CFRPシートとコンクリートの付着挙動(その1)

The properties of reinforced concrete beams strengthened using carbon fiber-reinforced plastic (CFRP) sheets have been thoroughly studied, establishing a firm knowledge of analysis and design procedures. Snapping of CFRP sheets during loading is a typical failure mode in such strengthened structures. Applying epoxy resin to bond CFRP sheets to the reinforced concrete beam creates a new composite material. This paper presents the effect of damage initiation criterion in the composite CFRP material as well as the interface behavior on the performance of CFRP-strengthened reinforced concrete beams. Hashin damage in the CFRP sheets, cohesive behavior in the interface material, and concrete damage plasticity models are used to simulate typical snap patterns of composite CFRP material, capturing interaction between CFRP debonding, concrete cracking, and failure mechanisms. A parametric study is conducted to investigate the effects of the undamaged response of the CFRP material and damage initiation criterion in terms of tensile strength, compressive strength, and shear strength in the axial and transverse directions. Finite element model results are found to be in close agreement with flexural beam test results in terms of both strain and deflection. It is concluded that Hashin damage properties are the main parameters influencing snapping failure mode. This study may serve as a valuable reference to aid in understanding the behavior of retrofitting with CFRP–epoxy composite material in a bridge or building models.

Steel plates strengthened by carbon fibre-reinforced polymer (CFRP) sheets were extensively studied because they can be utilized to strengthen deficient structures with irregular shapes. Although the effective bond length for strengthening plain steel structures is well known, the effective bond length for deficient steel plates remains unclear. In addition, debonding failure is a critical issue that limits the widespread application of this technique. Considering these problems, the tensile behaviour of steel plates with and without notches strengthened by CFRP sheets was experimentally studied in this paper. Semi-circular notches were created at the centre of the steel plates. CFRP sheets with different bond lengths were applied for strengthening. Furthermore, to prevent debonding failure, a G-shaped anchorage system was applied. As observed, the bond strength increased with the bond length until the bond length exceeded 400 mm. For specimens with notches in the centre, a stress concentration formed near the notch where the debonding initiated. After applying the anchorage system, the bond strength improved significantly, but debonding failure was still observed. Thus, the bond length for a steel plate with defects could be longer than that for a plain steel plate, and the weak point is the point in the specimen that undergoes the greatest change in stiffness. More importantly, the G-shaped anchorage system effectively resisted the increase in normal stress and improved the bond strength. However, due to insufficient shear stress resistance, the system ultimately could not prevent debonding and needs further improvement.

A Simplified Model for Crack Width Prediction of Flexural-Strengthened High Pre-Damaged Beams with CFRP Sheet

Fiber-reinforced polymer (FRP) sheet bonding methods are used in practice as a way of strengthening reinforced concrete (RC) structural members under static and quasistatic loading. The applicability of RC members under impact loading has been investigated since 1990. Generally, carbon FRP (CFRP) sheets and aramid FRP (AFRP) sheets have been used in Japan as strengthening materials for FRP sheets in RC infrastructure. Although only one material is normally used for an AFRP sheet, three types of materials are used for a CFRP sheet: high strength, medium elasticity and high elasticity. Usually, a high-strength sheet is applied for strengthening RC members because it has the largest fracture strain of the three types, and medium- and high-elasticity sheets are used for steel members because their Young’s modulus values are more than twice those of steel members. In this work, static and drop-weight impact loading tests for flexurally strengthened RC beams with medium-elasticity bonding (Beam ME) were conducted to investigate the applicability of this sheet to flexurally strengthened RC beams. RC beams with high-strength (Beam HS) bonding sheets of similar axial stiffness to Beam ME and without the bonding FRP sheet (Beam N) were also tested to compare the load-carrying behavior of the RC beams. The results are as follows: Beams ME and HS fail by sheet rupturing and debonding, respectively, under static loading and impact loading; Beam ME can assure the calculated load-carrying capacity statically; however, this beam reaches the ultimate state under a lower impact energy than Beam HS does.

CFRP (Carbon Fiber Reinforced Plastics) reinforcement has a significant effect and advantages of steel structure, has extensive application prospects in the field of engineering structure. However, both of the detection methods and effects evaluation are still in blank, which has restricted the application of CFRP reinforcing steel structures. This paper is based on Eddy Current Pulsed Thermography (ECPT) and focused on the detection of fatigue damage in steel structure strengthened with CFRP sheet. The main research following several parts: first, the mechanism of eddy current thermal excitation on multilayer anisotropic medium was analyzed. Second, the direction and length of steel crack can be found out in any streel crack image. Finally, the feasibility of numerical models and recognition algorithm are verified through experiments. The paper provided an effective method in damaged structures strengthened with CFRP based on ECPT, as well as establishing the theory and technique for developing ECPT instruments for CFRP sheet-strengthened steel structures.

The utilization of fiber-reinforced polymer (FRP), can be an efficient, and long-lasting solution for increasing the durability of reinforced concrete (RC) structures in hostile environments. FRP can be used as a reinforcement or as a strengthening technique that may recover the load capacity of a structure. This paper aims to investigate the flexural behavior of one-way concrete slabs with openings reinforced by glass fiber-reinforced polymers (GFRP) bars and strengthening using carbon fiber-reinforced polymer (CFRP) sheets. The experimental work consists of five one-way concrete slabs that were tested up to failure. All slabs had the same dimension, 750*2650 mm, with a thickness of 150 mm, and were reinforced with the same reinforcement ratio. The experimental work included one specimen without openings and without strengthening as a solid slab. While, the remaining slabs were fabricated with two different openings, rectangular and square 250*500 mm, and 250*250 mm respectively, and strengthened by CFRP sheets. The test results show that the failure load of existing slabs with mid-span openings is decreased by around 41% and 43%, for one and two openings respectively, compared to the solid slab. The utilization of CFRP sheets enhances the flexural load-carrying capacities by about 52% and 44% and improves the stiffness at the ultimate load by about 101%, and 95%, and decreases the deflection at a service load by about 56% and 54%, respectively compared with the un-strengthened slabs. Furthermore, the experimental data were used to validate a finite element (FE) model along with an additional parametric study.

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Creating sustainability and public infrastructure is a fairly recent subject the engineering community has been debating. Introducing new building materials or introducing new structural designs is a strategy for constructing buildings that have long-term reliability and low maintenance requirements. Fiber-reinforced polymers (FRP) are one of the innovative approaches in the field of civil engineering that offer promising results in this regard. In order to maximize the usage of FRP forms, researchers suggested the development of hybrid structural structures by mixing composite materials with standard materials, such as concrete, to enhance the stability, ductility and buckling resistance of single FRP members. Nevertheless, these composite solutions need more preliminary research to prove its feasibility due to the complexity and large range of hybrid components. However, as there is a current shortage of compulsory codes for the design of composite structures and consequently FRP-concrete members, accurate predictive models need to be created. Thus, the present work aims at testing the structural efficiency of hybrid slabs made of CFRP sheets under a concrete layer in bending and shear configurations by carrying an experimental and analytical analysis. Using Carbon Fiber Reinforced Polymer (CFRP) bonded with resin is usual to strengthen concrete slabs or other elements. This thesis introduces a novel technological definition of thin CFRP-concrete unidirectional hybrid slabs. In bending part, experimental quasi-static three-points bending tests and modal analysis tests were carry out to analyze the influence of the connection systems on the dynamic response. Moreover, the corresponding analytical methodology to calculate their response are presented. Four different connection strategies between CFRP sheet and concrete were tested. These included flexible mesh embedding and particle-based frictional enhancement. The maximum bending moment, the evolution of the neutral axis, the comparison between external moment (calculated from applied load) and internal moment (calculated from strain distribution), the CFRP-concrete interface shear stress, and the evolution of the vertical displacement at the loading point are the main results obtained from the tests. In shear part, this work investigates the shear behavior of hybrid slabs that used different types of particles and/or a flexible high strength fabric to connect both materials: concrete and CFRP sheet. Several pure-shear experiments have been carried out to characterize the interface shear response of these hybrid elements. These increase the experimental database on CFPR-concrete shear connection systems. Experimental results showed that the improvement resulting from fabric embedding is far more significant than other tested connection elements at increasing the shear connection strength between the parts of the composite slabs. Results are divided with technological and scientific contributions. The feasibility of using CFRP sheets in hybrid unidirectional slabs instead of steel sheets is the main technological contribution, which also offers the following advantages: lighter weight and resistance to corrosion. Qualitative and quantitative analysis of the CFRP-concrete connection alternatives point out that combining adherence and frictional based strategies is the most promising method. An analytical method for the modelling of concrete slabs with CFRP was developed. In function of full cross-section interaction some equations for bending ultimate limit states were suggested. The possibility of using simpler formulas for quantifying interlayer slip effects was analyzed in assessing deflections, flexural stiffness, bending efficiency and normal and shear stress distributions. The proposed analytical method was able to capture the structural behavior and performance of the specimens. La creació d'infraestructura pública i sostenible és un tema de plena actualitat que la comunitat de l¿enginyeria ha estat debatent des de fa anys. Els polímers reforçats amb fibra (FRP) són un dels materials innovadors en el camp de l'enginyeria civil que ofereixen resultats prometedors en aquest sentit. Per maximitzar l'ús de formes de FRP s'estan desenvolupant estructures híbrides barrejant materials compostos amb materials tradicional, com el formigó, per millorar l'estabilitat, ductilitat i resistència al vinclament de membres individuals de FRP. A més, com hi ha una escassetat actual de codis obligatoris per al disseny d'estructures compostes i, en conseqüència, elements de formigó FRP, cal crear models predictius necessaris perquè es puguin estandarditzar. Abordar els problemes esmentats anteriorment és essencial per augmentar la introducció de materials compostos avançats en tipus comuns d'obres i construccions públiques. Així, el present treball té com a objectiu provar l'eficiència estructural de lloses híbrides de làmines de CFRP amb una capa de formigó, en configuracions de flexió i tallant, mitjançant la realització d'un anàlisi experimental i analític. L'ús de polímers reforçats amb fibra de carboni (CFRP) unit amb resina és habitual per reforçar lloses i altres elements de formigó. Aquesta tesi introdueix una definició tecnològica innovadora de lloses híbrides unidireccionals de formigó-CFRP de làmina prima. A la part de flexió es van realitzar assajos experimentals de flexió quasiestàtics, de tres punts, i assajos d'anàlisi modal per analitzar la influència dels sistemes de connexió en la resposta dinàmica. Així mateix, es presenta la metodologia analítica corresponent per calcular la seva resposta. Es van provar quatre estratègies de connexió diferents entre la làmina de CFRP i el formigó. Aquestes van incloure l¿embegut de malla flexible en el formigó i la millora de la fricció basada en partícules. El moment flector màxim, l'evolució de l'eix neutre, la comparació entre el moment extern (calculat a partir de la càrrega aplicada) i el moment intern (calculat a partir de les deformacions), l'esforç tallant de la interfície CFRP-formigó i l'evolució del desplaçament vertical en el punt de càrrega, són els principals resultats obtinguts de les proves. Aquest treball investiga el comportament rasant de lloses híbrides on els materials de CFRP i formigó es van connectar mitjançant diferents tipus d'agregats i tèxtils flexibles d'alta resistència. S'han dut a terme experiments de tall pur per caracteritzar la resposta de la interfície d'aquests elements híbrids. Aquests assajos augmenten la base de dades experimental sobre sistemes de connexió de tall de formigó-CFPR. Els resultats experimentals van mostrar que la tela embeguda produeix una millora en l'augment de la resistència estructural de manera molt més significativa que amb altres sistemes de connexió provats. La viabilitat d'utilitzar xapes de CFRP en lloses unidireccionals híbrides, en lloc de xapes d'acer, és la principal aportació tecnològica que, a més, ofereix els següents avantatges: menor pes i major resistència a la corrosió. Els anàlisis qualitatiu i quantitatiu de les alternatives de connexió CFRP-formigó assenyalen que la combinació d'estratègies basades en adherència i fricció és el mètode més prometedor. Així mateix, es va desenvolupar un mètode analític per a la modelització de lloses de formigó amb CFRP. En funció dels principis de la interfície completa, es suggereixen equacions per calcular els estats límit últims. La possibilitat d'utilitzar fórmules més simples per quantificar els efectes de lliscament entre capes va ser analitzada en l'avaluació de deflexions, rigidesa de flexió, eficiència de flexió i distribucions d'esforços normals i tallants. El mètode analític proposat va ser capaç de capturar el comportament estructural i el rendiment mecànic de les mostres. La creación de infraestructura pública y sostenible es un tema de plena actualidad que la comunidad de ingenieros ha estado debatiendo desde hace años. La introducción de nuevos materiales de construcción o la introducción de nuevos diseños estructurales es una estrategia eficiente para construir edificios que tengan fiabilidad a largo plazo y requisitos de bajo mantenimiento. Los polímeros reforzados con fibra (FRP) son uno de los materiales innovadores en el campo de la ingeniería civil que ofrecen resultados prometedores en este sentido. Para maximizar el uso de formas de FRP se están desarrollando estructuras híbridas mezclando materiales compuestos con materiales estándar, como el hormigón, para mejorar la estabilidad, ductilidad y resistencia al pandeo de miembros individuales de FRP. Sin embargo, estas soluciones compuestas necesitan más investigación preliminar para demostrar su viabilidad debido a la complejidad y la amplia gama de componentes híbridos. Además, como existe una escasez actual de códigos obligatorios para el diseño de estructuras compuestas y, en consecuencia, elementos de hormigón FRP, es necesario crear modelos predictivos precisos para que puedan estandarizarse. Abordar los problemas mencionados anteriormente es esencial para aumentar la introducción de materiales compuestos avanzados en tipos comunes de obras y construcciones públicas. Así, el presente trabajo tiene como objetivo probar la eficiencia estructural de losas híbridas de láminas de CFRP con una capa de hormigón, en configuraciones de flexión y cortante, mediante la realización de un análisis experimental y analítico. El uso de polímeros reforzados con fibra de carbono (CFRP) unido con resina es habitual para reforzar losas y otros elementos de hormigón. Esta tesis introduce una definición tecnológica novedosa de losas híbridas unidireccionales de hormigón-CFRP de lámina delgada. En la parte de flexión se realizaron ensayos experimentales de flexión cuasi estáticos, de tres puntos, y ensayos de análisis modal para analizar la influencia de los sistemas de conexión en la respuesta dinámica. Asimismo, se presenta la metodología analítica correspondiente para calcular su respuesta. Se probaron cuatro estrategias de conexión diferentes entre la lámina de CFRP y el hormigón. Estos incluyeron el embeber una malla flexible en el hormigón y la mejora de la fricción basada en partículas. El momento flector máximo, la evolución del eje neutro, la comparación entre el momento externo (calculado a partir de la carga aplicada) y el momento interno (calculado a partir de la distribución de deformaciones), el esfuerzo cortante de la interfaz CFRP-hormigón y la evolución del desplazamiento vertical en el punto de carga, son los principales resultados obtenidos de las pruebas. En el estudio del cortante, este trabajo investiga el comportamiento rasante de losas híbridas donde los materiales de CFRP y hormigón se conectaron mediante diferentes tipos de agregados y textiles flexibles de alta resistencia. Se han llevado a cabo experimentos de corte puro para caracterizar la respuesta de la interfaz de estos elementos híbridos. Estos ensayos aumentan la base de datos experimental sobre sistemas de conexión de corte de hormigón-CFPR. Los resultados experimentales mostraron que la tela embebida produce una mejora en el aumento de la resistencia estructural de manera mucho más significativa que con otros sistemas de conexión probados. Los resultados de la tesis se dividen en contribuciones de tipo tecnológico y científico. La viabilidad de utilizar chapas de CFRP en losas unidireccionales híbridas, en lugar de chapas de acero, es el principal aporte tecnológico, que además ofrece las siguientes ventajas: menor peso y mayor resistencia a la corrosión. Los análisis cualitativo y cuantitativo de las alternativas de conexión CFRP-hormigón señalan que la combinación de estrategias basadas en adherencia y fricción es el método más prometedor. Asimismo, se desarrolló un método analítico para el modelado de losas de hormigón con CFRP. En función de los principios de la conexión completa se sugieren ecuaciones conceptuales para calcular los estados límite últimos. La posibilidad de utilizar fórmulas más simples para cuantificar los efectos de deslizamiento entre capas fue analizada en la evaluación de deflexiones, rigidez de flexión, eficiencia de flexión y distribuciones de esfuerzos normales y cortantes. El método analítico propuesto fue capaz de capturar el comportamiento estructural y el rendimiento mecánico de las muestras.

The bond–slip behaviour between self-compacting concrete (SCC) and carbon-fibre-reinforced polymer (CFRP) sheets was investigated using double shear pull-off concrete specimens. Concrete blocks of size 150 × 150 × 100 mm were made from two aggregate types (limestone and basalt), two aggregate gradations (12 mm and 19 mm) and three water-to-cement (w/c) ratios (0·30, 0·35 and 0·40). CFRP sheets were attached to the concrete specimens using three different bond widths (50, 100 and 150 mm) and four bond lengths (60, 80, 100 and 120 mm). The ends of the CFRP sheets were adhered to the concrete specimens at two parallel sides using a special epoxy; the middle was left free for the wrapping of an aluminium cylinder of 100 mm diameter before pull-off testing. The obtained results and literature data were employed in the development of a statistical model to estimate the ultimate shear strength and slippage between CFRP sheets and SCC. The results showed that the effect of aggregate type is insignificant, although the basalt aggregate samples showed higher bond strength and corresponding slippage than the limestone samples. The trend behaviour of the bond–slip curves for double shear pull-off specimens showed no noticeable difference between SCC mixtures made from two different aggregate gradations, but the resulting values showed a slight increase in bond strength and slippage for the concrete specimens made from the larger aggregate particles. Water-to-cement ratio was found to have a significant effect on bond strength and corresponding slippage: bond strength and slippage increased with a reduction in w/c ratio. There was a noticeable decrease in bond stress and a noticeable increase in corresponding slippage for increasing bond length and bond width. The statistical model developed shows an excellent fit to the data used, as indicated by high coefficients of determination.

This paper investigates the working performance of reinforcement concrete (RC) beams strengthened by Carbon-Fiber-Reinforced Plastic (CFRP) with different anchoring under bending moment, based on the structural stressing state theory. The measured strain values of concrete and Carbon-Fiber-Reinforced Plastic (CFRP) sheet are modeled as generalized strain energy density (GSED), to characterize the RC beams’ stressing state. Then the Mann–Kendall (M–K) criterion is applied to distinguish the characteristic loads of structural stressing state from the curve, updating the definition of structural failure load. In addition, for tested specimens with middle anchorage and end anchorage, the torsion applied on the anchoring device and the deformation width of anchoring device are respectively set parameters to analyze their effects on the reinforcement performance of CFRP sheet through comparing the strain distribution pattern of CFRP. Finally, in order to further explore the strain distribution of the cross-section and analyze the stressing-state characteristics of the RC beam, the numerical shape function (NSF) method is proposed to reasonably expand the limited strain data. The research results provide a new angle of view to conduct structural analysis and a reference to the improvement of reinforcement effect of CFRP.

Strengthening concrete beams for shear with CFRP sheets

Structural performance of corroded RC beams repaired with CFRP sheets

Reinforced concrete shear walls with features such as high stiffness, good performance in earthquakes, ductility, and high bearing capacity in earthquake-prone regions are widely used as convenient and reliable structural systems in medium- and high-rise reinforced concrete buildings. However, due to architectural limitations, the use of opening in shear walls is unavoidable. Fiber-reinforced polymer sheets with unique structural characteristics and easy implementation have been used in recent years for rehabilitating concrete structures, especially shear walls. In this study, using the finite element method, the effect of openings with different sizes and locations in reinforced concrete shear walls was studied. The effect of retrofitting specimens with openings by carbon fiber–reinforced polymer sheets with different patterns and thicknesses on the structural behavior of shear walls was also investigated. According to the results, opening reduced the bearing capacity, energy absorption capacity, and stiffness but increased wall displacement. Different reinforcement patterns and different thicknesses of carbon fiber–reinforced polymer sheets had different effects on improved structural behavior of shear walls. Reinforcement with carbon fiber–reinforced polymer sheets is one of the effective ways to rehabilitate concrete shear walls with opening.

This study was undertaken to attempt to establish the press-forming of carbon fiber-reinforced plastic (CFRP) sheets through a forming simulation. Since press-forming induces large plastic deformation of a material, a reliable simulation requires accurate modeling of the plastic deformation of resin. However, there has been little research on the deformation mechanism of thermosetting resins under large plastic forming, which is targeted in this study, and therefore no appropriate plastic deformation model of a resin has been established. Thus, a new model was constructed for a thermosetting resin on the basis of plastic deformation characteristics considering the microscopic mechanism. In the proposed model, the breakage of molecular chains of a thermosetting resin is considered. A molecular dynamics simulation of epoxy resin determined the effect of this molecular chain breakage. It was confirmed that the proposed model can appropriately represent the mechanical characteristics of an actual thermosetting resin. Furthermore, using this model, the numerical analysis of a CFRP sheet through its representative volume element was carried out, and the result explained the improved formability of CFRP at high temperatures, as observed in related experiments.

Progressive collapse is one of the factors which if not predicted at the time of structure plan; its occurrence will lead to catastrophic damages. Through having a glance over important structures chronicles in the world, we will notice that the reason of their collapse is a minor damage in structure caused by an accident like a terrorist attack, smashing a vehicle, fire, gas explosion, construction flaws and its expanding. Progressive collapse includes expanding rudimentary rupture from one part to another which leads to total collapse of a structure or a major part it. This study examines the progressive collapse of a 5-story concrete building with three column eliminating scenarios, including the removal of the corner, side and middle columns with the ABAQUS software. Then the beams and the bottom of the concrete slab were reinforced by (reinforcement of carbon fiber reinforced polymer) FRP and then the structure was re-analyzed. The results of the analysis show that the reinforcement of carbon fiber reinforced polymer sheets is one of the effective ways to rehabilitate and reduce the progressive collapse in concrete structures.