1,721,643 research outputs found
Tecniche innovative di adeguamento sismico in Italia. Raccolta di casi studio e linee guida progettuali per interventi con isolamento sismico e dissipazione di energia
No full textQuesto volume ha come obiettivi fondamentali la presentazione e la discussione critica delle principali metodologie e linee guida note in letteratura ed in campo tecnico per interventi innovativi di adeguamento sismico realizzati in Italia. Gli interventi presi in esame sono realizzati mediante la posa in opera di isolatori sismici, ovvero mediante l’inserimento di dispositivi a dissipazione di energia nella struttura da adeguare sismicamente. I temi trattati vengono contestualizzati mediante l’esame di una molteplicità di casi studio relativi ad interventi campione di rinforzo sismico di strutture esistenti. Si esaminano edifici con struttura portante in cemento armato, in acciaio ed in muratura, mettendo in risalto vantaggi e limitazioni delle soluzioni di protezione sismica adottate, sia dal punto di vista tecnico che sotto l’aspetto economico. La materia trattata include la presentazione di dispositivi di isolamento e dissipazione di tipo innovativo, attualmente in fase di studio e di sperimentazione
Monitoring of seismic isolated buildings: state of the art and results under high and low energy inputs
No full textInnovative seismic isolation devices based on lattice materials: A review
No full textThis paper reviews recent literature results on the mechanics of structures formed by layers of pentamode lattices alternating with stiffening plates, which can be effectively employed for the development of seismic isolation devices and vibration attenuation tools, with nearly complete band gaps for shear waves. It is shown that such structures, named pentamode bearings, can respond either in the stretching-dominated regime, or in the bending-dominated regime, depending on the nature of the joints connecting the different members. Their response is characterized by high vertical stiffness and theoretically zero shear stiffness in the stretching dominated regime, or considerably low values of such a quantity in the bending dominated regime. Available results on the experimental response of 3d printed models to combined compression and shear loading highlight that the examined structures are able to exhibit energy dissipation capacity and effective damping that are suitable for seismic isolation devices. Their fabrication does not necessarily require heavy industry, and expensive materials, being possible with ordinary 3- D printers
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
Seismic application of pentamode lattices
No full textLa categoria dei “metamateriali estremi” è stata introdotta in letteratura per definire materiali che esibiscano, contemporaneamente, modi di deformazione molto “soffici” e modi “rigidi” (materiali unimode, bimode, trimode, quadramode e pentamode, a seconda del numero di modi soffici). Questa definizione può essere applicata a classi speciali di metamateriali meccanici, quali, ad esempio, materiali compositi, schiume strutturali, materiali cellulari, ecc., che siano dotati di proprietà meccaniche speciali, non rinvenibili nei materiali ordinari. Sistemi pentamode sono stati proposti per realizzare l’isolamento dalle onde meccaniche dei corpi (“elasto-mechanical cloak”), mediante avvolgimento del corpo da
isolare con membrane elastiche a struttura reticolare pentamode. Tuttavia, il potenziale ingegneristico di tali materiali è stato sinora solo parzialmente esplorato. Il presente lavoro presenta nuove versioni di materiali pentamode, ossia cristalli strutturali artificiali che
esibiscano moduli di elasticità tangenziale marcatamente più bassi dei moduli di comprimibilità uniassiale e volumetrica. Architetture tensegrity sono impiegate per controllare i modi soffici e le proprietà meccaniche dei reticoli pentamode, attraverso l'inserimento di attuatori e cavi precompressi all'interno delle celle unitarie. Tali strutture sono proposte come dispositivi di isolamento sismico di tipo innovativo, che presentino proprietà di isolamento regolabili in base alle proprietà dinamiche struttura da isolare.The category of “extremal materials” has been introduced in the literature to define materials that simultaneously show very soft and very stiff deformation modes (unimode, bimode, trimode, quadramode and pentamode materials, depending on the number of soft modes). This definition applies to a special class of mechanical metamaterial – composite materials, structural foams, cellular materials, etc. – which feature special mechanical properties. Pentamode materials have been proposed for transformation acoustics and elasto-mechanical cloak, but their potential in different engineering fields is still only partially explored. We here present novel versions of pentamode materials: artificial structural crystals showing shear moduli markedly smaller than the bulk modulus. Novel pentamode lattices with tensegrity architecture are designed, through the insertion of actuated struts and/or prestressed cables within basic pentamode lattices. Such systems are proposed as tunable seismic base-isolation devices, profiting from their low and adjustable shear moduli, which can be easily adapted to the dynamic properties of the structure to be isolated
Assessment of shear forces on bridge abutments: Simplified method
No full textThe conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum
Mechanical response of tensegrity dissipative devices incorporating shape memory alloys
No full textTo optimize the seismic performance prescribed by modern structural codes, buildings and infrastructures must provide adequate safety for design level earthquake excitations, with limited levels of damage. This paper deals with the computational modelling of a bracing system with tensegrity architecture, which operates as a lightweight mechanical amplifier of longitudinal displacements in the transverse direction, efficiently limiting the interstory drifts while dissipating energy. The proposed brace is based on a D-bar tensegrity structure with a rhomboidal shape comprising Shape-Memory Alloy (SMA) tendons. The SMA tendons can develop austenitic-martensitic (solid to solid) transformations, which enable them to amplify the signals into wide super elastic hysteresis, while subjected to mechanical cycles, comprising strains up to 6÷8%, with no residual deformations. The enhanced energy dissipation of the proposed SMA-D-bar (SMAD) braces are demonstrated through computational simulations of the response of braced frame to real earthquake events. The efficiency of the intended bracing to minimize the seismic impact of the served structure lays the foundation for the development of novel seismic energy dissipation systems integrating principles of tensegrity with superelasticity
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