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The destruction of Amatrice and the surrounding villages in Central Italy after the 2016 seismic sequence was so impressive that engineers, authorities and local communities started sharing the common feeling that historical stone masonry buildings were too below current safety standards. The severe damage caused by the earthquakes led to a general distrust of traditional building techniques, leading to the conclusion that there is nothing to do but demolish and rebuild, perhaps with a false antique. Is there an alternative? Is there a way to combine safety and preservation of architectural heritage? This paper aims contributing to the understanding of the seismic behaviour of stone masonry by reproducing, through simulation on a shake table, the progressive loss of compactness of a real scale rubble masonry wall up to the ruinous collapse with the separation between the two external leaves. The laboratory simulation allowed to evaluate the decrease of the fundamental frequency with increasing damage and estimate the maximum displacement profile and the amount of cracking that the wall is able to sustain before failing. Eventually, two modelling strategies based on finite and discrete element methods were proposed and applied to verify the capability of simulating the out-of-plane seismic response and the failure mechanisms of rubble masonry.

Interest in small-to-medium magnitude earthquakes and their potential consequences has increased significantly in recent years, mostly due to the occurrence of some unusually damaging small events, the development of seismic risk assessment methodologies for existing building stock, and the recognition of the potential risk of induced seismicity. As part of a clear ongoing effort of the earthquake engineering community to develop knowledge on the risk posed by smaller events, a global database of earthquakes with moment magnitudes in the range from 4.0 to 5.5 for which damage and/or casualties have been reported has been compiled and is made publicly available. The two main purposes were to facilitate studies on the potential for earthquakes in this magnitude range to cause material damage and to carry out a statistical study to characterise the frequency with which earthquakes of this size cause damage and/or casualties (published separately). The present paper describes the data sources and process followed for the compilation of the database, while providing critical discussions on the challenges encountered and decisions made, which are of relevance for its interpretation and use. The geographic, temporal, and magnitude distributions of the 1958 earthquakes that make up the database are presented alongside the general statistics on damage and casualties, noting that these stem from a variety of sources of differing reliability. Despite its inherent limitations, we believe it is an important contribution to the understanding of the extent of the consequences that may arise from earthquakes in the magnitude range of study.

Detecting the onset of structural damage and its progressive evolution is crucial for the assessment and maintenance of the built environment. This paper describes the application of a computer-vision-based methodology for structural health monitoring to a shake table investigation. Three rubble stone masonry walls, one unreinforced and two reinforced, were tested under natural earthquake base inputs, progressively scaled up to collapse. White noise signals were also applied for dynamic identification purposes. Throughout the experiments, videos were recorded, under both white noise excitation and environmental vibrations, with the table at rest. The videos were preprocessed with motion magnification algorithms and analyzed through a principal component analysis. The natural frequencies of the walls were detected and their progressive decay was associated with damage accumulation. Results agreed with those obtained from another measurement system available in the laboratory and were consistent with the crack pattern development surveyed during the tests. The proposed approach proved useful to derive information on the progressive deterioration of the structural properties, showing the feasibility of this methodology for real field applications.

The development of urban mobility implies the construction of tunnels, often interacting with valuable masonry structures. It is thus necessary to develop rational and reliable procedures to estimate the potential excavation-induced damage, which imply the analysis of the related soil-structure interaction problem. Classical approaches to soil-structure interaction are often characterised by relatively simple schematisations for either one or both components of the problem, as, for example, springs for the soil or equivalent plates for the structure. Such simplified assumptions prove to be appropriate for conventional soil-foundation cases, while show all their limitations when tackling more complex problems, as those involving the excavation in the vicinity or beneath masonry structures. In such cases, the need for reliable prediction of the potential damage induced by construction activities on surface structures justifies the adoption of more advanced numerical approaches, based on realistic constitutive assumptions for both soil and masonry, together with an accurate modelling schematisation of the excavation process. This is what proposed in this paper, where a 3D Finite Element approach is adopted to realistically model the multidimensional and progressive nature of the excavation process, the strongly non-linear soil behaviour and the non-linear anisotropic response that characterises masonry structures, here included accounting for their 3D geometrical characteristics. All the analyses are carried out with reference to a sample masonry building founded on strip footings, interacting with a shallow tunnel in a typical London soil profile, already examined in the literature. Different configurations of the structure, considering the sole facade or the whole building, are examined. Also, different relative positions of the tunnel and the structure, in terms of skew angle and eccentricity, are considered. In all the analyses, the excavation is simulated either reproducing the whole three-dimensional advancement of the tunnel or through a simplified single-step analysis. A critical review of the deformation regimes and related plastic points patterns resulting from the different analyses point out in which cases it is necessary to accurately model the 3D tunnel advancement to detect the transient effects governing the onset of structural damage.

Two techniques for the seismic strengthening of fair faced rubble masonry walls are proposed and tested on a shake table. The first solution entails the use of carbon fibre reinforced polymer connectors installed from outside through the natural stone units, without perforating the entire wall thickness, thus leaving the internal wall surface undisturbed. In the second solution, stainless-steel cords are embedded in repointed mortar joints of the fair face and connected, by means of stainless-steel bars, to a thermo-insulating composite reinforced mortar applied to the internal side. Shake table tests were performed under natural accelerograms on real scale multi-leaf rubble masonry walls, built with the stone units retrieved from the debris of a hamlet heavily damaged in the 2016 Central Italy earthquakes. Both strengthening solutions proved effective in enhancing the seismic capacity by preventing leaf separation and masonry disintegration, and in limiting damage development under earthquake excitation. Thanks to the compatibility with original materials and the preservation of the fair face, they are suitable for mitigating the seismic vulnerability of architectural heritage.

Failure mechanisms and crack patterns characterizing the nonlinear response of masonry under both vertical and horizontal load conditions are strongly affected by its intrinsic anisotropic behaviour. Moreover, in case of ancient masonry walls, typically constituted by high strength units (stone blocks or bricks) and weak mortar, texture is one of the key elements that determine failure morphological features. Some analogies between this material and fissured rocks can therefore be envisaged: the discontinuities of a rock mass and their orientation drive failure similarly to mortar joints in masonry walls and in both cases cohesion and friction characterize the response along these weakness planes. However, peculiar features such as interlocking due to staggered head joints and the periodic nature of masonry need to be considered and make its constitutive response more complex. In this research work the in-plane and the out-of-plane behaviour of masonry walls are analysed. The adopted constitutive model has been formulated stemming from a pre-existing one, originally conceived to simulate the behaviour of jointed rock layers, and has been implemented in the commercial code PLAXIS 3D. It is a three-dimensional model based on the identification of preferential orientation of failure planes, on which a Mohr Coulomb failure criterion holds in conjunction with a tensile stress cut-off. Elastic properties are derived from a relatively simple homogenization procedure and geometrical characteristics of blocks as well as the effect of staggered arrangement of head joints are accounted for. Some case-studies for different geometrical configurations are analysed. Results are compared with both experimental evidences and the numerical outcomes obtained resorting to a different constitutive model in which masonry is described as a homogenized anisotropic medium. The proposed model is also adopted for the simulation of a real-scale static soil-structure interaction problem, aiming at highlighting the capability of the model to describe the macroscopic behaviour in terms of collapse mechanism and collapse multiplier. In spite of its simplicity, the proposed approach is able to account for the role of texture with low computational cost and a relatively limited number of mechanical parameters.

Every year landslides occur all over the world as a consequence of specific ground conditions, geomorphological, physical or man-made processes. Such phenomena, often triggered by heavy rainfalls or earthquakes, can affect buildings and infrastructures, causing economic and life losses. This work investigates the effects of a landslide, occurred on the 26th of November 2018, on the Monastry of Santa Scolastica in Subiaco (Rome), one of the most ancient and well-preserved examples of medieval architecture in Central Italy. The evolution of the damage pattern observed on the structure is discussed and related to its different causes, aiming at evaluating if possible worsening effects should or not be ascribed to the occurred landslide or to possible future similar events. The study relies on an accurate geometrical description of both the slope and the building, made possible by advanced survey tools. Most of the analyses used to simulate the history of the events occurred to the Monastry were performed by a three-dimensional non-linear finite element model. Elastic-perfectly plastic constitutive assumptions were adopted for the soil, while the structure was modelled by a three-dimensional anisotropic elastic-perfectly plastic constitutive model, specifically conceived for masonry, accounting for block dimensions and staggering joints effects. Finite element approach has proven to be very effective in the analysis of such a coupled interaction problem, leading to a realistic representation of the interplay between the soil displacements and their effects within the structure. The safety conditions of the structure could then be assessed, and the causes of the damage pattern identified, showing that the slope movement did not worsen the pre-existing damage conditions, which should instead be ascribed to the original soil-structure interaction phenomena occurred when an extension of the original structure had been built.

Numerical modeling of masonry structures is nowadays still an active research field, and this is partly due to a number of open issues related to preservation and restoration of historical constructions and the availability of computational tools that have become more and more refined. This work focuses on the analysis of settlement-induced failure patterns characterizing the in-plane response of two-dimensional dry-joints masonry panels, which differ in terms of texture, geometry, and settlement configuration. Brick-block masonry, interpreted as a jointed assembly of prismatic particles in dry contact, can be modeled as a discrete system of rigid blocks interacting through contact surfaces with no tensile strength and finite friction, modeled as zero thickness elasto-plastic Mohr-Coulomb interfaces. Different approaches and numerical models have been adopted herein: Limit Analysis (LA), a discrete model DEM, and a continuous Finite Element Model (FEM). Limit Analysis is able to provide fast and reliable results in terms of collapse multiplier and relative kinematics. In this work, a standard LA procedure was coded through Linearized Mathematical Programming to take into account sliding mechanisms through dilatant joints. Discrete models are particularly suitable to study historical masonry materials, where rigid bodies interact between contact and friction. Here, a combined Finite/Discrete Element approach (FEM/DEM) is adopted. Finally, analyses are conducted through the Finite Element approach, resorting to a continuum anisotropic elastic perfectly plastic constitutive model. Some selected case studies have been investigated and found to have adopted the above mentioned models, and numerical results have been interpreted to highlight the capability of the approaches to predict failure patterns for various geometrical features of the structure and settlement configurations.

Modern repairing and retrofitting methods for existing structures make use of composite materials, consisting of high strength textiles and a matrix, which can be either polymeric or inorganic. These kinds of techniques have been largely applied to masonry structures, since they significantly improve structural performance with a small increase of weight and a minimum invasiveness. However, the application of organic gluing agents on masonry has revealed some well-known drawbacks, which are almost all overcome resorting to inorganic matrixes, namely cement or lime mortars. An entire class of composites is thus identified as TRM (Textile Reinforced Mortars) or FRCM (Fibre Reinforced Cementitious Matrices). Among them, Steel Reinforced Grout (SRG) are characterized by Ultra High Tensile Strength Steel (UHTSS) cords embedded in mortar matrix and their use to improve the structural performance of existing historical masonry buildings is becoming more and more diffused. Qualification tests and acceptance criteria for SRG have just been defined. Nonetheless, numerical simulation of current available test procedures is mandatory to identify peculiar aspects of the response that at a following stage become an integral part of large scale models, when entire reinforced structures or portions need to be analysed. To this end, this work presents the numerical modelling of two different direct tensile tests on SRG systems: the Clamping-grip setup (RILEM Technical Committee 232-TDT 2016) and the Clevis-grip setup (ICC-ES AC434 2016). Numerical models able to replicate experimental tests and catch fundamental differences in their failure mechanisms are present

The use of composite materials as structural retrofitting tools has been strongly encouraged by their capability of improving structural performance causing minimum invasiveness and reduced weight increment. For decades, Fiber Reinforced Polymers were considered the most suitable composites for retrofitting purposes but, more recently, technological issues have revealed some drawbacks, mainly related to their applications on masonry substrates. A viable alternative is represented by Fabric Reinforced Cementitious Matrix (FRCM), a class of composites made of high-strength textiles with inorganic matrix. Among them, Steel Reinforced Grout (SRG) systems, made of Ultra High Tensile Strength Steel cords embedded in cement or lime-based mortar, are widely used, particularly for repairing or strengthening masonry constructions. Qualification tests and acceptance criteria of these composites have been recently proposed. Numerical simulations of current available experimental test procedures need to be performed to provide a more rigorous insight into the mechanisms that control the composite response up to failure, namely the brittle cracking of the matrix, the ductile response of the steel and the debonding at the mortar-fabric interface. These aspects not only affect the microscale, but are indeed responsible for the macroscopic response of the composite. In this work a finite element simulation of direct tensile tests on SRG systems is presented. Two different gripping methods have been considered, the clamping-grip and the clevis-grip, which identify two standardized test procedures according to RILEM and ACI respectively. Numerical results are first compared with the experimental outcomes to assess the accuracy of the model in reproducing the quantitative and qualitative aspects of composite tensile response. Then, the effects of different boundary conditions on failure mechanisms are investigated, analysing damage and stress patterns in the constituents.