1,721,124 research outputs found
Numerical Simulation of Geogrid Reinforced Adobe Walls
No full textThe paper describes the finite element model simulation of reinforced adobe walls to assess the feasibility of an innovative strengthening technique for earthen constructions, which improves the seismic performance. The retrofitting technique is based on the application of geogrids on both sides of the earthen wall. The geogrid is comprised in the mud plaster layer, which is applied to the wall surface in two steps. No additional connections are put in place, and the connection between the geogrid and the wall is granted exclusively by the mud plaster. The numerical simulation accounted for the presence of adobe blocks and clay joints, as well as for the presence of the reinforcing geogrid and of the mud plaster. The nonlinear behavior of the material was modeled with smeared cracking in tension and plasticity in compression, allowing to minimize the number of fitting material parameters. The numerical results are compared with the output from experimental tests [1] performed on almost twenty small walls without reinforcement, or with different types of geogrids available from the market. The laboratory tests included simple compression, diagonal shear, and three-point bending. The tests and the numerical simulation revealed that the retrofitting system is particularly effective from the mechanical point of view thanks to the optimal ratio between the wall and the geogrid stiffness and strength. The reinforced samples showed increased strength and greatly increased ductility, which is very promising in particular with respect to the seismic load behavior. The material compatibility between the geogrid and the mud plaster and the earthen wall is also very good, mainly due to the fact that geogrids were developed primarily for soil stabilization applications. The analyzed retrofitting system looks very promising for both the seismic improvement of existing vernacular heritage and for application in new bio-architecture building contexts
Uniaxial tensile test and fractal evaluation of softening damage in concrete
No full textIn a previous work (Carpinteri et al. 1998) the authors showed how to acquire the meso-structural characteristics of undamaged concrete-like materials by a peculiar laser equipment (Carpinteri et al. 1999). In order to extend the analysis to damaged disordered materials, a new direct tension test equipment has been developed, that minimizes flexural effects by freely rotating boundary conditions. Increasing levels of damage are obtained, after reaching the peak load, by proceeding along the descending strain-softening curve. After the desired damage level is reached, the load is removed and the specimen is cut to permit the laser acquisition of the most damaged zone. The progressive rarefaction of the effective stress-carrying cross section is described by means of fractal concepts. It is worth noting that both the fractal dimension and the measure of the stress carrying cross section decrease after the peak load, and vanish when the specimen is broken apart. Finally, a powerlaw relation is proposed for the fractal dimension of the effective cross section as a function of damage
Chapter 6: Ageing of the support
No full textIn Tunnel Maintenance: Catalogue of Behavioural Laws and Numerical Modellin
Fractal characterization of concrete damage in the strain-softening regime
No full textIn a previous work the authors showed how to acquire the meso-structural characteristics of undamaged concrete-like materials by a peculiar laser equipment. In order to extend the analysis to damaged disordered materials, a new direct tension test equipment has been developed, that minimizes exural eects by freely rotating boundary conditions. Increasing levels of damage are obtained, after reaching the peak load, by proceeding along the descending strain-softening curve. After the desired damage level is reached, the load is removed and the specimen is cut to permit the laser acquisition of the most damaged zone. The progressive rarefaction of the eective stress-carrying cross section is described by means of fractal concepts. It is worth noting that both the fractal dimension and the measure of the stress carrying cross section decrease after the peak load, and vanish when the specimen is broken apar
Numerical crack modelling of tied concrete columns under compression
No full textIn the present paper the problem of monotonically compressed concrete columns is studied numerically, accounting for transverse steel reinforcement and concrete cracking. The positive confinement effect of the ties on the core concrete is modeled explicitly and studied in the case of distributed or concentrated vertical load. The main aim is to investigate the influence of transverse reinforcement steel characteristics on the column load carrying capacity and ductility, in order to provide an evaluation about some standards requirements about the class and ductility of steel to be used for ties. The obtained results show that the influence of transverse reinforcement steel class of ductility is negligible both on the column load carrying capacity and on its ductility. Also the dissipated energy is basically unchanged. In view of these evidences, some standards requirements about the steel class of ductility to be used for ties appear to be rather questionable
Numerical analysis of the cutting interaction between indenters acting on disordered materials
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Simulazione numerica della frattura fragile nei fenomeni di contatto
No full textSi presenta una simulazione numerica dei quadri fessurativi che si osservano con maggiore frequenza nei fenomeni di contatto tra materiali fragili. Partendo da alcune evidenze sperimentali, si analizza la propagazione della frattura mediante il codice agli elementi finiti FRANC2DTM, in grado di risolvere problemi di Meccanica della Frattura Elastica Lineare in stati deformativi piani ed assialsimmetrici. Innanzitutto viene studiato il problema del contatto di Hertz, caratterizzato dalla formazione del tipico cono di frattura (Hertzian cone). Successivamente vengono considerate anche le tensioni tangenziali, responsabili dell'eventuale distacco di frammenti (chipping). Il presente studio permette di evidenziare le differenze nella traiettoria di propagazione della frattura, che risulta stabile od instabile a seconda del problema considerato. I risultati ottenuti sono presentati in forma adimensionale mettendo in luce le caratteristiche invarianti del problema. L'interesse applicativo delle simulazioni ottenute riguarda numerosi processi, in un esteso intervallo dimensionale, dal fenomeno microscopico ell'indentazione Vickers al cosiddetto problema del punzonamento a scala macroscopic
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