Journal of Materials and Engineering Structures
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Reinforced Concrete Beams with Drop-in- Ends of Vertical and Inclined Reinforcement and having Pockets Loaded by In-Plane Static Forces
Full text linkThis research presents an experimental investigation on the behaviour of RC dapped end beams with loaded openings that have been strengthened initially with four different techniques including steel fibre concrete, inclined crossed bars, jacketing with steel plates and the composite section technique. Ten specimens with a rectangular opening at the midspan are tested under in-plane point load within opening. Such beams are categorized into two groups with five specimens per group. The dapped end zone of the first group is reinforced with standard vertical stirrups, while for the other groups inclined bar reinforcement has been used. Two main parameters have been considered which are the detailing of the reinforcement around the opening and the effect of inclusion of the dapped ends. The response has been discussed in terms the first cracking load, ultimate load, maximum deflection, failure modes, load-deflection curves, crack patterns, crack width, to recognize the optimum strengthening proposal of the opening. Results indicated that the modified reinforcement configurations of the dapped ends yielded better response and the ultimate load increased when adopting the composite section method in (21-23%) relative to the conventional beams. Regarding strengthening by steel SFRC method, an improvement in load capacity by (8-10%) has been observed. Whereas, strengthening with crossed inclined bars yielded an enhancement of (8.5-11%). Furthermore, using steel plates increases the load capacity by about (11-13%)
Etude de l’effet d’adhérence acier-béton sur la réponse non-linéaire des piles de pont en BA
Full text linkCet article discute de l’importance d’inclure l’effet de l’adhérence acier-béton dans l’étude du comportement non-linéaire des piles de pont en BA. La sensibilité de la réponse non linéaire à l’adhérence par glissement a été étudiée en considérant un modèle EF multifibre. Des analyses Pushover (cyclique et monotone) ont été conduites et les résultats ont été discutés en considérant différents indicateurs de performances sismiques. L’importance de ce phénomène a été également démontrée en quantifiant les différents états limites de dommages et sa contribution dans le déplacement total de la pile de pont. Les résultats indiquent que l’introduction de l’effet de l’adhérence par glissement des barres d’acier longitudinales peuvent modifier de manière significative les prédictions du comportement non-linéaire des piles de pont en BA où une surestimation de la rigidité initiale et de l’énergie de dissipation des piles de pont ont été observées. De ce fait, la prise en compte de ce phénomène dans la modélisation non linéaire des colonnes en BA est indispensable
Band Gaps of structures based on concrete-steel and concrete-molybdenum. Comparison between structures with square and hexagonal periodicities
Full text linkIn this article, a study of the frequency dispersion curves of a periodic structure was made. The cell units of the base model are made of steel cylinders coated with a rubber layer embedded in a concrete thin mat. The results show the existence of three band gaps which means that we have no propagation waves. In second step, the steel core has been substituted with molybdenum. A noticeable shift towards the low frequencies has been achieved together with an improvement in the relative widths of the band gaps. In addition, a comparison of band gaps was made between a finites two-dimensional structure with square periodicity and hexagonal periodicity. The results showed that a square periodicity of a two-dimensional structure is more favourable for the field of civil engineering wich is necessary to be in a low frequencies
Etude de la pouzzolanicité de deux argiles de Kindia (Guinée) en vue de leur utilisation dans la formulation de liant hydraulique
Full text linkThis work presents, firstly, the results of pozzolanicity tests on two varieties of clay, codified respectively ABD and ARD, taken at Débélé. In a second step, the physical properties of the mortars obtained from these two clays by substitution of cement at a rate of 20% are presented and discussed. The mechanical behaviour of the mortars shows acceptable variations with apparent densities between 1.800 and 2.090 g/cm3. The mechanical resistance is lower than that of the control mortar for hybrids based on raw clays, but those of hybrids based on calcined clays are higher than that of the control mortar beyond the 28th. These results attest to the pozzolanic character of the Débélé clays and constitute a contribution to their valorisation in the formulation of hydraulic bindersCe travail présente, dans un premier temps, les résultats d’essais de pouzzolanicité de deux variétés d’argile, codifiées respectivement ABD et ARD, prélevées à Débélé. Dans un second temps, les propriétés physiques des mortiers obtenus à partir de ces deux argiles par substitution du ciment au taux de 20 % sont présentées et discutés. Le comportement mécanique des mortiers manifeste des variations acceptables avec des masses volumiques apparentes comprises entre 1,800 et 2,090 g/cm3. Les résistances mécaniques restent inférieures à celle du mortier témoin pour les hybrides à base d’argiles brutes, mais celles des hybrides à base d’argiles calcinées sont supérieures à celle du mortier témoin au-delà du 28ème. Ces résultats attestent le caractère pouzzolanique des argiles de Débélé et constituent une contribution pour leur valorisation dans la formulation des liants hydrauliques
Reinforcement of concrete using Glass Fiber Reinforced Polymer
Full text linkThe use of composite materials such as fiber reinforced polymers in strengthening and repairing of structural elements, particularly those made of reinforced concrete, is widely spreading. Among the fiber reinforced polymers (FRP) used for concrete strengthening, GFRP because they are more ductile and cheaper than carbon fibers and can be considered as an alternative solution to repair and strengthen concrete elements. The GFRP enhance significantly the ductility and strength of concrete by forming perfect adhesive bond between the wrapping material and concrete. Present study mainly emphasizes on effectiveness of external GFRP strengthening for concrete beams and columns. Total five circular concrete columns of 320 mm in height and 160 mm in diameter, and 30 concrete rectangular beams with a section of 40 mmx40 mm and 160 mm in length. Two columns were control and the rest three columns were strengthened with three types of GFRP. For beams, fifteen of them was control and the others were strengthened by GFRP with U-shape. All the test specimens were loaded to fail in axial compression and strain for columns, and under three-point bending for beams. The test results clearly demonstrated that compared with the ordinary concrete, the axial load carrying capacity and flexural strength increase for the reinforced concrete no matter the kind of the GFRP used even if it was in different storage condition
Modelling the Viscoelastic Behavior of asphalt Concrete at the Nanoscale
Full text linkThe main purpose of this paper is to investigate the mechanical properties “hardness H and elastic modulus E” of asphalt concrete AC at the nanoscale to get its mechanical behavior comparing to the distinct behaviors of its different phases got from experimental works. AC is generally composed of coarse aggregates that have an elastic mechanical behavior, a viscoelastic or viscoplastic binder and interface transition zone ITZ. For this; as bituminous material we have used an asphalt concrete sample which is subjected to a nanoindentation simulation test using a Berkovich indenter tip with a load of 2500 µN for 10 s of loading and 10 s of unloading. AC is supposed to be a viscoelastic material; so the Prony series are introduced and different coefficients of prony are obtained from an experimental relaxation’s master curve of AC. Finite element software ABAQUS 6.13 is used to simulate this mechanical behavior where our study is carried out at a temperature of 25°C. The results showed that hardness and young’s modulus values are closer to the aggregates phase than to the fine matrix results, in other words it seems that our asphalt concretes responds of an elastic behavior at the nanoscale
Analysis of a Prestressed Sleeper for Railway Turnout under the Effect Static Load with a Unilateral Contact Model and Support Stiffness of Existing Railway Bed of a Railway Section in Vietnam
Full text linkIn the process of analyzing prestressed sleepers for turnout on elastic foundations with large lengths, authors around the world often use the one-stiffness model of Winkler or the two-stiffness model of the Filonenko-Borodich and Pasternak. Railway bed stiffness is assumed to be a constant value from the design to the end of the operating process. In this study, the authors use a one-stiffness model to simulate the interaction between the prestressed sleepers for turnout and the railway bed, which helps to describe the contact and non-contact between the prestressed sleepers of turnout and the railway bed, the phenomenon that the many traditional models do not implement yet. In addition, the railway bed stiffness included in the analysis is obtained by testing at the field of a railway section in operation in Vietnam. The authors use the finite element method and combine it with the Newton iteration method. Accordingly, the analysis results of prestressed sleepers for turnout will be more consistent with actual behavior. We need to check the actual stiffness of the foundation before it is included in the analysis because the actual stiffness of the foundation gives more accurate results during analysis
Mise en Equations des Propriétés Physiques, Mécaniques, et Thermiques des Bétons Contenant des Déchets Plastiques
Full text linkResearch on concrete containing plastic waste has made it possible to understand their behavior and to demonstrate the relevance of their use. But it is clear that equations governing the behavior of this type of concrete are lacking. In this logic, this study is in line. The objective is then, to propose formulas governing the physical, mechanical and thermal properties of concrete containing plastic waste. The proposed formulas were validated by referenced test values. In total, five hundred and twenty-four experimental and theoretical values were processed and analyzed. The experimental values were collected and analyzed and compared with the theoretical values from the proposed equations. The results obtained allowed to conclude that the proposed equations are all relevant. La recherche concernant les bétons contenant des déchets plastiques, a permis de comprendre leur comportement et à démontrer la pertinence de leur utilisation. Mais force est de constater que des équations qui régissent le comportement de ce type de béton font défaut. Dans cette logique, s’inscrit donc cette étude. L’objectif est alors, de proposer des formules régissant les propriétés physiques, mécaniques et thermiques des bétons contenant des déchets plastiques. Les formules proposées ont été validées par des valeurs d’essais référenciées. Au total, cinq cent vingt-quatre valeurs expérimentales et théoriques ont été traitées et analysées. Les valeurs expérimentales ont été collectées et analysées puis comparées aux valeurs théoriques issues des équations proposées. Les résultats obtenus ont permis de conclure que les équations proposées sont toutes pertinentes.
A Comparative Study of Life Cycle Assessment for Sustainable Concrete Mixes
Full text linkDeveloping countries need infrastructure for development thereby increasing the demand for concrete. The production of raw materials, manufacturing of concrete, and transportation process emit a large amount of greenhouse gases and particulate matters in the atmosphere which has increased energy consumption as well as global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP) impact. In the present study, a comparative Life Cycle Assessment (LCA) is performed on five types of concrete mix and two fuels like coal and agricultural waste. The controlled mixed concrete CM-O was prepared by 100% OPC and the other four types of agricultural waste concrete were prepared by partial replacement of cement with agricultural waste ash in one cubic meter concrete. Optimum replacement level of cement was obtained based on 28 days compressive strength of concrete. LCA was evaluated by using CML methodologies on Microsoft excel for Cradle - to - gate boundary system. Similarly, environmental load due to the burning of coal and agricultural waste was evaluated. The results indicated that agricultural waste concrete has the potential to decrease the environmental load of the manufacturing of concrete. The environmental load is 1701.985 kwh, 501.051kg, 4.327kg and 466.091g for energy consumption, GWP, AP, and EP respectively for one cubic meter of controlled mix concrete. The results indicated that Rice husk ash at a replacement level of 12.5% of cement has 4.3%, 10%, 7.1%, and 3.7% lesser environmental impact for energy, GWP, AP, and EP respectively when compared with controlled mixed concrete. Further, the use of agricultural waste as fuel emits very less amounts of greenhouse gases mainly CO2, SO2, and NOx, and has an overall less impact on environmental compared to coal. This study would encourage the industrialists to make decisions about the use of agricultural waste as supplementary cementitious materials (SCMs) and fuel
Experimental sensitivity analysis of sensor placement based on virtual springs and damage quantification in CFRP composite
Full text linkThis paper suggests a method for vibration sensor placement in Carbon Fibre Reinforced Polymer (CFRP) composite structures in small structure applications where the measuring instrument weight can affect the vibrational characteristics. Considering the actual weight of the beam and the actual weight of the vibrational sensor and connecting cables. We performed a set of structural vibration experiments in various sensor positions and used the experimental results as a reference through the inverse problems technique. And Finite Element Analysis (FEA) for numerical modelling, in which the sensors are modelled as an additional mass on the beam and the virtual springs are modelled with variable rigidity. We employ the Teaching-Learning-Based Optimization Algorithm (TLBO) to identify the optimal sensor placement location. The results indicate that this application can explain the effect of sensor placement. In a second application, we consider the problem of the cracked beam and the prediction of damage severity and crack depth with the help of a formulation for crack location. Results of this Application show that the proposed approach can serve in solving both problems.