Browsing by Author "Assih J."

Now showing 1 - 7 of 7
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    Application of natural fiber composite materials in the strengthening of reinforced concrete structures
    (2020-11-02) Ivanova I.; Assih J.; Dontchev D.
    This paper presents an experimental investigation of strengthened reinforced concrete structure by bonded natural fiber composite materials. Nonetheless, the composite plates are externally constituted of a matrix based on epoxy adhesive in which the aligned continuous natural fibers are embedded. In recent years, the natural fibers are of great interest as a result of policies to reduce the negative impact on the environment. They are a renewable source, helping to capture carbon dioxide during their cultivation. Numerous technical, economic, and environmental advantages such as low cost, high strength-to-weight ratio, low density, and non-corrosive properties make them very attractive to use. The objective of this research is to assess the strengthened capacity of natural fibers. This research mainly used hemp and flax natural fibers. So, these natural fibers are an alternative to synthetic reinforcing fibers like carbon fiber or glass fiber, which are widely used in civil engineering. This article briefly presents the results of the tests carried out on concrete prismatic specimens strengthened by external bonding different composite plates based on natural fibers. The tests were presented by examining the influence of reinforcement on the ultimate capacity and the element of rigidity. The results show a significant increase in the ultimate load of the strengthened concrete prismatic specimens compared to the reference specimen. The cracking and failure modes are presented. The results show that the natural fibers are a good alternative to glass and carbon fibers.
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    Composite materials based on natural fibres applied for structural reinforcement
    (2022-01-07) Bou Abdallah G.; Ivanova I.; Assih J.; Diagana C.; Dontchev D.
    Environmental problems and environmental protection triggered a rapid development of natural fibres as sustainable materials for the reinforcement of reinforced concrete structures. Synthetic fibre polymer composite materials have been widely accepted by the construction industries as an effective external reinforcement material to rehabilitate deficiencies in existing structures. These materials have exceptional performance such as high strength to weight ratio, corrosion resistance and lightness. However, the disadvantages include high costs during manufacturing and end-of-life services, less environmentally friendly and causing adverse effects on human health. This article presents an experimental program on the use of natural fibres as reinforcement in composite materials for structural strengthening. Different types of natural fibre fabrics (hemp, flax, mixed hemp and cotton) in terms of their mechanical properties were studied. The fibre and fibre fabric sheets were tested in tension test and compared with carbon and glass fibre fabric sheet as reference. So, this study carries out the effect of natural hemp and flax fibre fabric thickness on ultimate loads of specimens. In addition, the ultimate load and stiffness of strengthened beams were investigated. In fact, the results show that the reinforcement technique allows to increase the load-bearing of strengthened structure by 8% to 35% in bending tests.
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    Concrete damaged analysis in strengthened corbel by external bonded carbon fibre fabrics
    (2015-12-22) Assih J.; Ivanova I.; Dontchev D.; Li A.
    This paper describes an experimental and theoretical analysis of strengthened damaged reinforced concrete corbel by gluing carbon fibre fabrics. The main objective of this study is to investigate the damage effect on the strengthening of reinforced concrete structures, especially on short reinforced concrete corbel and to propose an analytical model. Therefore, an experimental program was developed to evaluate the mechanical damaging effect on short corbels behaviour by using strain gauges. According to this program, five reinforced concrete corbels were tested under a three-point bending up to failure. Three of them were damaged at 45, 65 and 90 % of their ultimate load. After the specimens were repaired with carbon fibre fabrics and the loading was conducted till their failure. The fourth corbel which was not damaged. It was strengthened and tested until its collapse. The last one is the reference specimen corbel which was not reinforced. The test results with corbel specimens which were strengthened and unstrengthened are given. The significance to member performance is also explained. The measured load versus strain was too measured in the same way (with precision strain gauges) for others materials such as composite fibre fabrics, steel bar and concrete at the cross section of corbel. The study shows that the composite fibre fabrics using bonding technique could be a convenient and effective strengthening method for concrete structures. Thus, steel reinforcement and carbon fabrics played a major role in the repair of corbels. A theoretical analysis is presented describing the behaviour of strengthened damaged concrete corbel using the damage theory of reinforced concrete beams.
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    Contribution to strengthened reinforced concrete structures by externally bonded carbon fibres fabrics
    (2018-01-01) Dontchev D.; Ivanova I.; Assih J.
    The present paper reports results from an experimental investigation of the mechanical behavior of reinforced concrete structures externally strengthened by bonded carbon fibers fabrics (Carbon Fiber Reinforced Polymer or CFRP). The focus is on the local and global strain distribution, the load-carrying capacity and the mode of failure. The effect of fibers fabrics configuration and some geometrical parameters are presented. The CFRP reinforced concrete beams are subjected to four points bending. The extensometer technique based on electrical strain gauge is used to study the local behavior of the structure. This technique allows measuring the strain of steel, carbon fabrics and concrete. The effect of the same parameters on the strengthening structure local behavior is examined. The tests show better results in case of unidirectional fibers and wrapped strengthening use. The ultimate load and strain of the specimens are compared to the reference specimen. The structures cracking and the different failure modes are studied. The cracking mechanisms and the mode of failure under static loading are presented and analyzed. The results show not only an increase of more than 82 % of the load carrying capacity of the corbels and 210 % of that of the reinforced concrete beam but also improvement of their rigidity. The theoretical analysis based on the classical theory of beams and deformation compatibility relationship enables meaningful comparisons between the theoretical and the experimental results.
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    Experimental and analytical study of bio-based epoxy composite materials for strengthening reinforced concrete structures
    (2021-01-01) Assih J.; Ivanova I.
    This paper presents a new approach to strengthen reinforced concrete structures using natural fiber composites. Natural fibers are often used in civil engineering for thermal or acoustic insulation, but rarely are they employed to strengthen structures. Natural fiber composites are constituted of a matrix based on epoxy adhesive and aligned continuous fiber reinforcements. In this study, we investigate several fibers (carbon, hemp, fiberglass, and linen) in tensile and bending tests. The bending results show twice the magnification of the ultimate bending load in a strengthened specimen. The study also evaluates the stress distribution in the structure. In the case of a beam strengthened by a bonded carbon plate, the functioning of an assembly single lap and the optimal anchor length was determined by analogy. The analytical study describes the shear and peel stresses in the adhesive, composite, and concrete joints, revealing the optimum values of shear stress near the ends of the adhesive joint. The same was observed in concrete. The tests showed the influence of strengthening on the ultimate load and stiffness as well as the concentration of shear stresses at the ends of the adhesive joint.
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    Numerical simulation of shear strength in a short reinforced concrete corbel strengthened with composite material compared with experimental results
    (2018-01-01) Ivanova I.; Assih J.; Stankov V.; Dontchev D.
    This paper describes a numerical analysis carried out to assess the shear strength of strengthened short reinforced concrete corbel by using Carbon Fiber Reinforced Fabrics (CFRF). To extend the life and shear strength of the reinforced concrete structures often used technique for external bonding of composite materials. This study provides a comparison of curves obtained with numerical model and experimental curves of corbels. Results show that in general, ultimate load, crack patterns and deformation capacity were satisfactorily reproduced. The Finite element model results are successful compared and validated by experimental results.
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    Static and dynamic experimental study of strengthened reinforced short concrete corbel by using carbon fabrics, crack path in shear zone
    (2015-10-01) Ivanova I.; Assih J.
    The paper presents an experimental analysis of tracking the path of the cracks and crack growth in strengthened or repair reinforced concrete short corbels bonded by carbon fiber fabrics under static and dynamic loads. The reinforced short concrete corbel is a used precast element, for industrial buildings and structures. In fact, their functioning interestingly unconventional is compared to classical beam type elements. Then the effects of bending and shearing are combined in this case. The horizontal reinforced steel is localized to resist to tensile strength induced in bending top and a transversal strength-absorbing contribution. The introduction of carbon fiber composite in the field of Civil Engineering allows to strengthen or repair reinforced concrete structures using adhesive. So the carbon fiber material has many advantages as its low weight, flexibility, easier handling and also interesting physicochemical properties. However maintenance of civil engineering works is to protect them by ensuring better sealing or limiting corrosion. Then strengthening is to repair structures by using bonding technique to compensate their rigidity loss and limit the cracking. This allows to improve their performance and durability. Bonding of composite material in tensile zone of corbel retrieves most tensile stress and allows the structure to extend their load-bearing capacity. The local behavior of the structure is measured by means of the extensometer technique based on electrical strain gauges. This technique allowed to measure strains of steel, carbon fiber fabrics and concrete. The results of this investigation showed that strengthened reinforced concrete corbel bonded by carbon fiber fabrics can improve the ultimate load to twice and stiffens less than a third. The ultimate load, strain and displacement of the specimen are compared to reference experimental model of monotonic and cyclic applied loads. The success of strengthening depends strongly on surface preparation conditions. The cracking mechanisms and collapse modes under static and dynamic loadings are presented. The strengthened reinforced concrete short corbel behavior can be presented in three areas: overall elastic area, crack propagation area and opening of diagonal crack area.