1,721,168 research outputs found
Influence of the displacement of the supports on the collapse behavior of masonry semi-circular arches
No full textDisplacements of the supports affecting masonry arch systems and vaulted structures can determine a condition of collapse because of gradual changes in geometry. The paper presents an experimental study for the evaluation of the magnitude of the horizontal displacements of the supports that can be sustained by the masonry structure subjected to its self-weight before collapse. To this aim, both the arch prototypes and testing machine have been designed ad-hoc and realized by means of the use of the 3D printing technique. Two semi-circular configurations of the arch have been studied. The first one is a 1:2 scale version of the arch system studied by Ochsendorf in 2002 and characterized by a mean radius of 110 mm, a number of voussoir equal to 16 and a thickness-mean radius ratio equal to 0.23. The second configuration, defined by the same values of mean radius and number of voussoirs and by a higher thickness-mean radius ratio, equal to 0.3, has been set to investigate the effect of the slenderness on the behavior of the arch. The effect of the displacement of the supports on the stability the arch has been investigated in terms of collapse mechanism, evolution of the position of the hinges and ultimate displacement capacity. A comparison of the experimental outcomes has been also performed with numerical results obtained with a tool previously developed by the same authors in the framework of the rigid in compression no tension model for the masonry material and based on the approach of the kinematical theorem of the collapse state
La nuova rappresentazione della performance economica nei bilanci delle imprese quotate alla luce della prima applicazione dello IAS 1 revised: evidenze empiriche da Italia e Francia
No full textIl paesaggio non è tutto rose e fiori
Full text linkIl paesaggio è presentato come una delle più potenti espressioni delle collettività, nella quale sono compresenti, come in tutte le arti, Weltanschaung e Kunstwollen. Paradigmi e aspirazioni delle genti che abitano o attraversano i territori, si incidono nei paesaggi. La forma del paesaggio si costruisce attingendo a forme primitive che sono tecnicamente necessarie, ma non sufficienti in sé a rispecchiare visioni complesse nelle quali le collettività possano riconoscersi: vengono prima del paesaggio e ne costituiscono la sostanza necessaria. Oggi la sfida del paesaggio si individua nelle forme necessarie alla nuova infrastrutturazione e all’upgrade di quella esistente; nei relitti delle infrastrutture obsolete e in quelli delle fabbriche dismesse; nelle opere di messa in sicurezza del territorio; nella gestione delle risorse naturali e dei rifiuti di ogni tipo. È in ambiti come questi che la ricerca sul paesaggio trova oggi necessaria cogenza
Rocking of cracked masonry walls under constant impulse acceleration
No full textMulti-storey walls with openings, composed by wall piers and spandrels, represent the main resistant structural components of a masonry building. The in-plane seismic forces are countered by means of their weights, which oppose to the action of the horizontal forces. The behaviour of masonry constructions results to be very far from the one characterizing ductile structures, because of the lack of energy dissipation during the deformation. Masonry constructions endeavour in fact to elude the seismic action, activating a rocking motion rather than deforming with doubtful dissipating mechanisms. A strength resource of masonry structures, properly reinforced in order to avoid early local failures, consists in exhibiting rocking behaviour, until a failure condition is attained. Aim of the paper is to investigate the dynamic behaviour of masonry multi-storey walls, according to Housner's studies and properly introducing the effect of diagonal cracks, shown by typical post-earthquake cracking patterns. Cracks start from the toe of the wall piers, developing along a diagonal direction and identifying a masonry volume that remains ineffective during the development of the mechanism, without taking part with its weight to the opposing action against the overturning. Starting from the evaluation of the incipient rocking acceleration of the system, in presence of cracking of the masonry wall piers, the free and forced motions of the wall are examined. A simple constant horizontal acceleration impulse of given duration has been considered to represent schematically the seismic action. An ad hoc energy dissipation model is also specifically implemented, according to the classical Housner's approach
Collapse state of elliptical masonry arches after finite displacements of the supports
No full textIn this paper, the failure condition of elliptical masonry arches subjected to dead loads in case of
finite displacements of the supports is investigated. This is achieved by adopting the kinematic
approach of Limit Analysis and considering the deformed configuration of the structure, modelled
as a system of rigid blocks in frictional contact. At this aim, a new numerical tool for the
evaluation of the horizontal collapse displacement of the springings and of the relative thrust is
proposed. An innovative aspect of the proposed modelling consists in the definition of the collapse
condition, considering the classical attainment of a kinematic admissible mechanism and
including a check regarding the activation of sliding phenomena as well. A parametric survey is
carried out to investigate the influence of the involved parameters. Finally, to the advantage of
structural engineers, abaci of the horizontal collapse displacement and of the relative thrust are
provided
Wind strength of gothic cathedrals
No full textAim of the paper is the evaluation of the wind strength of one of the most amazing structural typology of the Middle Age, the Gothic Cathedral. Among his most significant structural problems, wisely solved by the ancient builders, there was the need to realize structures with high lateral resistance, in order to counteract the action of the wind. Deformations of the cathedral under the wind action are negligible, both in longitudinal and in transverse direction, owing the high stiffness of the structure. Wind action is therefore essentially static and it can be represented by a suitable distribution of horizontal forces. In this framework the paper evaluates the collapse wind load according to the kinematic approach of the Limit Analysis considering various failure mechanisms as, among them, the semi-global mechanism, involving only the leeward side and the global, interesting both sides of the structure. The analysis is performed making reference to a cathedral modulus similar to that of the Cathedral of Notre-Dame of Amiens, one of the most important examples of Gothic Cathedrals. The paper shows that the stone skeleton of these cathedrals is able to sustain the action of fierce winds whose intensities are larger than those prescribed by actual codes
Evaluation of the bearing capacity of fiber reinforced concrete sections under fire exposure
No full textAim of the paper is the evaluation of the bearing capacity of fiber reinforced concrete (FRC) sections, without any traditional steel reinforcement, subjected to different values of the fire duration. At this purpose, bending moment (M)-axial force (N) interaction envelopes are defined, through an analytical model based on the direct integration of the hot or residual mechanical properties of the material, throughout the member cross section. Finally, a parametric survey, specifically related to tunnel segments, with different geometries and FRC materials allows highlighting the worst (or better) scenarios
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