1,721,109 research outputs found
Procedura semplificata per meccanismi di danno di strutture murarie nel piano e fuori dal piano
No full textIn questo lavoro si propone una procedura semplificata per lo studio di strutture murarie sotto sisma con l’analisi dei possibili meccanismi di danno nel piano e fuori dal piano, al fine di valutare maggioranti e minoranti delle azioni sismiche che attivano tali meccanismi in funzione della geometria delle pareti, dei rapporti dimensionali dei blocchi, e del coefficiente d’attrito. In particolare, scelte due classi di meccanismi e rinunciando ad un’analisi discreta con microblocchi, si assume che le lesioni avvengano con la formazione di distinti macroblocchi, come la stessa esperienza suggerisce. I meccanismi sono così caratterizzati dai moti relativi tra i macroclocchi compatibili con le lesioni. Ad ogni tipo di moto corrisponde un valore della resistenza attritiva che si sviluppa lungo una lesione. La resistenza massima si attiva solo con meccanismi caratterizzati ovunque da scorrimento puro. All’opposto, nel caso di distacco puro o di rotazioni alla Heyman lungo tutte le superfici individuate da una lesione la resistenza d’attrito è nulla. Tutti i casi intermedi riguardano i meccanismi combinati, in pratica quelli più realistici. Ha senso quindi definire, con riferimento al tipo di spostamento relativo lungo una lesione, un dominio di resistenza della lesione. Ne risulta che per i meccanismi combinati il moltiplicatore esatto (quello relativo al modello discreto con microblocchi) sarà più piccolo di quello calcolato per i macroblocchi con la totale presenza delle resistenze d’attrito e più grande di quello calcolato senza tali resistenze. A tal fine, si procede innanzitutto alla valutazione delle massime resistenze attritive e poi, per i meccanismi combinati scorrimento-rotazione, nel piano e fuori dal piano, alla definizione di maggioranti e minoranti della soluzione, caratterizzati rispettivamente dalla totale presenza e dalla totale mancanza delle resistenze attritive. Gli estremi dell’intervallo sono definiti col classico approccio cinematico ricercando, in ciascuna classe di cinematismi, l’inclinazione della lesione cui corrisponde il minimo valore del moltiplicatore cinematico in relazione ai parametri geometrici e meccanici sopra introdotti. Si valuta anche l’influenza del sovraccarico di un eventuale solaio con orditura variabile. Opportuni grafici mostrano gli intervalli di variabilità delle soluzioni in funzione dei parametri più significativi
Rocking response of rigid blocks subjected to ground motion
No full textThis work deals with the rocking response of a rigid free-standing block under the action of ground motion, as basic reference for the seismic analysis of masonry structures. A new computational strategy for representing the seismic input is suggested in order to define such an amplitude resonance as representing the most disadvantageous conditions for the block. The rocking response to artificial accelerograms is then analysed by means of a simplified equation of motion between two impacts. The coefficient of restitution is assumed as a variable of the problem to account also for other damping effects (e.g. local plastic deformations). A stabilised phase of the motion is identified for which an upper-bound of the maximum rotation angle of the block can be defined in closed form. The results are plotted in a kind of resonance spectra which point out the influence of such meaningful parameters as the coefficient of restitution and the size and slenderness of the block
RISK FACTORS FOR THE DEVELOPMENT AND PROGRESSION OF RENAL DISEASES IN DISADVANTAGED POPULATIONS: ROLE OF THE RENIN-ANGIOTENSIN SYSTEM BLOCKADE
No full textChronic kidney disease is becoming a public health challenge due to the high risk of progression to end-stage kidney disease, the increased cardiovascular burden and management costs, especially among disadvantaged communities. Although the high prevalence of hypertension and diabetes in these populations are recognized risk factors and a leading cause of chronic kidney disease, ethnic populations show a greater likelihood of developing end-stage kidney disease regardless of these cardiovascular risk factors. The association between low socioeconomic status and the prevalence/progression of chronic kidney disease observed in population-based studies suggests that socioeconomic disadvantage could be a plausible reason for the increased burden of renal disease among minorities. Interventions for management and prevention of chronic kidney disease include angiotensin converting enzyme inhibitors and angiotensin receptor blockers. Few studies of these agents have been conducted in indigenous populations, but there is evidence that angiotensin converting enzyme inhibitors are effective in reducing premature deaths and progression of chronic kidney disease, as well as being highly cost-effective, especially in terms of renal replacement therapies avoided. It is plausible that these disadvantaged groups may benefit more than others from a renal and cardiovascular prevention program, but considerable under-recognition and under-treatment of these conditions still exist. (Ethn Dis. 2009 [Suppl 1];19: S1-86-S1-89
Dynamic analysis of a sdof model of a masonry lintel and peers system
No full textThe dynamic behaviour of a block-like masonry system consisting of a lintel supported by two peers standing free on their foundation is examined. A single-degree-of-freedom model is assumed, the lintel being the rigid block where the mass is concentrated and the peers being the “semi-rigid” blocks with mass neglected. The shear resistance of the peers is calculated by defining inelastic strut elements inside the blocks which involve plastic deformations during the oscillation of the system. The features of these resistant elements are assumed to depend on both the normal forces acting on the peers and their eccentricity. A non-linear elastic model, characterised by a tri-linear shear-displacement relationship for the peers and neglecting impact between blocks and hysteresis loops, is therefore defined. Firstly the free vibration of the model is herein investigated by means of a standard explicit time-history algorithm. The numerical results show that, mostly for thick peers subjected to large normal compressions, a simplified shear-displacement law and the shear resistance independent of the horizontal displacement can be adopted. It involves the concept of very large stiffness of the peers so that the eccentricity of the normal forces jumps discontinuously from one side to the other. Although the free vibrations are represented by a periodic motion, the natural frequency of the model depends on the initial conditions, owing to the non-linearity of the shear-displacement relationship. This non-uniqueness of the natural frequency involves difficulties in the analysis of the seismic response. Nevertheless, when analysing free vibrations only, an equivalent linear elastic single-degree-of-freedom system can be defined for each choice of initial conditions. Finally, some issues regarding the forced vibration are discussed
G-convergence of elliptic and parabolic operators depending on vector fields
Full text linkWe consider sequences of elliptic and parabolic operators in divergence form and depending on a family of vector fields. We show compactness results with respect to G-convergence, or H-convergence, by means of the compensated compactness theory, in a setting in which the existence of affine functions is not always guaranteed, due to the nature of the family of vector fields
Maz'ya-Shaposhnikova formula in magnetic fractional Orlicz–Sobolev spaces
Full text linkIn this note we prove the validity of the Maz'ya-Shaposhnikova formula in magnetic fractional Orlicz-Sobolev spaces. This complements a previous asymptotic study of the limit as s ↑ 1 performed by the second author in (Studia Mathematica (2020))
Upgraded formulations for the onset of local mechanisms in multi-storey masonry buildings using limit analysis
No full textUnreinforced stone masonry (URSM) buildings without a box-like behaviour are very vulnerable to out-of-plane failure modes in seismic prone areas. These may involve partial or total collapses of walls with severe civil protection implications in terms of hazard to people, structures, and road network in the surroundings. In this paper, an advanced macro-block model accounting for frictional resistances is used to calculate the onset load factors for two classes of local mechanisms in multi-storey URSM buildings: the rocking-sliding and the flexure mechanisms. Based on the application of the kinematic approach of limit analysis, the presented formulations are an upgrade of the load factors identified within the FaMIVE (Failure Mechanism Identification and Vulnerability Evaluation) procedure existing in the literature and developed by the last author. These take into account a revisited evaluation of the in-plane frictional forces for the rocking-sliding mechanisms and the torsion-shear-flexure interactions for the horizontal flexure mechanisms. Moreover, the position of the hinge along the height of the building is identified more accurately, since it can be found at the story level or between two storeys, depending on the accounted mechanism. Other innovative issues concern upgrades of the former formulations for the vertical and horizontal flexure mechanisms. The final perspective of the presented abacus of local mechanisms in multi-storey URSM buildings is the next implementation of the proposed formulations in the FaMIVE procedure, after a sensitivity analysis of the main physical and geometrical parameters affecting the “hierarchy” among the all possible mechanisms. The identification of the most probable mechanisms, through a comprehensive but at the same time relatively rapid assessment, can be very useful for civil protection purposes
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
Un riferimento di base per la sicurezza delle strutture murarie sotto sisma
No full textSi analizza il moto rotatorio sotto sisma del blocco rigido quale riferimento fondamentale per l’analisi sismica delle strutture murarie. Gli studi presenti in letteratura, condotti con accelerogrammi registrati, hanno mostrato che un blocco di una data snellezza può ribaltare senza che il ribaltamento si manifesti per un blocco più snello. La parametrizzazione del problema appare quindi estremamente difficile. Pertanto in questo lavoro si propone una schematizzazione semplificata dell’azione sismica dotata di opportune regolarità e tale da fornire, con buona probabilità, un limite superiore per le situazioni più sfavorevoli che possano verificarsi. Si tratta di una combinazione di moduli di base. Ogni modulo è caratterizzato da tre impulsi elementari alla Dirac e dall’intervallo di tempo che li separa, ed ubbidisce alla proprietà di dar luogo a valori nulli dello spostamento e della velocità del suolo. L’intervallo del singolo modulo è opportunamente calibrato in funzione della velocità di rotazione del blocco. In particolare l’accelerogramma è costruito in modo che il moto del blocco nell’intervallo fra due impulsi sia un moto naturale caratterizzato solo da una certa velocità angolare iniziale. La risposta dinamica del blocco è poi valutata tramite una forma semplificata dell’equazione del moto del blocco nell’intervallo fra due urti, e l’urto è rappresentato dal coefficiente di restituzione. L’analisi fornisce un limite superiore degli angoli di rotazione e i parametri più significativi sono la snellezza, il coefficiente di restituzione e le dimensioni. L’influenza di questi parametri è mostrata nella sperimentazione numerica condotta. I risultati sono infine confrontati con le indicazioni fornite dall’Allegato 11.C dell’OPCM 3431, confermando il carattere estremo del modello
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