Modern techniques and innovative materials are often quite rapidly proposed and allowed in current practice, even for restoration of historical constructions, in which essential preservation criteria ...must be taken into account. The considerable variability and complexity of masonry structures and types means that choosing the most appropriate structural models and interventions is particularly difficult, since they must be based on suitable knowledge of both existing and new materials, and on their interactions in environmental and loading conditions. This paper discusses the potentials and limitations of externally bonded composite materials in masonry structures and components, in the light of knowledge acquired from research in the field, together with the requirements and recommendations of codes and restoration documents. The analysis of some case studies is presented, to highlight the advantages and constraints in the use of composites for strengthening historical buildings.
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.
Failure pattern prediction in masonry De Felice, Gianmarco; Malena, Marialaura
Journal of mechanics of materials and structures,
12/2019, Volume:
14, Issue:
5
Journal Article
The out-of-plane collapse of the façade represents one of the major threats and the most frequent cause of damages of churches due to strong earthquakes. Due to the slenderness of the façade and the ...lack of adequate connections to the side walls and the wooden roof, the seismic action can trigger the overturning. A detailed assessment is therefore required to judge whether or not to intervene. This paper presents an approach for the seismic assessment of the stability of the façade, through a discrete element model based on a photographic survey, with the aim of representing the actual geometry and arrangement of the stone units and their effects on the kinematics of the overturning. The collapse mechanism is simulated with both, quasi-static pushover and dynamic pulse-based analyses and the results compared to those of conventional rigid-body kinematics. The proposed approach is then applied to seven masonry churches that suffered severe damages during the 2009 L’Aquila (Italy) earthquake and the failure mode provided by the analyses is compared to the damages caused by the earthquake. The method is able to give a reliable estimate of the expected failure mechanism, taking into account the quality of the masonry and the connections to the side walls, while also providing the seismic acceleration required to trigger the motion and the ultimate displacement beyond which collapse occurs.
Textile Reinforced Mortar (TRM), also known as Fabric Reinforced Mortar or Fabric Reinforced Cementitious Matrix, composites are an emerging technology for the external repair and strengthening of ...existing structures. For most applications, the effectiveness of the TRM reinforcement relies on its bond performance. This recommendation identifies the best practice to characterize the bond behaviour of TRM. A shear bond test method is proposed to determine the peak axial stress (associated with the maximum load that can be transferred from the structural member to the externally bonded TRM reinforcement), the stress–slip relationship and the failure mode that controls the TRM-to-substrate load transfer capacity. Guidelines on specimen manufacturing, experimental setup, test execution, and determination of test results are provided.
Externally bonded mortar based composites have become a popular technique for strengthening masonry arches and vaults. The effect of the curved substrate on the bond properties is one of the key ...factors affecting their structural behaviour. This paper presents the results of an experimental campaign of debonding tests on straight and curved substrates made of bricks assembled with mortar and strengthened either with Carbon Fibre Reinforced Cementitious Matrix (CFRCM) or Steel Reinforced Grout (SRG). The experimental results get insight into the failure mechanisms that take place in mortar based composites and disclose the effect of the substrate curvature on the interfacial strain distribution and on the load–displacement response. The experimental results are compared with the outcomes of a predictive model, proposed in this work, which provides a closed-form analytical solution to the debonding process of a thin plate on a rigid substrate with constant curvature. The model, which is based on an interface cohesive law, coupled in the tangential and normal directions, as a consequence of the curvature, is able to predict the decrease in bond stiffness and strength for increasing curvature, as shown by experimental results.
Digital Image Correlation (DIC) is a full-field contactless optical method for measuring displacements in experimental testing, based on the correlation of the digital images taken during test ...execution. It is used in several fields of experimental solid mechanics, but its potential application to the characterization of composite reinforcements has not been fully investigated yet. In this paper DIC is used in tensile and bond tests on composite reinforcements comprising different textiles and matrices. Results obtained by two DIC software programs are validated by comparison with displacement and strain transducers. DIC provides additional information on damage pattern (crack location and width) and composite-to-substrate load transfer mechanism (effective bond length and local stress concentrations). It also offers the advantageous possibility of selecting several measurement points after the test, overcoming some drawbacks of traditional transducers. On the other hand, since only on the outer surface of the specimen is monitored, no information is directly available on the textile embedded in the matrix. The combination of DIC and traditional sensors in laboratory testing allows improving the understanding of the mechanical behaviour of composite reinforcements and the identification of their fundamental properties.
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