CFRP Sheets Research Articles

Flexural reliability of corroded RC beams strengthened with CFRP sheets considering longitudinal corrosion non-uniformity of steel bars

The corrosion of steel bars in RC beams along the longitudinal direction is usually non-uniform, thereby increasing the variabilities of failure mode and flexural behavior of corroded RC beams strengthened by CFRP sheets. This paper analyzed the flexural reliabilities of CFRP sheet-strengthened corroded RC beams, which considered the corrosion non-uniformities of longitudinal steel bars along the beam length. Based on the failure mode-based calculation method and Monte-Carlo simulation, the beams were discretized into a series of units along the beam length and the failure probabilities of the beams were considered as the failure probabilities of the serial units. Meanwhile, the occurrence probabilities of failure modes at bending failure were also studied. Parametric analysis results showed that the occurrence probabilities of failure modes were affected by steel reinforcement corrosion degrees, CFRP strengthening ratios and initial strains at concrete tensile edge. Meanwhile, the longitudinal corrosion non-uniformity could significantly affect the occurrence probabilities of different failure modes and degrade the flexural reliabilities; e.g., for RC beams under third-point bending, when the corrosion degree is 0.3, the predicted reliability index with considering longitudinal corrosion non-uniformity can be 28.3% lower than that without. The proposed reliability calculation method could accurately assess the impacts of longitudinal corrosion non-uniformity on flexural reliabilities and lay a solid foundation for calibrating design factors used in CFRP sheet-based strengthening designs, thereby contributing to both evaluating the safety of existing CFRP sheet-strengthened corroded RC beams and designing the strengthening CFRP sheets for existing corroded RC beams, which improve the safety and maintenance of existing RC structures in corrosive environments.

Stitching of T-deep beams with large openings by CFRP sheets and NSM steel bars

AbstractIn the present study, a comparison has been conducted to investigate the efficiency of stitching using the near-surface mounted steel bars and externally bonded carbon fibers reinforced polymers technique for strengthening the T-deep beams having large opening within the shear spans and with deficient shear reinforcement. Eight specimens with two locations of openings were tested. It was found that stitching of beams by steel bars with openings located flush to the flange yielded improvement in capacity in range (10–39%). Furthermore, Stitching by external bonded carbon sheets yield enhancements in capacity was 96 and 78% for the top location compared to the control specimen and the vertical near-surface mounted stirrups system. The respective values for the bottom location were 62 and 42% respectively.

An experimental study on RC beams externally strengthened by anchored CFRP sheets monitored by Digital Image Correlation

During the past few decades, strengthening and rehabilitation of reinforced concrete (RC) structures using fiber-reinforced polymer (FRP) composites have been considered one of the most promising techniques to achieve the required strengthening and structure life span. This paper analyzes the effects of different anchorage increments using the Externally Bonded Reinforcement (EBR) strengthening technique with CFRP on the mechanical properties and deformability capacity of reinforced concrete beams subjected to bending. Axial compression, ultrasonic pulse velocity, and elastic modulus tests were carried out on cylindrical concrete specimens, and the Digital Image Correlation (DIC) technique was used to monitor the total surface deformation and track the development of cracks in the reinforced concrete beams. Strain Gauges (SGs) were used to monitor the tensile reinforcement, the compressed concrete, and the CFRP strain. Experiments on twelve beams are carried out, and the measured data from the monitoring devices are compared. The accuracy of DIC for strain and displacement monitoring matches the performance of traditional methods, with the added benefit of providing full-field monitoring.

Flexural performance of RC beams using hybrid anchored ​CFRP sheets with bond defects

Hybrid anchorage technique can effectively prevent end debonding and impede intermediate debonding of CFRP sheet in strengthened reinforced concrete (RC) beams. However, its effectiveness in the presence of bond defects at the CFRP-concrete interface is unclear. Therefore, this study conducted four-point bending tests on CFRP-strengthened RC beams, considering two factors: bond defects (with and without) and strengthening methods (externally bonded and hybrid anchorage). The results showed that bond defects can lead to premature intermediate debonding of the CFRP sheet, resulting in a 22.49% decrease in debonding load due to local stress concentration around them. Owing to the effectiveness of the hybrid anchorage method, the propagation of the intermediate debonding is significantly impeded, leading to a 4.32% and 21.61% higher in ultimate load and deflection, respectively. This is because the hybrid anchorage can control the distribution of local cracks and improve the overall stress distribution of CFRP. A finite element analysis was performed and compared against the experimental results which shows good agreement. Then, parametric analyses were conducted to further analyze the flexural behavior of the strengthened beams with bond defects. Finally, an analytical model was proposed to predict the flexural capacity of the hybrid strengthened beams with bond defects.

Flexural property of damaged steel-concrete composite girders strengthened with CFRP sheet

Flexural property of damaged steel-concrete composite girders strengthened with CFRP sheet

Experimental Study of Punching Shear on Reinforced Concrete Waffle Slabs Strengthened by CFRP Sheets

Experimental Study of Punching Shear on Reinforced Concrete Waffle Slabs Strengthened by CFRP Sheets

Experimental and numerical study on the flexural properties of RC beams with different CFRP-strengthened schemes

This study conducted a four-point bending experiment investigation on the flexural performances of the RC beams strengthened with various CFRP schemes. Four beams were employed, i.e., the ordinary RC beam (L0), the RC beam bonded with CFRP sheet (L1-C), the CFRP U-wrapped RC beam (L2-U), and the RC beam using CFRP rivets (L3-A). Test results highlighted the obvious improvement in the flexural performances of CFRP-strengthened beams in terms of enhancing load-carrying capacities and limiting overall deformations compared to beam L0. In addition, end anchorage systems, including CFRP U-hoop and CFRP rivets, changed the failure mode, restricted crack propagation, and mitigated the bottom CFRP sheet debonding effectively. The ultimate loads of beams L1-C, L2-U, and L3-A were 27.4 %, 36.4 %, and 41.6 % higher than beam L0, respectively, indicating that CFRP rivets performed the best in improving the beams' flexural properties. Finite element analysis was developed to simulate the bending experiment process. The numerical results comply well with the experiments in terms of the crack distribution pattern and bending force history. Then, parametric studies for the design suggestions with the use of the modes reveal that the implementation of the CFRP rivet with a depth of 80 mm and a diameter of 10 mm seems to be an ideal optimization plan for the beams herein.

Energy dissipation damage constitutive relation of CFRP passively confined coal sample

In view of the stability problem of coal pillars left over during coal resource mining, (Carbon Fiber Reinforced Polymer) CFRP sheet is applied in coal pillar reinforcement. Uniaxial compression tests of CFRP passively confined coal samples are carried out to explore the mechanical response mechanism of passively confined coal samples under different layers, and the energy dissipation damage constitutive relationship of CFRP passively confined coal samples is established based on the energy dissipation principle. The conclusions are: As CFRP layers increased, the local damage of coal samples before the peak evolved from a 'cliff-like jagged' to a 'capillary jagged', with post-peak instability marked by a shift to more 'cliff-like' characteristics. The tests revealed improvements in peak strength and elastic modulus, with a defined functional relationship between these properties and CFRP layers. The energy storage capacity of passively confined coal samples improved with CFRP layers, requiring less axial deformation to achieve equivalent energy levels. The energy dissipation rate showed an initial decrease followed by an increase, with a minimum inflection point, the elastic energy consumption ratio tends to decrease slowly and then rapidly during post-peak instability. A damage constitutive relationship and evolution equation were developed, highlighting that the CFRP sheet significantly inhibits damage, with diminishing effectiveness beyond two layers. The study concludes that three-layer CFRP sheets provide optimal confinement, offering a novel strategy for the reinforcement of coal pillars and the prevention and control of rock burst, without considering the actual coal pillar dimensions and shape. To sum up, the use of CFRP sheet to strengthen coal pillar has considerable potential research value in strengthening coal pillar and improving the recovery rate of coal resources.

Experimental study on the fatigue behavior of CFRP-strengthened cracked steel plates under eccentric axial tension

In this paper, an experimental investigation has been conducted to study the fatigue behavior of single edge-notch steel plates strengthened with CFRP (laminates/sheets). The plates have been subjected to eccentric fatigue under axial loading conditions. The experimental study includes fourteen specimens and has been tested under axial loading until failure. The constant parameters in the study are steel material grade, steel plate dimensions, and fatigue loading conditions. Meanwhile, the studied parameters are steel plate initial edge crack size, CFRP configurations (length, one or two-sided, and laminates or sheets), and adhesive material strength. The experimental results revealed that the fatigue life for specimens strengthened with CFRP sheets or CFRP laminates can be improved by a factor of 1.15 to 3.87 and 1.47 to 6.32, respectively, compared with the un-strengthened specimens. The results show that using CFRP can be considered an efficient way to repair the initial cracks in steel elements under eccentric axial fatigue loading.

Improve the Flexural Behavior of One-Way Ribbed Slab by Using CFRP Sheet

One of the most important research projects in the recent years is strengthening structures. The significance of these studies was to modify the ability of buildings to withstand high loads without utilizing materials that hurt the environment. Six one-way ribbed slabs were experimentally tested in the present study to determine the effect of carbon fiber reinforcement polymer sheets on the structure. One of the specimens, used as a reference, was unstrengthen. Two specimens were strengthened with carbon sheets on 50% and 100% of the rib width. To prevent sheet debonding, two others used 50-mm-wide U-shaped strips. A complete rib wrap served as the final method of strengthening. All the specimens underwent concentrated load testing to investigate the ultimate capacity, deflection, stiffness, and ductility. According to the findings, all specimen’s deflection decreased in a ratio ranging from 4% in whole rib wrap to 46%. Also, the stiffness increased in all specimens, and the width of the carbon sheet insignificantly affected the stiffness, while the way of strengthening did. In the end, strengthening with 50% width has no discernible effect on the ultimate load (3%), whereas strengthening with 100% width raised by 41%, while adding U-shaped stripes increased the ultimate load capacity by 74% and completely wrapping the ribs increased by 132%.

FRP strip wraps for enhancing the fire resistance of RC beams strengthened with CFRP sheets bonded using the EBROG method: An experimental study

In recent decades, the application of fiber-reinforced polymers (FRP) composites in strengthening structural members has increased due to their low weight, high strength, and easy implementation. However, one of the main weaknesses of these materials is that as the temperature rises, the resin resistance and, consequently, the bond strength between the FRP and concrete member rapidly diminish. This causes the FRP to separate from the concrete substrate and prematurely fail the member. Therefore, previous studies have widely suggested fire protection materials to mitigate this weakness. However, it increases costs and exacerbates architectural problems. To eliminate the need for fire protection systems or reduce their thickness, this paper evaluates the combined effect of using FRP mechanical anchors and utilizing the EBROG Grooving method on reinforced concrete beams for flexural strengthening FRP. A total of six rectangular control beams were tested under flexural loads at ambient temperature, and four beams were examined under simultaneous flexural loading and fire conditions. The proposed anchorage system included two-layer wrapped CFRP strips along the beam axis at specified intervals and fan anchorage with holes with 120 mm spacing. To assess the effectiveness of the proposed anchorage systems and determine the maximum capacity of the beams, they were first examined at ambient temperatures. The results showed that under standard fire conditions, due to the formation of a tangential cable mechanism, RC beams strengthened with one and two layers of flexural CFRP and anchored with two-layer wrapped CFRP strips withstood constant loads of 7,85 KN and 9.8 KN for 77 and 66 min, respectively. Also, the RC beam resisted fire for up to 106 min under the applied load.

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.

Behavior of Fatigue Damaged Reinforced Concrete One-Way Slabs Repaired With CFRP Sheets

Abstract The results of experimental research involving nine one-way slabs are detailed in this report. The objective was to investigate the impact of different parameters on the structural performance of these slabs in their absence and with strengthening. Externally bonded CFRP sheets strengthened six of the nine slabs; the three remaining slabs served as control specimens. Before subjecting the specimens to monotonic loading, pre-fatigue damage of 50% and 70% repeated loading was induced. An exhaustive assessment was conducted on each slab, in which it was compared to its control slab. Several crucial elements were incorporated into the evaluation, including the ultimate load capacity, the reason for failure, crack patterns, and load-deflection curves. Examining these metrics was intended to provide insight into the efficacy and structural performance of the employed fortification technology. Compared to unenhanced reinforced concrete slabs (control slab), the highest stresses on slabs supported with bonded CFRP sheets are between 20 and 44% better. Compared to the control slab, an almost 70% reduction in deflection was observed. The flexural performance of compromised reinforced concrete slabs repaired with this technology can be brought up to date and enhanced.

Experimental-numerical study on axial compression performance of square concrete columns confined by new-type BFRP

Abstract Facing the substantial protection requirements for reinforced concrete structures exposed to severe erosion conditions, a novel composite material(Basalt Fiber Reinforced Polymer, BFRP) based on epoxy silicone resin as a matrix was introduced in this study. This material exhibits notable enhancements in resistance to acid and alkali corrosion, ultraviolet irradiation, as well as high and low temperature extremes. However, it exhibits lower elastic modulus and higher ductility. To evaluate the effectiveness of this new BFRP composite material in reinforced concrete structures, a comprehensive investigation was conducted by model testing, numerical simulations, and theoretical analysis. This study analyzed the impact of wrapping configuration, number of wrapping layers, concrete strength, and spacing-to-bandwidth ratio on the mechanical properties of concrete square columns. The findings revealed that the loading curve trends for specimens reinforced with the new BFRP sheet and CFRP sheet (Carbon Fiber Reinforced Polymer, CFRP) were almost similar, although the reinforcement effect was comparatively worse for the former. When both layers were fully applied, the axial compression bearing capacity increased by 28.45% and 64.73%, respectively. The number of wrapping layers and the parameters related to concrete strength significantly influenced the reinforcement effect, whereas the influence of spacing-to-bandwidth parameters was less pronounced. Current specifications demonstrate suitable applicability for CFRP-reinforced specimens but limited applicability for BFRP. The calculation model proposed in this paper accurately predicted the axial compression bearing capacity of a new BFRP-reinforced columns, with an error margin kept within 5%.

Hybrid strengthening of RC beams with externally bonded carbon fiber reinforced polymer laminate and engineered cementitious composites transition layer

This paper presents the experimental study on the reinforced concrete (RC) beam strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) laminate and engineered cementitious composites (ECC) material. A total of six beams were tested under the four-point bending test to investigate the influence of strengthening scheme, type of CFRP laminate and the width of CFRP plate on the flexural response. The results revealed that hybrid strengthened beam with the technical of EB-CFRP and ECC transition layer significantly enhanced the crack load (29.0%–133.3%), yield load (50.9%–96.5%) and ultimate load (50.0%–81.9%) of the beams relative to the control beam. The employment of ECC material was an ideal transition layer for delaying the interfacial debonding of CFRP laminate, where the ultimate tensile strain of CFRP plate in hybrid strengthened beams was 13.2%–33.33% higher than that of beam merely strengthened with EB-CFRP plate. Beams strengthened with CFRP sheet had the greater flexural performance and higher utilization of CFRP than its counterparts strengthened with CFRP plate. Moreover, the predicted model associated with ultimate bearing capacity of the hybrid beams was provided based on ACI 440.2R-08, which was relatively conservative with a margin for the ultimate load of the hybrid strengthened beams.

Experimental Investigation of Ductility in GFRP RC Beams by Confining the Compression Zone

Nowadays, building structures in corrosive environments requires some considerations. Being lightweight, high tensile strength, and corrosion resistance are the features that make fiber-reinforced plastic (FRP) bars an alternative component for longitudinal steel reinforcement of concrete. On the other hand, the linear elastic behavior of FRP bars, alongside the brittle behavior of concrete, makes brittle members without considerable ductility. In this paper, the effect of compression region confinement with CFRP sheets on the FRP-reinforced concrete beams was experimentally investigated. Eight GFRP reinforced beams with 2 m length, including one reference beam and seven confined beams, were constructed and tested under a four-point bending test. Based on the type of confinement, specimens are categorized into four groups. Flexural behavior improvements, including load carry capacity, energy dissipation capacity, and ductility, were observed in at least one specimen of each confined group. According to the results, the specimen that was spirally confined with a 30 mm ribbon width and angle of 10° had the best total energy absorption up to about 110% improvement in comparison to the unconfined specimen. On the other hand, vertically confined specimens with 50 mm ribbon width showed the highest improvement in ductility indices and load carrying capacity up to 60% and 11% in comparison to unconfined specimens, respectively. Due to concrete compression zone fractures in flexural failure mode, the over-reinforce method is considered the design philosophy. Results indicate that regardless of the confinement type (discrete vertical, discrete spiral, or continuous spiral confinement), there is an optimal amount for width, blank space between ribbons, and depth of confinement to achieve the best flexural behavior.

Identification of Optimum Retrofitting Approach for Strengthening RC Beams using CFRP Sheets

Identification of Optimum Retrofitting Approach for Strengthening RC Beams using CFRP Sheets

Investigation on the joining process and strength of laser circle welding between Al5052 and CFRP dissimilar materials

Laser welding is an effective approach to joining metal and composite. In the present research, laser circle welding was proposed to join the Al5052 sheet and PA6-CFRP as the first try. A process window was suggested according to the welding results and joint appearance. Single lap shear test was employed to evaluate the mechanical performance of welded joints under different welding conditions. The cross-section and fracture surface were subjected to multi-scale characterizations to subdivide the joining zone and understand the joining process. The result showed that 10 sets in 18 groups of welding parameters can achieve successful bonding. The welding results can be classified into four categories: non-connected, aging-failing, effective-joining and burn-through. The joining zone of laser circle welding was divided into three subregions. The adhesive zone (AZ) presented an interfacial fracture while the local failing passed through plastics basement in cohesive (CZ). The overheating of CFRP generated decomposed zone (DZ). The signal peak of O-C=O bond disappeared in the entire joining zone on CFRP sheet and the intensity of carbide was significant in DZ. The laser circle welded joint presented brittle and ductile fracture modes, which were related to the joining zone component. The joining strength can reach about 656 ± 22 N, 2135 ± 331 N and 3223 ± 257 N under one-circle, double-circle and three-circle scanning, respectively. Increased scanning numbers can decrease the required laser power and improve joining strength by extending heating time, while it also increased the risk of burn-through.

Effect of different anchorage schemes on the flexural behavior of RC slabs strengthened with CFRP sheets

This research investigated the behavior of RC slabs subjected to four points loading with five different CFRP sheet numbers (1, 2, 3, 4, 5) and three different anchorage systems (Type 1 used CFRP strips in the transverse direction, Type 2 used galvanized steel end plates without grooving, Type 3 used galvanized steel end plates with grooving). A total of twenty reinforced concrete (RC) solid slabs were cast to fulfill the study objectives. Results showed that the presence of CFRP strips enhanced the slab's ultimate load capacity by 102 %, reduced mid-span deflection by 12 %, also improved energy absorption capacity and stiffness by 36 % and 32 %, respectively. Type 2 anchorage system without grooves and type 3 anchorage system with grooves both used galvanized steel end plates and enhanced the flexural capacity of the slabs by 119 % and 125 %, respectively, also improved the RC slab properties and shifted the failure mode from delamination to a CFRP strips rupture. The introduced anchorage system without grooving was found to be an efficient and easily applied technique with high efficiency in terms of capacity and serviceability.

Behavior of reinforced concrete inverted T-girders with hollow webs strengthened by CFRP sheets in flexure

Behavior of reinforced concrete inverted T-girders with hollow webs strengthened by CFRP sheets in flexure