The effect of density on the delicate balance between structural requirements and environmental issues for AAC blocks: An experimental investigation

Among other construction materials, Autoclaved Aerated Concrete (AAC) offers several advantages to face the pressing need to build more sustainable and energy-efficient buildings. From the building side, the low thermal conductivity of AAC allows the realization of energy-efficient building envelopes, with interesting savings in terms of heating and cooling processes. The equilibrium between structural performances (related to safety issues) and energy efficiency requirements is, however, very delicate since it is strictly related to the search for an “optimum” material density. Within this context, this work discusses the results of wide experimental research, showing the dependency of the most important mechanical properties (compressive strength, elastic modulus, flexural strength and fracture energy) from density, as well as the corresponding variation in thermal conductivity. In order to identify the better compromise solution, a sort of eco-mechanical index is also defined. The big challenge for future researches will be the improvement of this eco-mechanical index by working on pore structure and pore distribution within the material without significantly reducing the density and/or by improving the strength of the skeleton material

Non-orthogonal Theory of Polarons and Application to Pyramidal Quantum Dots

We present a general theory for semiconductor polarons in the framework of the Froehlich interaction between electrons and phonons. The latter is investigated using non-commuting phonon creation/annihilation operators associated with a natural set of non-orthogonal modes. This setting proves effective for mathematical simplification and physical interpretation and reveals a nested coupling structure of the Froehlich interaction. The theory is non-perturbative and well adapted for strong electron-phonon coupling, such as found in quantum dot (QD) structures. For those particular structures we introduce a minimal model that allows the computation and qualitative prediction of the spectrum and geometry of polarons. The model uses a generic non-orthogonal polaron basis, baptized the "natural basis". Accidental and symmetry-related electronic degeneracies are studied in detail and are shown to generate unentangled zero-shift polarons, which we consistently eliminate. As a practical example, these developments are applied to realistic pyramidal GaAs QDs. The energy spectrum and the 3D-geometry of polarons are computed and analyzed, and prove that realistic pyramidal QDs clearly fall in the regime of strong coupling. Further investigation reveals an unexpected substructure of "weakly coupled strong coupling regimes", a concept originating from overlap considerations. Using Bennett's entanglement measure, we finally propose a heuristic quantification of the coupling strength in QDs.Comment: 17 pages, 11 figures, 3 table

Role of floor diaphragms on the seismic response of reinforced concrete frames

In existing Reinforced Concrete (RC) framed buildings, floor structural components (i.e. RC topping and joists) may play a crucial role in the seismic performance of the structure. The interaction between floor diaphragms and seismic-resistant frames can lead to different effects, depending on the relative stiffness and resistance of the elements belonging to the structures and on the adopted construction details. In this work, these aspects are deepened with reference to the institute “A. De Gasperi – R. Battaglia”, located in Norcia, Italy, chosen as case study. The seismic response of the building is investigated through pushover analyses by adopting a multi-layered shell element approach, where the mechanical nonlinearity is evaluated by using the PARC_CL 2.1 crack model, implemented as user subroutine in Abaqus FE package. The obtained results highlight that the modelling of the diaphragm increases the flexural capacity of the beams, so determining an increase of the seismic global response for frames characterized by ductile failure modes. The modelling of diaphragms may also alter beam-column strength hierarchy and stresses’ magnitude in beam-to-column joints, leading to anticipated brittle failures, that cannot be detected through the modelling of the bare fram

Editorial. Sport in the Context of Migration and Health Crises

Recent crises, from the economic and migratory to the recent COVID-19 pandemic, have dramatically affected all areas of individual and collective life – and sport and physical activity are no exception. The main aim of this special issue is to bring researchers interested in sports and physical activity to propose their works. The focus of this special issue lays in the new challenges that sociology of sports and physical activity have to face to understand these new complex scenarios, the main issues we had to face, the successes, the criticalities and the lessons learned

Time-dependent seismic fragility curves for existing RC core-wall buildings exposed to corrosion

This work aims at investigating the seismic response of existing reinforced concrete core-wall buildings with corroded bars erected in the marine environments, with the main focus on the dependency of seismic fragility curves on aging and degradation effects caused by environmental actions. The structural capacity is predicted by nonlinear finite-element analyses, where the effect of chloride corrosion is implemented within the framework of PARC_CL_2.1 crack model. The proposed methodology is applied to a pre-code six-story reinforced concrete (RC) building with moment-resisting (MR) frames and an internal core assumed as a testbed. For a given exposure class, pushover analyses are performed for different ages of the building. Time-dependent fragility curves are then obtained through a procedure based on incremental static analysis. Different corrosion scenarios are assessed by considering deterioration effects applied either on the sole RC walls or on both walls and columns. The obtained results highlight that time-dependent fragility curves are strongly affected by corrosion, therefore the date of construction should be considered in seismic risk mapping, not only for evaluating the effect of obsolete standard codes used in the design but also in terms of damage induced by aging and deterioration

Experimental and Numerical Assessment of Flexural and Shear Behavior of Precast Prestressed Deep Hollow-Core Slabs

Abstract The paper presents the results of flexural and shear tests up to failure on full-scale hollow-core slabs (HCS) having a depth of 500 mm. A detailed non-linear 2D finite element model is also developed to predict the stress distribution and crack pattern within the slabs, providing a well match with experimental results. Experimental and numerical results are compared with analytical calculations provided by Product Standard EN 1168, highlighting the inaccuracy of technical regulations in predicting shear behavior. The proposed numerical procedure is instead viable and sound for the design and the strength assessment of HCS, and can be extended easily to the analysis of whole floor systems

Experimental and numerical assessment of flexural and shear behaviour of precast prestressed deep hollow-core slabs

The paper presents the results of flexural and shear tests up to failure on full-scale specimens having a depth of 500 mm. A detailed non-linear 2D finite element model is also developed to predict the stress distribution and crack pattern within the slab, providing a well match with experimental results. Experimental and numerical results are compared with analytical calculations provided by Product Standard EN 1168, highlighting the inaccuracy of technical regulations in predicting shear behavior. The proposed numerical procedure is instead viable and sound for the design and the strength assessment of HCS, and can be extended easily to the analysis of whole floor systems

A transversal educational proposal for prospective primary teachers: The theme of Time

Time is a transversal topic that plays a fundamental role in our every-day experience and represents a natural conceptual bridge between common sense ideas and scientific knowledge. Two classes of Prospective Primary Teachers (PPTs) at the Universities of Udine and Verona were introduced to the theme of Time in a formative intervention organized into a) the discussion of various educational and multidisciplinary approaches aimed to deal with different aspects of Time and b) the exploration/experimentation of various instruments for time measurement. In this work, we study and compare the learning outcomes in terms of planning and implementation of educational projects built by PPTs following two different Rubrics

High-resolution Rayleigh-wave velocity maps of central Europe from a dense ambient-noise data set

We present a new database of surface wave group and phase-velocity dispersion curves derived from seismic ambient noise, cross-correlating continuous seismic recordings from the Swiss Network, the German Regional Seismological Network (GRSN), the Italian national broad-band network operated by the Istituto Nazionale di Geosica e Vulcanologia (INGV). To increase the aperture of the station array, additional measurements from the Mediterranean Very Broad-band Seismographic Network (MedNet), the Austrian Central Institute for Meteorology and Geodynamics (ZAMG), the French, Bulgarian, Hungarian, Romanian and Greek stations obtained through Orfeus are also included. The ambient noise, we are using to assemble our database, was recorded at the above-mentioned stations between 2006 January and 2006 December. Correlating continuous signal recorded at pairs of stations, allows to extract coherent surface wave signal travelling between the two stations. Usually the ambient-noise cross-correlation technique allows to have informations at periods of 30 s or shorter. By expanding the database of noise correlations, we seek to increase the resolution of the central Europe crustal model. We invert the resulting data sets of group and phase velocities associated with 8-35 s Rayleigh waves, to determine 2-D group and phase-velocity maps of the European region. Inversions are conducted by means of a 2-D linearized tomographic inversion algorithm. The generally good agreement of our models with previous studies and good correlation of well-resolved velocity anomalies with geological features, such as sedimentary basins, crustal roots and mountain ranges, documents the effectiveness of our approac