CFRP-reinforced Concrete Beams Research Articles

The impact of using prestressed CFRP bars on the development of flexural strength

Abstract The load-carrying capacity and ductility of conventional steel reinforcement may be greatly increased by using ordinary and prestressed carbon fiber-reinforced polymer (CFRP) bars, resulting in reinforced concrete structures with greater sturdiness. This research investigates the flexural behavior of CFRP-prestressed beams with bonded tendons as opposed to conventional steel-prestressed beams. This article examines a less explored topic that often fails because post-tensioned beams with unbonded CFRP tendons are crushed by concrete. The linear-elastic behavior of CFRP accounts for much of the experimentally observed considerable variations in flexural characteristics between CFRP and steel-prestressed beams. Compared to unbonded CFRP specimens, bonded CFRP specimens are much stronger. Our knowledge of CFRP reinforcement in concrete infrastructure is advanced by this work, which highlights the need for better design techniques to increase strength and ductility. It is recommended that CFRP bars be bonded with epoxy resin to restrict fast energy dissipation and avoid concrete failure. As a result, CFRP-reinforced concrete beams will react less linearly and more ductilely. CFRP may improve prestressed concrete beam performance and lifespan in a number of scenarios, as shown by comparative research with traditional steel reinforcement. Six 1,800–mm-long RC beams with a 200 × 300 mm cross-section were examined and divided into three groups, analyzing important loading phases (i.e., cracked, ultimate, and mid-span deflection) using CFRP bars as prestressed tendons to replace the bottom steel rebars. The load-carrying capabilities and ductility of CFRP-reinforced beams were much greater than those of the reference beam. A single beam using normal CFRP bars for reinforcement showed a 21.2 mm mid-span deflection and an ultimate load of 157.2 kN, with a 57.7-kN fractured load. Another beam with normal CFRP bars also showed enhanced performance, with a mid-span deflection of 21.2 mm, an ultimate load of 160.6 kN, and a cracking load of 57.5 kN.

Experimental and Theoretical Study on Anchorage Loss of Prestressed CFRP-Reinforced Concrete Beams

To investigate the anchorage loss mechanism of externally prestressed CFRP tendons in concrete beams, this study introduces a novel theoretical calculation system (TCS) developed through both the finite element method (FEM) and experimental validation. Firstly, the FEM and the proposed TCS were employed based on the mechanism of anchorage loss to compute the deformation of each part of the prestressed tendon–main beam connection system, ensuring result accuracy through mutual validation. Subsequently, field tests, designed according to FEM guidelines, measured the anchorage loss in externally prestressed CFRP tendons, with long-term monitoring included. Finally, experimental data were then used to refine the TCS. The results indicate that deformation at the connecting screw and the front end of the steel reaction frame constitutes approximately 95% of the total deformation, with theoretical calculations aligning closely with the FEM results. The field tests revealed that the anchorage loss of a 12 m long CFRP tendon under 950 MPa prestress accounted for about 35% of the total prestress loss. The discrepancy in deformation compared with the theoretical results was due to a gap of approximately 0.4 mm between the two threaded connections, which can be minimized by improving construction techniques. After correction, the calculation error was reduced to about 5%. Control variable studies confirmed that anchorage loss is influenced by the prestress level, the dimensions of the steel reaction frame front end, the connecting screw length, and the number of thread gaps. This study provides a comprehensive approach for accurately predicting and mitigating anchorage loss in externally prestressed CFRP tendons, with significant implications for future engineering applications.

Effect of Bond Property Between CFRP Bar and Concrete on Nonlinear Behavior of Circular CFRP Reinforced Concrete Beams

Effect of Bond Property Between CFRP Bar and Concrete on Nonlinear Behavior of Circular CFRP Reinforced Concrete Beams

Inverse analysis based on DFOS technology for the study of the bonding behaviour of FRP to concrete beams

This paper proposes a methodology for the inverse analysis to predict the interface shear stress in reinforced concrete (RC) structures strengthened using externally bonded carbon fibre-reinforced (CFRP) polymers. The model is calibrated employing experimental results obtained by testing two beam configurations with two steel ratios under 4-point bending and three specimens in a double-lap shear test. The interface information is obtained by adopting a smart CFRP fabric bonded on the bottom side of the beams. A smart CFRP consists of two texture fabrics inside which a distributed fibre-optic sensor (DFOS) is inserted. During the test, the sensor measured the mechanical strain distribution of the composite with a millimetric spatial resolution. The recorded strains were used to deduce the evolution of bond shear stresses at the CFRP/concrete interface. Simultaneously crack openings along the beams were detected and measured using digital image correlation (DIC).The obtained model from inverse analysis and the experimental results allows calculating the concrete-CFRP interface stress value, using the measured crack width as input data. The scientific interest of this model lies in its ability to monitor the evolution of a key structural performance parameter of CFRP-reinforced concrete beams: the crack induced debonding. This debonding can be predicted by comparing at each point the shear stresses obtained by the proposed model with the maximum debonding stress.

Experimental and Theoretical Study on Flexural Behavior of GFRP- and CFRP-Reinforced Concrete Beams after High-Temperature Exposure.

In this study, in order to study the flexural behavior of fiber-reinforced polymer (FRP) bars with reinforced concrete beams under static loads after high-temperature exposure, seven pieces of FRP-reinforced concrete beams were subjected to static bending tests and calculation model derivations. Four-point bending tests were carried out on FRP-reinforced concrete beams after high temperature treatment. The effects of high temperature and types of FRP bars on the cracking load, crack development, deflection and ultimate capacity, and failure mode of concrete beams were investigated. The test results show that the maximum crack width, deflection, and ultimate bearing capacity of GFRP- and CFRP-reinforced concrete beams decrease obviously with a rise in high temperature. After the exposure of 400 °C for 2 h, compared with the behavior of concrete beams at room temperature, the maximum crack width of GFRP and CFRP-reinforced concrete beams increased by 42.9% and 41.7%, respectively, the deflection increases by 103.6% and 22.0%, and the ultimate bearing capacity decrease by 11.9% and 3.9%. Meanwhile, through the analysis of the existing research results and test results, the calculation models for the maximum crack width, deflection, and residual ultimate capacity of FRP-reinforced concrete beams after exposure of high temperature were proposed. For FRP-reinforced concrete beams after high-temperature exposure, the errors between the measured maximum crack width, stiffness, residual bearing capacity, and their corresponding calculated values using the model were mostly less than 10%. The calculated value using the proposed model in this research is in good agreement with the measured value. The mechanical properties of FRP-reinforced high-strength concrete structures after high-temperature exposure can be preliminarily predicted, which provides a new theoretical basis for the application of FRP-reinforced concrete structures.

Nonlinear Mechanical Responses of Concrete Beams Reinforced with High-Performance CFRP Tendons

The nonlinear mechanical responses of concrete beams with carbon fiber-reinforced composite (CFRP) tendons were studied with the finite element model constructed within the nonlinear mechanics theory. The two typical prestressed CFRP-reinforced concrete beams were subject to nonlinear analysis, the stress behavior of the tendons was investigated, the latter and common steels were compared. Experimental data and calculated results are in good agreement. The cracking, yielding, and crushing characteristics of concrete can be well described with the smeared crack model via the Owen yielding criterion and the Hinton crushing criterion. The prestressed CFRP tendons are accurately simulated with combined nonlinear elements, and the corresponding analytical procedure was quite reliable. The CFRP tendons exhibit high strength, retaining their properties even when beam specimens are damaged. In comparison with common steels acting in the tension zone, the CFRP tendons are still in the elastic deformation region during the whole process.

Fatigue behavior of concrete beams reinforced with glass- and carbon-fiber reinforced polymer (GFRP/CFRP) bars after exposure to elevated temperatures

This paper deals with fatigue performance of concrete beams reinforced with fiber reinforced polymer (FRP) bars after exposure to elevated temperatures. A total of 13 concrete beams reinforced with glass- and carbon-fiber reinforced polymer (GFRP/CFRP) bars were tested under static and fatigue loading after exposure to different levels of elevated temperatures. The influences of elevated temperature, holding time, fatigue load level and FRP bar type on the fatigue behavior of beams were investigated. The results showed that the elevated temperature exposure reduced more severely the fatigue life of GFRP-reinforced concrete beam than that of CFRP-reinforced beam below 400 °C, and GFRP- and CFRP-reinforced beams both lost their bearing capacities when the exposure temperature reached 600 °C. The elevated temperature accelerated the development of concrete strain, crack width and deflection of FRP-reinforced concrete beams with the number of fatigue cycles. The mid-span deflection was predicted using some existing models, and the CEB-FIP model showed the best accuracy with the coefficient of variation of 2.8–7.0%. The fatigue strength of GFRP- or CFRP-reinforced concrete beams is not affected by elevated temperatures up to 400 °C for 2 h.

Debonding Detection and Monitoring for CFRP Reinforced Concrete Beams Using Pizeoceramic Sensors.

The bonding status between Carbon Fiber Reinforced Polymer (CFRP) and concrete is one of the key issues for the safety of CFPR-reinforced structures, thus it is of great importance to detect the debonding as early as possible. Instead of detecting the debonding which is artificially set at the very beginning, this paper investigates the feasibility of using low-cost piezoceramic sensors to detect and monitor the debonding of CFRP-reinforced concrete beams in situ. For existing debonding detection, a concrete beam reinforced with CFRP sheet was loaded through the three-point bending test till failure to induce debonding between CFRP sheet and the concrete substrate, and piezoceramic sensors were used to detect the existing debonding by analyzing the receiving ultrasonic waves. In addition, the debonding detection results were further compared with and verified by the vision-based strain testing results. For in-situ debonding monitoring, 10 piezoceramic sensors were used as an array to track the wave transmission changes during the loading process of a CFRP-reinforced concrete beam, and the debonding development process was successfully monitored. The test results show that the low-cost piezoceramic sensors are very effective to generate and receive ultrasonic waves, and are capable of detecting the existing debonding and monitoring of the in-situ debonding process as well.

Exploratory experimental study on flexural behavior of CFRP-reinforced concrete beams subjected to acidic loading effect

This article presents an exploratory study on the flexural behavior of carbon fiber–reinforced polymer–reinforced concrete beams subjected to acidic loading effect. To this end, an artificial acid rain with a pH level of 1.5 was prepared by mixing sulfate and nitric acid solutions. Eight reinforced concrete beams with/without carbon fiber–reinforced polymer applications were constructed and conditioned using the artificial acid rain. During conditioning, bending loads were applied to the top surfaces of the beams to simulate the acidic loading action. Three carbon fiber–reinforced polymer reinforcement schemes (corrosion reinforcement, reinforcement corrosion, and cracking reinforcement) were considered. After conditioning, the length and quantity of initial cracks in the beams were recorded. A combined ultrasonic–rebound method was then adopted to measure the strength and corrosion depth of the concrete and evaluate the beams’ integrity. Next, four-point bending tests were conducted to study the beams’ flexural behavior. It can be concluded that all beams deteriorated with the increase of the corrosion time. Carbon fiber–reinforced polymer–reinforced concrete beams performed better than normal reinforced concrete beams under the acidic loading effect. The initial cracks can influence the flexural behavior of carbon fiber–reinforced polymer–reinforced concrete beams.

Guided waves for debonding identification in CFRP-reinforced concrete beams

Ultrasonic guided waves excited and sensed by surface-bonded piezoelectric wafers were simulated and used to quantitatively evaluate the debonding between concrete beams and carbon fibre reinforced polymer (CFRP) overlay. Eight concrete specimens reinforced by composite overlay were prepared with different bonding conditions, which were simulated by inserting different sizes of Teflon films when the overlay was cured. A continuous wavelet transform based signal processing method was implemented to filter out broad-band environmental noise in the experiments. In consideration of the inevitable discrepancies in different specimens due to concrete preparation and sensor installation, a time-reversal process was applied to individual specimens to achieve self-comparison between the originally emitted and reconstructed wave signals which were sent back to the actuator. That procedure highlighted discrepancies in specimens, caused by different debonding conditions. Debonding indices were successfully calculated to quantify the severity of debonding, showing the potential of guided waves for integrity evaluation of CFRP-reinforced concrete structures.

Study on Thermal Stress of Concrete Beams with Carbon-Fiber- Reinforced Polymers at Low Temperature

Concrete beams reinforced with carbon-fiber-reinforced polymers (CFRPs) are subjected to considerable thermal stress at low temperatures. To mitigate this problem, this study conducts a series of tests on three concrete specimens at various temperatures, analyzes the change rule of thermal stress in CFRP-reinforced concrete beams, and discusses the influence of CFRPs on thermal stress in terms of the elastic modulus, thickness, thermal expansion coefficient, beam height, and concrete grade. The results show that when the temperature decreases, CFRP has an obvious restraining effect on the thermal curve of concrete beams. The thermal stress on the interface of CFRP-reinforced concrete beams is sufficiently large and should not be ignored. In particular, in cold areas, thermal stress should be taken into account when reinforcing structures such as concrete bridges. The CFRP sheet’s elasticity modulus and thickness are the main factors affecting the thermal stress; in comparison, the expansion coefficient and beam height have lesser effect on the thermal stress; finally, the concrete grade has little effect on the thermal stress. Thermal stress can be prevented feasibly by using prestressed CFRP sheets to reinforce concrete beams. This study can serve as a reference for concrete reinforcement design.

Analysis on Flexural Property of CFRP Reinforced Concrete Beam

It is repair and reinforcement for damaged buildings that has become the main method to save investment and to avoid waste of resources. CFRP reinforcement is one of the reinforcement methods widely applied in recent years, which has advantages such as high strength, light self weight, small thickness, and good durability, etc. In this paper a reasonable constitutive model is selected and a simulation model of CFRP reinforced concrete beam is established by using ANSYS finite element software. The influences of different CFRP layers and concrete strength to the flexural property of reinforced concrete beams is analyzed in this paper. Moreover, a comparison is made with unreinforced concrete beams. The results show that the ultimate load of the beam reinforced by CFRP has greatly improved and mid-span deflection has been limited. With increase of CFRP layers, flexural property of the reinforced beam is enhanced. Under the circumstance of same number of CFRP layer, the higher the concrete strength is the better the reinforcement effect will be.

Finite Element Modeling of Mode I Failure of the Single Contoured Cantilever CFRP-Reinforced Concrete Beam

The single contour cantilever beam (SCCB) test method has been developed with the intent to capture Mode I opening failures of CFRP-reinforced concrete beams. Recent development in the method explores possible shifting damage into the concrete substrate by using the International Concrete Repair Institute (ICRI) Surface Profile Level Three (SP3) as the desired CFRP bonded interface to concrete. To validate and explain the interface fracture behavior, finite element analysis using special cohesive elements has been performed. The cohesive element allows separation of the concrete substrate from the CFRP. This paper presents the simulation of laboratory test results, where failure in the substrates has been successfully reproduced. The simulation results indicate that finite element method using cohesive elements can successfully replicate Mode I critical strain energy release rate and the peak capacity of the laboratory tests and may have the potential to simulate actual applications.

The Application of CFRP Reinforced Concrete Beams

This paper expounds the excellent characteristics of CFRP in engineering application, analyzes the scope of application of CFRP reinforced plastics.This paper introduces the principle and the carbon fiber composite reinforcement method and frame beams and carbon fiber reinforced beam in the structure of the calculation results were analyzed .By SAP2000 software analyzing, results show that after using CFRP reinforced plastics has dramatically enhanced the bearing capacity of the frame beam, improve the ductility of the components, prolong the life span of the structure .

Experimental Research on the Stiffness of CFRP Reinforced Concrete Beam

This thesis analyses the destruction mode, the crack developing and beam deflection changes of 20 reinforced concrete beams including un-strengthened beam, direct strengthened beam and secondary load reinforced beam through tests and researches. The results show that using CFRP to strengthen the reinforced concrete beams will not only effectively increase the bearing capacity of the beam, but also inhibit the beam cracking and improve the flexural rigidity of the beam during normal use. In addition, the initial damage will have a certain impact on the stiffness of the strengthened beam.

Study on Shear Resistance and Durability of CFRP Reinforced Concrete Beams

Through carrying capacity test of CFRP strengthened test beam and unstrengthened comparison beam under corrosion of chlorine ion, thispaper analyzes the shear resistance and durability of CFRP repaired and strengthened concrete beam. Crack generation, deflection, electrochemical index and deformation of reinforced concrete beam under service are comparedand analyzed. It is indicated that CFRP can play a favorable screening role and can effectively prevent crack development. There is no shear failure after load is applied. So CFRP can obviously improve the shear bearing capacity and durability of reinforced concrete beam. Besides, different strengthening methods have relatively obvious influence of its durability.

Evaluation of bond stress-slip models for FRP reinforcing bars in concrete

In this paper several currently available bond stress-slip models for steel and FRP reinforcing bars in concrete are firstly reviewed, and both merits and demerits of these models are discussed. The models which are promising to be used for describing the bond-slip behaviour of FRP reinforcing bars in numerical analysis are evaluated through finite element analysis of FRP-reinforced concrete beams with bond-slip effect taken into account. A newly developed composite beam element with bond-slip is employed for finite element analysis of a GFRP-reinforced concrete beam and a CFRP-reinforced concrete beam with the selected bond stress-slip models built in the finite element model. The suitability and capability of the bond stress-slip models informed from the finite element analyses are summarised and concluded. Finally, parametric study is carried out on the most appropriate bond stress-slip model to investigate the effect of different surface conditions of reinforcing bars on the structural behaviour.

Deflection and cracking behavior of RC beams externally reinforced with carbon fiber laminates

This article presents the results and discussions of experimental and analytical work on CFRP-strengthened RC beams investigating the cracking and deflection performance. The aim of this study is to evaluate the time-dependent behavior by different degrees of strengthening scheme and two types of sustained loads. Eight RC beams were cast and tested under sustained loads for cracked and uncracked section. An analytical method based on EMM is developed to predict the time-dependent behavior of CFRP externally bonded RC beams. A simplified tension stiffening model for calculating the time-dependent deflection is modified for CFRP-reinforced concrete beams.

The Shear and Durability of CFRP Reinforced Concrete Beams

At present, the research on the performance of the shear and durability of CFRP reinforced concrete beams is few, the destruction of the curved and scissor section is often much subtle and suddenly. Based on the experimental investigation on the durableness of the CFRP concrete beams which has been shear reinforced and non-reinforced in the chloride ion erode, a comparative analysis on the fissure development, deflection, electrochemistry index and strain of the concrete beam were given under load. The results indicate that carbon fiber could limit the fissure development efficiently, and there were not the shear failure after loading, the beams with carbon could improve its shear capacity and durability efficiently, But The increase of durability is more depends on the reinforcement way.

Optimal efficiency factor in strut-and-tie model for FRP-reinforced concrete short beams with (1.5 < a/d < 2.5)

A new model for the efficiency factor of the concrete strut in the strut-and-tie model is proposed in this study for FRP-reinforced concrete short beams with (1.5 < a/d < 2.5). The ultimate load capacity of tested FRP-reinforced short beams was evaluated using the proposed model along with other models for the efficiency factor used in strut-and-tie models of design codes such as the ACI, CSA, and AS3600. It was found that efficiency factor models used in existing reinforced concrete design codes do not predict the ultimate load capacity of FRP-reinforced short beams as accurately as they do for steel-reinforced short beams. This can be attributed to not accounting for the effect of the shear span to effective depth ratio, a/d and the axial stiffness of the flexural reinforcement on the efficiency factor of the concrete strut in reinforced concrete short beams. Ultimate shear load capacity predictions by the proposed model were in agreement with experimental data obtained on 15 GFRP and CFRP-reinforced concrete short beams tested in the laboratory. The proposed model for the efficiency factor was shown to be statistically more accurate yielding the lowest standard deviation and coefficient of variation compared to those of the ACI, AS3600, and CSA A23.3 models. It was also found that shear equations recommended for FRP-RC beams by design guidelines such as the CSA S806-02, ISIS, JSCE, and ISE render very conservative predictions of the ultimate load capacity of FRP-reinforced short beams.