1,720,991 research outputs found
Matrix-embedded metamaterials: applications for the architectural heritage
No full textA rather unexplored question and a very challenging problem consist in the synthesis and modeling of composite metamaterials consisting of at least two phases. The study of this problem may have a huge impact in the field of Civil Engineering, where such kind of composite materials found several applications, for instance, in application to architectural and civil engineering heritage. More precisely, the aim of this work is to study the mechanical properties of a fibrous metamaterial embedded in a softer matrix. Numerical simulations, obtained by means of a commercial Finite Element code, are carried out on a soft matrix reinforced by stiffer fibers arranged according to a geometry defined by the fiber directions and compared with results achieved using an effective model in which the micro-structure is homogenized. The role of the fibers and the matrix is reinterpreted with regard to these models. Finally, the employed models are calibrated to reproduce the mechanical behavior of a simple experiment
Homogenization of random porous materials with low-order virtual elements
Full text linkA fast statistical homogenization procedure (FSHP) based on virtual element method (VEM) - previously developed by the authors has been successfully adopted for the homogenization of particulate random composites, via the definition of the representative volume element (RVE), and of the related equivalent elastic moduli. In particular, the adoption of virtual elements of degree one for modeling the inclusions provided reliable results for materials with low contrast, defined as the ratio between mechanical properties of inclusions and matrix. Porous media are then here described as bimaterial systems in which soft circular inclusions, with a very low value of material contrast, are randomly distributed in a continuous stiffer matrix. Several simulations have been performed by varying the level of porosity, highlighting the effectiveness of FSHP in conjunction with virtual elements of degree one
On the structural behaviour of existing RC bridges subjected to corrosion effects: Numerical insight
No full textThe evaluation of the structural behaviour of existing reinforced concrete (RC) bridges represents one of the most current structural engineering research topics due to their strategic importance, especially if they are subjected to corrosion effects which can lead to a significant reduction of load-bearing capacity of the main structural elements (e.g., the piers). In the last decades, different types of numerical approaches have been proposed for the evaluation of the structural behaviour of these strategic infrastructures, especially after the recent collapses that have affected this type of structures during last years. In this paper, the structural behaviour of an existing RC bridge subjected to corrosion effects due to carbonation is analysed by means of an efficient procedure based on the implementation of a Finite Element Model (FEM) where the main structural elements are implemented using only Timoshenko beam elements. The safety level of the bridge has been evaluated considering different load conditions (e.g. traffic load, seismic action, etc.) calculated according to the Italian Design Code (NTC2018). Finally, a retrofitting intervention is proposed in order to guarantee and adequate safety level of the bridge under the considered different load combinations
FROM LIDAR DATA TOWARDS HBIM FOR STRUCTURAL EVALUATION
Full text linkIn HBIM processes, the extraction of geometric components from 3D point clouds data can sometimes be a complex process. The so-called "Scan to BIM" process has been widely utilized: deriving 3D models from point clouds often a local modelling of geometric components is necessary. This leads in most cases to use external modelling tools or complex local modelling processes. In both cases, we often get a model that cannot be reused for other items belonging to the same category, contravening the BIM philosophy. Vaulted systems are a typical example of complex elements that we can find in historical architecture. The paper presents the first results of an ongoing research on geometric modelling and structural evaluation of masonry ribbed vaults. An algorithm is developed to generate a NURBS surface of masonry vaults that, starting from the data extrapolated from the point cloud, allows to obtain an HBIM family. The research aims to overcome the inability to reference to standardised objects in local modelling of historical architecture elements. Directed to a standardization in the geometric modelling process of 3D laser scan data, the developed workflow is a possible alternative to commonly used workflows. Particular attention is focused on a case study of stellar vaults, a special class of masonry ribbed vaults whose three-dimensional geometry features a star-shaped projection on the horizontal plane. The work is carried out to verify that this family can be used for the structural analysis of stellar masonry vaults
Strong Ellipticity Within the Strain Gradient Elasticity: Elastic Bar Case
No full textIn this note we discuss the strong ellipticity condition within the nonlinear strain gradient elasticity. Considering a one-dimensional case, i.e. an elastic bar loaded by a tensile force, we analyze the correspondence of violation of the strong ellipticity condition and compare the results with classic nonlinear elasticity. The correspondence of ellipticity loss to the non-uniqueness of solutions are discussed in more detail
Structural behaviour of corrugated shells: A look at the Flaminio dome in Rome
No full textThe dome designed by P. L. Nervi in 1961 for the roof of the Palazzetto dello Sport in Flaminio district, Rome, has a remarkable feature: The ondulated shape of its edge provides significant enhancements of its structural behaviour. In particular, corrugation increases the bending stiffness at the edge providing a significance reduction of the dome thickness. This contribution deals with the mechanical analysis of corrugated shells. Attention is paid to the definition of their mathematical and geometrical descriptions and to the realization of a mesh suitable to perform FE analysis. Two significant case studies are considered: The no more existing rooftop of Fav-ini’s gas station in Sesto San Giovanni and the Nervi’s dome of Flaminio Palasport
Statistical homogenization of random porous media
Full text linkIn recent times, the scientific community paid great attention to the influence of inherent uncertainties on system behavior and recognize the importance of stochastic and statistical approaches to engineering problems [21]. In particular, statistical computational methods may be useful to the constitutive characterization of complex materials, such as composite materials characterized by non-periodic internal micro-structure. Random porous media exhibit a microstructure made of randomly distributed pores embedded into a continuous matrix. They can be modelled as a bi-material system in which circular soft inclusions (pores) with random distribution and variable diameters are dispersed in a stiffer matrix. A key aspect, recently investigated by many researchers, is the evaluation of appropriate mechanical properties to be adopted for the study of their behaviour. Differently from classical homogenization approaches, in the case of materials with random microstructure it is not possible to 'a-priori' define a Representative Volume Element (RVE), this being an unknown of the problem. Statistical homogenization procedures may be adopted for the definition of equivalent moduli able to take into account at the macroscale the material properties emerging from the internal microstructure with random distribution [26]. Here, a Fast Statistical Homogenization Procedure (FSHP) based on Virtual Element Method (VEM) approach for the numerical solution-previously developed by some of the authors [13] has been adopted for the definition of the Representative Volume Element (RVE) and of the related equivalent elastic moduli of random porous media with different volume fraction, defined as the ratio between mechanical properties of inclusions and matrix. In particular, FSHP with virtual Elements of degree 1 [2] for modelling the inclusions provides reliable results for materials with low contrast
Micromodels for the in-plane failure analysis of masonry walls with friction: Limit analysis and dem-fem/dem approaches
Full text linkDespite 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. In this work a comparison of different models and techniques for the assessment of the mechanical behaviour of two-dimensional block masonry walls subjected to the static action of in-plane loads is presented. Panels are characterized by different height-to-width ratio as well as various masonry textures. Brick-block masonry, perceived as a jointed assembly of prismatic particles in dry contact, is modelled as a discrete system of rigid blocks interacting through contact surfaces unable to carry tension and resistant to sliding by friction, modelled as zero thickness elasto-plastic Mohr-Coulomb interfaces. Different approaches and numerical models are considered: Limit Analysis (LA), Discrete Element Model (DEM) and Finite Ele-ments/Discrete Element Model (FEM/DEM). Limit Analysis is able to provide fast and reliable results in term of collapse multiplier and relative kinematism. Here a standard Limit Analysis is adopted via an own made procedure based on Linear Mathematical Programming, taking into account friction at interfaces
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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