Browsing by Author "Dontchev D."
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Item 5-Arylisothiazol-3(2H)-one-1,(1)-(di)oxides: A new class of selective tumor-associated carbonic anhydrases (hCA IX and XII) inhibitors(2019-08-01) Cornelio B.; Laronze-Cochard M.; Miambo R.; De Grandis M.; Riccioni R.; Borisova B.; Dontchev D.; Machado C.; Ceruso M.; Fontana A.; Supuran C.T.; Sapi J.Sixteen 5-aryl-substituted isothiazol-3(2H)-one-1,(1)-(di)oxide analogs have been prepared from the corresponding 5-chloroisothiazol-3(2H)-one-1-oxide or −1,1-dioxide by a Suzuki-Miyaura cross-coupling reaction and screened for their inhibition potency against four human carbonic anhydrase isoenzymes: the transmembrane tumor-associated hCA IX and XII and the cytosolic off-target hCA I and II. Most of the synthesized derivatives inhibited hCA IX and XII isoforms in nanomolar range, whereas remained inactive or modestly active against both hCA I and II isoenzymes. In the N-tert-butylisothiazolone series, the 5-phenyl-substituted analog (1a) excelled in the inhibition of tumor-associated hCA IX and XII (Ki = 4.5 and Ki = 4.3 nM, respectively) with excellent selectivity against off target hCA I and II isoenzymes (S > 2222 and S > 2325, respectively). Since the highest inhibition activities were observed with N-tert-butyl derivatives, lacking a zinc-binding group, we suppose to have a new binding mode situated out of the active site. Additionally, three free-NH containing analogs (3a, 4a, 3i) have also been prepared in order to study the impact of free-NH containing N-acyl-sulfinamide- (-SO-NH-CO-) or N-acyl-sulfonamide-type (-SO2-NH-CO-) derivatives on the inhibitory potency and selectivity. Screening experiments evidenced 5-phenylisothiazol-3(2H)-one-1,1-dioxide (4a), the closest saccharin analog, to be the most active derivative with inhibition constants of Ki = 40.3 nM and Ki = 9.6 nM against hCA IX and hCA XII, respectively. The promising biological results support the high potential of 5-arylisothiazolinone-1,(1)-(di)oxides to be exploited for the design of potent and cancer-selective carbonic anhydrase inhibitors.Item 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.Item 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.Item Concrete and structure with recycled aggregate(2013-12-01) Li A.; Buyle-Bodin F.; Delmas Y.; Dontchev D.; Petit C.Item 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.Item 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.Item 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.