Carbon Fiber Reinforced Polymer Sheets Research Articles

Behavior of FRP-Retrofitted Wall-like RC Columns after Preloading to Simulate In-Service Conditions

In the Middle East, wall-like reinforced concrete (RC) columns are a common choice in multistory buildings. Sometimes, these columns need axial retrofitting for increased load capacity. In practice, unstrengthened columns bear their load, and if retrofitting is necessary, the load is released before the upgrade—unlike in past research studies that overlooked this real-world scenario. This study aimed to investigate the response of preloaded wall-like RC columns after being retrofitted using different configurations. In the experimental campaign, two half-scale columns were cast and axially loaded to 80% of their capacity, and the load was then totally released. After that, these specimens were strengthened with two different schemes, and hence, they were concentrically loaded until failure. In both schemes, the section shape was not modified. The first scheme comprised wrapping carbon FRP (fiber-reinforced polymer) sheets together with near-surface mounted (NSM) steel rebars. However, the second technique was composed of wrapping glass FRP (GFRP) sheets together with NSM steel rebars and bolted steel plates. The second scheme was found to be superior to the first one due to the extra confinement provided by the bolted steel plates. This scheme improved the peak load, stiffness, and dissipated energy by 115%, 75%, and 524%, respectively. Other than the testing campaign, nonlinear numerical modeling was undertaken to examine the behavior of tested specimens. The models were utilized to conduct a parametric study, exploring the influence of the percentage of preloading and the amount of load release on the response of columns strengthened with the second scheme.

Numerical, Theoretical, and Experimental Analysis of LVL-CFRP Sandwich Structure.

Optimization of structural elements via composition of different components is a significant scientific and practical point-of-view problem aimed at obtaining more economical and environmentally friendly solutions. This paper presents the results of a static work analysis of small-size laminated veneer lumber (LVL) beams reinforced by a Carbon Fiber Reinforced Polymer (CFRP) sheet. The nominal dimensions of LVL beams were 45 × 45 × 850 mm, and 0.333- and 0.666-mm thick reinforcement layers were used. The reinforcement was applied on opposite sides of the cross section obtaining a sandwich-type structure. An epoxy resin was used as a bonding layer. The bending tests were conducted in the so-called four-point bending static scheme in edgewise and flatwise conditions. The results of experimental tests confirmed the validity of this combination of materials. The highest load-bearing capacity was obtained for configuration, where CFRP sheets with a thickness of 0.666 mm were placed on the sides of the core, parallel to the direction of loading and the veneer's grain in the core. The increase in this case was up to a maximum of 57% compared to the core alone. The highest bending stiffness increase, 182% compared to the core alone, involves placing two layers of sheets perpendicular to the direction of loading, i.e., on the upper and lower surfaces. The presented novel sandwich structure can be competitive against traditional steel and reinforced concrete elements in civil engineering and can be utilized as beams or slabs.

Rehabilitation of reinforced concrete beam: Sustainable restoration mortar with waste materials

The current application of epoxy resin in the installation of fiber sheets for concrete beam restoration presents practical challenges, limited fire resistance, and lacks environmental sustainability. Additionally, epoxy resin cannot be used on wet surfaces as it compromises adhesion and reduces durability. In this study, we propose an effective mortar formulation that incorporates waste materials such as marble powder (MP), red mud (RM), and electric arc furnace dust (EAFD) for fiber sheet installation. The performance of the developed mortar was comprehensively assessed through various experiments, evaluating compressive and tensile strengths, water absorption (WA), sulfuric acid resistance (SAR), and microstructural characteristics of the restoration mortars. Furthermore, three reinforced concrete (RC) beams were constructed and subjected to a four-point bending test. One beam was strengthened with carbon fiber-reinforced polymer (CFRP), while the other two utilized fiber-reinforced cementitious material (FRCM) with either CFRP mesh or glass fiber-reinforced polymer (GFRP) bar. The findings reveal that RC beams strengthened with CFRP mesh-restoration mortar and GFRP rebar-restoration mortar exhibit load-carrying capacities 13% and 36% higher, respectively, compared to that reinforced with CFRP sheets. This study lays the foundation for future research by demonstrating, for the first time, the superior performance of mortar-based restoration over epoxy resin, thereby opening up new possibilities for the development of concrete element restoration.

Experimental and numerical evaluations of the shear performance of recycled aggregate RC beams strengthened using CFRP sheets

Conserving the ecosystems of the globe, protecting natural resources, and improving environmental conditions can all be achieved by considering sustainability in the construction industry. Recycling of building and demolition waste is one of the key approaches being investigated to accomplish this target. Twelve reinforced concrete (RC) beams were constructed for the current study in order to analyze the shear behavior of recycled aggregate concrete (RAC) beams externally strengthened with carbon fiber reinforced polymer (CFRP) sheets. The main goal of the experimental matrix was to investigate the effect of the recycled aggregate ratio on the shear response of RAC, where three recycled coarse aggregate ratios of 20%, 60%, and 100% were suggested. Additionally, the effects of incorporating two or four CFRP strengthening layers on the ultimate load, failure pattern, load-deflection responses, and stiffness of RAC beams were also investigated. Results revealed that, when different ratios of recycled aggregate estimated at 20%, 60%, and 100% were substituted for natural aggregates, the compressive strength decreased by 4.3%, 24.2%, and 40.0%, respectively, compared to natural aggregate concrete. Moreover, the RC beam that was cast utilizing 20% recycled aggregates and strengthened with four CFRP sheets exhibited the highest ultimate load among all the tested RAC beams of 84.8 kN, which was 22.9% higher than the un-strengthened specimen totally cast with natural aggregate. Furthermore, a three-dimensional (3D) non-linear finite element model (FEM) was constructed using the ABAQUS program in order to compare the effects of employing continuous CFRP sheets for the whole critical shear span length to intermittent strips that had been experimentally tested.

Static and seismic strengthening of RC frame joints by using CFRP sheets with various anchoring methods

This study proposes an indirect strengthening method using carbon fiber-reinforced polymer (CFRP) and hybrid bolt-plate locking anchored CFRP hoops, which is more suitable than direct externally bonding strengthening on the reinforced concrete frame joints due to the orthogonal beam and slabs and debonding problem, especially for improving seismic performance. To understand the structural behavior of the joint using the proposed strengthening method, static and quasi-static cyclic tests were carried out on 8 joint specimens in a scale of 1:2. Three different anchoring systems were compared including through-slab CFRP closed hoops, border-beam-slab U-shaped CFRP anchored hoops, and the newly proposed hybrid bolt-plate locking anchored CFRP hoops. Results show that the hybrid bolt-plate locking anchored CFRP hoops has the least damage to the original structure and can be the most effective method in delaying the slip of the longitudinal rebars and the debonding of the CFRP on the beam, which can significantly enhance the seismic performance of the joint. Compared with the unstrengthened case, the yield load, ultimate load and ductility coefficient improved 25%, 19.7% and 55.7%, respectively. Under the cyclic loading, the utilization ratio of longitudinal CFRP sheet can be further improved with respect to the other two methods, up to 1.5 and 1.75 times respectively. Additionally, theoretical calculations were performed to predict the bearing capacity of the joints, which shows good agreement with the experimental values. The findings are significant in the engineering application to improve the structural behavior and performance of the joint using the proposed strengthening method.

Investigation on interference and damage behaviours of electromagnetic riveted double-sided countersunk 30CrMnSiA/CFRP joints

Carbon fibre reinforced polymer (CFRP) structures benefit from electromagnetic riveting (EMR). However, incorrect riveting parameters could result in damages in CFRP structures during the EMR process. Excessive interference size may introduce initial damages to the joints. As a result, in this paper, the damage behaviours and the interference characteristics of the 30CrMnSiA/CFRP double-sided countersunk electromagnetic riveted joints are investigated. The riveting damage experiment was conducted, with the regular pressing riveting (RPR) process as a comparison. Moreover, a progressive damage FE model considering multiple typical damage modes of CFRP was developed for EMR damage prediction. The results show that when the rivet-hole diameter increases by 5% (4.08mm to 4.28mm), the average interference size of the joint under EMR and RPR processes decreases by 41% and 53%, respectively. Double-sided countersunk riveted joint interference size along the rivet axial distribution is not uniform, the CFRP sheet side of the interference size is relatively small. The EMR achieves a tighter, more uniform interference fit, while causing more severe riveting damages to the CFRP structure. Initial riveting damage exhibits a variety of modes, with delamination damage showing most significant sensitivity to rivet hole clearance.

Fatigue performance of electromagnetic self-pierce riveting-bonding hybrid joint under alternating load and corrosion coupling conditions

Electromagnetic self-pierce riveting (E-SPR) process was suitable for joining carbon fiber reinforced plastics (CFRP) and aluminum sheets. The E-SPR joints of dissimilar material still suffered from corrosion, and bonding could be an auxiliary process to improve corrosion resistance of joints. This paper investigated the fatigue characteristics of electromagnetic self-pierce riveting-bonding hybrid joints under alternating load and corrosion coupling conditions. Neutral salt spray (NSS) test, microscope observation, and fatigue test were conducted. Results showed that the adhesives not only improved the joint’s corrosion resistance, but also its mechanical properties. Specifically, the shear curves contained two peak loads, namely peak A and peak B. Corrosion was the greatest at 840 h, where peak A was 42.86% less than at 0 h, but peak B had little effect. Moreover, the addition of adhesives significantly impacted the fatigue characteristics of the joints after corrosion. The E-SPR-bonded joints still appeared good anti-fatigue characteristics within 168 h of corrosion. The fatigue failure modes were fractures in the CFRP sheets and the rivets remaining in the aluminum sheets. The influence mechanism of corrosion on fatigue was revealed. The water molecule and chloride ions penetrated the adhesives to cause hydrolysis, increased the plasticity of the adhesives and decreased the bond strength, which reduced the fatigue characteristics. The results provided theoretical guidance for E-SPR-bonded joints applied in engineering applications.

Shear Strengthening of Reinforced Concrete Beams Using Engineered Cementitious Composites and Carbon Fiber-Reinforced Polymer Sheets

This study evaluates the performance of Reinforced Concrete (RC) beams enhanced in shear using Engineered Cementitious Composites (ECCs) and Carbon Fiber-Reinforced Polymers (CFRPs). The experimental study encompasses fifteen RC beams. This set includes one control specimen and fourteen beams fortified in shear with Externally Bonded (EB) composites. Two of these specimens were enhanced with ECC layers, while the remaining were augmented with combined CFRP-ECC layers. Variables in the test included the ECC layer thickness, matrix type, number of CFRP layers, and strengthening configurations such as full wrapping, vertical strips, and inclined strips. The results indicated that the shear capacity of the fortified beams increased by 61.1% to 160.1% compared to the control specimen. The most effective structural performance was observed in the full wrapping method, which utilized a single CFRP layer combined with either 20 mm or 40 mm ECC thickness, outperforming other techniques. However, the inclined strip method demonstrated a notably higher load-bearing capacity than the full wrapping approach for beams with double CFRP layers paired with 20 mm and 40 mm ECC thicknesses. This configuration also exhibited superior ductility compared to the rest. Furthermore, the experimental shear capacities obtained were juxtaposed with theoretical values from prevailing design standards.

Providing a strategy to restore damaged RC beam-column joints with the combination of CFRP and HPFRCC

This paper endeavors to assess the seismic performance of 3D reinforced concrete (RC) beam-column joints situated on the exterior of buildings, but lacking special ductility requirements. The joints have been rehabilitated by High-Performance Fiber-Reinforced Cement Composites (HPFRCC) and retrofitted using Carbon Fiber Reinforced Polymer (CFRP) wrap methodology. In this context, five beam-column joints located on the exterior of a structure have been subjected to cyclic lateral loading, while being scaled down to half their original size. The present study entailed an investigation into the cyclic behavior of three control specimens in its initial stage. Following the initial examination, it was observed that the control specimens, lacking any designated ductility standards, experienced significant core damage. During the subsequent phase of experimentation, the impaired concrete sections of the control samples were remediated through substitution with HPFRCC matter. Additionally, CFRP sheets were implemented for retrofit purposes. The modified specimens were then exposed to comparable cycles of loading. An analysis is conducted on the empirical findings of the specimens under investigation. The findings of this study indicate that the utilization of HPFRCC materials and CFRP sheets in the restoration and enhancement of deteriorated joints has led to a notable enhancement of their strength and displacement capacity. Specifically, this approach has facilitated the creation of a flexural plastic hinge and impeded the occurrence of shear failure within the core, leading to an improved overall behavior of the repaired damaged joint, which is comparable to that of undamaged seismic joints. The application of this technique demonstrates a high degree of efficacy in the rehabilitation and enhancement of edifices with deficient seismic details that have sustained damage subsequent to an earthquake event.

Square concrete-filled steel tube strengthened with carbon fiber-reinforced polymer grid-reinforced engineered cementitious composite under axial loading

This paper presents an investigation on axial compression behavior of square concrete-filled steel tube (CFST) columns strengthened with carbon fiber-reinforced polymer (CFRP) gird-reinforced engineered cementitious composite (CFGRE). A total of 19 columns, including 3 un-strengthened CFST columns, 1 CFST column strengthened with CFRP sheets, and 15 CFST columns strengthened with CFGRE, were prepared and tested. The main test parameters involved the strengthening strategy, number of CFRP grid layers, width-to-thickness ratio of the steel tube, and concrete strength grade. The CFST columns strengthened with CFGRE showed a ductile failure, with the CFRP grid rupturing at the corner. The CFGRE provided confinement to the original column in the transverse direction and, along with the bearing load contribution of engineered cementitious composite in the longitudinal direction. This resulted in a significantly greater enhancement in load-bearing capacity compared to the CFST columns strengthened with CFRP sheets. The CFST columns strengthened with CFGRE demonstrated a similar developing trend in load–deformation curves as the CFST columns during the entire loading process, indicating its strong adaptability to the original structural system. A finite element model was established to evaluate the failure process of the strengthened columns. A calculation formula was proposed to predict the load-bearing capacity of the CFST columns strengthened with CFGRE, taking into account the effect of the uneven confining pressure on the confinement provided by CFGRE.

Efficiency of Flange-Bonded CFRP Sheets in Relocation of Plastic Hinge in RC Beam–Column Joints

Beam–column connection zones are high regions of interest in reinforced concrete (RC) structures, which are expected to respond elastically to seismic loads. Using carbon fiber-reinforced polymers (CFRP) to improve these connections, performance is critical in retrofitting deficient RC frames because existing slabs may pose numerous limitations in the design and wrapping of CFRP sheets in joints. The main aim of this research is to develop a new design for flange-bonded CFRP retrofit of frames, including slabs, for the relocation of plastic hinges of the connection area toward the beam and to develop beam–column joint capacity and building stability in cases of subjection to dynamic loads. The performance of these proposed retrofittings was explored both experimentally and numerically. Two full-scale fabricated interior RC joints of a real moment-resisting frame with moderate ductility were subjected to monotonic loads before and after retrofitting, and the results were used to detail the numerical progress and verify of the beam–column connection. Moreover, a parametric study was conducted on CFRP sheets’ optimal thickness to examine its influence on plastic hinge relocation in the connection region. Results show that the retrofitting method can efficiently relocate the plastic hinge to the mid-span of the beam, which, in turn, leads to improved capacity and achievement of the RC frame and guarantees better structural safety a lower cost.

Compressive Performance of Longitudinal Steel-FRP Composite Bars in Concrete Cylinders Confined by Different Type of FRP Composites.

This paper presents an experimental study on the compressive performance of longitudinal steel-fiber-reinforced polymer composite bars (SFCBs) in concrete cylinders confined by different type of fiber-reinforced polymer (FRP) composites. Three types of concrete cylinders reinforced with (or without) longitudinal SFCBs and different transverse FRP confinements were tested under monotonic compression. The results showed that the post-yield stiffness of SFCBs is higher when confined with high elastic modulus carbon fiber-reinforced polymer (CFRP) composite than with low elastic modulus basalt fiber-reinforced polymer (BFRP) composite. Decreasing confinement spacing did not significantly improve the compressive strength of SFCBs in concrete cylinders. The compressive failure strain of SFCBs could possibly reach 88% of its tensile peak strain in concrete cylinders confined by CFRP sheets, which is significantly higher than the value (around 50%) in previous studies. Existing design equations, which applied a strength reduction factor or a maximum compressive strain of concrete to consider the compressive contributions of SFCBs in concrete members, underestimate the load-carrying capacity of SFCB-reinforced concrete cylinders. The design equation that considers the actual compressive stress of SFCBs gives the most accurate prediction; however, its applicability and accuracy need to be verified with more experimental data.

Unbonded Pre-Tensioned CF-Laminates Mechanically Anchored to HSC Beams as a Sustainable Repair Solution for Detachment of Bonded CF-Laminates

The present article outlines a Finite Element Model (FEM) that was created and validated by comparing it to prior experimental investigations to estimate the flexural performance of HSC beams strengthened with exterior bonded, unbonded, and unbonded pre-tensioned Carbon Fibre Reinforced Polymer (CFRP) sheets in several patterns. Nonlinear analysis was performed on three-point-loaded beams using ANSYS software, incorporating the constitutive characteristics of various components (concrete, CFRP, and steel). The comparison of FE-models and experimental data, namely for load-deflection curves, crack patterns, and failure modes, revealed that the developed numerical FE-models and experimental outcomes are in good accord. There has been numerous prior research on the behavior of beams strengthened with externally bonded CFRP sheets, but few on those reinforced with externally unbonded CFRP laminates, and even fewer on HSC beams reinforced with externally unbonded pre-tensioned CFRP laminates. Therefore, the major contribution of this article is to investigate the flexural behavior of HSC beams strengthened utilizing externally unbonded pre-tensioned CFRP laminates. The analysis revealed that the bending performance of RC-beams strengthened using external unbonded pre-tensioned CFRP-laminates is quite similar to that of bonded CFRP-strengthened beams, indicating a high potential for tackling the durability issues caused by detachment of bonded CFRP-strips in such structural elements. The existence of a fully wrapped CF sheet forced the beam to develop diagonal shear cracks in the region between the wrapped CF sheet and beam supports while also enhancing the flexural cracked zone at mid-span to change from smeared to discrete fractures. The flexural fractures spread over a deeper and wider area of the beam as a result of the incorporation of a half-wrap CF laminate. Externally unbonded CFRP-sheets pre-tensioned with 45% of the CFRP ultimate strength utilizing various patterns (straight and U-wrap) performed similarly to bonded CFRP-sheets, with a slight boost in load capacity of around 4.5% and notable reduces in deflection ranging from 9.7% to 16.24%. Using exterior unbonded CFRP laminates to strengthen RC-beams resulted in a flexural capacity increase ranging from 22.3% for NC beams to 71.6% for HSC beams.

Flexural behavior of steel fiber reinforced concrete beams comprising coarse and fine rubber and strengthened by CFRP sheets

Despite having many advantages, using rubber to produce reinforced concrete members like beams is still restricted. When there is more waste tire rubber in concrete structures, rubber concrete's flexural and compressive strengths gradually decrease. However, this study used steel fibers to improve compressive strength and externally bonded carbon fiber-reinforced polymer (CFRP) sheets to increase flexural strength. Four groups of three reinforced concrete beams each were established for the study's use. The first and third groups of concrete beams used a volumetric replacement of fine and coarse aggregates with 5% and 10% waste tire rubber. However, steel fibers were added to the second and third groups at a rate of 1.25% of the concrete volume. Waste tire rubber and steel fibers were not replaced or added to the fourth group, the main reference group. The dimensions of each beam were 2.1×0.2×0.3 m. A concrete beam's first member is always free of external reinforcement, followed by its second member, which has one layer, and its third member, which has two layers of CFRP sheet. ABAQUS, a finite element analysis program, was used numerically to represent the third strengthening layer. The results showed that strengthening the reinforced rubberized concrete beams with a single layer of CFRP sheets increased the load at first crack and failure by 8.57% and 17.64%, respectively, compared to the unreinforced reference beam, compensating for the loss caused by the production of rubberized concrete and adding additional flexural strength. These loads increased by 31.43% and 26.45%, respectively, due to the steel fibers added to the beams containing these waste tire rubber. Strengthening with two layers of CFRP sheets increased the load at first crack and failure by 17.14 and 34.27, respectively. The steel fibers added to the beams that contained these amounts of waste tire rubber, on the other hand, caused these loads to increase by 42.86 and 49.23%, respectively. Strengthening with three layers numerically results in an exponential increase in load at the first crack and the failure by 8.03 and 52.88%, respectively. On the other hand, the loads on the beams that contained these quantities of waste tire rubber increased by 50.49% and 104.47%, respectively, when steel fibers were added to them.

Experimental and theoretical investigation of the structural behavior of reinforced glulam wooden members by NSM steel bars and shear reinforcement CFRP sheet

Abstract Reinforcing the wooden structural members is considered as a challenging matter to overcome the drawbacks of using wood in the construction field. The current investigation, therefore, presents an attempt to evaluate the effectiveness of utilizing steel bars as reinforcements in glulam timber beams using the near-surface-mounted (NSM) technique in conjunction with carbon fiber-reinforced polymer (CFRP) sheet wraps. A series of flexural testing was carried out until failure for both reinforced and unreinforced glulam members in a simple support system. Eleven specimens were examined in two groups to compare them with the control beam. Five reinforced glulam (RG) beams of the first group were reinforced with different schemes at tension and compression zones using the same bar size. The other five specimens of the second group were reinforced with shear reinforcement using fully wrapped strips made of CFRP sheet in addition to the same flexural reinforcement schemes as the first group. Each glulam beam has a span of 1.35 m and a rectangular section sized 85 mm × 175 mm. Based on experimental outcomes, theoretic modeling was provided to estimate the ultimate load capacity and bending rigidity of reinforcing glulam members. Though several theoretical predictions of flexural capacity were overstated when compared to experimental predictions, these disparities were frequently about 10%, confirming that the proposed theoretical model was accurate, and the mean of ultimate loading capacity and deflection between experimental and theoretical results were 1.01 and 1.09, respectively. Experimental results presented show that the RG beams performed much better than the unreinforced reference beams in terms of structural behavior, with improvements in ultimate load capacity ranging from 16 to 49%. On the other hand, the shear reinforcement for RG members slightly improved flexural performance, and the ultimate load capacity increased by 2–7%. Therefore, it was concluded that the NSM techniques using ordinary steel bars were effective ways in strengthening the glulam members in terms of flexural stiffness with increasing ultimate load capacity.

The behavior of reinforced lightweight concrete beams with initial cracks

This research examines the performance of reinforced lightweight concrete beams subjected to several degrees of damage (50%, 60%, 70%, and 100%). It can use a sheet made of Carbon Fiber Reinforced Polymer (CFRP) to reinforce. The Full U-wrapping rehabilitation method was tested in the presented experimental program. In this method, CFRP sheets are attached to the bottom only and the side and bottom of the beam section. Experiments proved that the service load (Ps) increases by 7.06 % from a damage level of 50 % to 70 %, rises by 1.21 % from a damage level of 60 % to 70 %, and falls by 3.07 % from a damage level of 100 %. The result also rose for the fortified sample by 11.99%. Increases of 42.67 %, 33.07 %, and 23.73 % in the stiffness ratio (k) were observed at damage intensities of 50, 60, and 70 %, respectively. Damage at lower severity levels is increasing at a faster rate. The ductility of the restored LWC beams is more excellent than the control, as with the stiffness. Damage levels of 50%, 60%, and 70% saw increased ductility of 35.60, 34.92, and 34.69 %, respectively.

Experimental study on the effectiveness of strengthening reinforced concrete slab-column connections using CFRP sheets

This paper presents an experimental study on the effect of externally bonded carbon fiber-reinforced polymer (CFRP) sheets on the punching shear behavior of interior slab-column connections. Two square slabs with a concentric column were fabricated, measuring 1200 ´ 1200 ´ 80 mm for the slabs and 200 ´ 200 mm for the column. One specimen served as an unstrengthened control specimen, while the other specimen was strengthened using CFRP sheets. The specimens were simply supported along their edges and subjected to punching tests, with the vertical load applied through the central column. The experimental results revealed that the application of CFRP sheets significantly improved the performance of the slab-column connections. The strengthened slab exhibited a 16.3% increase in punching capacity compared to the control specimen. Additionally, a calculation was conducted to determine the punching shear strength of the test specimens, taking into account the interaction between shear and flexural capacities in a two-way flat slab. This calculation provided a deeper understanding of the impact of CFRP sheet strengthening on the enhancement of the strength of the slab-column connections.

Experimental investigation and analytical prediction on bond behaviour of CFRP-to-concrete interface with FRP anchors

Hybrid bonded technology with fiber-reinforced polymer (FRP) anchors can effectively improve the load capacity of carbon fiber-reinforced polymer (CFRP)-to-concrete interface. To investigate the reinforcement effect of FRP anchors, tensile shear tests of seventeen CFRP-concrete bonded joints with additional FRP anchors were conducted in this paper. The effects of the construction sequence, anchor position, and type of FRP anchor were considered in the experimental investigation. It was found that bonding CFRP sheet before installing FRP anchor and construction simultaneously could ensure the integrity of FRP anchor and provide a better anchor effect. The ultimate load-carrying capacity was increased with the increasing of plate length after anchor, that is the effect of anchor position. From the results of specimens with different types of FRP anchors at the same location, the FRP anchor composed of multiple small anchors can take effect earlier. By fitting the test results, the exponential bond-slip model for the CFRP-to-concrete interface and the elastic constitutive model for the FRP anchor were obtained. Further, substituting the two constitutive models, analytic theoretical models for load-slip curves and strain distribution were derived to predict the bond behavior of FRP anchored CFRP-to-concrete interface in this paper. The comparison between the prediction results and experimental data shows the good predictive accuracy of these analytical models.

Effect of Fireproof Coatings on the Post-Fire Behavior of CFRP Composite Sheets

This study examines the effect of two self-developed novel fireproof coatings on the fire resistance of carbon fiber-reinforced polymer (CFRP) composite sheets. The post-fire flexural properties were chosen as important indicators of fire resistance. This research involves two distinct fire conditions, the standard fire condition and the large-space fire condition, to simulate general interior fires and large-space fires. The post-fire flexural performance of CFRP sheets coated with two different self-developed fireproof coatings was evaluated through three-point bending tests after fire exposure. The experimental findings demonstrated a significant reduction of up to 80% in the post-fire flexural properties of CFRP sheets without fireproof coatings. However, CFRP sheets coated with fireproof coatings exhibited a substantial enhancement in their post-fire flexural properties. Under the large-space fire condition, the fire-resistance duration of CFRP sheets coated with fireproof coatings of at least 25 mm thickness exceeded 2 h, satisfying the requirements of GB50016-2014 fire-resistance class III (columns), class I (beams), and class I (floor slabs), respectively. Under the standard fire condition, CFRP sheets covered by fireproof coatings of 35 mm thickness exhibited a fire-resistance duration of 0.75 h, meeting the requirements of GB50016-2014 fire-resistance class IV (columns), class IV (beams), and class III (floor slabs), respectively.

Compression behavior of RC wall-like columns strengthened using NSM/CFRP system without shape modification

The wall-like columns are commonly employed in high-rise buildings for carrying heavy loads without affecting the usable space. However, the retrofitting of these columns often becomes essential under some circumstances. Thus, the designers are looking for strengthening schemes that do not cause changes in the column section for which a combination of near-surface mounted (NSM) bars and carbon fiber reinforced polymer (CFRP) confinement can be adopted. This study was undertaken with the objective of developing such a scheme and studying the confinement provided by CFRP wrapping on wall-like columns. In this study, besides testing two control columns, four columns strengthened using different schemes were tested in axial compression. The performance of the schemes was assessed in terms of the failure modes, load-carrying capacity, and different characteristics of the load-displacement plots. The best scheme was found to be the one wherein the column was strengthened using NSM steel bars connected to the column heads, along with the wrapping of three CFRP sheets covering the NSM rebars. Two analytical models were proposed to estimate the peak load. The first model used the approach of both the ACI 318-19 code and ACI 440.2R-17 guidelines, whereas, the second model utilized the formulas of both Eurocode 2 and the ACI 440.2R-17. The second model predicted the peak load of retrofitted columns more accurately than the first one with prediction errors for the second model varying from 2% to 9%.