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Abstract

Despite its complexity, the accurate structural modelling of masonry still represents an active field of research, due to several practical applications in civil engineering, with special reference to the preservation and restoration of cultural heritage items. The above-mentioned tasks call for very accurate analyses of masonry structures, able to capture their peculiar mechanical features in the nonlinear range. With this purpose, in this work, two different models are compared to predict the behaviour of masonry: a FEM-based couple-stress multiscale model and a combined Finite-Discrete Element Model (FEM/DEM).. On the one hand, the FEM-based couple-stress multiscale model, relying on a standard finite element method, may be regarded as an enhanced version of the multi-level domain decomposition approach, recently applied to masonry [1]. Both the micro-constituents (i.e. units and joints) are modelled in a standard Cauchy continuum setting, while the homogenized masonry material employed at the macro-scale is represented as a couple-stress continuum, i.e. a constrained version of the Cosserat model [2], which is able to take into account the size effects related to the bending deformations. A suitable macro-to-micro switching criterion is introduced, in order to adaptively zoom-in the regions affected by damage initiation, thus reducing the overall computational costs. On the other hand, the FEM/DEM method, initially developed for the study of granular materials, has been recently adopted for the study of masonry material [3]. FEM/DEM is based on a micro-modelling approach. Here blocks are modelled as rigid bodies and mortar joints are modelled as zero thickness elasto-plastic Mohr-Coulomb interfaces. The method is a combination of classic FE and DE models. The model relies on a triangular discretization of the domain with embedded crack elements, that activate whenever the peak strength is reached. FE allows to reproduce elastic strain while DE are able to model the frictional cohesive behavior exhibited by masonry. A numerical comparison is proposed to evaluate the field and limit of application of the two models.