Carbon Fiber Reinforced Polymer Confinement Research Articles

Axial stress versus strain responses of CFRP confined concrete containing electronic waste aggregates

This research work investigates the axial stress versus strain responses of un-strengthened and carbon fiber reinforced polymer (CFRP) composites strengthened concrete specimens made with electronic waste coarse aggregates. For this purpose, 36 circular and non-circular 300 mm high concrete specimens constrained with CFRP sheets and partially replaced with E-waste coarse aggregates were prepared. The effect of cross-sectional geometry, 20% partial substitution of natural coarse aggregates with E-waste aggregates, corner effect of non-circular concrete specimens, confinement of specimens with CFRP sheets, and effect of the number of confinement sheets were also studied. In control concrete specimens, the coarse aggregates were 848 kg/m3 and E-waste aggregates were 212 kg/m3. The cement was 475 kg/m3 and fine aggregates were 655 kg/m3. Test results indicated that compressive strength is reduced by substituting natural coarse aggregates with E-waste aggregates. At the same time, compressive strength increased to 71%, 33%, and 25% for circular, square, and rectangular concrete specimens, respectively, by CFRP confinement. Whereas the axial strain increased to 1100%, 250%, and 133%, for circular, square, and rectangular concrete specimens, respectively, by CFRP confinement. CFRP sheets also enhanced the Poisson's ratio. Because of the greater confinement given by a double CFRP layer, it is more effective than a single layer. Furthermore, results also indicated that strength reduction in non-circular concrete specimens was greater than in circular concrete specimens for all studied cases. In the end, for theoretical calculations, strength and strain models for confined concrete suggested by different researchers were applied and compared with experimental results. In comparison to the experimental findings, theoretical data showed that most of the models were either on the higher or on the lower side, while only some model results matched well with the experimental data.

Comparative evaluation of flexural response and damage assessment of concrete columns confined with CFRP and self-prestressing iron-based SMA

This paper experimentally compares the seismic retrofitting effects of carbon fiber-reinforced polymer (CFRP) and iron-based shape memory alloy (Fe SMA) for RC columns. Four circular RC columns with insufficient transverse reinforcement were provided with different retrofitting schemes and tested under quasi-static lateral cyclic loading. All specimens confined with CFRP and Fe SMA exhibited satisfactory global responses in terms of lateral strengths and flexural ductility up to ±7 % drift ratios. From the visual and nondestructive damage evaluations, it was found that the Fe SMA confinement yielded lower damage accumulation in concrete, compared to the CFRP confinement, by virtue of the prestressing effect.

Experimental and analytical model of CFRP-confined spontaneous combustion coal gangue aggregate concrete

In this study, carbon fiber reinforced polymer (CFRP) confined cylindrical concrete specimens were tested under monotonic axial loading. The effects of the replacement ratio of the spontaneous combustion coal gangue aggregate (SCGA) and stiffness of the CFRP confinement on the mechanical properties of concrete were mainly considered. The results showed that the confinement efficiency of CFRP on the concrete decreases with increasing SCGA content. Despite the increase in the confinement stiffness, the confinement efficiency of the CFRP confinement on high-content SCGA concrete (SCGAC) will also be significantly reduced. Evidently, the influence of aggregate properties on confined concrete cannot be ignored. A CFRP-confined analysis model considering the SCGA replacement ratio was established. Through the verification of existing test data, its accuracy meets the requirements.

CONFINED REINFORCED CONCRETE VERTICAL ELEMENT DUCTILITY UNDER LATERAL LOAD: INFERENCE FROM TEST RESULTS

Vertical elements fail during earthquakes due to lateral load. Carbon-fiber-reinforced polymer (CFRP) can play a significant role in preventing sudden collapse due to lateral load. Confinement provided by transverse shear reinforcement and polymer sheets increases both the compressive and lateral strength of concrete. To test the effect of CFRP confinement on concrete columns, seven square and four circular vertical specimens were tested and results were compared with theoretical predictions at Bangladesh University of Engineering and Technology. The specimens were wrapped at the vertical portion on an intermittent basis so that CFRP strips fell at the gap of horizontal reinforcements of the specimens’ vertical portion. Cyclic shear test was performed while maintaining axial compression. The test results were close to the theoretical predictions. The results thus suggest that CFRP wraps can contribute increased shear strength and ductility of vertical elements. High-strength concrete specimens did not reach their maximum strength due to the testing facility’s limitations, but they provided the expected results in the lower bound.

Comparative study of compressive behavior of confined NSC and UHPC/UHPFRC cylinders externally wrapped with CFRP jacket

This study conducted a fundamental investigation on compressive behaviors of carbon fiber-reinforced polymer (CFRP)-confined normal-strength concrete (NSC) and ultra-high performance concrete (UHPC)/ultra-high performance fiber-reinforced concrete (UHPFRC) subjected to concentric axial loading. The mechanical behavior of confined UHPC/UHPFRC, such as the failure mode, stress-strain response, and lateral dilation behavior, was found different from that of confined NSC. Specifically, the passive confining behavior of UHPC/UHPFRC was distinguished from NSC in terms of concrete crack evolution. Diverse cracking propagation patterns resulted in distinct dilation ratios and CFRP efficiency factors. The CFRP confinement could delay the formation of shear cracks, resulting in a linear increasing stage of the first branch in the stress-strain curve of CFRP-confined UHPC/UHPFRC. Moreover, existing stress-strain models available for CFRP-confined UHPC/UHPFRC were profoundly evaluated in this study.

Finite element analysis on compressive behaviour of tin slag polymer concrete with fibre reinforced polymer composites confinement

Finite Element Analysis (FEA) forecasts how tin slag polymer concrete with confinement would react to real-world stresses, minimizing the need for a physical prototype. Currently, there is no research on FEA designated for tin slag polymer concrete with fibre reinforced polymer (FRP) confinement. The purpose of this study is to investigate the compressive behaviour of tin slag polymer concrete (TSPC) with FRP confinement through finite element method (FEM). Carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) were used to enhance the compressive properties of TSPC column. A comparison was made between the finite element result and the experimental result by analysing the stress–strain response. According to the comparison, the finite element model and experimental sample for unconfined and confined TSPC share a similar bilinear stress–strain curve. It was also discovered that TSPC with GFRP confinement has substantially more accurate stress–strain curve with 4.46% compared to 13.47% for CFRP, a percentage difference of 9.01%. TSPC with CFRP confinement has higher compressive strength than GFRP. The highest strength increment from one layer to the next occurs between one and two confinement layers. According to the simulation, the failure mode of finite element model is similar to the experimental sample.

Multi-objective optimization of high performance concrete columns under compressive loading with potential applications for sustainable earthquake-resilient structures and infrastructures

High performance column composites are multifunctional composites designed to improve resilience of structures and infrastructures to natural and unforeseen multiple loads during service. As a result of their superior mechanical performance, high performance column composites have been found attractive to improve resilience of medium and high-rise buildings as well as long-span structures and infrastructures in earthquake-prone regions. Scientometric analysis revealed limitations of traditional design standards and inadequate earthquake engineering to reduce collosal damage during seismic impact and the need for investment in alternative green energy to reduce anthropogenic-induced earthquakes linked to oil and gas projects. High performance CFRP (carbon fibre reinforced polymer) composite was investigated as potential laminate reinforcement and confinement for recycled concrete column using performance-based Taguchi-Response surface methodology optimization. Though columns wrapped with two layers CFRP confinement and reinforced with internal laminate CFRP reinforcement obtained higher maximum load and favourable failure mode, the optimized result, which comprises column confined with two layers of external CFRP confinement only, obtained 36.3% and 36.19% greater fracture toughness and fracture energy respectively, 1.4 times better displacement ductility index, 2.78 times strain ductility index and comparable load capacity. The superior mechanical performance of high performance recycled concrete column composite and favourable failure mode was attributed to strain hardening effect which depends on the CFRP confinement. Further studies are required to improve the mechanical performance and failure mode of high performance column composite for construction of resilient structures and infrastructures in the built environment.

Modelling of CFRP-Strengthened RC Shear Walls with a Focus on End-Anchor Effects

This study first provides an overview of the development of a novel tube anchor system for the seismic strengthening or repair of reinforced concrete (RC) shear walls with carbon fibre-reinforced polymer (CFRP) sheets. The new anchor system can significantly improve the load transfer mechanism between the CFRP and supporting RC structural elements, resulting in ductile behaviour of the strengthened shear walls with increases of lateral load capacity and ductility by up to 2.6 and 8.3 times, respectively. The study then presents a new finite element modelling technique capable of capturing the complete cyclic response, i.e., from the elastic behaviour to the ultimate collapse of CFRP-strengthened RC shear walls with the newly developed tube anchor system. Two different modelling approaches are proposed to consider the effects of the tube anchor system. Additionally, other important CFRP- and RC-related mechanisms, including CFRP debonding effects, confinement enhancement, tension stiffening, compression softening, and strength and stiffness degradation under cyclic loads, are also considered in the model. By comparing the analytical and experimental results, it is demonstrated that the proposed modelling approach can accurately replicate the complex behaviour of CFRP-strengthened shear walls with a wide range of aspect ratios, from the ductile flexural behaviour of slender walls to the brittle shear failure of squat walls, without requiring detailed modelling of the anchor system.

Long-term exposure of RC columns immersed in seawater or crude oil confined with CFRP fabrics under monotonic or cyclic loading

A combination of fiber reinforced polymer (FRP) and concrete subjected to seawater or crude oil is a desirable solution to reduce resource shortage and environmental issues. In current decades, numerous investigations have considered the utilization of FRP composites as a way for concrete confinement. Such composites have been typically limited to wrapping concrete columns at ambient temperatures. This raises the question of whether such composites can be utilized in some other applications. For that reason, the effectiveness of carbon fiber reinforced polymer (CFRP) wrapped concrete under seawater or crude oil exposure for 90 days and 720 days long-term impacts at ambient temperature concentrations have been tested experimentally. To accomplish this objective, 16 column specimens were prepared and tested. The impacts of exposure conditions, exposure time, loading type, and CFRP thickness were examined. Although it is evident that control columns' load-bearing capacities are reduced when immersed in seawater or crude oil, there is a noticeable improvement in load-bearing capability for columns immersed in seawater for a prolonged period of time for 720 days compared to those immersed in crude oil for the same amount of exposure. The strength of the confined control column and the columns submerged in seawater or crude oil significantly improved as compared to the unwrapped column without soaking in seawater or crude oil under monotonic or cyclic loading. The results of the experiment and the available design-oriented strength models can encourage the widespread use of FRP confined seawater or crude oil concrete in artificial islands and offshore structures. It was determined that these models are insufficient for predicting the strength of RC columns that had been submerged in seawater or crude oil and then encased in CFRP confinement.

A novel seawater and sea sand concrete-filled CFRP-carbon steel composite tube column: Seismic behavior and finite element analysis

The seismic behavior of a novel seawater and sea sand concrete (SSC)-filled carbon fiber-reinforced polymer (CFRP)-carbon steel composite tube (SFSCT) column under combined axial compression and reversed cyclic loadings was studied in this paper. This structure makes use of seawater and sea sand resources, and CFRP was adopted to isolate the corrosion by chloride ions on the steel tube. Tests of eight composite columns were carried out. The test parameters include the axial compression ratio, the number of CFRP layers and the bonding direction. The test results revealed that all of the specimens displayed superb seismic performance with a drift ratio over 4%. The failure of the SFSCT column exhibits a typical compressive-flexural failure mode. Compared with the results of the SSC-filled steel tube columns, the hoop strain of the specimen under additional CFRP confinement is reduced by 1.6 times, and the flexural strength and drift capacity increase by 22% and 17%, respectively. A fiber model was created by finite element analysis, and parametric studies of the main design parameters were performed. The effects of the steel tube and CFRP on the seismic performance were evaluated. Using experiments and finite element analysis, the relationships among the drift capacity, axial compression ratio and confinement level were investigated. A design method for predicting the drift capacity of SFSCT columns was proposed.

Experimental investigation into FRP-confined concrete-filled steel tubular columns under axial compression

The mechanical behavior of 66 carbon-fibre-reinforced polymer (CFRP)-confined concrete-filled steel tubular (CFST) short columns and 42 non-CFRP-confined CFST short columns under axial compression are studied. The typical failure modes and load–displacement curves of the specimen are obtained, and the stress mechanisms of the specimen are analysed. The effects of fiber-reinforced polymer (FRP) layers, core concrete strength and cross-section forms on the axial mechanical properties of CFST short columns are discussed. The test results show that there is a positive correlation between the improvement coefficient of bearing capacity and the confinement effect coefficient of FRP. Based on the superposition principle, the bearing capacity calculation formulas of circular and square CFST columns without CFRP confinement are proposed. On this basis, taking the confinement effect of FRP into account, the calculation formula of axial bearing capacity of FRP-confined CFST short columns is proposed. The comparison between the calculated values of the model and the measured values of the experiments shows that the model has good prediction effect.

Numerical Investigation of Carbon Fiber Reinforced Polymer Confined Concrete-Filled Steel Tube Columns under Eccentric Load

Recently, Fiber Reinforced Polymer (FRP) materials have emerged as a viable alternative to confined columns due to their high ultimate tensile strength to weight ratio and corrosion resistance under harsh and corrosive environments. Many previous studies were focused on the confining capability of FRP on concentric axial loads. This study presents a nonlinear finite element (FE) investigation of the effects of the thickness of Carbon Fiber Reinforced Polymer (CFRP), the thickness of steel tube, cross-sectional shape, and slenderness effect of an FRP confined concrete-filled steel tube (FCCFST) column under eccentric load. The FE model was validated by comparing the results with experimental data available in the literature, and good agreement was found. From the FE results, it was found that the steel tube and CFRP confinement improved the load resistance capacity by about 34% to 39%, and the axial shortening of the column at the peak load, from 136% to 57%, in rectangular and circular cross-sections, respectively. The efficiencies of steel tube and CFRP confinement first increase with an increasing eccentricity of the axial load and then start to decrease as the failure mode of the column changes to stability.

NLFEA of Sulfate-Damaged Circular CFT Steel Columns Confined with CFRP Composites and Subjected to Axial and Cyclic Lateral Loads

It is rather costly and difficult to experimentally evaluate the performance of concrete-filled tubular (CFT) circular steel columns exposed to combined axial and cyclic lateral loads. This research paper uses the nonlinear finite element (NLFEA) technique to assess the influence of using carbon-fiber-reinforced polymer (CFRP) laminates on the structural response and failure mode of damaged-by-sulfate CFT circular steel columns. At the beginning, twenty-one CFT circular steel column models were devised and checked for soundness using the findings of previously conducted research. Next, the models were broadened to investigate how the models’ behavior was influenced by the CFRP number of layers and the level of sulfate damage. For experimental purposes, the numbers of CFRP layers were set to be zero, five, six, seven, eight, nine, and ten, while there were three levels of sulfate damage, namely: level 0 (undamaged), level 1 (73 days), and level 2 (123 days). Some of the models were left unconfined with CFRP wraps for comparison. The CFRP confinement was at the end of the models due to its importance regarding the models’ capacity of lateral load. The columns’ ends were confined to prevent the models from outward local buckling, which led to higher strength, bigger net drift, and enhanced energy dissipation. The NLFEA models were then appropriately modified and adjusted in accordance with credible previously conducted experimental research; after which, a parametric study was performed to investigate how the models’ behavior was affected by the number of CFRP layers and the level of axial load. The study found that the CFT circular steel column models’ performance significantly enhanced when the models were wrapped with five to ten CFRP layers. It must be mentioned, though, that using eight, nine, and ten CFRP layers gave almost similar results. In addition, the NLFEA results revealed that when the damaged-by-sulfate models were repaired externally with CFRP wraps, there was an improvement in the models’ cyclic behavior, as they showed a raise in the load capacity, an enhancement in the horizontal displacement, a greater displacement ductility, better energy dissipation, and little deterioration in secant stiffness. The study found that using wraps of CFRP proved a great efficiency with the change in the sulfate damage level.

Axial behaviour of strengthened circular hollow reinforced concrete column with CFRP partial confinement

Circular hollow reinforced concrete column will experience deterioration due to many causes such as natural disaster, corrosion, low quality and others. Therefore, structural strengthening is required since replacing the deteriorated column is costly. Carbon fibre reinforced polymer (CFRP) confinement is one of the common method used for column strengthening. However, being a non- biodegradable material, the usage of CFRP will contribute to environmental issues. Therefore, this study investigates the effect of using partial CFRP confinement in a strengthened circular hollow reinforced concrete column. Six specimens of 2 m height with 250 mm and 110 mm for outer and inner diameter were tested. The effectiveness of partial CFRP confinement is analyzed by investigating the tested specimens’ axial and transverse displacement and strain behaviour. This study has shown that with CFRP partial confinement the strength is increased up to 44% from the unconfined circular hollow reinforced concrete column. The results of the study showed that, circular hollow reinforced concrete column with CFRP partial confinement able to enhanced the column load carrying capacity.

Finite Element Analysis of CFRP Strengthened Bundle RC Column Subjected to Repeated Impact Load

This paper studied numerically the behavior of carbon fiber reinforced polymer (CFRP) confined bundle reinforced concrete (BRC) columns subjected to repeated impact load. To verify the numerical models with previous experimental tests, Abaqus/Explicit based nonlinear finite element (FE) model was developed. Based on the proposed FE analysis, a parametric study was conducted to investigate the effects of different factors such as CFRP confinement, eccentric axial load, bundle reinforcement arrangement, and column height on repeated impact capacity of RC column. While modeling the structural element, concrete damage plasticity (CDP) model is adopted to account for the plastic and strain rate-dependent behaviors of concrete material under impact load. From the nonlinear FE analysis result, it was found that CFRP confinement improved the impact capacity of bundle reinforced concrete column. As column height increased, the column impact resistance was found to decrease. Moreover, when the CFRP strengthened BRC column specimens were repeatedly impacted, the continuous matrix material was severely damaged, while the fiber showed only minor and gradual compressive failures.

Effect of partial replacement of E-waste as a fine aggregate on compressive behavior of concrete specimens having different geometry with and without CFRP confinement

Nowadays, the improper disposal of electronic waste (E-waste) is leading to environmental pollution and health problems majorly in developing countries. The current research examines the behavior of shredded E-waste fine aggregate concrete strengthened by the use of carbon fiber-reinforced polymer (CFRP) confinement under axial compressive load. The main objective of this study is to investigate the structural behavior of circular and non-circular concrete specimens by partial replacement of E-waste as fine aggregates and confined with CFRP sheets. Tests were performed on a total of 36 concrete specimens. The parameters considered were cross-sectional geometry of circular, rectangular and square concrete specimens, 20% partial replacement of fine aggregates by E-waste, the effect of the corner in case of non-circular specimens, and the number of CFRP sheets. These tests portrayed that the partial replacement of fine aggregates by E-waste aggregates results in decreasing axial compressive strength of concrete specimens. However, the external CFRP confinement increases the axial strength of specimens (a maximum of 71% for circular specimens, 33% for square specimens, and 25% for rectangular specimens). It was also observed that partial replacement of natural fine aggregates by E-waste increased the failure time. For the case of square and rectangular concrete specimens, the ultimate strength was lower than circular specimens for both (with and without CFRP confinement) specimens. Finally, existing strength and strain models developed for FRP-confined concrete were used for theoretical calculations. The theoretical declaration of the existing models indicates that a few of the ultimate strain models lie on the high side and few of the ultimate strain models on the low side in comparison with the experimental findings.

Dynamic splitting behaviour of ultra-high-performance concrete confined with carbon-fibre-reinforced polymer

Fibre-reinforced polymer (FRP) wrapping is highly effective in enhancing the compressive properties of concrete. However, the dynamic splitting performance of FRP-confined ultra-high-performance concrete (UHPC) remains unexplored. This study investigated the impact resistance of carbon FRP (CFRP)-confined UHPC under splitting loads. The UHPC cylinders were wrapped in CFRP jackets of thicknesses from one to three plies. Several impact tests were conducted using a Ø100mm split Hopkinson pressure bar apparatus at different strain rates ranging from 2 s−1 to 17 s−1. The dynamic behaviours of the specimens were investigated and compared with those under quasi-static loading. The results indicated that the splitting properties of UHPC exhibited a strong strain-rate dependency; however, the confinement of CFRP reduced the strain-rate sensitivity of UHPC. The rupture of the CFRP following UHPC cracking governed the failure of CFRP-confined UHPC under dynamic splitting loads. Although the quasi-static splitting tensile strength could be improved approximately linearly by the CFRP confinement ratio, the CFRP confinement effect decreased with increasing strain rate. A new model that considers the effects of confinement ratio and core concrete inertia is proposed to predict the splitting tensile strength of CFRP-confined UHPC under impact loading.

Effect of Sulfate Attack on Reinforced Concrete Columns Confined with CFRP Sheets under Axial Compression

Sulfate ions in saltwater can considerably deteriorate the strength and durability of reinforced concrete (RC). To date, there has been no study that systematically investigates the effects of a sulfate attack on the capacity of mid-/large-scale RC columns confined with carbon fiber–reinforced polymer (CFRP). The capacity of CFRP-confined concrete columns subjected to sulfate attacks with various schemes and durations (up to 210 days) was examined in this study. The primary objectives of this study were to (1) examine the effect of a sulfate attack on the structural properties of midscale RC columns confined with CFRP; (2) quantify the contribution of the sulfate-damaged concrete core and CFRP confinement to the load-carrying capacity of the columns; and (3) propose a new formula to estimate the compressive strength of FRP-confined sulfate-damaged concrete considering the exposing time, number of FRP layers, and concrete strength. The experimental results showed that the sulfate attack significantly reduced the initial axial stiffness of the column up to 36% and increased its ultimate axial displacement up to about 40%. These influences in the CFRP-strengthened columns were slightly lower than those of unstrengthened ones. The sulfate attack considerably reduced the strength of the unstrengthened columns (up to 29.4%), but it only slightly affected the capacity of the strengthened columns with a 3.7% reduction. The strength reduction increased with the number of wet–dry cycles. CFRP confinement effectively mitigated the penetration of sulfate ions into the concrete core and, thus, slowed the degradation of the strength up to 90%. An empirical formula was proposed to estimate the strength of the CFRP-confined concrete subjected to a sulfate attack with close predictions regarding the experimental results.

Behavior of CFRP-confined Concrete-filled square steel tube columns with section circularized under axial compression

Eight carbon fiber-reinforced polymer (CFRP)-confined concrete-filled square steel tube (CFSST) specimens and twelve CFRP-confined CFSST specimens with section circularized were tested under axial compression to investigate the effect of different loading conditions and CFRP layers on axial compressive behavior of CFRP-confined CFSST columns with section circularized. Experimental results indicated that section modification method (circularization) improves the CFRP confinement and increases bearing capacity of CFSST columns. Meanwhile, the effect of CFRP layers on the bearing capacity of CFSST columns is also evident. Combination models of Han–Lam & Teng and Mander–Pham & Hadi are suggested in this study for calculating the bearing capacity under different loading conditions. Results showed that predictions are consistent with the experimental results.

Impact Behavior of Fiber-Reinforced Concrete with Polypropylene Fibers and Carbon Fiber–Reinforced Polymers

Abstract In this study, the influences of bidirectional carbon fiber–reinforced polymer (CFRP) confinement along with polypropylene fibers on the impact resistance of concrete samples were experimentally studied. Forty-nine concrete cylindrical samples (with compressive strengths of 20, 30, and 40 MPa) with polypropylene fibers (with content ratios of 0 %, 1 %, 1.5 %, and 2 %) were subjected to weight (46.7 and 66.8 kg) dropping at a height of 1.6 m above the cross-section of the sample. Moreover, half of the samples were tested with CFRP confinement. The number of weight releases required to destroy the samples and the weights of the samples after each release were recorded. The results indicated that the concrete without fibers and fiber-reinforced polymers (with compressive strengths of 20, 30, and 40 MPa) did not have sufficient impact resistance and were swiftly destructed. However, as the content ratios of polypropylene fibers increased, the number of cracks and weight droppings (to reach 70 % of the initial sample weight) increased. Moreover, it was observed that the concrete samples wrapped with the CFRP sheets also withstood impact loading better than fiber-reinforced concrete samples without the confinements. Besides, it was indicated that the prevailing failure mode of the samples with CFRPs was CFRP rupturing. Finally, it was observed that the more the compressive strength of concrete, the more the impact resistance.