Pedro Roca Fabregat

Numerical validation of Equivalent-Frame Models for URM walls

In the last decades increasing attention has been devoted to masonry structures both from researchers and professionals. This is due to the awareness of the great importance of these structures in the historical urban context, together with the great risk that they suffer in seismic areas. Growing success has been obtained by a simplified approach that models masonry walls through “equivalent” plane frames, with concepts and procedures drawn from the study of reinforced concrete and steel frames. In this approach, known as Equivalent Frame Method (EFM), each masonry resisting wall is modelled as a system of linear (frame) elements repre-sentative of the behaviour of finite portions of the wall (pier and spandrel panels). Up to now EFM has proven to be effective in the case of new buildings characterized by regu-lar geometrical configurations and with openings’ dimensions for which the frame-like as-sumption is suitable. Critical issues emerge from existing buildings in European historical centres, where irregularities are almost always present and geometrical anomalies can be detected even in the case of regular walls. For the specific case of geometrically regular URM walls, this paper presents sample cases tested with linear and non-linear analyses, with the aim to explore the applicability of EF procedures and to identify its limits. A comparison between an EFM procedure with a fiber approach and a more detailed FEM method with plane elements, is adopted as a validation tool, to evaluate the accuracy of the results provided by the EFM for walls characterized by different geometrical configurations.

Finite element micro-modelling for the characterization of inclined head joints archaeological masonry: the case of Villa Diomede in Pompeii

Villa Diomede is a great roman building located on the western corner of the modern archaeological site of Pompeii, built during III century BC and discovered between 1771 and 1774 during archaeological excavations. The system is composed by three levels: the road level, the garden level, which hosts the portico structure, and the underground level. The building includes diverse types of masonry with a wide range of unit shapes, dimensions and materials (i.e. tuff, limestone, volcanic stone, clay brick etc.). Besides, an unconventional tuff masonry type was observed on some structures of the garden; it reveals inclined head joints, whose structural function is still unknown. The paper reports the numerical micro-modeling of this particular texture of masonry, where the constitutive materials (tuff units and mortar) are discretized. The main goal of the work is the assessment of inclined masonry joints as an aseismic detail compared with widespread traditional tuff running bond masonry. Micro models of masonry wallettes were created assigning a non-linear constitutive behavior, i.e. total strain crack model (with a parabolic behavior in compression and an exponential softening behavior in tension, whereas damage due to tensile cracking was modeled adopting a rotating crack model). Moreover, brittle 2D interfaces were modeled between mortar and units at inclined joints surfaces. The paper focuses on numerical prediction of compressive response of masonry models subjected to uniaxial compressive tests.

Micro-mechanical modeling of masonry: parametric study

Masonry structures, usually being composed of a repeating geometric pattern, lend themselves well to analysis using periodic unit cells. Based on stress and strain equilibriums and rational assumptions concerning the interaction of the components of the cell, one may propose micro-mechanical models using simple analytical expressions which simulate well the behavior of masonry. Models describing the nonlinear behavior of masonry constituent materials may be implemented in such models and used to simulate the failure modes anticipated to arise in the composite. In this way, the nonlinear behavior of masonry composites may be derived, as defined by the interaction of its two main material phas-es: units and mortar. Taking advantage of the low computational cost of models based on analytical expres-sions, which is only a fraction of those based on finite element simulations, wide and in-depth parametric analyses can be performed with ease. In this paper, a model for the nonlinear behavior of masonry is presented and used in a parametric study, investigating the influence of various material properties on its compressive strength. The results indicate a strong dependence of the compressive strength of masonry on material parameters that are difficult to measure accurately or are often ignored, particularly in existing and historic masonry structures.