Hydro-Mechanics Coupling on Rammed Earth Material: Drying Experiment at Structural Scale

Rammed earth structures are very sensitive to hydric conditions. Experimental studies have been undertaken to understand the link between liquid water transfer and mechanical behavior at structural scale. This study was done on a prismatic rammed earth sample of 15cm x 15cm x 45cm, structured as a wall element with several layers. Samples were subjected to one dimensional drying in an indoor environment. Humidity and temperature sensors were placed on each layer inside the sample. The kinetic of drying was monitored by continuous weighing the sample and humidity measurement at a regular interval. Results of water content evolution suggest that samples dry in two stages; the first stage is associated with relatively high evaporation flux of 13.88 g m-2h-1 while the second stage has very low flux of moisture evaporation. Unconfined compressive strength was performed in drying samples after 0, 2, 6 and 8 weeks of drying. In parallel, digital image correlation was used to determine the stiffness of samples. Results show an increase in compressive strength by the rate of 98 kPa per week in the first two weeks, then this rate reduces to 23 KPa per weeks after 8 weeks. These experimental results will allow to enhance the 3D hydro mechanical numerical model developed in the laboratory.

A two-level macroscale continuum description with embedded discontinuities for nonlinear analysis of brick/block masonry

A great proportion of the existing architectural heritage, including historical and monumental constructions, is made of brick/block masonry. This material shows a strong anisotropic behaviour resulting from the specific arrangement of units and mortar joints, which renders the accurate simulation of the masonry response a complex task. In general, mesoscale modelling approaches provide realistic predictions due to the explicit representation of the masonry bond characteristics. However, these detailed models are very computationally demanding and mostly unsuitable for practical assessment of large structures. Macroscale models are more efficient, but they require complex calibration procedures to evaluate model material parameters. This paper presents an advanced continuum macroscale model based on a two-scale nonlinear description for masonry material which requires only simple calibration at structural scale. A continuum strain field is considered at the macroscale level, while a 3D distribution of embedded internal layers allows for the anisotropic mesoscale features at the local level. A damage-plasticity constitutive model is employed to mechanically characterise each internal layer using different material properties along the two main directions on the plane of the masonry panel and along its thickness. The accuracy of the proposed macroscale model is assessed considering the response of structural walls previously tested under in-plane and out-of-plane loading and modelled using the more refined mesoscale strategy. The results achieved confirm the significant potential and the ability of the proposed macroscale description for brick/block masonry to provide accurate and efficient response predictions under different monotonic and cyclic loading conditions.

PEDAGOGIA DECOLONIAL PSICODRAMÁTICA

Pedagogical practice focused on the exclusive cognitive assimilation of concepts has been limited in the effect of improving the understanding of Decolonial Critical Theories. Even though these theories represent facts of a structural scale, and thus of a high level of abstraction, we presuppose that it is necessary to bring them closer to the students’ experiences so that they can be better decoded. This allows students to improve their critical assimilation and their personal and citizen position taking. There are several pedagogical possibilities with this assumption, but in this research, we problematize: can J.L. Moreno’s psychodramatic method help to develop decolonial pedagogical practices? The basis of this article was the development of a university extension project, with the participation of students and teachers at Universidade Federal do Rio Grande do Sul (2018–2019), from which this article lists reflections on: (1) potentials of the method; (2) role of the teacher; (3) students’ perceptions; (4) challenges of the method.

Sensitivity of Ultrasonic Coda Wave Interferometry to Material Damage—Observations from a Virtual Concrete Lab

Ultrasonic measurements are used in civil engineering for structural health monitoring of concrete infrastructures. The late portion of the ultrasonic wavefield, the coda, is sensitive to small changes in the elastic moduli of the material. Coda Wave Interferometry (CWI) correlates these small changes in the coda with the wavefield recorded in intact, or unperturbed, concrete specimen to reveal the amount of velocity change that occurred. CWI has the potential to detect localized damages and global velocity reductions alike. In this study, the sensitivity of CWI to different types of concrete mesostructures and their damage levels is investigated numerically. Realistic numerical concrete models of concrete specimen are generated, and damage evolution is simulated using the discrete element method. In the virtual concrete lab, the simulated ultrasonic wavefield is propagated from one transducer using a realistic source signal and recorded at a second transducer. Different damage scenarios reveal a different slope in the decorrelation of waveforms with the observed reduction in velocities in the material. Finally, the impact and possible generalizations of the findings are discussed, and recommendations are given for a potential application of CWI in concrete at structural scale.

Sensitivity of Ultrasonic Coda Wave Interferometry to Material Damage - Observations from a Virtual Concrete Lab

Ultrasonic measurements are used in civil engineering for structural health monitoring of concrete infrastructures. The late portion of the ultrasonic wavefield, the coda, is sensitive to small changes in the elastic moduli of the material. Coda Wave Interferometry (CWI) correlates these small changes in the coda with the wavefield recorded in intact, or unperturbed, concrete specimen to reveal the amount of velocity change that occurred. CWI has the potential to detect localised damages and global velocity reductions alike. In this study, the sensitivity of CWI to different types of concrete mesostructures and their damage levels is investigated numerically. Realistic numerical concrete models of concrete specimen are generated and damage evolution is simulated using the discrete element method. In the virtual concrete lab, the simulated ultrasonic wavefield is propagated from one transducer using a realistic source signal and recorded at a second transducer. Different damage scenarios reveal a different slope in the decorrelation of waveforms with the observed reduction in velocities in the material. Finally, the impact and possible generalizations of the findings are discussed and recommendations are given for a potential application of CWI in concrete at structural scale.

Multi-scale semi-analytical model for fatigue life prediction of trans-tibial prosthetic sockets

The trans-tibial socket is an essential component of the prosthesis that connects it to the residual limb. Socket misalignments and permanent deformations reduce the comfort of the amputee. In order to forestall such issues, sufficient information about the socket lifespan needs to be acquired, which is fairly difficult given the lack of calculation methods that estimate the fatigue life in the literature. In this paper a semi-analytical model is proposed based on experimental results. It highlights the effects of the amputee average daily walking time on the socket fatigue life. A proportionality relationship is demonstrated linking the Burgers model parameters at the structural scale to those at the macroscopic scale. Hence, it becomes possible to evaluate the permanent deformation that induces a misalignment in the socket. These results are useful for the designers to predict the fatigue life of the socket, and also for clinicians to monitor the mechanical degradation of the trans-tibial socket and schedule maintenance or replacement.

Analogue modelling of strike-slip tectonics from basin to structural-scale comparing silica sand and new rock-analogue materials

<p>Strike-slip fault zones commonly display complex 3D geometries, with high structural variability along strike and with depth and their architecture and evolution are difficult to analyse. In this regard, analogue modelling represents a powerful tool to investigate the structural, kinematic and mechanical processes in strike-slip fault systems with variable scales. In detail, dynamically scaled experiments allow the direct comparison between model and nature. The geometrical scale factor defines the model resolution, in terms of model/prototype length equivalence, and depends on the physical properties of prototype and model material. Therefore, the choice of the analogue material is critical in scaled analogue experiments.<br>Granular materials like dry silica sand are ideal for the simulation of upper crustal deformation processes due to similar non-linear strain-dependent deformation behaviour of granular flow and brittle rock deformation. Comparing the geometrical scaling factor of the common analogue materials applied in tectonic models, we identified a model resolution gap for the simulation of fault-fracture processes corresponding to the structural scale (1 m – 100 m) observed in fault zones and damage zones in outcrops, field studies or subsurface well data. We developed a new Granular Rock-Analogue Material (GRAM) for the simulation of fault-fracture processes at the structural scale. GRAM is an ultra-weak sand aggregate composed of silica sand and hemihydrate powder capable to deform by tensile and shear failure under variable stress conditions. Based on dynamical shear tests, the new GRAM is characterised by a similar stress-strain curve as dry silica sand and has a geometrical scaling factor L<sup>*</sup>= L<sub>model</sub>/L<sub>nature</sub> = 10<sup>-3</sup> (1 cm in model = 20 m in nature).<br>We performed strike-slip experiments at two different length scales, applying as model material dry silica sand and the new GRAM. Digital Image Correlation (DIC) time-series stereo images of the experiments surface allowed the comparison of the developed structures at different stages of dextral displacement above a single planar basement fault. The analysis of fractures localisation and growth in the strike-slip zone with displacement and strain components enabled the comparison of the different structural styles characterising dry silica sand and GRAM models. The application of the developed GRAM in scaled experiments can provide new insights to the multi-scale investigation of complex deformation processes with analogue models. </p>