Investigation of Rubble-Masonry Wall Construction Practice in Latium, Central Italy

The 2016-2017 Central Italy seismic sequence severely affected existing unreinforced-masonry constructions in four regions. Those in Latium region proved the most prone to fragmentation because of an unfortunate combination of undressed natural stone units and very low lime content in mortar. Within the framework of a research project funded by the regional government, shake table tests are planned to investigate masonry disintegration as well as possible intervention techniques, as described in a companion paper. All specimens will have natural stone units retrieved from the debris in Collespada, a settlement of the municipality of Accumoli, one of the most affected by the seismic sequence. To push further the representativeness of the specimens with respect to field conditions, wall geometry, masonry fabric and mortar recipe are carefully designed. The wall thickness will be approximately equal to 0.5 m, close to average thickness surveyed in the area. Following the survey of several vertical sections of actual masonry walls, the specimens will present unconnected external leaves with a limited nucleus. Based on tests on mortar sampled from collapsed buildings, mortars will be prepared by a part of natural lime every nine parts of sand. Shear tests on sampled mortar delivered apparent cohesion and friction coefficient that are used as preliminary values of a finite-discrete element model, which can account for masonry fragmentation in dynamic non-linear analyses. The numerical model was tested under the envisioned sequence of records, belonging to the Amatrice station and related to the East component, approximately fault normal, of the two main seismic events, 24 August and 30 October, 2016

Microstructure and morphology changes in MgH2/expanded natural graphite pellets upon hydrogen cycling

Compacted mixtures based on ball-milled magnesium hydride (MgH2) have gained significant research interest as suitable materials for hydrogen storage tanks. The issue related to their stability during practical service conditions is one of paramount relevance. In this work, we investigate the microstructure and morphology of pellets obtained by the compaction of ball-milled MgH2/Nb2O5 powders mixed with expanded natural graphite. The pellets are subjected to repeated hydrogen sorption cycles to measure hydrogen storage properties and its stability with cycling. Moreover, the effect of air-exposure on the hydrogen sorption behavior is studied. Electron microscopy observations of as-prepared and cycled pellets point to a dramatic modification of the material’s microstructure upon repeated hydrogen cycling. In particular, the appearance of MgH2 particles depleted of the Nb2O5 catalyst and the formation of hollow MgO shells are highlighted. These findings are discussed by a simple model which takes into account the basic mechanisms intervening during the metal-hydride transformation in the pellet

On the determination of the mechanical properties of wind turbine blades: Geometrical aspects of line based algorithms

This paper discusses the aspects relating the geometric discretization of anisotropic wind turbine blade cross sections via line elements and the calculation of its mechanical properties. The geometrical reconstruction of the blade is done through an algorithm that reads a table that contains the representation of the aerodynamic profile of the blade as a set of connected line segments. The composite material theoretical background is based on a vector variant of the classical lamination theory embedded into a geometrically exact large deformation-small strain thin-walled beam formulation; transverse shear and out of plane warping effects are considered. The impact of the geometric reconstruction in the accuracy of the mechanical properties is studied using both rectangular and trapezoidal elements. It is found that a proper geometrical reconstruction of the cross section must be ensured to obtain small errors in the mechanical properties. It is shown that line based algorithms can give very accurate results provided the cross section geometry is adequately represented.Fil: Saravia, César Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; ArgentinaFil: Gattia, Claudio D.. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; ArgentinaFil: Ramireza, José M.. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; Argentin