External Reinforcement Systems Research Articles

Aging of Adhesives of External Reinforcement Systems of Building Structures. Part 2. Structural Studies

The structural changes of cross-linked epoxy polymer adhesive for external reinforcement systems of building structures after exposure to artificial climatic factors have been studied by the method of IR Fourier spectroscopy. The aim of the study was to determine the significance of influencing factors (UV radiation, temperature, water and alkaline environment) for the development of a method for accelerated assessment of the durability of selected systems. The objectives of the study were to identify the mechanism of aging and obtain differential spectra of aged and initial samples. The processes of destruction of samples of cross-linked epoxy polymer of amine curing under the influence of artificial climatic factors of aging have been studied by IR spectroscopy. It has been established that the most significant factors influencing structural changes in the polymer are UV radiation and an alkaline solution of NaOH and KOH.

Aging of Adhesives of External Reinforcement Systems of Building Structures. Part 1. Investigation of the Significance of Influencing Factors

External reinforcement systems using carbon composite materials are one of the modern methods of strengthening building structures. As the results of existing scientific research show, the component most susceptible to external factors in these systems is an epoxy adhesive. In the present work, experimental studies have been carried out in order to obtain data for the development of a standard method for accelerated assessment of the durability of building structures reinforced with external reinforcement systems with polymer composites. The importance of influencing factors such as: UV radiation; temperature; moisture and alkaline solution on the aging rate of adhesives for external reinforcement systems has been revealed. A step stress method is proposed to predict the creep of the initial and aged adhesive samples.

POLYMER COMPOSITES FOR EXTERNAL REINFORCEMENT OF BUILDING STRUCTURES

Key aspects of developing effective systems for the external reinforcement of building structures, made of composite polymer materials containing carbon fibers and no-bake polymer binders, ensuring shape formation in the temperature range of 15 - 40 °С no more than 24 hours, characterized by operability in the temperature range from minus 45 ° C to plus 60 ° C.. PCM-based SVA has a number of advantages compared to clips and metal profiles traditionally used for repairing building structures: the load-bearing capacity of the rods increases, the cost of the strengthening of load-bearing structures is reduced, and the seismic resistance of engineering structures is increased. In relation to composite SVA building structures, the following types of construction chemicals are used: primer, putty, adhesive, protective coating. The production of unidirectional tapes was carried out on a Dornier double rapier loom, modernized for processing carbon fibers. The results of experimental studies of the developed polymer binders and carbon reinforcing fillers are presented. It is shown that the developed materials can be successfully used to strengthen and repair engineering structures. The technological features of strengthening and repairing building structures with composite external reinforcement systems using the contact molding method and ready-made lamellas are described. Installation of composite clamps on vertical surfaces is carried out by fixing the canvas in the extreme position, followed by laying, smoothing and rolling along its length. Rolling is done from the middle to the edges. Before gluing the blanks, the lamellas are laid out on a work table (workbench) and thoroughly wiped with a rag moistened with acetone. Results of the large-scale implementation of these new materials and technologies in the construction industry are presented.

Гібридні конструкції балок на транспорті із застосуванням металу

To analyze the future use of hybrid and combined structures for floors of buildings and structures for civil and industrial purposes, including in transport, to expand the range of beam structures, to develop an innovative design solution for a hybrid beam with low material consumption with increased reliability and durability of the structure. Analysis of the advantages of hybrid structures, materials used for their design, calculation of a metal-composite beam using existing engineering methods according to STO “Strengthening steel structures with composite materials. Design and production technology of works ”and numerical methods of calculation with the involvement of calculation programs. The advantages of hybrid and combined structures were revealed, a decrease in the material consumption of a metal-composite beam reinforced with boroplastic was revealed in comparison with a steel one. The proposed constructive solution of the beam can be used in floors and roofs of buildings and structures, transport facilities, especially in aggressive environments, as well as in the overhaul and reconstruction of industrial and civil facilities. New developments of beams using steel concrete and composite materials for designed and reinforced structures are presented. An innovative design of a metal-composite beam was developed - a steel beam reinforced with an external reinforcement system made of a composite material, protected by a utility model patent, its static and structural calculation was performed using the SCAD computer complex, the stress-strain state was analyzed, an analysis was made of reducing the consumption of steel of a metal-composite beam and others. its advantages over traditional steel and reinforced concrete beam solutions.

Reinforcement on existing concrete that has been reinforced with CFRP

Implementing a box culvert system on bridges is an economical choice due to the reduced material use. This system has a joint that blends between the slab and the abutment walls and pillars. With a stiffer joint, the moment that occurs is smaller than a simple beam system. Box culvert foundations are commonly shallow foundations. Consequently, it is vulnerable to settlement, particularly the abutments that receive soil loads from the bridge embankment. Therefore, making the displacement in the abutments greater than in the pillars.
 The existing box culvert structure at the study site in Semarang, Indonesia has a span of 2 x 15 meters. Reinforcement has been previously carried out using Carbon Fiber Reinforced Polymer (CFRP) to treat cracks. Though, as time passed, the treated cracks reopened and new cracks developed. Structural cracks occur at a negative moment, so that the reinforcement yielded.
 A reinforcement using CFRP does not increase stiffness—thus, a reinforcement with adding external reinforcement system is used. This reinforcement is done by adding 400 x 200 WF profile—connected mechanically by attaching anchors to the slab. Reinforcement with a WF profile is safer due to its mechanical system, which makes it easier to implement and monitor.

Гибридные конструкции балок на транспорте с применением металла и композитов

Purpose: To pursue the analysis of hybrid and combined frame possible usage for overlaps of buildings and structures for civil and industrial purposes, including on transport, to expand beam structure nomenclature, to develop innovative structural solution of hybrid beam with material low consumption but with frame increased reliability and durability. Methods: Analysis of the advantages of known hybrid frames, of materials, used for their projection; metal composite beam calculation using existing engineering techniques in accordance with STO 38276489.003-2017 “Strengthening of steel structures with composite materials. Projection and techniques of work production” and numerical calculation methods involving calculation software programs. Results: New workouts for beams with the use of steel concrete and composite materials for projected and strengthened structures are presented. Innovative frame of metal composite beam has been developed — steel beam strengthened with external reinforcement system of composite material, protected by a useful model patent, its static and structural calculation has been performed using SCAD computing complex; stress-strain state has been analyzed, the analysis of steel consumption reduction for a metal composite beam and of its other advantages in comparison with steel and reinforced concrete beam traditional solutions has been carried out. Practical significance: The advantages of hybrid and combined structures are revealed, the decrease in material capacity for a metal composite beam strengthened by boroplastics in comparison with a steel one is revealed. The proposed structural solution of a beam can be used in overlaps and coverings for buildings and structures, transport buildings, especially, in aggressive environment conditions as well as during major repairs and reconstruction of industrial and civil purpose facilities.

Research progress of FRP in steel and masonry bridge structures reinforcement

Fiber reinforced polymer (FRP) has been widely used in the reinforcement of concrete bridge structures, and it still has a good application prospect in the reinforcement of steel and masonry bridge structures. In order to summarize the research results of FRP in the reinforcement of steel and masonry structures, broaden the ideas of FRP strengthening bridges in China and promote its wide application in the field of bridge structure reinforcement, it is summarized from the aspects of anti-fatigue reinforcement, anti-buckling reinforcement, bearing capacity reinforcement and seismic reinforcement according to the different reinforcement mechanisms. The shortcomings of the existing studies were analyzed, some problems and ideas that can be further studied were put forward. Analysis result shows that the prestressed FRP reinforcement technology has a good application prospect because of its high material strength utilization rate. Generally, the method of prestressing FRP is used to strengthen the bridge steel members with fatigue cracks, and FRP and filler materials are used to form an external reinforcement system to improve the buckling resistance of steel members. FRP reinforcement can improve the bearing capacity and seismic performance of masonry structures. Follow-up studies should be continued to develop standardized prestressed FRP reinforcement and anchorage system with long-term reliable performance, further promote the engineering application of prestressed FRP reinforced steel structures and establish the specification system of FRP reinforced masonry bridges. The durability of FRP reinforced bridges under complex environment and coupling of various factors should be deeply studied.

Research progress of FRP in steel and masonry bridge structures reinforcement

Fiber reinforced polymer (FRP) has been widely used in the reinforcement of concrete bridge structures, and it still has a good application prospect in the reinforcement of steel and masonry bridge structures. In order to summarize the research results of FRP in the reinforcement of steel and masonry structures, broaden the ideas of FRP strengthening bridges in China and promote its wide application in the field of bridge structure reinforcement, it is summarized from the aspects of anti-fatigue reinforcement, anti-buckling reinforcement, bearing capacity reinforcement and seismic reinforcement according to the different reinforcement mechanisms. The shortcomings of the existing studies were analyzed, some problems and ideas that can be further studied were put forward. Analysis result shows that the prestressed FRP reinforcement technology has a good application prospect because of its high material strength utilization rate. Generally, the method of prestressing FRP is used to strengthen the bridge steel members with fatigue cracks, and FRP and filler materials are used to form an external reinforcement system to improve the buckling resistance of steel members. FRP reinforcement can improve the bearing capacity and seismic performance of masonry structures. Follow-up studies should be continued to develop standardized prestressed FRP reinforcement and anchorage system with long-term reliable performance, further promote the engineering application of prestressed FRP reinforced steel structures and establish the specification system of FRP reinforced masonry bridges. The durability of FRP reinforced bridges under complex environment and coupling of various factors should be deeply studied.

Численное исследование напряженно-деформированного состояния модифицированной деревянной балки

Preservation of wooden architecture monuments requires special attention since during their operation for 100 years and more wooden structures are exposed to environmental influences resulting in weakening their bearing capacity. The use of external reinforcement systems for buildings of historical value leads to a loss of architectural look. The proposed method of restoring the bearing capacity of the destructed wooden beams in the support zones is based on modification with a polymer composition. We have considered 3 types of pine beams: destructed, modified in the support zones; wooden, weakened by destruction; “healthy”. Numerical calculation of beams with a length of 6 m and a cross-section of 100×200 mm is performed in the Lira software package. The calculation model of the beams considered was created by adapting the initial data for the working environment of the software package used. The computational model is set as a three-dimensional body obtained by triangulation and “extrusion” of beam projection section. Shear stresses in the supporting zone, as well as vertical movements of the beams have been determined according to the developed method of calculation of wooden beams. The parameters of the modified beam and the reference “healthy” structure were compared. Shear stresses in the strengthened beam are 15–17 % higher than in the “healthy” beam. It was found that the strength of the destructed beam modified on supports increased by 16–18 % compared to the destructed beam. The boundary conditions for the modification of destructed wooden beams in the support zones to restore their bearing capacity have been determined on the basis of the obtained results. If the loss of bearing capacity is more than 35 %, then this method is not recommended due to the expediency of replacing such structures.

МЕТОДИКА РОЗРАХУНКУ ПІДСИЛЕННЯ ЗАЛІЗОБЕТОННИХ БАЛОЧНИХ ЕЛЕМЕНТІВ СИСТЕМОЮ КОМПОЗИТНИХ МАТЕРІАЛІВ

The scientific work is devoted to the improvement of the calculation methodology of bending reinforced concrete beam elements strengthened with a system of composite materials (SCM) from carbon fiber. During the calculation based, on the limit state method, the recommendations of foreign standards (ACI 440.2R-02) were taken into account. The determination of the cross-sectional area of the external reinforcement was carried out by an iterative method, setting some initial value with subsequent adjustment based on the results of moment strength calculations. To prevent possible debonding of SCM from the concrete base, the coefficient ΚM, with which it is possible to limit the achievement of the limit value of tensile deformation (rupture) of carbon fiber, was introduced to the general calculation. Based on the results of the calculation, the necessary geometric parameters of the strengthening material (width, thickness, number of layers) were established, with the specified normative strength and modulus of elasticity, which allows to significantly increase the strength of the studied cross-section with full use of the external reinforcement system strength. The results of this research can be used in future during the design of structures joints strengthening with systems of composite materials based on carbon fibers, glass, aramid, etc.

Огнезащита стальных и железобетонных конструкций производственных зданий и сооружений

Variants of progressive solutions for the use of efficient fire protection means for steel and reinforced concrete structures of the industrial buildings and structures are considered for the purpose of increasing the actual fire resistance and ensuring the requirements of fire safety norms. Distinctive features of the temperature regimes in the initial phase of a real fire from a standard fire were established when assessing the fire resistance of building structures. It is proposed to use such standardized temperature regimes of fire for assessing the fire resistance of building structures, as standard — in the industrial buildings; temperature regime of hydrocarbons combustion — for oil and gas, petrochemical enterprises, offshore stationary platforms; tunnel temperature regime — in the road and railway tunnels. Considering the operating conditions and performance of work on fire protection, the degree of aggressiveness of the environment, the structural and methodological scheme was developed for selecting passive fire protection for steel structures. Recommendations are given on limiting the use of intumescent paints for load-bearing steel structures involved in the overall stability of buildings, with the required fire resistance limit of no more than 30 minutes. To calculate the temperature over the section of the structure during its heating, the dependences of the change in the coefficients of thermal conductivity and heat capacity of fire-retardant linings under fire were obtained. Experimental studies were conducted related to the fire resistance of reinforced concrete floor slabs and slabs with an external reinforcement system based on the carbon composite material with various types of fire-retardant materials. The issue of protecting the lining blocks of road and railway tunnels from brittle (explosive) destruction of concrete in a fire is considered. It is experimentally confirmed that the addition of polypropylene fibers to the concrete mixture replaces the use of fire protection for the tunnels enclosing structures.

REINFORCEMENT OF REINFORCED CONCRETE STRUCTURES WITH COMPOSITE MATERIALS

Recently, in the Republic of Kazakhstan, as well as in other countries of theAsian region, it is becoming more and more urgent to strengthen the operated reinforcedconcrete structures with external reinforcement systems with carbon materials during thereconstruction of any engineering structures. In order to eliminate the consequences of concretedestruction and reinforcement corrosion as a result of long-term exposure to natural factors andaggressive environments, carbon fiber external reinforcement systems are widely used during the operation of structures designed to repair and strengthen the load-bearing structures of artificialstructures. External reinforcement is used to increase the seismic resistance, strength andreliability of the structures being built, as well as to increase the time between repairs. The repairsystem provides for the use of materials and technologies that ensure stopping and preventingfurther corrosion of reinforcement and concrete, reliable adhesion of repair compounds with oldconcrete, increased water resistance, frost resistance and chemical resistance. This articledescribes FibARM carbon materials that are used to strengthen columns and pylons, broadbandreinforcement of slabs, beams, crossbars and structures with increased requirements forreinforcement joints, covering reinforcement of concrete with large-scale grid cracking.The mainmethods of strengthening the stretched and bent elements of building structures of artificialstructures are considered, and the technology of work on strengthening the structures of artificialstructures is also given.

Reinforcement of concrete structures with external reinforcement system with composite materials

In the article propose two methods of strengthening of concrete beams with carbon fiber. The mechanism of destruction of samples and the maximum breaking stress depending on the method of reinforcement and the density of the carbon fiber are studied. The obtained results indicate the efficiency of the system of external reinforcement of concrete beams with composite materials.

The use of FRP of increased thickness for strengthening structures

The external reinforcement system based on carbon fiber has been used for decades to strengthen reinforced concrete elements. At the same time, it is impossible not to recognize that the existing calculation methods are largely based on empirical dependencies obtained from experimental studies. One of these issues is related to the application of the methodology for materials of heterogeneous origin-tapes and laminates. In general, the possibility of applying the calculation methods accepted in the norms for laminates of generally accepted thicknesses up to 1.6 mm is determined. The question related to the possibility of using laminates of greater thickness is not sufficiently studied. This article deals with the calculation of the reinforcement of the normal cross sections of the bent reinforced concrete elements with the reinforcement of laminates with a thickness of 5 mm.

ПРОЧНОСТЬ МАЛОАРМИРОВАННЫХ ЖЕЛЕЗОБЕТОЕННЫХ КОНСТРУКЦИЙ С МЕЖБЛОЧНЫМИ СТРОИТЕЛЬНЫМИ ШВАМИ, УСИЛЕННЫХ ПРЕДВАРИТЕЛЬНО НАПРАВЛЕННОЙ БАЗАЛЬТОКОМПОЗИТОРНОЙ АРМАТУРОЙ

Many slightly reinforced concrete structures of operating hydraulic structures need strengthening. Traditional methods of strengthening (by reinforced concrete, metal structures, etc.) have significant disadvantages. A method of strengthening by external reinforcement systems based on carbon fiber which is effective in cases where there is an access to the tension zone of the reinforced structures begins to spread. The authors propose to strengthen slightly reinforced concrete structures of the operated hydraulic structures with pre-stressed basalt composite reinforcement placed in the pre-drilled holes in the concrete of the reinforced structures. To substantiate the proposed technical solutions there was carried out a set of experimental studies of characteristic slightly reinforced concrete structures of hydraulic facilities (including those with inter-block construction joints) reinforced with pre-stressed basalt composite reinforcement. The results of experimental studies have shown the effectiveness of strengthening low-reinforced concrete structures of operating hydraulic facilities with inter block construction joints by means of pre-stressed: longitudinal basalt composite reinforcement and transverse reinforcement.

Wooden beams with local wood modification

The purpose of this work is to study the strength of wooden beam structures with local modification of wood in the compressed zone. To achieve this goal, the physical and mechanical characteristics of modified wood were determined using modifiers based on ed-20 epoxy-diane resin, urea-formaldehyde resin, and dimethacrylic polyester. The best physical and mechanical characteristics were obtained for samples using dimethacrylic polyester: the ultimate strength was 84 MPa, the elastic modulus was 21 GPa. The increase in strength compared to solid wood was 46%, and the increase in the modulus of elasticity was 54%. Tests of beam structures with a span of 4.5 m and a cross section of 100x200 mm with local modification of wood in the compressed zone with a polymer composition based on dimethacrylic polyester were carried out. The increase in the strength of beams with local modification in the compressed zone compared to solid wood was 11% within the design loads, and the increase in stiffness by 18%. The “load-strain” relationships are constructed based on the test results. It is established that the greatest effect can be achieved when using external reinforcement systems together in a stretched zone by reducing the influence of defects and defects in beam structures and local modification of the extremely stressed compressed zone.

CFRP composites for strengthening wooden structures

The purpose of this work is to study the strength of wooden beam structures with local modification of wood in the compressed zone. To achieve this goal, the physical and mechanical characteristics of modified wood were determined using modifiers based on ed-20 epoxy-diane resin, urea-formaldehyde resin, and dimethacrylic polyester. The best physical and mechanical characteristics were obtained for samples using dimethacrylic polyester: the ultimate strength was 84 MPa, the elastic modulus was 21 GPa. The increase in strength compared to solid wood was 46%, and the increase in the modulus of elasticity was 54%. Tests of beam structures with a span of 4.5 m and a cross section of 100×200 mm with local modification of wood in the compressed zone with a polymer composition based on dimethacrylic polyester were carried out. The increase in the strength of beams with local modification in the compressed zone compared to solid wood was 11% within the design loads, and the increase in stiffness by 18%. The “load-strain” relationships are constructed based on the test results. It is established that the greatest effect can be achieved when using external reinforcement systems together in a stretched zone by reducing the influence of defects and defects in beam structures and local modification of the extremely stressed compressed zone.

Calculation Of Carbon Fiber Anchors For Pull-Out And Shear When Installing External Reinforcement Systems

The operation of external reinforcement systems based on carbon fibers when strengthening normal and inclined sections of bending reinforced concrete elements depends largely on the anchoring to the body of the reinforced structure. In addition to adhesion, one of the options for ensuring the required level of anchoring of external reinforcement is the installation of anchoring elements, including those based on carbon fibers. This article discusses the calculation of anchors based on carbon fibres used in the arrangement of the external reinforcement system. Two principles of anchor arrangement operation are highlighted: for shear and for pull-out. Separate design provisions have been developed for each, taking into account the parameters of anchoring elements and the nature of the destruction obtained during experimental studies. The proposed calculation methods are based on experimental studies of both bending elements reinforced by external reinforcement systems and directly anchoring elements. In addition, the development of these methods takes into account the provisions available in the regulatory documents on the calculation of anchors and composite materials.

Features of strengthening metal structures with composite materials under the influence of an aggressive environment

Introduction. This article is devoted to the issues of reinforcing metal building structures with external reinforcement systems with composite materials. The application of these strengthening methods in domestic literature and in practice has not been fully studied. As a result, it is relevant to study the characteristics of strengthening under the action of an external aggressive environment, namely when exposed to galvanic corrosion, elevated ambient temperatures and extreme temperatures from firing. The purpose of the study is to establish the effectiveness of reinforcing metal structures with composite materials under the influence of various force factors, including cyclic loads, and under the action of an external aggressive environment.
 Materials and methods. The methodological basis of scientific research was the analysis of publications of domestic and foreign scientists on the theoretical and practical experience of using composite materials to strengthen metal structures. During the study, when describing the dependences of physical quantities on external and internal force and non-force factors, scientific methods of induction, deduction, generalization and comparison were used.
 Results. Performed a comprehensive study of the effectiveness of the use of composite materials to enhance the metal structures in hostile environments. The dependence of the increase in strength of reinforced steel samples on the length of the adhesive joint of external reinforcement is analyzed, the possibility of applying reinforcement at fatigue stresses is investigated. Recommendations on the use of protective insulating systems and materials that prevent the reduction of the bearing capacity of structures from external non-force factors are given.
 Conclusions. The effectiveness of reinforcing metal structures using composite carbon fiber materials is revealed. The bearing capacity of reinforced structures may be increased by 59 %. When the glass transition temperature of carbon fiber materials is reached, the increase in the bearing capacity from external amplification systems decreases by 50 %, and when the temperature is increased to 60 °C, the external amplification systems are ineffective and do not increase the bearing capacity. To achieve the required fire resistance of the amplification systems, equal to at least one hour, it is necessary to use external fire insulation.

Calculation Method Analysis for Structure Strengthening with External Reinforcement

This article describes the main provisions of the calculating method for the gain of reinforced concrete structures by the system of external reinforcement. As an example, the calculation of monolithic reinforced concrete slab with carbon fiber material using the SCAD Office software package was considered and analyzed, which most accurately reflects the geometry and physico-mechanical parameters of the structure. The calculation of reinforced concrete structures includes engineering survey to determine the existing physic-mechanical characteristics of materials, perform calibration calculations and stress calculations in reinforced concrete structures of buildings and structures, taking into account the existing stiffness characteristics, designing reinforcement engineering solutions, the calculation of the forces in the structures and verification of the structures bearing capacity after the reinforcement is completed. During the survey of reinforced concrete structures, it is determined existing loads, deformations, deflections, physico-mechanical characteristics for the subsequent selection of the composite material cross section and taking them into account after the concrete structure’s reinforcement. The external reinforcement systems is used for reinforcing concrete structures and rely on tensile stress perception, taking into account the joint deformations of the composite material used for reinforcement and the concrete structure. The calculation of reinforced concrete structures carried out on the first and second limit state. If the load after reinforcement with a composite material does not increase compared with the loads at the stage of the reinforced concrete structure operation, the calculation for the second group of limit states is not performed. The reinforced concrete structures calculation using an external reinforcement system made of composite materials is carried out from the joint operation conditions of the installed external reinforcement and the concrete base before the limit state onset. The calculation is performed in two stages: at the first stage, the reinforced concrete structure is calculated without reinforcement taking into account the existing loads and deformations, at the second stage, after the work on reinforcement, the design is calculated taking into account the efforts and deformations in the first stage.