External Composite Reinforcement Research Articles

ПРОЧНОСТЬ НОРМАЛЬНЫХ И НАКЛОННЫХ СЕЧЕНИЙ ИЗГИБАЕМЫХ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ, ПОВРЕЖДЕННЫХ КОРРОЗИЕЙ И УСИЛЕННЫХ ВНЕШНИМ КОМПОЗИТНЫМ АРМИРОВАНИЕМ

The study is focused on the development of a methodology for calculating the strength of normal and inclined sections of bending reinforced concrete elements that have been exposed to corrosion and reinforced with external composite reinforcement. The study examined concrete structures exposed to an aggressive chloride environment that causes corrosion. The use of a diachronic model of deformation of corrosion-damaged elements made it possible to take into account changes in the mechanical properties of materials during corrosion and to make calculations based on analytical dependencies. Taking into account the external polymer-composite reinforcement helped to improve the strength characteristics of damaged elements. The use of the iterative Picard method ensured the accuracy of calculations. The results of the study showed that the proposed method effectively evaluates the strength of bending reinforced concrete elements subject to corrosion. Taking into account changes in the characteristics of materials and the impact of an aggressive environment ensures high accuracy and reliability of calculations. The use of external reinforcement helps to increase the stability and durability of structures. The developed method is an important tool for improving the operational reliability and extending the service life of reinforced concrete structures exposed to aggressive environments.

Computational and Experimental Substantiation of Strengthening Reinforced Concrete Structures with Composite Materials of Power Plants under Seismic Action

In Russia, a significant number of power facilities built in the 1960s and 1970s are located in regions where seismic effects were revised upward. This has led to an increase in the seismicity of the sites of facilities’ locations by magnitude 1–2 (MSK-64) in comparison with the data of design documentation. During the long-term operating period of power facilities, the load-bearing capacity of building structures, as a rule, decreases. This article presents the results of computational and experimental studies of reinforced concrete structures of thermal power plants and hydroelectric power plants for seismic effects in the range of magnitude 4–10 (MSK-64). The computational studies were carried out using ANSYS 16.0 software, and experimental studies were carried out on stands modeling seismic impacts with the help of hydraulic cylinders. The results of the studies showed that cracking of reinforced concrete structures without strengthening occurs at magnitude 6.0 (MSK-64) of seismic impact, and destruction occurs at magnitude 7.5. Thus, the seismic resistance of structures without reinforcement does not meet the requirements for seismic resistance, and strengthening is required. This study considers a variant of strengthening based on external composite reinforcement with CFRP. It is shown that the strengthening of structures with composite material increases their earthquake resistance up to magnitude 9–10 (MSK-64). This article presents recommendations on the CFRP strengthening of building structures of power facilities, both after receiving damage under seismic impact and in a planned manner to increase seismic resistance. The novelty of this work lies in the fact that quantitative results of increasing the seismic resistance of structures depending on the placement and number of layers of composite material are given.

Stress-strain modelling for a composite reinforced concrete beam

The study is aimed at the features of modeling the stress-strain state of a concrete beam, reinforced with two types of fibrous composites. The necessity of strengthening existing reinforced concrete structures can be caused by the reconstruction or technical re-equipment, which often entails an increase in the load on the load-bearing structures of buildings and facilities, as well as during the elimination of the consequences of factors that led to a decrease in the bearing capacity or a failure of loadbearing structures. In order to study the applicability of the model, we analysed the results, obtained during bending and axial compression tests of T-section reinforced concrete beam specimens with welded frame reinforcement that were in operation and the results of a numerical study in a LIRA software suite. The stress-strain state of specimens was modelled in a nonlinear formulation using the finite element method. The conducted analysis and theoretical studies have shown the applicability of models, developed based on a limited test database, unclear, especially with regard to a wide range of compression coefficients, while the results of modeling the behavior of reinforced concrete beams have demonstrated sufficient accuracy for applying in the strengthening design using external composite reinforcement.

ИССЛЕДОВАНИЕ НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ ПЕРЕМЫЧЕК ГАЗОБЕТОННЫХ СОСТАВНЫХ

In this paper, the authors study the stress-strain state of composite jumpers made of aerated concrete blocks with steel reinforcement rods and external composite reinforcement when working in bending. Rod reinforcement of jumpers is carried out by inserting steel reinforcing bars into the body of aerated concrete in the longitudinal and transverse directions. Composite reinforcement is performed with carbon fiber tapes in the stretched edge of the element over the entire width, as well as parts of tapes on the flange sides of the aerated concrete block at the vertical seam or in the center of the element. The test results are assessed by comparing the strength of the normal section and the deformability of aerated concrete bending jumpers, the effectiveness of gluing carbon fiber tapes and aerated concrete, and the optimal use of various types of reinforcement. It has been established that external composite reinforcement at a load of up to 60% of the breaking load reduces the deformability of aerated concrete bending elements due to an increase in flexural rigidity, and at a load of more than 60% due to a change in the design scheme. Jumpers with rod reinforcement have a brittle nature of destruction, while those with external composite reinforcement fail plastically. In general, the load-bearing capacity of composite aerated concrete jumpers reinforced with external composite reinforcement is sufficient to withstand operational loads

ПРОГРАММА И МЕТОДИКА ЭКСПЕРИМЕНТАЛЬНЫХ ИССЛЕДОВАНИЙ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ С ВНЕШНИМ АРМИРОВАНИЕМ КОМПОЗИТНЫМИ МАТЕРИАЛАМИ ПРИ ИЗГИБЕ С КРУЧЕНИЕМ

External reinforcement of reinforced concrete structures with composite materials is successfully used for strengthening of damaged elements. At the same time, torsion with bending of such reinforced concrete structures is poorly studied and requires experimental and theoretical investigation. The scientific literature presents the results of the study of strength and deformability in bending with torsion of reinforced concrete elements of different cross-sectional shapes under static and dynamic loads, elements of composite cross-section. For reinforced concrete structures strengthened with external reinforcement by composite materials, such studies were carried out only for bending elements. The authors have developed a program and methodology of experimental studies of such structures. The results of experimental investigations according to the proposed methodology will allow us to verify the assumed design model, the working assumptions put in its basis and reveal the regularities of deformation of reinforced concrete structures with external composite reinforcement under bending with torsion.

Experimental studies of reinforced concrete beams with external reinforcement of the tensioned face using composite fabrics

The object of the study is reinforced concrete beams that are reinforced with technical polyamide (kapron) fabric produced by Branch “Khimvolokno Plant” JSC “Grodno Azot”, and fiberglass, manufactured by JSC “Polotsk-Steklovolokno”. The relevance of the stems from the need to obtain and study experimental data of the load-bearing capacity, fracture pattern, crack resistance and cracking of reinforced concrete beams reinforced with composite fabrics, since the topic of restoring the load-bearing capacity of reinforced concrete structures or their strengthening is currently very relevant. Reinforcement of bent reinforced concrete structures with composite fabrics allows using fabrics along the outer edges of the structure, as they are resistant to the external environment and are not subject to corrosion, and represent external composite reinforcement, which, together with metal reinforcement, perceive tensile forces. The most common system for the restoration of reinforced concrete structures is currently the system of external reinforcement of carbon tapes, but the use of this material is limited by high cost. The aim of the study is to experimentally confirm the possibility of effective use of technical polyamide (kapron) fabric, produced by Branch “Khimvolokno Plant” JSC “Grodno Azot”, and glass fabric, produced by JSC “Polotsk-Steklovolokno”, to strengthen the stretched face of reinforced concrete bent structures. Two reinforcement options are presented: gluing horizontal tapes along the entire length on the lower stretched face and the device of a U-shaped clip of fabrics in the stretched zone. Experimental studies have shown that the external reinforcement of the stretched zone with technical polyamide (kapron) fabric produced by Branch “Khimvolokno Plant” JSC “Grodno Azot”, and fiberglass manufactured by JSC “Polotsk-Steklovolokno” change the nature of destruction, increase load-bearing capacity of reinforced concrete beams by 16–38 % in depending on the material and method of reinforcement, affect the crack resistance and crack formation. The results of experimental studies made it possible to solve an important applied problem of the effective use of these composite materials as external reinforcement of the tension face of bending reinforced concrete beams.

ПРЕДВАРИТЕЛЬНОЕ ОПИСАНИЕ РАБОТЫ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ С ВНЕШНИМ АРМИРОВАНИЕМ КОМПОЗИТНЫМИ МАТЕРИАЛАМИ ПРИ ИЗГИБЕ С КРУЧЕНИЕМ

The calculation methods of reinforced external reinforcement elements when working on torsion are considered succinctly in available sources and current regulatory documents. This article discusses a number of existing proven methods for calculating reinforced concrete bendable elements with external composite reinforcement, including when working with torsion. The necessity of introducing into the existing calculation dependences of the prerequisites for substantiating the behavior of reinforced concrete bendable elements, including those with external composite reinforcement, when working in a complex stress-strain state is described. The cases of occurrence of additional torsional forces in the conditions of classical variants of loads and impacts on the element are considered. A description of the work of reinforced concrete elements with external reinforcement with composite materials during bending with torsion is proposed. The main provisions of the work of reinforced concrete structures in bending with torsion are given. The main limiting states are presented. An assumptions are made about the possible presence of additional limiting states of reinforced concrete elements with external reinforcement with composite materials. A variant of the condition of proportionality of longitudinal relative deformations for reinforced concrete elements with external reinforcement with composite materials during bending with torsion is proposed.

Proposals for Determining the Relative Deformations Design Value of ε<sub>b3</sub> Concrete in Volumetric Deformation Conditions

The article presents the studies’ results on the deformability and strength of reinforced concrete racks reinforced with composite materials with the characteristics stretching beyond the limits established by the norms of Russia, namely: the λh structures flexibility exceeding the value 15, the ratio of the cross-section sides equal to 1.5 and the eccentricity of the load application e0 exceeding 0.1h. The results of the tested racks calculations are analyzed according to BC 164.1325800.2014, which in some cases confirmed the inexpediency of using composite materials. However, according to the results of our experiment, an increase in the strength of a number of racks with the characteristics that go beyond the recommended standards was found. The purpose of this study is to check the methodology for calculating Russian norms for the compressed reinforced concrete elements, the parameters of which are outside the limits recommended by the norms, to develop proposals for improving the calculation based on the obtained experimental data and to determine the concrete deformability effect on the change in bearing capacity. The article discusses flexible struts, reinforced with composite materials, located in the transverse direction. The experimental data results on the deformability of concrete and the strength of struts reinforced in the transverse direction are presented. The calculation methodology, compiled in accordance with Russian standards, the calculation results of which are the theoretical values ​​of the deformability of concrete and the strength of the racks, is considered. After comparison, a significant underestimation of the theoretical strengths and a mismatch in the struts’ concrete deformations were revealed. It was found that the change in compressive deformations of concrete depends on the external composite reinforcement. Theoretical values , calculated according to the current standards, have significant discrepancies with the experimental ones. Based on the experiments’ results analysis, in the methodology of norms for calculating the ultimate compressive deformations of concrete the suggestions that take into account the type and percentage of composite reinforcement and ensure a good agreement between experimental and theoretical values have been made. After the introduction of the coefficient into normative calculation, new data on the theoretical strength of the struts were obtained, which showed significantly better convergence with the experimental data.

The beams with composite reinforcement inclined sections’ finite element modeling operation results comparison with the results of the laboratory samples’ tests

The results of a numerical experiment are presented, within the framework of which finite element modeling of the reinforced concrete beams support sections with external composite reinforcement beams inclined sections operation was carried out, as well as their comparison with the results of an experiment carried out on real laboratory samples, similarly reinforced on the support areas by external composite U-shaped cross clamps. The strength of inclined sections of both real laboratory specimens and their design models was considered. Both numerical and real experiments were carried out at three values of the shear fracture span: 1.5h0; 2.0h0 and 2.5h0. The obtained results of the numerical experiment are compared with the results of laboratory tests on beams in order to analyze the accuracy of the calculation results and to find the optimal method for modeling and taking into account the external composite reinforcement clamps in the design models that would most accurately reflect their contribution to the operation of the inclined section of bent reinforced concrete elements. For the numerical experiment, the method of finite element modeling of samples was used. An assessment of the method used for computational modeling of the operation of inclined sections reinforced with external composite reinforcement is given.

Strengthening of tensile zone of the reinforced concrete beams with composite fabrics

A fabric, tapes, that are glued to the outer tensile surface, which are considered as the external composite reinforcement with tensile steel reinforcement, are currently used to strengthen reinforced concrete beams. The results of the experimental studies presented in this article have shown the possibilities of effective application of technical polyamide (nylon) fabric produced by «Khimvolokno Plant» JSC «Grodno Azot», and glass fabrics, produced by JSC «Polotsk-Steklovolokno» for strengthening the reinforced concrete beams. Experimental studies have shown that the external reinforcing of the tensile zone with technical polyamide (nylon) fabric and fiberglass changes the beam failure mode, increases the bearing capacity of reinforced concrete beams in comparison with beams without strengthening by 16% – 38%, depending on the material and the method of strengthening.

To the Issue of Strengthening the Monolithic Reinforced Concrete Slab with Carbon Canvases

The main issue of the study is the modern ways to improve the bearing capacity of building structures. As one of these methods may be strengthening composite materials. Structural degradation of reinforced concrete structures is largely due to their composite base. The aim of the study is a systematic integrated approach to solving the problem of improving the reliability of structures through the use of composite materials. The main advantages and disadvantages of composites are considered. Their classification by type of reinforcing element is given. The main areas of application of composites in construction – in the composition of plastics, concrete, aluminum panels. Approbation of methodical provisions is carried out by calculation of a reinforced concrete plate (δ=0,3 m) in the program complex of the SCAD PC. The gain calculation was performed by the finite element method. The purpose of the calculation was to observe the stress-strain state of the plate before and after its strengthening, to check the correctness of the external composite reinforcement. The calculation results showed that in the case of composite reinforcement in the plate there is a decrease in vertical deformations (about 1.1%) and tensile stresses (1.5%). Conclusions: the results show the feasibility of using composite materials to improve the bearing capacity of building structures.

ПОЛЕ НАПРАВЛЕНИЙ ТРЕЩИН В ЖЕЛЕЗОБЕТОННЫХ ИЗГИБАЕМЫХ ЭЛЕМЕНТАХ, УСИЛЕННЫХ КОМПОЗИТНЫМИ МАТЕРИАЛАМИ

The design projection of the inclined section is an important factor in the estimation of strength of reinforced concrete structures by inclined sections. The problem of determination of the crack inclination angle is also essential for the elements strengthened by the external composite rein-forcement. The method of the inclination angle determination in any point along the span of strength-ened bending element is proposed. The design inclination angle of a crack corresponds to the minimum of external load causing its opening, which is obtained from the energy balance equation. The calculations of bending elements strengthened by composite materials have been carried out. The ob-tained dependence of cracks inclination angles on the conventional to composite reinforcement ratio and on the coefficient of the bilinear section hypothesis.

The Cut Span Effect on the Beams Inclined Sections Strength Reinforced with External Composite Reinforcement

The article presents the studies’ results of the oblique sections strength of 24 reinforced concrete beams, reinforced by three-sided U-shaped carbon fiber collars. The impact of the span section is estimated as 1.5h0 2,0h0 and 2,5h0 on the beams’ composite reinforcement efficiency in the initial inclined cracks presence and absence.

Comparison Crack Resistance of RC Beams with and without Transverse Reinforcement after Shear Testing

Abstract Main parameters, which characterize shear strength, are crack distribution, width of diagonal crack opening and angle of inclined crack. There are in this article, comparison crack resistant of testing reinforced concrete (RC) beams on the shear with such variable parameters like presence or absence internal reinforcement, different shear span, and presence or absence external composite reinforcement. Shear span (relative span to effective depth ratio) was acquired the following values: a/d=2, 1.5, 1. For internal reinforcement, rebar’s A240C with diameter 8 mm and steps 100 mm was chosen. The composite FRCM system was like external reinforcement with three stripe of composite fabric with width 70 mm and step 100 mm. Eight RC beams were tested. After testing, we discovered that the most influenced on the serviceability capacity was shear span. Internal transverse reinforcing increased shear strength on the same level and it was independent from shear span and other factors. Only quantity of reinforcing determine level of increasing shear capacity. FRCM system is efficient strengthening system, which significant increase shear crack resistant for RC beams. External FRCM reinforcing increase shear crack resistance on the same percentage and independent from presence or absence internal reinforcement.

Modeling of shear behavior of reinforced concrete beams strengthened with FRP

The response behavior of shear critical reinforced concrete beams was large investigated, and many studies were presented in literature. However, several issues, like the strain level of FRP at the shear failure, and the interaction between internal and external reinforcement, remain not completely understood. This paper presents an analytical model for the response behavior of reinforced concrete beams strengthened in shear with FRP. The proposed procedure has been based on the Modified Compression Field Theory and can reproduce the whole load-displacement curve. The stress and strain fields have been rigorously calculated for each load step. The effective failure strain of FRP reinforcement has been investigated by applying two different approaches. The reduction of the stirrups stress level in the presence of the external composite reinforcement has been alternately both neglected and taken into account, thus to obtain a comparison of the numerical predictions. The accuracy of the proposed model has been assessed using a database of 71 specimens reinforced with FRP. The results have showed that the proposed model has yielded accurate results and the influence of key parameters on the predictions has been highlighted. Furthermore, a simplified formulation for the evaluation of the shear strength has been derived.

Strength of Flexible Compressed Elements when Changing the Options of Composite Reinforcement and Application of the Load

The paper presents the research results of the strength of flexible () compressed elements reinforced with various options of external composite reinforcement. The purpose of the experiment is to determine various options of external transverse reinforcement efficiency for different types of stress – strain state of reinforced samples. Another task is to determine the possibility of reinforcing compression elements that exceed the normalized values in the ratio of section dimensions and elements flexibility.

The deformability of short pillars in various loading options and external composite reinforcement

The test results on deformation and rigidity of short compressed reinforced concrete pillars with various types of external transverse and longitudinal composite reinforcement are given. The samples from heavy concrete with design strength class B30-35 were tested, having the same cross-section 250x125 (h) mm and length 1200mm with flexibility λh = 10. The pillars were reinforced with 4Ø12A500 in the longitudinal direction and with tied clamps Ø6B500, installed with the step of 180 mm - in the transverse direction. The purpose of the experiment was to determine the effect of the rigidity of reinforced elements on the deformability of short experimental samples. It was necessary to determine how the eccentricity of the load application influences on the variation in the rigidity of the reinforced elements. The purpose was also to obtain data on the deformability of pillars loaded with small eccentricities, i.e. when e0 = 0.16h. It was found that the most effective type for short pillars reinforcement is a three-layer holder, which has maximum rigidity and minimal deformability. However, its efficiency gradually decreases when the eccentricity of the load application increases.

Mechanical performances increasing of natural stones by GFRP sandwich structures

Natural stone is generally used in the buildings decoration and furniture finishes for its aesthetic properties and durability. However, its brittle nature limits its applications, in fact the tensile strength of stone is considerably less than its compression strength; this disparity can limit the use of stone in applications where tensile and flexural strength capacity is required, such as for long spans or thin sections.The aim of this work is to investigate the use of sandwich structural laminate in composite materials as external reinforcement both to increase the mechanical resistance and to decrease weight of natural stone. High strength glass/epoxy laminates were bonded to the lower surfaces of marble and granite beams, and 3-point bend and short-beam tests were performed on reinforced and unreinforced specimens. Results indicate that external composite reinforcement can increase the mechanical property of both types of stone up to an order of magnitude as compared to unreinforced control samples.

Fibre Reinforced Cementitious Matrix confined concrete elements

This paper discusses outcomes of experimental research into FRCM (Fibre Reinforced Cementitious Matrix) and CFRPs (Carbon Fibre Reinforced Polymers) confined concrete elements. FRPs (Fibre Reinforced Polymers) composite materials use epoxy resin to bond concrete with external composite reinforcement, whereas FCRM uses composite jacket embedded in mineral mortar. Since mineral adhesive is used for FRCM composites, they are an alternative to FRP composites for applications in elevated temperatures. The two-stage comparative research was carried out to evaluate the confinement effectiveness and behaviour of FRCM and CFRP confined concrete elements. At the first stage, the effect of different number of transverse reinforcement layers of FRCM and CFRP sheets not exposed to elevated temperature was investigated. At the second stage, elements with single layer transverse reinforcement of FRCM and CFRP sheets was exposed to elevated temperature and then tested to failure. This paper reviews results of limit load capacity research, damage patterns were described and stress–strain curves were plotted and compared for both confinement types.

Investigations on rheological strains of compressed concrete elements strengthened with external composite reinforcement CFRP

The results of experimental studies on rheological strains of compressed concrete elements strengthened with surface CFRP materials are presented in this paper. The objective of the investigations was to estimate the influence of long-term load on strains and load-bearing capacity of compressed elements strengthened with CFRP materials. The studies were performed on specimens with various types of reinforcement. The specimens were strengthened with external composite reinforcement – longitudinal segments of CFRP strips and transverse confinement executed with CFRP sheets. The experimental studies were divided into two stages, in which specimens were subjected to long-term axial compression. The objects of the investigations were cylindrical specimens with a diameter of 113mm and height of 350mm. The plain concrete specimens were loaded with the level of about 1/3fcm,cyl (mean cylinder compressive strength of the concrete). After the period of initial loading the specimens were strengthened and the level of effort was increased to about 2/3fcm,cyl. The tests were conducted in constant thermal and moisture conditions. In the paper, the dependences of long-term strains increase in time are presented for the experimental elements. Additionally, theoretical studies connected with rheological model identification were performed.