CFRP Reinforcement Research Articles

Shrinkage behaviour of high-strength concrete plates reinforced with carbon textile reinforcement

Carbon textile reinforcement is a relatively new type of CFRP reinforcement which, when utilized with high-strength concrete, leads to the production of ultra-thin free-form concrete shells. However, such reinforcement usually suffers from weak resistance to compressive stresses, while high-strength concrete is susceptible to high shrinkage rates. This combination may lead to a boor shrinkage behaviour, and thus an excessive shrinkage-related craking. Therefore, this paper aims to study the shrinkage behaviour of high-strength concrete plates reinforced with carbon textile reinforcement. Additionally, the utilization of shrinkage-compensating concrete as a possible shrinkage mitigation method was also investigated. For this aim, twelve concrete plates of dimensions 500 mm × 150 mm x 30 mm were cast. The shrinkage and expansion behaviour of the specimens were monitored for six months using the distributed fibre optic sensor (DFOS) technology, and then all the specimens were tested till failure under a direct tension test. The results have revealed that the existence of textile reinforcement does not provide any significant resistance to the negative strains generated from the shrinkage of concrete, which, for restrained concrete plates, leads to the formulation of wide cracks. On the other hand, the utilization of shrinkage-compensating concrete not only eliminates the formulation of shrinkage-related cracks but also reduces the crack’s width resulting from the loading process by up to 35 % during all stages of loading as illustrated by the fibre optic sensors measurements. Additionally, shrinkage-compensating concrete exhibits a slightly higher compressive strength than normal concrete.

Fatigue performance criteria for CFRP Reinforcements Based on RC behavior in civil construction

Fatigue performance criteria for CFRP Reinforcements Based on RC behavior in civil construction

An interpretable machine learning-based model for shear resistance prediction of CFRP-strengthened RC beams using experimental and synthetic dataset

Existing analytical models for predicting the shear resistance of RC beams strengthened with externally bonded CFRP reinforcements exhibit deficient performance due to their inability to accurately capture the complex resisting mechanisms. Combined with significant statistical uncertainties in shear failure, driven by its brittle nature, this further undermines the reliability of these models. To address these limitations, this study leverages Machine Learning (ML) to develop more robust and reliable predictive tool. A rigorous feature-selection process identified eight predictors as the most influential. Subsequently, nine ML-algorithms were trained on a refined experimental dataset comprising 239 beams, with XGBoost emerging as the top performer. This model also outperformed established models likefib Bulletin-90 and ACI 2023 models. However, the limited scope of the experimental dataset constrained the model’s predictive performance especially when separately evaluated on beams strengthened with U-wraps, full wraps or side-bonded FRP configurations. Therefore, to achieve a more reliable model a synthetic dataset was generated using Tabular Variational Auto-Encoder. The XGBoost model trained with the synthetic dataset significantly improved the performance of the former model and exhibited better predictions for all strengthening configurations. Finally, to ensure the physical consistency of predictions, values obtained from the SHapley Additive exPlanations method were analysed.

Composite Fiber Wrapping Techniques for Enhanced Concrete Mechanics

This study systematically investigates the enhancement effects of different fiber-reinforced polymer (FRP) materials on the axial compressive performance of concrete. Through experimental evaluations of single-layer, double-layer, and composite FRP reinforcement techniques, the impact of various FRP materials and their combinations on concrete’s axial compressive strength and deformation characteristics was assessed. The results indicate that single-layer CFRP reinforcement significantly improves concrete axial compressive strength and stiffness, while double-layer CFRP further optimizes stress distribution and load-bearing capacity. Among the composite FRP reinforcements, the combination with CFRP as the outer layer demonstrated superior performance in enhancing the overall structural integrity. Additionally, numerical analyses of the mechanical behavior of the reinforced structures were conducted using ABAQUS 2023HF2 finite element software, which validated the experimental findings and elucidated the mechanisms by which FRP influences the internal stress field of concrete. This research provides theoretical support and empirical data for the optimized design and practical application of FRP reinforcement technologies in engineering.

Study on increasing load capacity of wooden arch bridge by CFRP strengthening: experimental and numerical Verification

The wooden arch corridor bridge is a typical representative of Chinese wooden bridges, holding significant historical research value. Currently, these bridges face issues of severe component deformation and insufficient load-bearing capacity. To address these problems, this study employs CFRP reinforcement on the components of wooden arch corridor bridges to reduce deformation and enhance load-bearing capacity. Experimental research on CFRP reinforcement has yielded the elastic modulus of the bonding interface. Given the lack of an accurate numerical model for wooden arch corridor bridges, this study establishes a precise numerical model by setting parameters based on load test data from wooden arch corridor bridges. The elastic modulus obtained from the experiments is input into the numerical model for analysis. The results indicate that CFRP exhibits excellent reinforcement performance, with the load-bearing capacity of the reinforced damaged components still reaching 75%–85% of their original capacity, while the load-bearing capacity of the reinforced undamaged components increases to 130%–140% of their original capacity. The failure modes of the CFRP-reinforced wooden components suggest that allowing for some gaps in the bonding of CFRP can enhance overall ductility. The application of CFRP to wooden arch corridor bridges also demonstrates favorable reinforcement effects, increasing the load-bearing capacity of the arch surface by approximately 20%, thereby providing a theoretical basis for the reinforcement of wooden arch bridge frameworks.

Investigation of buckling capacity behaviours of corroded tanks

The use of thin-walled steel shells is rapidly becoming widespread. Depending on their purpose, they can be susceptible to corrosion in the environments they are used in. This leads to metal loss and consequently a decrease in buckling strength. In this study, the effect of corrosion and CFRP reinforcement on thin-walled cylindrical steel tanks was experimentally investigated. Six samples with a length and diameter of 400 mm were tested; two samples were not subjected to corrosion, two samples were subjected to 2.5 % HCl corrosion, and two samples were subjected to 5 % HCl corrosion. The effect of CFRP usage was examined in both corroded and non-corroded samples. The results show that as the corrosion rate increases, the buckling strength decreases, and CFRP reinforcement recruitments the loss in buckling strength.

Experimental study on the behavior of damaged CFRP and steel rebars RC columns retrofitted with externally bonded composite material

The structural behavior of concrete columns reinforced with CFRP bars has been the focus of many researches over the past two decades. There is a dearth of comprehensive research concerning the axial compressive performance of retrofitted CFRP bars reinforced concrete (RC) columns. To fill this gap a thorough investigation was carried out to understand failure mode, load–displacement response, axial deflection, axial load-bearing strength, ductility index (DI), stiffness index (KI), and strength index (SI) of retrofitted CFRP bars RC columns. The experimental matrix comprised 14 short circular columns, seven reinforced with CFRP bars and hoops and the other seven with steel bars and hoops. Initial damage was induced through axial loading until a 35% reduction in peak axial strength was observed, after which damaged columns were repaired and retrofitted using CFRP sheets. The parameters of the study include concentric and eccentric compressions, transverse reinforcement spacing, CFRP wrapping, steel, and CFRP reinforcements. According to the findings, lowering transverse hoop spacing enhanced the utmost capacity and ductility of both types of retrofitted columns. The average peak strength and corresponding axial displacement of CFRP RC columns were 22.63% and 14.87%, and ductility (at a 20% load decrease) was 118% higher after CFRP retrofitting. The axial stiffness of damaged CFRP bars RC columns after strengthening with CFRP sheet were not fully rehabilitated and on average SI under concentric loading was 3.22% lower while DI under eccentric loading was 2.71% higher than steel RC columns.

Experimental and numerical investigation on the crashworthiness performance of double hat‐section Al‐CFRP beam subjected to quasi‐static bending test

AbstractNowadays, hybrid structures, which combine low‐density composites with low‐cost thin‐walled metals, have shown great effect in enhancing the performance of automotive body structures, especially the energy absorber components. This study focuses on the experimental and numerical investigation of the bending energy absorption behavior of CFRP/aluminum hybrid double hat‐section beams used in the side part of the car body. In the experimental section, two types of double hat‐section beams were fabricated: aluminum and Al/CFRP. These beams were then subjected to quasi‐static three‐point bending tests. The results demonstrated that the hybrid beam exhibited superior energy absorption capabilities compared to the single beam. Subsequently, a finite element model was developed using LS‐Dyna software and was validated by comparing the experimental and numerical load–displacement results. In‐depth numerical analyses were conducted to investigate the influence of various design parameters, including CFRP‐reinforcement configuration, numbers of CFRP layers, CFRP ply‐angle, CFRP reinforced length, and aluminum/CFRP mass, on crashworthiness indicators. The numerical findings indicate that the hybrid beam with , ply‐angles exhibited better crash force efficiency (CFE) and specific energy absorption (SEA) compared to other ply‐angles, respectively. Furthermore, increasing the number of CFRP layers within the total beam's mass improved its energy absorption capacity. It was also revealed that the CFRP length on the upper and lower hats could be considered as 42.5% of the total aluminum beam length, as opposed to the full CFRP length, providing enhanced energy absorption capabilities.Highlights Bending behavior of the Al and Al/CFRP double hat section beams. Effects of variable thickness and identical mass on the double hat section beam. Effects of variable ply angle and number of CFRP layers on the hybrid beams. Discrete effect of CFRP reinforcement configurations and inner CFRP lengths.

Investigating the effectiveness of CFRP strengthening in improving the impact performance of RC members

Rising global rail infrastructure expansion has increased accidents involving train derailments. Reinforced concrete (RC) elements require impact-resistance enhancement to prevent structural damage or failure. While extensive research has analyzed CFRP-strengthened concrete columns under dynamic loading, further understanding of CFRP's impact on RC members is needed. Considering dynamic factors, this study investigates CFRP-RC components' performance under asymmetric impact. Components wrapped in one, four, or six CFRP layers underwent high-energy asymmetric lateral impact testing to obtain deflection-time curves. Results showed that multiple CFRP layers significantly improved impact resistance by increasing plateau force, reducing maximum deflection to 42%, and shortening duration. Longitudinal-circumferential bonding conferred better reinforcement than other arrangements. However, multiple CFRP layers increased fracture susceptibility due to severe concrete damage. An equation was derived from dynamic equilibrium principles. Finite element modeling validated experimentally was used to simulate lateral impact. Impact force, deflection, and bending moment over time were compared. Impact resistance, flexural capacity, plastic deformation, and energy absorption were also examined. Internal force distribution and development were analyzed. A simplified calculation estimated maximum deflection. CFRP reinforcement methods' effects were examined. Results indicate CFRP elevates plateau impact force and average bending moment while significantly decreasing deflection and duration, greatly enhancing impact resistance and flexural bearing capacity.

Donatılı Zeminler için Alternatif Hafif Kompozit Panel Elemanları

Steel reinforced concrete facing members, which are used to fix geosynthetic reinforcements working against tensile forces inside soils and to resist active lateral earth pressures, have certain disadvantages, such as massiveness and corrosion. In addition, the aforementioned conventional panels are not economical since they frequently require maintenance and repair in terms of long-term stability. In this study, the utility of alternative composite panels is evaluated with the various arrangement and type of fiber reinforcements and a typical foam concrete. Panel tests and three-point bending tests are realized to determine the experimental behavior of steel, carbon fiber (CFRP) and glass fiber reinforced (GFRP) specimens, as well as unreinforced examples. Although CFRP wrapped specimens cannot reach expected levels, samples with GFRP present favorable performance as well as being cheaper. Specimens with mat GFRP enhance both strength and deformation capacities according to the results of axial and lateral deformations under diagonal loading condition. In addition, chopped GFRP applied foam concrete specimens have more strength in terms of bending test results, but CFRP reinforcements increase their displacement capacity.

Experimental Study on the Flexural Strengthening Performance of CFRP Reinforcement for RC Beams Deteriorated by Freezing and Thawing

Experimental Study on the Flexural Strengthening Performance of CFRP Reinforcement for RC Beams Deteriorated by Freezing and Thawing

Axial compression performance of square concrete filled double skin SHS steel tubular columns confined by CFRP

This paper focuses on the axial compression performance of 15 concrete-filled double skinned tubes CFDST columns with different CFRP reinforcement schemes. The design of this test used an outer square steel tube with a square steel tube inside, with concrete poured at the sandwich and the inner steel tube kept hollow. The structure is both cost effective and allows the hollow to be used for utility access. However, in recent years damage to CFDST has occurred due to fire, earthquakes, corrosion etc. Therefore, research into the reinforcement and repair of this structure is crucial. Compared to other reinforcement methods, FRP has the advantage of being lighter and more robust and does not significantly alter the original structure. In this study, the mechanical properties of the specimens were further analyzed from the data of load displacement, peak load and ultimate displacement by mainly observing and analyzing the damage mechanism of the specimens through the strengthening effect of different strengthening schemes for different hollow ratios. The results show that when the hollow ratio is not bigger than 0.33, the CFRP reinforcement effect is relatively obvious, especially the three-layer CFRP wrapped CFDST specimens have a substantial increase in bearing capacity and stiffness. Finally, an analytical study was carried out based on previous research and the experimental results agreed well with the calculated results.

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.

Prediction of shear strength for CFRP reinforced concrete beams without stirrups

Design guidelines in international codes show noticeable differences with regards to shear strength prediction of concrete beams reinforced with Fiber Reinforced Polymers, (FRP). These discrepancies in shear strength predictions are attributed to many factors affecting the shear behavior, such as shear span/depth ratio (a/d), beam size, rectangular and flanged cross-sectional shape (R-section and T-section), and concrete compressive strength. Shear resistance of beams longitudinally reinforced with carbon FRP, (CFRP), bars is not well defined in the literature compared to beams reinforced with steel bars. This is mainly attributed to the low modulus of elasticity of CFRP compared to traditional steel reinforcement resulting in relatively high strains generated in CFRP reinforcement and consequently wider cracks and lower contribution of the aggregate interlocking mechanism as well as dowel action in shear resistance. This paper numerically investigates the behavior of concrete beams reinforced in flexure with CFRP bars without transverse reinforcement to quantify concrete contribution in shear resistance. Specimens with R and T sections having different shear span-to-depth ratio, concrete compressive strength, and longitudinal CFRP reinforcement ratios are studied to determine the concrete contribution to shear resistance. The nonlinear program ATENA is used to simulate the actual behavior of concrete beams failing in shear and is verified against experimental results gathered from the literature to check the validity of the numerical model. The comparison shows good agreement between experimental and numerical results with a difference of 6% and then a parametric study is conducted to provide a better understanding of the effect of each parameter on the shear behavior of concrete beams reinforced with CFRP bars. The results of numerical models are compared to their counterparts predicted using different equations in codes and guidelines. It is found that the shear capacity of T-section is higher than R-section by about 15% to 25% mainly due to a change in cracking pattern due to the presence of the flange. Furthermore, the shear failure load increased by increasing the longitudinal reinforcement ratio as a result of decreasing strain and enhancement of dowel action. The effect of increasing concrete compressive strength was more pronounced on the shear capacity in arch action as opposed to diagonal tension regions. Finally, an equation is proposed to predict the shear capacity of concrete beams reinforced in flexure with CFRP bars. The shear capacity predicted by the proposed equation provided a good agreement with experimental results for 163 beams with a mean value of 1.01 and COV of 0.17.

Strengthening of deep RC coupling beams with FRP composites: A numerical study

Currently, most buildings have earthquake-resistant systems such as coupled shear walls and couple beams, designed based on previous code specifications. Also, due to specifications of new codes, diagonal reinforcement details in coupled beams are introduced, which due to the high reinforcement congestion, creates problems in fabrication and pouring. The main goal of this paper is to numerically study retrofitting with polymer composites reinforced with carbon fiber with external bonding for reinforced concrete coupling beams. The previous studies are divided into three categories. The first part concerns using externally bonded composite FRPs and the effect of fiber arrangement and thickness on the coupled beam behavior. The maximum displacement ductility in shear reinforcement patterns belonged to I and 2I patterns, which had the maximum ductility coefficients of 7.04 and 8.87. By comparing 7 CFRP reinforcement patterns, results showed that due to the mixed failure mode (flexural-shear) of the coupling beam, the U-X reinforcement pattern increased the load-bearing capacity by 18% compared with the base sample. By using suitable anchorage and preventing premature debonding, this method could be introduced as an effective method for improving the coupling beam’s behavior. In the second category, reinforcement with composite FRPs was compared with diagonal reinforcement and strengthening by installing steel plates and the accompanying behavior diagrams were given. Compared with other reinforcement methods in terms of load-bearing capacity and ductility, the specimen reinforced with CFRP and steel plates had a 49% and 70.4% increased load-bearing capacity of the control specimen. Among the studied specimens, the best performance belonged to the specimen with diagonal reinforcements, which had an increased load-bearing capacity and ductility of 124% and 4.2% compared with the base specimen. Finally, the third part is about the effective parameters of the coupling beam such as span length to height ratio and longitudinal reinforcement value regarding coupling beam behavior.

Axial compression performance of concrete filled double skin (SHS outer and CHS inner) steel tubular columns strengthened by CFRP

This paper reports the compressive behavior of concrete-filled double skin steel tubular (CFDST) columns strengthened by CFRP under axial loading. The outer skin was made of square hollow sections (SHS), while the inner skin was made of circular hollow sections (CHS). Twelve CFDST columns strengthened by CFRP and three CFDST columns were tested. The failure mode, load-displacement relationship, axial load-carrying capacity and initial stiffness are given and analyzed. The results showed that the CFDST columns strengthened by CFRP have better mechanical properties than the column without CFRP reinforcement (i.e. the CFDST columns). The CFDST columns strengthened by CFRP eventually failed due to CFRP rupture or buckling of the external steel tube near the end and cracked concrete damage from the outer steel tube. The stiffness and axial load bearing capacity of the column can be improved as the number of CFRP layers increases. A simplified design formula of CFDST columns strengthened by CFRP is proposed, which is in good agreement with the experimental results.

Buckling response of externally pressurised sealed and retrofitted steel cylindrical shells

Buckling response of steel cylindrical shells with no reinforcement or seal, cylindrical shells reinforced with CFRP, and cylindrical shells sealed against leakage was experimentally compared. Twelve cylindrical shells were tested; four had no reinforcement/seal, four were reinforced with CFRP, and four were sealed. The cylindrical shells had the same radius-to-thickness ratio of 445 but had various height-to-radius ratios of 2, 4, and 6. Results indicated that the buckling capacity of the shells decreased with increasing the shell height. Whilst a post-buckling response was established for the sealed shells, CFRP-reinforced shells had no post-buckling response. CFRP reinforcement significantly increased the shells' initial and overall buckling load, but the sealing was only effective in the initial buckling load.

Mechanical Properties on Various FRP-Reinforced Concrete in Cold Regions

The evaluation of frost resistance varies with different reinforcement methods, but it is a hot research topic for concrete reinforced with Fiber-Reinforced plastic (FRP). Freezing and thawing tests of FRP-reinforced concrete prisms and cylinders are presented to simulate beams and piers of buildings in cold climates. To evaluate the specimens’ frost resistance, tests with various reinforcement techniques, morphological analysis, weight tests, and relative dynamic modulus of elasticity tests were used. Examined also were the variations in stress–strain curves for axial compression tests and load–displacement curves for bending tests following various freeze–thaw cycles. The findings indicated that after 100 freeze–thaw cycles, the weight of unreinforced concrete cylinders decreased by 9.7%, and its compressive strength decreased by 27.6%. On the other hand, CFRP-reinforced concrete cylinders (Carbon-Fiber-Reinforced Plastics) and GFRP (Glass-Fiber-Reinforced Plastics) gained 1.1% and 1.58% in weight, respectively, while the compressive strength decreased by 7.4% and 8%. After 100 freeze–thaw cycles, the weights of concrete prisms with reinforcement, without reinforcement, and with CFRP reinforcement decreased by 12.13%, 8.7%, and 9.6%, respectively, and their bending strength was reduced by 20%, 42%, and 53%, respectively. The frost resistance of the two FRP-reinforced concrete types had significant differences under freeze–thaw cycles because the prismatic specimens were not fully wrapped with FRP materials. Finally, finite element software ABAQUS was used to simulate the freeze–thaw cycle test of the two specimens. Calculated values were compared to experimental results for the load–displacement curve and the axial stress–strain curve under bending load. The comparison of peak displacement produced a maximum error of 8.6%, and the FRP-reinforced concrete model validity was verified.

A comparative cradle‐to‐gate life cycle assessment of carbon fiber‐reinforced polymer and steel‐reinforced bridges

AbstractCarbon fiber‐reinforced polymer (CFRP) has proven to be an excellent replacement for conventionally used steel in the construction industry. This is especially relevant in bridge engineering, where its corrosion resistance, low weight‐to‐strength ratio, and outstanding fatigue properties can be put to appropriate use, for example, to prestress the bridge girders. These properties are a huge part of the success of prestressed CFRP bridges, which tremendously increase the structural and material efficiency and hence help facilitate the construction of slender and durable bridges. However, apart from the structural performance of the bridges, the aspect of sustainability (environmental viability, economic feasibility, and social acceptance) plays a vital role in determining the overall efficiency. Prior studies have illustrated that the CFRP reinforcements in themselves are relatively unsustainable as compared to conventional steel reinforcements. However, owing to the extraordinarily high material efficiency generally associated with structures built with CFRP reinforcements, it can be hypothesized that these are equally or even more sustainable as compared to their counterparts. In this study, an aspect of sustainability, namely, environmental impact, is addressed. As a first part of the study, cradle‐to‐gate CO2 emissions for conventional building materials and CFRP have been thoroughly reviewed and documented. Attributed to the heterogeneity of the data available for CO2 emissions from CFRP reinforcements, three scenarios (favorable, realistic, and unfavorable) were drawn up. Based on these values, a comparative life cycle assessment was undertaken for two bridge systems, namely, Rosensteinsteg II (already constructed) and an overpass over German highway A‐20 (design in process). For each bridge system, two separate variants with steel and CFRP reinforcements were considered. For Rosensteinsteg II, a reduction of approximately 28% was observed in the CO2 emissions (favorable global warming potential values for CFRP) once the steel was replaced with prestressed CFRP. A total of 18% reduction was observed for the A‐20 bridge with CFRP reinforcements. With the help of the current study, it could be concluded that, especially for bridges not experiencing heavy vehicular loads, prestressed CFRP bridges are the most environmentally feasible option.

Experimental Study on Fatigue Performance of Welded Hollow Spherical Joints Reinforced by CFRP

The risk of fatigue failure of welded hollow spherical joints (WHSJs) under alternating loads increases due to the inherent defects, the disrepair, and the demand for tonnage upgrades, of suspension cranes. The finite element analysis results revealed that the ranking of the stress concentration factor at the WHSJ was as follows: weld toe in steel tube of tube–ball connection weld > weld toe in steel tube of tube–endplate connection weld > weld toe in sphere of tube–ball connection weld > weld toe in plate of tube–endplate connection weld. Moreover, the peak stress at the weld of the tube–sphere connection was reduced by 32.93% after CFRP bonding reinforcement, which was beneficial for improving the fatigue performance. In this study, 16 full-scale specimens of Q235B WHSJs were tested by an MTS fatigue testing machine to study the strengthening effect of CFRP on the fatigue performance. It was found that the fatigue fracture of WHSJs was transferred from the tube–sphere connection weld to the tube–endplate connection after CFRP reinforcement. According to the fitted S-N curves, the fatigue strength could be increased by 13.26%–18.19% when the cycle number increased from 10,000 to 5,000,000.