External Reinforcement Research Articles

Experimental and numerical investigation on the flexural performance of RC slabs strengthened with EB/NSM CFRP reinforcement and bonded reinforced HSC layers

In this paper, one-way reinforced concrete (RC) slabs were strengthened using External Bonding (EB) and Near Surface Mounted (NSM) techniques and tested under flexural loading until failure. The area of internal and external reinforcement, shape of strengthening elements (bars, strips, and reinforced high strength concrete (HSC) layers) and strengthening method (EB and NSM) were the experimental tested variables. The experimental results showed significant increases in the load capacities of the upgraded slabs ranging between 133.8% and 264.5% compared to their corresponding un-strengthened slabs. Consequently, the NSM technique showed higher load efficiency than the EB, even though they had nearly the same strengthening properties and area. Compared to the control slab, using NSM strips instead of EB strips or NSM bars amplified the slab load capacity by about 51.7% and 33.2%, respectively, while using NSM HSC layer instead of EB HSC layer increased slab load capacity by 74.7%. Moreover, doubling the area of EB strips improved the load capacity by 10.3%, while increasing the internal steel area by 195% enhanced the slab load capacity by 21% to 48 %, depending on the strengthening method. However, depending on the distance between internal and external strengthening elements the cracks were initiated at the ends of the strengthening element causing the slab shear failure at dissimilar loads. Finally, a verified finite element (FE) model was built to study the effect of bond length, material, and area of the strengthening element on the slab behavior.

Influence of waste foundry sand on microstructural and mechanical behavior of self consolidated concrete filled steel columns

The impacts of leftover foundry sand on steel sections filled with high strength Self-Consolidated Concrete (SCC) were investigated and addressed in this study. 24 steel sections were examined under progressive axial pressure to establish the optimal proportion of leftover foundry sand, a byproduct. 24 samples were divided into 12 columns with eight circular cross sections of 50 mm in radius and 500 mm in length, and eight additional specimens with square sections of 500 mm in length and 100 mm on each side. Additional 12 columns with eight circular specimens measuring 50 mm in radius and 1000 mm in height and eight square specimens measuring 100 mm on each side and 1000 mm in length. The twelve sections can be divided into hollow steel sections and SCC filled sections. The predicted outcome from the studies show that the capability of carrying axial loads and ductility of the SCC-filled steel sections are affected by the use of leftover foundry sand. Additionally, the steel section parts serve as external reinforcement to promote lateral stability and decrease local buckling. The square sections use 25% less steel than the circular sections. By substituting leftover foundry sand for some of the cement, SCC mixes are made. In this project, steel sections filled with self-consolidated concrete were made using varying amounts of leftover foundry sand, including 0%, 4%, 8%, 12%, 16% and 20%. According to the analysis, steel columns with leftover foundry sand have a higher ultimate load than standard concrete, which results in a 12% reduction in construction costs. The work offers a remedy for efficient byproduct management that lessens environmental risk and creates an atmosphere that is eco-friendly.

FIELD EXPERIMENTAL STUDY ON EXTERNAL PRESTRESSING REINFORCEMENT OF A 420M PC CONTINUOUS BEAM BRIDGE

In this paper, the practical engineering of a 420 m PC continuous beam bridge is taken as the research object, and an external prestressing reinforcement method is proposed to reinforce the damaged and cracked girder. The paper is to study the structural performance of PC continuous beam bridge before and after reinforcement. The heavy vehicle loading test of reinforced PC continuous beam bridge was carried out. A total of three test spans were selected, and each test span selected seven deflection test section and a strain test section. The corresponding finite element model was established and verified by the test results. Finally, it was concluded in this study that the external prestressing reinforcement method has a good effect on improving the loading capacity and overall performance of damaged bridges.

EFEKTIVITAS ANGKUR EPOKSI TERHADAP KEKANGAN EKSTERNAL BALOK BETON BERTULANG DENGAN PERKUATAN CFRP

Externally Bonded Carbon Fiber Reinforced Polymer (EB-CFRP) with U-wrap is one of the alternative external strengthening of modern reinforced concrete beams, which has been proven effective in significantly increasing flexural and deformation capacities. Although quite effective in increasing the structural capacity, external reinforcement needs to be studied further about its failure behavior, the avoided failure is called debonding, an interface bond failure between the FRP composite material and the concrete material. Epoxy has a fairly high material resistance, but its use as a reinforcing composite bonding material needs further investigation. Adding epoxy anchors at the ends of CFRP can mobilize the tensile strength in CFRP, eliminating or delaying debonding failure. Epoxy anchors (epoxy-filled grooves) are expected to be effective and flexible for application to various forms of components of reinforced concrete structures that have been reinforced with EB-CFRP. Currently, there are no standards and guidelines for applying FRP anchors. However, research has been conducted on the failure pattern of FRP anchors with U-style wrapping which can avoid debonding so that failure with FRP rupture can be achieved. This study examines the effectiveness of epoxy anchorage in improving the external strengthening of reinforced concrete beams with EB-CFRP reinforcement. The behavior of epoxy anchors in reinforced concrete beams with EB-CFRP will be investigated through experimental tests.

Determination of the load-bearing capacity increase coefficient of a steel-concrete cylindrical load-bearing element

Abstract. Problem. Steel-concrete cylindrical load-bearing elements are rational for reducing material intensity of individual elements and systems as a whole in construction. External sheet reinforcement of cylindrical elements, which is in the form of clamp, simultaneously performs the power, protective and technological functions. The clamps in steel-concrete cylindrical load-bearing elements restrain the movement of concrete in the transverse direction and lead to the gain in concrete strength among other. The concrete in the middle of the shell-clamp, in turn, increases its stability. Goal. The purpose of these theoretical researches is to determine the load-bearing capacity increase coefficient of a steel-concrete cylindrical load-bearing element based on the fundamental theories and criteria of material resistance and the theory of elasticity. Methodology. Research was performed using the analysis of scientific literature, systematization and unification of various theoretical methods and criteria for the strength of materials and the stress-strain behavior of individual elements and the structure as a whole. Results. Theoretical calculations to determine the load-bearing capacity increase coefficient of a steel-concrete cylindrical element made by enclosing a concrete core in a steel clamp are presented on the basis of the combined fundamental theories and criteria of material resistance along with the theory of elasticity. Originality. The scientific novelty of the work consists in the fact that specific fundamental theoretical methods and criteria for assessing strength and determining the stress-strain behavior of structural elements were comprehensively analyzed and systematized, taking into consideration current regulatory requirements. Practical value. The presented results of the work are significantly different from most of the presented methods in the direction of calculating the stress-strain behavior and determining the load-bearing capacity of steel-concrete cylindrical load-bearing elements. Firstly, this would enable scientists to look at the problem of calculating such load-bearing elements from a new angle in further research, and secondly, it would accelerate the possibility of rational using of steel-concrete cylindrical load-bearing elements in all directions of construction.

Bridging the gap between mathematical optimization and structural engineering: Design, experiments and numerical simulation of optimized concrete girders

AbstractConcrete, as the most widely used construction material, is associated with a high environmental impact. Within the present study, structural optimization is the method of choice to counter this issue. The entire process, from optimization, to design, experiments and numerical simulation is outlined. Embedded in the framework of a design competition (Concrete Girder Optimization Competition 2021), a bridge between structural engineering and mathematical optimization is demonstrated. Two design concepts for optimized concrete girders, one with internal and one with external reinforcement, yet both based on strut‐and‐tie modeling, were investigated. Within the boundaries of the competition, several conclusions can be drawn: The results indicate the importance of an adequate structural interpretation of topology optimization results to obtain satisfying structural performance. The environmental evaluation outlines that the reinforcement mass has a substantial share in the total Global Warming Potential. A successful numerical re‐simulation of selected girders can serve as a modeling base for other researchers. Compared to a conventionally designed girder an increase in resource efficiency, measured by load‐carrying capacity versus environmental impact, of more than 30% was achieved.

IMPORTÂNCIA DO REFORÇO POSITIVO PARA O DESENVOLVIMENTO DE COMPETÊNCIAS SOCIAIS EM ADOLESCENTES ATRAVÉS DO TREINO DE HABILIDADES SOCIAIS

In the process of socialization in adolescence, it is common to identify relationship problems, often resulting from low repertoire of social skills or inadequate communication. It is also common to observe low self-esteem, cognitive distortions or a low sense of self-efficacy, which can lead to the development of depression as a result of social isolation and lack of external reinforcers. Therefore, it is necessary to develop social skills, especially in childhood and adolescence, for the development of emotional health in adult life. The objective of this work is to demonstrate how Social Skills Training together with Positive Reinforcement can be tools for developing social skills, with a focus on assertiveness. Result demonstrated with the case study of a teenager during her internship at PUC, who had behavioral changes, showing greater emission of assertive behaviors in new social situations, with this, expanding her social repertoire. Demonstrating effective social skills training for adolescents through positive reinforcement.

THEORETICAL ASPECTS OF AVOIDING DELAMINATION OF COMPOSITE MATERIALS DURING STRENGTHENING OF REINFORCED CONCRETE STRUCTURES

The scientific work is devoted to the improvement of the calculation methodology of reinforced concrete elements, using verification of the FRP delamination prevention, during structures strengthening with a system of composite materials (SCM) from various fibers types. During strengthening of reinforced concrete elements with composite material systems, the role of adhesion between concrete and FRP is of great importance due to the fragility of the failure mechanism due to delamination (loss of adhesion). The adhesion strength is generally much higher than the tensile strength of the concrete, so delamination always starts in concrete itself with the separation of FRP layer of different thickness. According to the load-bearing capacity requirements, such a failure mechanism should not precede the failure of the strengthened element during bending or shear. To solve the problem of possible strengthening delamination of composite materials systems, it is necessary to consider different failure modes of FRP. Due to imperfection of domestic building codes, a detailed analysis of the solution to the problem of FRP delamination was carried out in accordance with the recommendations of a number of foreign regulatory documents (ACI, CNR, FIB). The main failure modes, with subsequent initiation of delamination of FRP material from concrete base, are systematized, namely: FRP delamination due to surface irregularities, separation of FRP due to shear cracks, longitudinal shear stresses in the yield zone, excessive deformations in FRP material (FRP rupture), longitudinal shear stresses near the FRP edges, failure in anchoring (fixing) zone of FRP material. Six criterions are proposed that need to be verified during design of structures strengthening systems with FRP materials. During formulation of specified criterions, the main theoretical aspects necessary for application in structural calculations of the studied connection are given. The results of research can be used in future during the design of structures joints strengthening with systems of composite materials based on carbon fibers, glass, aramid. Keywords: system of composite materials, external reinforcement, FRP strengthening, reinforced concrete, failure mode, calculation, delamination.

Performance assessment of deteriorated RC shield tunnels integrated with stochastic field-based modeling for nonuniform steel corrosion

For a corrosion-affected reinforced concrete (RC) shield tunnel, the corrosion of steel reinforcements is always nonuniform and spatially distributed. Ignoring the nonuniformity of steel corrosion shall not accurately estimate the performance of the deteriorated RC shield tunnel due to a drastic simplification of structural corrosion condition. In this study, a novel approach is presented to estimate the structural performance of a deteriorated RC shield tunnel with an emphasize on the spatial correlation and variation of steel corrosion. A random field integrated with Gumbel model is established to simulate the nonuniform steel corrosion in a segment. A random field-based numerical model for the deteriorated RC segmental lining and an analytical model to evaluate the load-bearing capacity of a corroded RC segment are developed. Monte Carlo simulation incorporating with numerical analysis is performed to estimate the failure probability of a deteriorated RC shield tunnel. In an illustrative example, the effects of corrosion degree and nonuniformity of the internal and external steel reinforcements on structural performance of a RC shield tunnel are investigated.

Study on reinforced concrete elements of buildings and structures with cracks, reinforced with composite polymer materials

With the rapid development of modern construction practice around the world, serious problems arise in the application and subsequent operation of reinforced concrete structures. Today, the problem of reconstruction and restoration of buildings and structures requires an urgent solution. The deterioration of the environmental situation threatens the reliability of buildings and structures, a sharp deterioration in their condition is observed in almost all countries and climatic zones. In our case, the trend towards wear is developing due to the imperfection of regulatory documents and the need for proper maintenance of objects. The development of the construction industry and the use of innovative composite polymer materials in construction and the strengthening of existing buildings and structures with modern methods are relevant. Often very rare, expensive, historically significant structures require reliable operation, and their dismantling or replacement is more expensive than repair, or even impossible. Reinforcement of building structures using composite polymer materials (CPM) is by far the most “cautious” measure for their restoration and improvement of performance. In our research, the main attention is paid to the technology of external reinforcement of reinforced concrete beams using CFRP to increase their load-bearing capacity at shear. To reduce material consumption when strengthening the structure, it is more efficient to use CFRP in the form of strips, however, this practice has not been practically studied. Previous researchers have concentrated their attention mainly on external reinforcement, generally ignoring the effect of internal reinforcement. However, it is known that internal and external reinforcement complement each other and the destruction during shearing of reinforced concrete elements is mainly influenced by such factors as steel clamps, longitudinal reinforcement and the ratio of the shear span to the working height of the section. Therefore, in our studies, special attention was paid to considering the influence of these factors on the overall bearing capacity of beams. In addition, the work studied the ability to transfer shear stresses through cracks in reinforced concrete beams reinforced with external reinforcement from CFRP compared to the same unreinforced ones.

Structural Performance of Infilled Steel–Concrete Composite Thin-Walled Columns Combined with FRP and CFRP: A Comprehensive Review

Fiber addition enhances the composite action between the steel tube and concrete core, increasing the strength of the concrete core. To better understand how fiber-reinforced infilled steel-concrete composite thin-walled columns (SCTWCs) behave, multiple investigations have been conducted using both experimental and analytical methods. This article provides a comprehensive review of SCTWCs' confinement approaches using fiber-reinforced polymer (FRP) and carbon fiber-reinforced polymer (CFRP). In this research, the behavior and formation of FRP and CFRP wrappings of the SCTWCs are reviewed and discussed. The ability of the FRP to serve as a confining material and reinforcement for the columns has increased its use in columns applications. The FRP can be applied to reinforce the structures from the exterior. By applying the CFRP strips, the columns' load-carrying capacity is improved up to 30% when compared with their corresponding un-strengthened columns. External bonding of the CFRP strips efficiently creates external confinement pressure, prevents local buckling of the steel tubes, and enhances the load-carrying capacity of the SCTWCs. The primary goal is to facilitate a clear understanding of the SCTWCs. This article helps structural researchers and engineers better understand the behavior of the SCTWCs that include the FRP and CFRP composites as external reinforcement. Future research directions are also suggested, which utilize previous research works.

Comparative Study of Fiber Glass Reinforced Polymer and Carbon Fiber Reinforced Polymer on Cube and Cylinder

A comparative analysis of polymers reinforced with glass fiber and polymers reinforced with carbon fiber was carried out on a cube and a cylinder in the laboratories of Baghdad. 36 samples were taken with fiber percentages of 1.0, 2.5 and 5.0 % by weight of cement. The methodology of this study included the use of composite polymer fibers in the external reinforcement of concrete beams for the purpose of improving their performance when bending by gluing polymer fibers to the surface. Group A tests of non-reinforced concrete beams with other reinforced polymer fibers were also implemented. Excellent results were obtained by adding two types of polymer fibers to a concrete sample. It was found that the polymer reinforced with glass fiber showed better results than the polymer reinforced with carbon fiber when testing samples for bending strength. However, in splitting strength, the carbon fiber reinforced polymer achieved higher performance than the glass fiber reinforced polymer. Whereas the results of a group of previous studies conducted to study the effect of fiber additives on the mechanical properties of concrete proved that their addition led to an increase in compression, tensile and bending resistance at rates that reached 25, 75 and 80 %, respectively.

Entering into a self-regulated learning mode prevents detrimental effects of feedback removal on memory

Incentives can decrease performance by undermining intrinsic motivation. How such an interplay of external reinforcers and internal self-regulation influences memory processes, however, is less known. Here, we investigated their interaction on memory performance while learning the meaning of new-words from their context. Specifically, participants inferred congruent meanings of new-words from semantic context (congruent trials) or lack of congruence (incongruent trials), while receiving external feedback in the first or second half of trials only. Removing feedback during learning of congruent word meanings lowered subsequent recognition rates a day later, whereas recognition remained high in the group, which received feedback only in the second half. In contrast, feedback did not substantially alter recognition rates for learning that new-words had no congruent meanings. Our findings suggest that external reinforcers can selectively impair memories if internal self-regulated processes are not already established, but whether they do so depends on what is being learned (specific word-meanings vs. unspecific incongruence). This highlights the relevance of self-regulated learning in education to support stable memory formation.

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.

Results Of Experimental Research Of Steel-Concrete Composite Beam Under Cyclic Freezing-Thawing

One of the ways to improve the efficiency and quality of reinforced concrete structures is the development and implementation of new building structures, the use of which ensures a decrease in material consumption and cost. These effective structures include steel-concrete structures. An important problem when using steel-concrete structures is to ensure the joint work of steel and concrete, which is determined by the adhesion of materials. Reinforced concrete structures must meet the requirements for safety, serviceability and durability. The question of the operation of steel-concrete structures with external reinforcement in the form of a box section remains poorly understood. At the same time, the question of the influence of cyclic freezing and thawing on the adhesion strength between the metal shell and concrete remains open. In order to identify the features of the work of bent steel-concrete elements with external reinforcement at alternating temperatures, experimental studies were carried out, the results of which on strength and deformability are presented in this article. Investigations were carried out in two directions: first, the influence of the CFT on the change in the adhesion strength between the metal shell and concrete under compression; the second influence of CFT on the joint work of concrete and metal in bent steel-concrete elements.

Strength of reinforced concrete T-beams of bridges reinforced with external reinforcement from fabric polymeric composites

Work is devoted to rehabilitating damaged, injured reinforced concrete T-beams of bridges of carbon fibre-reinforced plastic materials. Estimating beams' resistance at shear depended on the percent of longitudinal working reinforcing- μ, attitudes of flight of shear to a working height of section - av/ho, an interval, quantity, and orientation of CFFM strips. The mechanism of destruction and estimation of bearing ability strengthened damaged and intact Т-beams are investigated at shear. Results of deformations of the stretched working and cross-section armature, deformations of concrete on the height of beams and in strips CFFM from loading. The influence of CFFM on the bearing ability and character of the destruction of beams is investigated.

Flexural Behavior of Rubber-Filled Reinforced Concrete Beams Strengthening with CFRP Sheets

Although there are many advantages to using rubber to produce reinforced concrete substrates, there are still few applications for rubberized concrete substrates like beams, where the mechanical properties of rubber-infused concrete, such as flexural strength, begin to decline. On the other hand, flexural strengthening constitutes a sizeable portion of the structural uses for externally carbon fiber reinforced polymer (CFRP) sheets when used to strengthen reinforced concrete beams. For this study's rubberized concrete beams, the externally adhered (CFRP) sheets were used as a substitute for the loss of flexural strength. The study's reinforced concrete beams were split into two groups, each consisting of three beams. The first group's concrete mixture was included as a filler (5) % of the cement weight in the form of waste tire rubber with a size not more than (0.075) mm. Any group of concrete beams always had a first beam without any external reinforcement, a second beam with one layer, and a third beam with two layers of (CFRP) sheet. The results indicate that the load at the first crack increases to be equal to that of the un-rubberized beam when the rubberized reinforced concrete beam is strengthened with one layer of (CFRP) sheets, and it increases by (20%) when reinforced with two layers of (CFRP) sheets. When reinforced with one or two layers, the load at failure rises by 23.58 and 42.75 percent, respectively. The first crack deflection rises by 88.11 and 120.24 percent, while the failure deflection falls by 2.97 and 6.01 percent, respectively. On the (load-deflection) curve, the deflection decreases at symmetrical loads.

Behavior of fiber reinforced polymer laminates strengthening prestressed concrete beams

Pre-stressed concrete constructions' service life may be extended considerably by using fibre reinforced polymer (FRP) reinforcement. It is necessary to have knowledge of the real performance of the strengthened members in order to deploy the technology properly. Determining the static response of pre-stressed concrete beams with externally bonded fiber-reinforced polymer is the main objective of this work. A total of 14 beams of 3 m long, 150 mm × 250 mm cross-sectional beams were cast and put to the test in the lab. Twelve other beams had Glass Fiber Reinforced Polymer laminates added to their soffits to strengthen them, while the other two post-tensioned beams that weren't bonded functioned as reference beams. Three distinct GFRP laminates of two different thicknesses (3 mm and 5 mm) were used to reinforce seven M 35 concrete beams. The strengthened beams were put to the test with loads that increased monotonically as manual readings were collected. The remaining seven M60 concrete beams were reinforced using three different GFRP laminates of two different thicknesses 3 mm and 5 mm, and they were put to test with monotonically increasing loads while having hand readings obtained. All of the variables—concrete grade, GFRP laminate type, and GFRP laminate thickness—were assessed. Uni-Directional Cloth, Woven Roving, and Chopped Strand Mat were some of the GFRP laminates with various configurations (UDC). According to strength, stiffness, ductility, the combined action of the concrete and external reinforcement, and associated failure, all the beams that were tested under static stress underwent evaluation. Deflection ductility, yield load, deflection at yield load, ultimate load, and deflection at ultimate load were the main subjects of this work. According to static testing, pre-stressed concrete beams reinforced with externally bonded GFRP laminates have increased strength, flexural stiffness, ductility, and composite action until failure. The experiment's outcomes were discovered to be rather closely connected. Laminates were suggested for pre-stressed concrete beams with and without externally bonded GFRP in order to forecast the crucial performance factors.

Review on the design and application of concrete canvas reinforced with spacer fabric

Concrete canvas reinforced with spacer fabric has increasingly gained popularity due to its lightweight, great flexibility, high strength and low contamination compared to ordinary concrete. In order to fully explore the structure and performance of this novel composite, this review illustrates how to design high-performance concrete canvas and presents a summary of recent application status of it. Firstly, the structure and properties of knitted and woven spacer fabric and concrete material that comprise concrete canvas is introduced. Secondly, internal and external mechanisms affecting the properties of concrete canvas have been described. To illustrate how to evaluate and test the mechanical behavior of concrete canvas, typical mechanical experiments such as tensile and flexural experiment and failure mechanisms are explained. In terms of the characteristics of concrete canvas, the present article reviews current applications of it in disaster relief tent, slope protection, ditch lining and furniture design areas. Nevertheless, its practical applications are still in the preliminary stage, it is of great necessity to expand its application from the point of view of replacing traditional materials, changing structural design, external reinforcement and perfecting performance evaluation system.

The Power Source of Mathematics Teachers' Teaching Reflection

No matter traditional education or wisdom education, rationality and validity of teaching practice are eternal demands. The rationality and effectiveness of teaching practice are realized in teachers' continuous reflection. Although the social constraint of education determines that teachers' reflection needs various external reinforcement and external support. However, this paper mainly studies the four factors that push mathematics teachers to reflect on teaching, which are educational theory learning, teaching self-evaluation, "problem solving" in mathematics, dialogue and communication among teaching subjects.