Fiber Reinforced Polymer Bars Research Articles

An optimized prediction of FRP bars in concrete bond strength employing soft computing techniques

The precise estimation of the bonding strength between concrete and fiber-reinforced polymer (FRP) bars holds significant importance for reinforced concrete structures. This study introduces a new methodology that utilizes soft computing methods to enhance the prediction of FRP bars' bonding strength. A significant compilation of experimental bond strength tests is assembled, covering various variables. Significant variables that affect bonding strength are found in the study of this database. The prediction process is optimized using soft computing methods, particularly Gene Expression Programming (GEP) and the Multi-Objective Genetic Algorithm Evolutionary Polynomial Regression (MOGA-EPR).The proposed soft computing approaches accommodate complex relationships and optimize prediction accuracy depending on the input variables. Results demonstrate its effectiveness in predicting bond strength and comparing it with existing codes and other models from the literature. The results have shown that the MOGA-EPR and the GEP models have high R2 values between 0.91 and 0.94. The proposed new models enhance the reliability and efficiency of designing and assessing FRP-reinforced concrete.

Flexural Performance of Steel-Continuous-Fiber Composite Bar and Fiber-Reinforced Polymer Bar Hybrid-Reinforced Sustainable Sea-Sand Concrete Beams: Numerical and Theoretical Study

To investigate the flexural performance of steel-continuous-fiber composite bar (SFCB) and fiber-reinforced polymer (FRP) bar hybrid-reinforced sea-sand concrete (SSC) beams, a total of 21 SSC beams were numerically studied. The concrete damaged plasticity model (CDPM) and FRP brittle damage model were adopted, and the bond-slip behavior between the reinforcement and concrete was considered. Parametric studies were conducted to study the effects of the SSC strength, sectional steel ratio of the SFCB, core steel bar yield strength of the SFCB, out-wrapped FRP elastic modulus of the SFCB, and the ultimate tensile strength of the SFCB on the flexural performance of the beams. The results indicate that increasing the SSC strength and out-wrapped FRP modulus enhanced the bearing capacity and stiffness but reduced the ductility, shifting failure from concrete crushing to FRP bar fracture. A higher SFCB sectional steel ratio markedly improved the flexural stiffness, transforming the load–deflection curve. Elevated core steel bar yield strength maintained the cracking load and deflection while increasing the yield and ultimate loads. For SFCB fracture, higher ultimate tensile strength in the out-wrapped FRP enhanced the ultimate load and deflection, but not in concrete crushing failure. In addition, three failure modes were defined based on the proper assumption, with the proposed bearing capacity formulas aligning well with the FE results.

Durability assessment of GFRP bars embedded in UHP-ECCs subjected to an accelerated aging environment with sustained loading

Ultra high-performance engineered cementitious composites (UHP-ECCs) have garnered significant attention in the field of civil engineering primarily due to their exceptional tensile strain-hardening performance and excellent compressive strength. To further enhance their tensile strength, particularly in meeting the rigorous environmental and mechanical demands frequently encountered in marine environments, fiber-reinforced polymer (FRP) bars can be employed as the internal tensile reinforcement for UHP-ECCs (referred to as “FRP-UHP-ECC members”). While numerous studies have focused on the durability of FRP bars in concrete environments, the durability of FRP bars embedded within UHP-ECCs, especially with sustained loads, remains unexplored. Glass FRP bars are commonly utilized in civil engineering due to their cost-effectiveness and favorable mechanical properties. Therefore, this paper investigated the durability performance of GFRP bars made from three different matrix resins (i.e. epoxy, vinyl ester and polyester). These bars were centrally embedded in UHP-ECCs and subsequently immersed in alkaline solutions at elevated temperatures while under sustained loads. Their tensile properties over a specified period were evaluated after exposure. The test results revealed a larger degradation in polyester-based GFRP bars compared to vinyl ester-based and epoxy-based bars. In addition, GFRP bars with UHP-ECC covers exhibited less degradation than the bare bars, but this protective effect diminished under sustained loads. Scanning electron microscope (SEM) and X-ray computed tomography (CT) analysis demonstrated that the degradation of GFRP bars was primarily attributed to matrix hydrolysis, which led to a reduction in stress transfer efficiency between fibers, contributing to the tensile strength reduction in GFRP bars.

Digital image correlation and cracked hinge model applied to notched beams reinforced with GFRP bars

In this study, three-point bending fracture tests of notched beams reinforced with a glass fiber-reinforced polymer bar are conducted. Plain concrete beams are also tested for comparison. Two different widths are considered for the beams. Digital image correlation (DIC) is used on the lateral surface of the beam to study the fracture process zone (FPZ) and neutral axis depths at different load stages. A non-linear analytical model named cracked hinge model and cross-sectional analysis are used to obtain the force in the bar and the interfacial slip between bar and concrete, which are compared to the results from pull-out tests.

Seismic behavior of BFRP bar reinforced shear walls strengthened with ultra-high-performance concrete boundary elements

Reducing the amount of steel reinforcement in construction is imperative, driven by the objectives of reducing carbon emissions and mitigating steel corrosion. Among the various alternatives to steel reinforcement, basalt fiber reinforced polymer bar (BFRP) is considered a promising solution. The aim of this study is to examine the seismic performance of shear walls entirely reinforced with BFRP bars, utilizing BFRP for both longitudinal and transverse reinforcement. To address the inherent limitations of BFRP bars, a novel composite shear wall, incorporating BFRP bars, ultra-high-performance concrete (UHPC) and normal strength concrete, is proposed. Specifically, UHPC boundary elements are employed to strengthen the potential compression zone of BFRP reinforced shear walls. Four shear wall specimens, fully reinforced with BFRP bars, were fabricated and tested for their seismic performance, with two specimens incorporating UHPC boundary elements. Comprehensive test results, including failure modes, load-bearing capacity, ductility, energy dissipation, stiffness degradation and rebar strain, are presented and discussed. A detailed discussion of the effects of axial load ratio (ALR) and UHPC boundary elements is included. The test results indicate that the specimens featuring UHPC boundary elements showed significant improvements in deformability, lateral strength and energy dissipation capacity. This reveals that the integration of UHPC boundary elements considerably enhances the seismic performance of BFRP bar reinforced shear walls. Moreover, although all test specimens experienced failure due to concrete crushing in the compression zone, those with UHPC boundary elements manifested higher tensile strain on the BFRP bars on the tension side, facilitating more effective utilization of the high tensile strength of the BFRP bars. Ultimately, a method to ascertain the flexural capacity of BFRP bar reinforced shear walls, both with and without UHPC boundary elements, is proposed and validated by the test results.

Early-age bond behavior of embedded CFRP bars in UHPFRC: Test study and theoretical analysis

The combination of carbon fiber-reinforced polymer (CFRP) bars and ultra-high-performance fiber-reinforced concrete (UHPFRC) has great potential for use in producing structures with exceptional mechanical properties. Nevertheless, a research gap exists regarding the early-age bond behavior of embedded CFRP bars in UHPFRC, which is key to evaluating structural crack resistance. To address this gap, in this study, a series of tests was conducted on 90 pull-out specimens consisting of UHPFRC and CFRP bars. The influences of the concrete age (t), bond length (lb), and cover thickness-to-bar diameter ratio (C/D) on bond behavior were investigated. Each pull-out test generated the acquisition of a complete bond stress–slip curve. The bond interface was analyzed mechanically using the thick-walled cylinder theory and elasticity theory. A bond strength theoretical model that accounted for the surface wear of CFRP bars was proposed. The results of the pull-out test and theoretical analysis indicated that the bond strength tended to grow as t and C/D increased and was negatively correlated with lb. The model predictions agreed well with the test results while exhibiting excellent predictive accuracy compared to existing models. Furthermore, a three-branch bond stress–slip model was established to depict the bond behavior, demonstrating acceptable consistency with test curves.

Investigation of the Experimental Shear Resistance of RC T-beams after Strengthening with Carbon Fiber-Reinforced Polymer (CFRP) Bars

This study investigates the stiffness and shear resistance of T-reinforced concrete beams that have been strengthened against shear using the embedded through-section approach. The beams were exposed to a monotonic one-point load until failure. The experimental methodology included the investigation of 12 T beams made of reinforced concrete, consisting of 2 reference beams that were not subjected to any strengthening measures and 10 reinforced beams. The 12 beams were classified into two primary categories: those with stirrups and those without stirrups. The primary factors from each group encompassed the spacing and angle of inclination pertaining to the Carbon Fiber-Reinforced Polymer (CFRP) bars placed along the central axis of the section. Various configurations were used, including varied spacing intervals and degrees of inclination. The results showed that the ratio of the CFRP shear resistance to the total section (Vf / Vsec) ranged between 10 to 21% in group one (with stirrups). This means that the Embedded Through Section (ETS) technique with CFRP bars is useful in increasing the shear resistance of reinforced concrete beams. For group two (without stirrups), this ratio ranged between 56 to 58.5%. That is, ETS with CFRP bars significantly increases the shear resistance of reinforced concrete beams without stirrups.

Bending moments redistribution in two‐span reinforced concrete beams reinforced with FRP bars based on collected data research

AbstractThis article presents a review of state of the art on nonmetallic reinforcement in terms of bending moment redistribution in double‐span elements. The authors present a summary of existing research programs focused on moment redistribution in FRP (Fiber Reinforced Polymer) reinforced concrete (RC). On this basis authors created a database of concrete elements with all the important construction properties of the elements. Gathered data are presented with quantitative analysis of several variables effecting moment redistribution in published articles. In the following publication authors show a research review which includes an analysis of the influence of variable parameters from the point of view of the database, concerning: degrees of longitudinal reinforcement, ratio between degrees of reinforcement in span and over the support, type of reinforcement (FRP/steel/hybrid), concrete class and transverse reinforcement.

Machine learning-based evaluation of punching shear resistance for steel/FRP-RC slabs

With the emergence of fiber-reinforced polymer (FRP) reinforcement as a substitute for conventional steel reinforcement, different design codes have been developed to account for the different mechanical properties of the FRP, specifically the elastic modulus. The ACI 440.11-22, CSA/S806-12, and JSCE-97 are well-known standards for FRP-reinforced concrete structures. In particular, these design standards show significant variations in estimating the punching shear resistance and accounting for the elastic modulus. This study provides a statistical and machine learning-based evaluation of the punching shear models in design standards. An Artificial neural network (ANN) framework is used to develop a generalized punching resistance model of flat slabs reinforced with steel and FRP bars utilizing a large experimental dataset with 539 tests. The study presents a parametric study to examine the effect of different factors on the punching shear strength. The parametric study provided a graphical presentation and comparison between the design models and the developed ANN model.

Estimation of the Bond Strength of Fiber-Reinforced Polymer Bars in Concrete Using Artificial Intelligence Systems

Fiber-reinforced polymer (FRP) bars have recently been introduced to the market as an alternative to steel for internal reinforcement for concrete construction exposed to situations that could cause corrosion. The bond behavior of FRP bars varies from that of steel bars, mostly due to variations in material properties and surface textures. Because of the unexpected nature of the crucial FRP–concrete interfacial (FCI) bond strength, the bond strength between FRP bars and concrete cannot be exactly determined. Numerous experimental investigations have been conducted with related empirical models established in an attempt to resolve this problem. These models were found to have a restricted capacity for generalization due to the small sample sizes of the experiments. Therefore, a more powerful numerical technique capable of processing large data sets with all possible parameters that may affect the relationship and considering the nonlinearity of data tendency is needed. In this study, the artificial neural networks technique and adaptive neuro-fuzzy inference system were utilized to predict the FRP–concrete bond behavior based on 238 data points collected from different studies in the literature. The performance of the ANN and ANFIS models in predicting the bonding strength was compared to other models published in the literature and codes. The results showed that the ANN and ANFIS models gave higher prediction performance than other models, with a slight advantage for the ANN model. For instance, the R-squared values of the proposed ANN and ANFIS were 0.94 and 0.92, respectively, for 20 data points that were not used to develop the ANN and ANFIS models. Based on the sensitivity analysis, the FRP diameter and compressive strength of concrete were found to be the most effective parameters on the bond strength in both the ANN and ANFIS models. In contrast, the bar position and surface texture had a lower importance index.

Effects of eccentric loading on performance of concrete columns reinforced with glass fiber-reinforced polymer bars.

Glass fiber-reinforced polymer (GFRP) reinforcements are superior to traditional steel bars in concrete structures, particularly in vertical elements like columns, and offer significant advantages over conventional steel bars when subjected to axial and eccentric loadings. However, there is limited experimental and numerical research on the behavior of GFRP-reinforced concrete (RC) columns under eccentric loading having different spacing of stirrups. In this study, six specimens were cast under three different values of eccentricities (25mm, 50mm, and 75mm) with two groups of stirrups spacing (50mm and 100mm). The experimental results showed that by increasing the eccentricity value, there was a reduction in the load-carrying capacityof the specimens. The finite element ABAQUS software was used forthe numerical investigation of this study.The results from the finite element analysis (FEA) were close to the experimental results and within the acceptable range. The maximum difference between theexperimental and FEA resultswas 3.61% for the axial load and 12.06% for the deformation.

Rational prediction of moment redistribution in continuous concrete beams reinforced with FRP bars

In continuous fiber reinforced polymer (FRP) reinforced concrete (RC) beams, moment redistribution is typically not allowed in the design owing to the lack of ductility of FRP bars. However, this simplification cannot be justified as moment redistribution depends primarily upon the difference in stiffness along the beam length. This study aims at improving the current state-of-the-art redistribution quantification in continuous FRP RC beams. Redistribution behavior against neutral axis depth (c/d) of continuous FRP RC beams are numerically assessed, focusing on the impact of ρr1/ρr2 (ρr1, ρr2= tensile reinforcement ratios at positive, negative moment zones). It is shown that continuous FRP RC beams may experience marked positive or negative redistribution of moments, depending on ρr1/ρr2. However, the importance of ρr1/ρr2 is neglected in c/d-based code models (EC2, BSI and CSA). A modified BSI model is proposed to estimate the moment redistribution in continuous FRP RC beams. By introducing ρr1/ρr2, the proposed simplified model accounts for the structural characteristic and demonstrates a rational prediction of moment redistribution in these beams.

Experimental and statistical investigations of the material properties of FRP reinforcement in compression

Internationally leading standards currently do not permit to consider the contribution of reinforcement made of fibre reinforced polymers (FRP) to a concrete member’s compressive load-bearing capacity due to a lack of reliable knowledge regarding FRP’s material properties in compression. Thus, there is a very high demand for carefully specifying an optimised test setup for FRP bar reinforcement that accounts for both theoretical considerations and established standards from other industry branches. This paper presents an extensive literature review on mechanical approaches to describe FRP material properties in compression, existing test setups from various industry branches as well as experimental studies that have been conducted in order to research the compressive material properties of FRP reinforcement. Based on experimental results from literature a database was compiled. Following a reasonable choice of a test setup based on the literature study, an experimental campaign was setup, in order to investigate the influence of different fibre materials (carbon, glass, basalt), polymer matrices and bar diameters on the compressive material properties of FRP reinforcement bars. In addition to the experimental determination of the material properties, the joint evaluation of the total sample size of n = 95 own experimental test results and the results from the database generated from literature allows for statistical investigations. Thus, the determination of material scatter and the estimation of the distribution type by means of a statistical analysis applying the Kolmogorov-Smirnov test provides the basis for further research towards the reliability of concrete structures reinforced with FRP bars in compression.

Performance of doubly reinforced concrete beams with GFRP bars

Abstract The study focused on examining the behavior of six concrete beams that were reinforced with glass fiber-reinforced polymer (GFRP) bars to evaluate their performance in terms of their load-carrying capacity, deflection, and other mechanical properties. The experimental investigation would provide insights into the feasibility and effectiveness of GFRP bars as an alternative to traditional reinforcement materials like steel bars in concrete structures. The GFRP bars were used in both the longitudinal and transverse directions. Each beam in the study shared the following specifications: an overall length of 2,400 mm, a clear span of 2,100 mm, and a rectangular cross-section measuring 300 mm in width and 250 mm in depth. To apply loads for testing, two-point static loads were placed at the middle third of the beam’s span, creating a shear span of 700 mm in length. The beams were categorized into three groups depending on the GFRP longitudinal reinforcement ratio in the tension and compression zones of the section. GFRP bars with a diameter of 15 mm were employed as longitudinal reinforcement, while closed GFRP stirrups with a diameter of 8 mm at 100 mm were utilized as transverse reinforcement throughout the structural element. Test results have indicated that the ultimate load capacity of doubly GFRP-reinforced concrete beams varies compared to singly GFRP-reinforced beams. The range of variation observed is between an increase of 8% and a decrease of 4%. Accordingly, the contribution of the GFRP bars in the compression zone is insignificant and could be ignored in design calculations. It was observed that the loading level at which crack spacing stabilized ranged between 31.3 and 87% of the experimental failure load. It seems that the crack spacing decreased with the increase in the reinforcement ratio.

Durability of carbon/basalt hybrid fiber reinforced polymer bars immersed in alkaline solution

AbstractUsing basalt fiber‐reinforced polymer (BFRP) bars to substitute for steel rebar in seawater sea‐sand concrete (SSC) members is one of effective solutions to steel corrosion. However, there is a concern about the durability of BFRP due to the alkaline of SSC. In this study, a layer of carbon fibers coating (volume fraction was set at 10% and 20%) was used to improve the alkaline resistance of BFRP, which named as carbon/basalt fiber‐reinforced polymer (C/BFRP) hybrid bars. The tensile properties, interlaminar shear strength, and water absorption and diffusion behavior of the C/BFRP were examined by laboratory acceleration methods. The immersion solution temperatures were set at room temperature, 40 and 60°C, immersion mediums were tap‐water and two kinds of alkaline solutions (pH = 10 or 13). Carbon fiber coating is beneficial for improving the mechanical properties of the composite. The higher the fiber volume fraction, the better the long‐term resistance of C/BFRP can be found. However, carbon‐basalt fiber interface is still a weak part in the durability of C/BFRP. The higher the volume fraction of the coating carbon fibers, the greater the quasi‐equilibrium water uptake, which can be attributed that the smaller diameter of carbon fibers embedded the voids between basalt fibers. Reducing environment alkalinity is also beneficial for increasing the service life of C/BFRP, and the tensile strength retention increased by 12% when pH decreased from 13 to 10 after 50‐year.Highlights Carbon fiber coating is beneficial for improving the properties of BFRP. Carbon‐basalt fiber interface is a weak part for the durability of C/BFRP. Reducing alkalinity can improve the durability of BFRP.

Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) panel reinforced with FRP bar/grid: Development and flexural performance

In this study, Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) panels with Fiber-Reinforced Polymer (FRP) reinforcement (i.e., FRP bars and girds) were proposed for the construction of sustainable marine structures. Based on four-pointed bending tests, the mechanical performance of FRP-reinforced UHS-ECC [with 2% polyethylene (PE) fibers] and FRP-reinforced ultra-high-strength concrete (UHSC, without fibers) panels were investigated and compared to understand the composite action between UHS-ECC and FRP. Compared with the FRP-reinforced UHSC panel, the FRP-reinforced UHS-ECC panel showed significantly higher ultimate load (139-173% higher), stiffness, and deformation capacity. It was also found that the use of seawater as the raw material had almost no effect on the mechanical performance of FRP-reinforced UHS-ECC (UHSC) panels. An analytical investigation was conducted to predict the load capacities of the tested panels, and the prediction error was acceptable. For FRP-reinforced UHS-ECC (UHSC) panels, it was revealed that using UHS-ECC to replace UHSC improved the stress transfer and deformation compatibility with FRP because the multiple cracking behavior of UHS-ECC lowered the crack-induced shear stress concentration along the FRP reinforcement. The developed FRP-reinforced UHS-ECC system showed great potential in the construction of durable and sustainable marine infrastructure.

Effectiveness of FRP bar anchors for prestressed concrete members

Prestressed concrete members are widely used around the world to realize different types of structure, including bridges and skyscrapers. Steel strands are generally employed to apply a compression force into the concrete. Recently, fiber-reinforced polymer (FRP) composite bars have been considered for replacing traditional steel strands in specific applications. The main advantage of FRP bars is their resistance to corrosion. Furthermore, they may have a higher tensile strength-to-weight ratio and fatigue resistance compared to steel strands. Although using prestressed FRP bars may entail for advantages over traditional steel solutions, the anchorage system is an open issue for this technology. Indeed, the anchorage should guarantee a high level of tensile stress into the bar and, at the same time, avoid local failures.In this paper, the preliminary results of an experimental campaign comprising tensile tests of glass and carbon FRP bars with different anchors are provided and discussed. The experimental campaign was aimed at investigating the effectiveness of newly developed wedges in properly anchoring the composite bars. Tensile test results and modes of failure are discussed, shedding light on the main parameters that affect the mechanical behavior of the bars considered.

Review on NSM-CFRP Method for Enhancing Shear Capacity in Reinforced Concrete Deep Beams

The demand for improved strengthening techniques for current concrete structures is on the rise. Many structures that will still be in use two decades from now have already been constructed. A portion of these structures must undergo enhancements or be replaced, as they are deteriorating not only from natural processes but also from mistakes made during their design and construction. Near-surface mounted (NSM) utilizing Fiber-Reinforced Polymer (FRP) bars has proven to be a successful method in enhancing the flexural and shear performance of both existing and new Reinforced Concrete (RC) elements. This technique is considered innovative and rapidly developing, attracting significant attention from researchers. Therefore, this study aims to analyze previous and current research on the shear strengthening of RC deep beams using NSM-CFRP bars. The research findings were gathered from four prominent databases: ASCE, EBSCO, SCOPUS, and Science Direct. A thorough literature review was conducted, focusing specifically on NSM-CFRP for shear strengthening. A total of 56 articles were categorized into three main groups. Group 1 consisted of studies examining the use of NSM for shear strengthening, while Group 2 focused on articles related to the structural behavior of RC members in shear. Group 3 included articles discussing the theoretical aspects of NSM-FRP in enhancing shear strength, aiming to develop a new method for calculating shear effects provided by NSM-FRP. In conclusion, this study highlights three fundamental aspects of this field: (1) the rationale behind utilizing NSM-FRP bars for shear reinforcement and their practical applications, (2) existing challenges and barriers to widespread adoption, and (3) recommendations for enhancing the acceptance and utilization of NSM-FRP bars.

Strengthening of GFRP Reinforced Concrete Slabs with Openings

Using fiber-reinforced polymer (FRP) could effectively improve the strength and endurance of reinforced concrete (RC) constructions. This study evaluated the flexural behavior of one-way concrete slabs with openings reinforced with glass fiber-reinforced polymers (GFRP) bars. It strengthened using carbon fiber-reinforced polymer (CFRP) sheets around the openings. The experimental program of this study is adopted by casting and testing four one-way concrete slabs with dimensions of (150*750*2650) mm. These slabs are divided into two groups based on whether they were strengthened or un-strengthened. For each group, two different openings (either one rectangular or two square) measured 250*500 mm and 250*250 mm, respectively, were fabricated within the pure flexural zone of the specimens. The experimental results indicate that using CFRP strips increases the maximum load capacity by around 29% for the slab with one rectangular opening and 21% for the slab with two square openings compared to the un-strengthened slabs. On the other hand, the deflection at a service load is decreased by about 35% and 37% for the slabs mentioned above, respectively.

An investigation on the bond behavior of basalt fiber reinforced polymer (BFRP) rebars embedded in conventional concrete

This research investigates the bond behavior of basalt fiber-reinforced polymer (BFRP) bars in conventional concrete, focusing on its relation to mild steel bar bond behavior and the magnitude of variation. Using BFRP as a replacement for traditional mild steel reinforcement has gained attention due to its inherent corrosion resistance and high tensile strength properties. In environments where steel corrosion poses a significant threat to structural integrity, BFRP offers a promising alternative for improving the long-term durability and longevity of reinforced concrete members and structures. The study aims to evaluate the bond strength between BFRP rebars embedded in conventional concrete through experimental testing and analysis. Various factors affecting bond performance, including surface preparation, embedment length, and concrete mix design, are considered. The findings of this research contribute to a better understanding of the feasibility and effectiveness of utilizing BFRP reinforcement in concrete structures, particularly in mitigating the challenges associated with steel corrosion. Ultimately, the results aim to inform engineering practices and promote the adoption of sustainable and corrosion-resistant materials for infrastructure development, thereby addressing a critical need in the field. The results are also compared to the current ACI 440 bond equation and database of other BFRP data collected by the authors.