Emanuele Reccia

FEM-DEM modeling for out-of-plane loaded masonry panels: a limit analysis approach

In this work the performances of the Discrete Element Method (DEM) applied to kinematic limit analyses of the out-of-plane behavior of masonry wall panels (with different textures) are investigated. A discrete model of masonry is proposed, which assumes that rigid blocks are connected by a mortar interface: this is ap- propriate for historical masonry, where mortar is much more deformable than blocks and joints thickness is negligible. Therefore blocks can be modeled as rigid bodies connected by zero thickness Mohr-Coulomb-type interfaces. The applied method is known as FEM/DEM, which combines finite and discrete element models. A comparison with well-known and meaningful examples presented by Giuffre has been carried out in order to validate this method for studying the behavior of masonry. For this purpose, 2D DEM models reproducing walls sections have been considered: they reproduce masonry walls with different staggered blocks, in particular stack bond and running bond patterns, subjected to lateral loads.

DEM & FEM/DEM models for laterally loaded masonry walls

The wide amount of historic masonry constructions in Italy and other European countries makes of paramount importance the development of reliable tools for the evaluation of their structural safety. Masonry is a heterogeneous structural material obtained by composition of blocks connected by dry or mortar joints. The use of refined models for investigating the in-plane nonlinear behavior of periodic brickwork is an active field of research. The mechanical properties of joints are usually considerably lower than those of blocks, therefore it can be assumed that damages occur more frequently along joints. Thus, a key aspect is represented by the evaluation of the effective behavior of joints and its reliable description into numerical models. With this purpose, in this contribution, different models are defined to simulate, with an appropriate accuracy, the behavior of masonry: Discrete Element Model (DEM) and a combined Finite Element and Discrete Element Model (FEM/DEM). Models are based on rigid block hypothesis and joints modeled as Mohr-Coulomb interfaces. These assumptions may be suitable for historical masonry, in which block stiffness is larger than joint stiffness, allowing to assume blocks as rigid bodies, moreover joint thickness is negligible if compared with block size. Analysis is performed in the nonlinear field to investigate the behavior of masonry walls subject to lateral loads, in order to simulate their seismic response, with particular attention to the determination of limit load multipliers.

A Procedure to Investigate the Collapse Behavior of Masonry Domes: Some Meaningful Cases

ABSTRACT Masonry domes represent an important part of the architectural heritage. However, the literature about domes analysis seems less consistent than that referred to other masonry structures. The collapses that have happened in recent years as a consequence of seismic actions or lack of maintenance show the need for detailed studies. Here a limit analysis to evaluate the masonry domes behavior is presented. An algorithm based on the kinematic approach has been developed to evaluate the geometric position of the hinges that determine the minimum collapse load multiplier. The proposed procedure is validated by a comparison with some meaningful cases—the collapse of Anime Sante Church in L’Aquila, the collapse of San Nicolò Cathedral in Noto, the crack pattern of San Carlo Alle Quattro Fontane Church in Rome, and the analysis developed on Hagia Sofia in Istanbul. The comparison with real cases shows a good agreement between the model results and the phenomenological crack patterns.

Multi-Leaf Masonry Walls with Full, Damaged and Consolidated Infill: Experimental and Numerical Analyses

Multi-leaf masonry walls constitute the construction typology most widely adopted in historic buildings. This aspect, together with the intrinsic structural complexity, heterogeneity and irregularity, directs the present research towards a topic not yet sufficiently investigated by the research community of architects and civil engineers. In this paper, the case of multi-leaf masonry wall has been investigated, and with the aim of reproducing historical buildings structural elements, three different typologies of multi-leaf masonry walls have been considered: (i) full infill, (ii) damaged infill, (iii) consolidated infill. A comparative analysis has been performed and results of experimental tests have been compared with numerical ones obtained by means of Finite Element (FE) models.

Sensitivity to Damage Imperfection for Multileaf Masonry Walls Based on Vibrational Analyses

Damage-imperfection indicators based on variation of dynamic parameters allow to identify the intrinsic discontinuity and the damage of structures. Here, the structural health monitoring through the vibration-based approach has been carried out by two steps on three different multileaf masonry specimens (full infill, damaged infill, and strengthened infill) subjected to uniaxial compressive load. In the first step, the characterization of initial conditions based on the investigation of the intrinsic discontinuity and the manufacturing imperfections has been done. In this phase, the detection, localization, assessment, and prediction of damage have been given by the comparison between the experimental and numerical modal data calculated by the commercial finite element code. Subsequently, in the second step, starting from the identification of undamaged condition, the damage effects on changes of the dynamic parameters have been recorded. As well known, the incoherent response between the leaves is related to frequency values, damping ratios, and modal shapes.

Discrete model for out-of-plane loaded random masonry

In this contribution, a simple and effective discrete element model based on rigid blocks and elastic interfaces with fixed contact topology, originally introduced for modeling regular masonry panels, is extended to the case of random masonry by introducing a perturbation parameter able to vary the width of each block. The proposed model is then able to better reproduce the microstructural behavior of historical masonry, that is characterized by dry or weak mortar joints between strong blocks, and, in particular, that is characterized by blocks often arranged irregularly. The hypothesis of rigid blocks, together with fixed contact topology between blocks due to the small displacements assumption, allows adopting an efficient solution method based on the determination of the stiffness matrix of the masonry assemblage. In this case, the stiffness matrix is able to account for the irregular block arrangement and, similarly to the case of regular masonry, the stiffness matrix is based on local joint stiffness, given that the contact actions along the joints are function of the relative displacements between adjacent blocks and the corresponding interface stiffness. Several numerical tests varying the random perturbation parameter are performed in order to evaluate the influence of randomness on masonry specimen behavior with respect to the regular case. Particular attention is given to the dynamic field by performing out-of-plane modal analysis of masonry panels. Furthermore, a homogenization procedure is applied to the random masonry and a numerical evaluation of the scatter between the discrete models and a 2D Reissner-Mindlin plate model is performed for varying perturbation parameter and for increasing heterogeneity parameter. As expected, when the number of heterogeneities in the structure is large enough, the average response of the random discrete model converges to an asymptotic response. D. Baraldi, E. Reccia and A. Cecchi