Journal of Materials and Engineering Structures
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Correlation between the tribology of concrete and the rheology of the corresponding mortars
Full text linkThe present work aims to study the possibility of characterizing the pumpability of concrete from the rheology of the derived mortars, i.e. concrete mortar (CM) and concrete equivalent mortar (CEM). As concrete is a material that is heavier than mortar, it is better to carry out tests on mortar. To this end, two test campaigns are presented in this article; the first campaign concerns the formulation of admixed concrete based on two mineral additions, namely limestone fillers and blast furnace slag. The aim of this first campaign was to study the tribological behavior of the formulated concretes. In the second test campaign, the formulations of the mortars were derived from the formulations of the corresponding concretes. Afterwards, a rheological study was carried out on these mortars. Analysis of the results obtained showed that there is a good correlation between the developed concretes and their corresponding CEMs, with fairly high determination coefficients
Numerical study of the effects of crown discharge on the separation bulbs of the leading edge with low Reynolds numbers
Full text linkSurface atmospheric plasmas can act on the boundary layer of a flow along a profile. Different types of plasma actuators are currently being studied in specialized laboratories. The objectives in the aerodynamic domain can be to control the laminar-turbulent transition, the decrease in drag, the increase in lift, the reduction of noise and consumption.The object of this work is to use plasma actuators by characterizing their physical properties and their effects on flows. Two configurations were used: surface discharges with strip electrodes and wire electrodes. The ionic wind induced by these actuators is of low speed (a few m/s). This mechanical property was used to modify the boundary layer developing on a flat plate. The leading edge detachments from the profile flow have been delayed or even eliminated. The digital modeling and resolution of flow subjected to surface corona discharges, consists of a study based on the numerical simulation of the stationary behavior of a corona discharge in air at atmospheric pressure, carried out using the FLUENT software
Numerical simulation of heat losses from a slab-on-ground structure using Comsol-Multiphysics
Full text linkA transient two-dimensional numerical simulation using the COMSOL-Multiphysics software, is carried out for an experimental structure (Minnesota Experiment), and using the same thermo-physical properties of the soil and the same indoor and outdoor climatic conditions. The general heat transfer equation in unsaturated porous media has been used to simulate energy losses. A mathematical approach has also been developed in order to calculate the thermal conductivity of different materials with the aim of making them closer to real values. The main goal is to compare the results of the simulated temperatures with the values measured in-situ. An excellent correlation between the simulated temperatures and those resulting from the experimental structure was obtained. At the same time, the exhaustive analysis of heat fluxes crossing the soil-structure interface has enabled us to propose practical solutions for reducing losses through the slab-on-ground.Une simulation numérique bidimensionnelle en régime transitoire en utilisant le logiciel COMSOL-Multiphysics est effectuée pour une structure expérimentale (Minnesota Experiment), en reprenant les mêmes propriétés thermo-physiques du sol et les mêmes conditions climatiques intérieures et extérieures. L'équation générale de transfert de chaleur dans les milieux poreux non saturés a été exploitée pour simuler les déperditions énergétiques. Une approche mathématique a été également mise au point pour le calcul de la conductivité thermique des matériaux afin de les rendre plus proches des valeurs réelles dans le but de comparer les résultats des températures simulées avec les valeurs mesurées in-situ. Une excellente corrélation entre les températures simulées et celles issues de la structure expérimentale a été obtenue. En parallèle, l'analyse exhaustive des flux de chaleurs traversant l'interface sol-structure nous a permis de proposer des solutions pratiques en vue de réduire les déperditions à travers le plancher bas.A transient two-dimensional numerical simulation using the COMSOL-Multiphysics software, is carried out for an experimental structure (Minnesota Experiment), and using the same thermo-physical properties of the soil and the same indoor and outdoor climatic conditions. The general heat transfer equation in unsaturated porous media has been used to simulate energy losses. A mathematical approach has also been developed in order to calculate the thermal conductivity of different materials with the aim of making them closer to real values. The main goal is to compare the results of the simulated temperatures with the values measured in-situ. An excellent correlation between the simulated temperatures and those resulting from the experimental structure was obtained. At the same time, the exhaustive analysis of heat fluxes crossing the soil-structure interface has enabled us to propose practical solutions for reducing losses through the slab-on-ground
A Solution of Plane Stress Problem Subjected to Horizontal Shear Force by Using Polynomial Airy Stress Function
Full text linkMany structural analysis problems in civil engineering and mechanical engineering can be treated as plane stress and plane strain problems introduced in the theory of elasticity. One of the popular analytical methods to tackle plane analysis is to determine Airy stress function. In general, the Airy stress function depends on the analyzed domain and the applied loads; however, the number of problems that can be solved by employing this method is limited because of the formidable challenges of guessing trial function. In many cases, the trial Airy stress functions are selected based on the results of a simple beam model or experimental results. This paper introduces a solution of the plane stress subjected to horizontal shear forces by using a polynomial Airy stress function, in which the trail function is predicted from the results of the elementary beam theory of an equivalent model. The numerical investigation on stress distributions was presented, and it showed that although the internal shear force acting on cross-sections have not appeared, shear stress still appeared, and the shear stress diagram had both negative and positive areas
Modified Method for prefabricated vertical drain consolidation analysis
Full text linkGround improvement with the prefabricated vertical drain (PVD) has become widely employed for soft ground treatment because of its economical and efficient method. While numerous numerical and analytical methods have been derived for PVD however, it is still an extensively high demand for a simpler and more accurate method for design steps. This paper proposes a method for solving the problem of one-dimensional (1D) consolidation with prefabricated vertical drains. The current approach introduces a 1D equivalent permeability, increasing linearly with depth to perform the consolidation of soft ground improved with PVD. The analytical solutions have been carried out and verified by analyses for two cases of one-way drainage and two-way drainage for uniform soil layer. The results show that the error of excess pore pressure determined by the proposed method is less than that obtained by the simpler method of Chai and smaller than 10% compared to the theoretical solution. The paper also compares the analytical solution with the FEM by ABAQUS software. It is found that the excess pore pressures and consolidation degrees obtained by these methods are similar and close to the theory. These confirm that the introduced 1D equivalent permeability can be employed to perform the consolidation of PVD improvement by analytical and FEM methods
Evaluation of variations of coarse aggregate types on hardened properties of concrete
Full text linkVariation in coarse aggregate types, shapes, textures and means of production are known to have a profound effect on mechanical properties of concrete such as compressive and flexural strengths. Two coarse aggregates; uncrushed gravel (UG) and crushed granite (CG) were used as coarse aggregates. Coarse aggregates were partially replaced with crushed granite at the incremental rate of 20% by weight of total coarse aggregate from 0% to 100%. Mix proportion of 1:2:4 and the water-cement ratio of 0.65 were used. The concrete design targeted compressive strength of 20Mpa on the 28th day. Aggregate Crushing Value (ACV) test was conducted on various coarse aggregate combinations. Compressive strength and modulus of rupture were determined at various mix proportion of concrete containing different per-cent of coarse aggregates replacements at curing ages; 7th, 14th, and 28th days. Across curing ages, an increase in percent of crushed granite lead to an increase in compressive strength (CS) and modulus of rupture (MOR). Statistical analysis established strong positive relationship between percent of CG replacement and CS at 28th day (R2 = 0.908 p 0.01), between percent of CG replacement and MOR at 28th day (R2 = 0.832 p 0.05), and between CS at 28th day and MOR at 28th day for different mix proportions (R2 = 0.878 p 0.01)
Prevention of alkali silica reaction risks in mortars by mineral admixtures.
Full text linkCette étude expérimentale a pour but de prévenir la réaction alcali-silice (RAS) des mortiers formulés avec des granulats réactifs, où on substitue des taux volumiques de ciment allant de 10% à 50% par des additions minérales telles que le laitier granulé, la pouzzolane naturelle et la fumée de silice. Leur efficacité à contrer les effets néfastes de la RAS, tel que les variations pondérales et dimensionnelles, la largeur et la densité des fissures et les pertes des performances mécaniques ont été étudiés.Les résultats obtenus montrent que le taux et la nature de l'addition influent sur leur efficacité. Pour le laitier granulé et la pouzzolane naturelle le taux idéal est 30%, pour la fumée de silice le taux 10%semble efficace à contrer les effets néfastes de la RAS. Cette efficacité est assurée par la réaction pouzzolanique favorisée par la haute température de l'essai et l'alcalinité du système.The experimental study aims to prevent the alkali-silica reaction (ASR) of mortars made with reactive aggregates, where the volume rates of cement ranging from 10% to 50% are substituted by mineral admixtures such as Granulated Slag, Natural Pozzolan and Silica Fume. Their effectiveness in countering the ASR adverse effects; such as weight and dimensional variations, the width and density of cracks and mechanical performance losses was studied.The results obtained show that the rate and the nature of the mineral admixtures influence their effectiveness, for Granulated Slag and Natural Pozzolan the ideal rate is 30%, for Silica Fume the 10% rate seems effective in countering ASR adverse effects. This effectiveness is ensured by the pozzolanic reaction favored by the high temperature of the test and the alkalinity of the system
Numerical simulation and reliability of behaviour until the rupture of reinforced concrete spacial structure members with circular cross section
Full text linkNumerical simulation of simple and composed bending behaviour of reinforced concrete spatial structure elements with circular cross section in the field of nonlinear elasticity, require a particular modeling’s technique of the cross section shape by a subdivision of the latter into trapezoids to best approximate the contour of the cross section. The input and output parameters of the materials behaviour modeling are simulated by random and deterministic variables. The present study aims at proposing a technique of the behaviour’s simulation up to failure taking into account the material non-linearity on the reinforced concrete structural elements with a circular cross section; a comparison was made between our simulation results and the experimental results. On the other hand, a numerical method has been modeled which makes it possible to estimate the reliability and the probability of failure of our simulation. To validate this modeling, we performed another comparison of the results obtained from our mechanical model by a Monte Carlo simulation with a reliable Hasofer-Lind metho
Evaluation of Mechanical Properties and Chemical Composition of Some Selected Steel Reinforcements Used in Nigeria
Full text linkMechanical properties and chemical composition of some selected steel reinforcement bars used for construction works in Nigeria were investigated. Six nominal sizes of bars from four selected brands, including: Real steel reinforcing pty Limited, code name Red; Phoenix steel mills, code name White; Pulkit alloy and steel limited, code name Blue; and African foundries limited, code name Black were evaluated. The tensile test was carried out at the mechanical engineering department, University of Ilorin using Universal Testing Machine (UTM) while the chemical compositions of the steel samples were analyzed using optical emission spectrometer at the laboratory of African foundries limited, Ikorodu Lagos State. The results obtained were compared with BS 449:2005 +A3:2016 standard provision. The outcome of the study showed that 70.8 % of the tested steel bars failed the characteristic tensile strength test, though with a very good percentage elongation satisfying the required specification. Chemical composition tests revealed that most of the failed samples contained low carbon content or excess phosphorus composition plus other impurities.
Rapid Seismic Vulnerability Assessment of Buildings in the Old Algiers
Full text linkThe selection of an appropriate seismic vulnerability method to evaluate buildings stock in urban area depends essentially on the available information. Information about buildings can be obtained essentially from field visual inspection. In this context, rapid visual procedure to collect buildings data can be used to identify vulnerable buildings based their structural characteristics. In this study, which aims to evaluate the seismic vulnerability of existing buildings in the old part of Algiers (Algeria), including Casbah and Bab El Oued areas, buildings data has been collected using rapid visual exterior examination. Then, with the main purpose to evaluate the physical damage and its relationship with the seismic intensity, empirical method using the vulnerability index, previously developed during the European project Risk-UE, is used. Results and conclusions of this work could be useful to define appropriate measures to upgrade seismic performance of existing buildings