159 research outputs found
Minimal mass and self-stress analysis for innovative V-Expander tensegrity cells
No full textTensegrity structures are an intriguing kind of structures by virtue of their deployability, scalability and high stiffness to mass ratio. Fraddosio et al. recently proposed a family of five innovative V-Expander elementary tensegrity cells, characterized by an increasing degree of geometrical complexity, and designed as a morphological evolution of a concept originally proposed by Motro and Raducanu. Here, we study the mechanical behavior of these innovative V-Expander elementary tensegrity cells by referring to different topologies; in particular, we analyze for such cells the feasible self-stress states in the cases in which the components in compression are composed of 2, 3, 4 and 6 struts, respectively. In addition, we evaluate the minimal mass of the cells taking into account the buckling strength of members in the self-equilibrium states according to the indications of standard building codes
Documentare, comprendere e conservare le eredità di Luigi Santarella / Documenting, Understanding and Preserving the Legacy of Luigi Santarella
No full textThis panel has brought together a group of scholars in the disciplines of engineering and architecture to discuss the figure of Luigi Santarella, offering interdisciplinary insights and concrete examples of how we might look at his work to better understand his legacy not only as a construction scientist and theorist or as a pioneer of reinforced concrete structures, but also as an educator committed to training a new generation of designers in such a founding period as the early Twentieth century. In line with the general topic of the Study Day and with the contributions from the invited speakers, this panel was designed to outline possible broader approaches for a further deepening of a well-known figure — but still not fully investigated in its complexity — as that of Santarella. Bringing together the points of view of Enzo Siviero (engineer and professor of Structural engineering at IUAV University), Giuseppina Uva (engineer and professor of Structural engineering at the Polytechnic University of Bari), Rita Vecchiattini (architect and professor of Architectural restoration at the University of Genoa), Aguinaldo Fraddosio (engineer and professor of Structural mechanics at the Polytechnic University of Bari) and Lorenzo Pietropaolo (architect and research professor in Architectural history at the Polytechnic University of Bari), panelists’ contribution suggests to further document and investigate Santarella’s work with a holistic approach so to address substantive issues — also in terms of training of the younger generations — such as the interaction between Architecture and Engineering in design processes or the urgent challenges to preserve reinforced concrete architectures of the Twentieth century. This means promoting specific communication and dissemination actions, and conceiving new research outlines on Santarella’s theoretical and built legacy that may intertwine historical and archival studies, methods and techniques for structural analysis, for conservation, restoration or adaptive reuse of reinforced concrete heritage
Ultrasonic goniometric immersion tests for the characterization of fatigue post-LVI damage induced anisotropy superimposed to the constitutive anisotropy of polymer composites
No full textWe study an ultrasonic experimental approach for the damage characterization of polymer composites. Our approach is based on the key concept that damage of polymer composites involves a damage induced anisotropy superimposed to the constitutive anisotropy of the material. Thus, we correlate the damage to the analysis of the change in the anisotropy of the acoustic response of the material, by using an innovative goniometric ultrasonic immersion device designed and built at our laboratory. The experiments are performed on a glass fiber–reinforced composite material (GFRP), damaged first by a low velocity impact (LVI), and then by fatigue load cycles. We first identify possible changes in symmetry axes (acoustic axes) and/or in the symmetry class of the material due to the damage; to this aim, we compare the velocity curves and the slowness curves of the composite before and after the damage. Then, starting from the velocity measurements acquired in goniometric ultrasonic immersion tests performed before and after the damage, we determine the variations of the elastic constants due to the damage. For a quantitative characterization of the damage, a suitable anisotropic damage model developed in the framework of the Continuum Damage Mechanics theory is employed. In this model, the damage is related to the relative variation of the elastic constants of the material. For the validation of the procedure, ultrasonic results are also compared with experimental data obtained by conventional mechanical tests. The obtained results show the effectiveness of the proposed approach for the damage characterization of polymer composites
Quantitative analysis of QSI and LVI damage in GFRP unidirectional composite laminates by a new ultrasonic approach
No full textOur work is focused on a new experimental approach for the comparison between Quasi Static Indentation (QSI) damage and Low-Velocity Impact (LVI) damage in polymer composites starting from the results of ultrasonic goniometric immersion tests. In particular, the comparison is performed through the analysis of the additional anisotropy induced by the damage in unidirectional Glass Fiber-Reinforced Polymer (GFRP) composites due to QSI and LVI damage tests performed with a low level of the employed energy. To this aim, we ultrasonically reconstruct the acoustic curves (velocity curves and slowness curves) before and after the damage. Ultrasonic experiments are performed by using a goniometric ultrasonic immersion device designed and built at our laboratory, aimed at the mechanical characterization of anisotropic materials. We highlight differences and similarities between QSI and LVI damage starting from the analysis of the variations of the acoustic behavior and by using a suitable anisotropic damage model developed in the framework of the Continuum Damage Mechanics theory. The proposed experimental approach can be suitably developed for in situ investigations on low-velocity impact damage in polymer composite components
A novel method for determining the feasible integral self-stress states for tensegrity structures
No full textThe form-finding analysis is a crucial step for determining the stable self-equilibrated states for tensegrity structures, in the absence of external loads. This form-finding problem leads to the evaluation of both the self-stress in the elements and the shape of the tensegrity structure. This paper presents a novel method for determining feasible integral self-stress states for tensegrity structures, that is self-equilibrated states consistent with the unilateral behaviour of the elements, struts in compression and cables in tension, and with the symmetry properties of the structure. In particular, once defined the connectivity between the elements and the nodal coordinates, the feasible self-stress states are determined by suitably investigating the Distributed Static Indeterminacy (DSI). The proposed method allows for obtaining feasible integral self-stress solutions by a unique Singular Value Decomposition (SVD) of the equilibrium matrix, whereas other approaches in the literature require two SVD. Moreover, the proposed approach allows for effectively determining the Force Denstiy matrix, whose properties are strictly related to the super-stability of the tensegrity structures. Three tensegrity structures were studied in order to assess and discuss the efficiency and accuracy of the proposed innovative method
Thrust Surface Method: An innovative approach for the three-dimensional lower bound Limit Analysis of masonry vaults
No full textWe propose a new computational equilibrium approach for the structural safety assessment of historical masonry vaults of any geometry under general loading conditions. This approach, called Thrust Surface Method (TSM), represents an innovative application of the lower bound theorem of Limit Analysis to masonry vaults modeled as continuous No-Tension bodies. In particular, on allowing for singular stresses, the search of statically admissible stress field is reduced to the search of purely compressed membranes in equilibrium with the applied loads and entirely contained into the thickness of the vault. Based on a convenient numerical procedure and the formulation of a suitable constrained optimization problem, TSM is a method of practical application that, looking for “extremal” or “optimal” solutions, is capable of fully exploring the entire load-bearing capacity spectrum of a vault having an arbitrary geometry. Since the particular formulation, TSM can take into account not only any kind of vertical loads, but also horizontal loads like those simulating the maxima inertia effects related to seismic actions. In addition, the proposed approach could be a useful tool for visualizing and understanding the complex three-dimensional behavior and the close relationship between form and structure characterizing masonry vaults. The effectiveness and the capabilities of the method are discussed in light of some representative case studies, allowing for suitable comparisons with the results of other analytical and experimental approaches in the literature
Phase Transitions, Hysteresis and Bifurcation for Generalized Mooney-Rivlin Elastic Bodies
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