Fiber Reinforced Polymer Bars Research Articles

Experimental and numerical study of the flexural behaviour of semi-precast slab reinforced with prestressed FRP bars

The performance of semi-precast slabs with prestressed basalt fibre-reinforced polymer (BFRP) bars under load is explored in this paper, using both experiments and computer simulations. The semi-precast slabs consist of precast concrete panels and cast-in-situ layers. The Precast panels are reinforced with BFRP bars prestressed at varying levels from 0% to 50% of their ultimate tensile strength. The experimental programme encompasses four-point bending tests conducted on five semi-precast slabs. For the numerical study, an ABAQUS model was used to perform finite element (FE) analysis, which aimed to simulate how the semi-precast slabs bent and to study how different factors affected their bending performance. The study parameters in this study were the grade of concrete and the reinforcement ratio. The results of this study show that prestressed BFRP bars significantly enhance load capacity and stiffness, while steel offers superior ductility. The computer models and the experiments matched well, as the average error between the two sets of data was less than 10%. Additionally, the parametric study reveals that enhancing the concrete grade or the reinforcement ratio can effectively enhance the flexural capacity and stiffness of the semi-precast slabs. In conclusion, this paper advocates for the utilisation of prestressed BFRP bars as an efficient and long-lasting reinforcement solution for semi-precast concrete slabs.

Enhancing Flexural Resistance in Pre-Damaged RC Beams with Near-Surface Mounted GFRP Bar and Bolt Anchoring System

The objective of this research was to explore the mechanical properties and failure mechanisms of reinforced concrete beams (RC beams) strengthened with near-surface mounted (NSM) glass fiber-reinforced polymer (GFRP) bars. This study focused on evaluating the effect of various factors on the load-deflection response and failure patterns of RC beams, including pre-existing damage, end anchorage, bar length, bar number, and the condition of concrete cover. The tested RC beams were divided into three groups. The first group included undamaged and damaged control beams. The second group involved the strengthening of beams after inducing damage, with variations in bar length, number, and cross-sectional area. This group also included beams strengthened by GFRP bars with and without anchors. In the third group, the effects of different cover materials, cover bonding techniques, and anchor bolts on the strengthening bars were examined. The results of the experiment indicated a notable decrease in both cracking and maximum load capacity for beams that were pre-damaged. The inclusion of anchor bolts appeared to have a noticeable effect, enhancing the load-carrying capacity and reducing mid-span deflection. Opting for two bars proved to be more effective than using three bars, leading to a higher maximum load and improved ductility. Moreover, prioritizing the bonding of the concrete cover at the end of the bars was found to be more important than bonding in the area of maximum moment.

The Structural Performance Of Short Circular Concrete Columns Made With Reactive Powder Concrete And Externally Reinforced With Textile Fabric

In the current laboratory investigation, the behavior of hollow circular concrete columns exposed to vertical compressive force is examined. The columns are externally strengthened with Glass Fibre Reinforced Polymer bars and textile fabric (one layer and two layers). The longitudinal reinforcement cast using concrete Reactive Powder Concrete has an outer diameter of (250 mm), a bore diameter of (100 mm), and a length of (1000 mm). The number of textile layers (one or two layers) is one of the main variables used in this experiment study. According to the experimental findings, the hollow circular concrete columns raised the tested concrete columns' bearing capacities by roughly (9.93%) and (17.8%), respectively, after the specimens were allowed to cure for 28 days. This improvement was made for strengthening columns that were subjected to compressive loads and had one or two layers of textile fabric.

Damage Detection in FRP-Reinforced Concrete Elements.

Fiber-Reinforced Polymer (FRP) composites have emerged as a promising alternative to conventional steel reinforcements in concrete structures owing to their benefits of corrosion resistance, higher strength-to-weight ratio, reduced maintenance cost, extended service life, and superior durability. However, there has been limited research on non-destructive testing (NDT) methods applicable for identifying damage in FRP-reinforced concrete (FRP-RC) elements. This knowledge gap has often limited its application in the construction industry. Engineers and owners often lack confidence in utilizing this relatively new construction material due to the challenge of assessing its condition. Thus, the main objective of this study is to determine the applicability of two of the most common NDT methods: the Ground-Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU) methods for the detection of damage in FRP-RC elements. Three slab specimens with variations in FRP type (glass-, carbon- and basalt-FRP, i.e., GFRP, CFRP, and BFRP, respectively), bar diameter, bar depths, and defect types were investigated to determine the limitations and detection capabilities of these two NDT methods. The results show that GPR could detect damage in GFRP bars and CFRP strands, but PAU was limited to damage detection in CFRP strands. The findings of this study show the applicability of conventional NDT methods to FRP-RC and at the same time identify the areas with a need for further research.

Investigation on the utilization of fiber clusters recycled from waste HFRP bars in concrete

The waste fiber reinforced polymer (FRP) bars are difficult to degrade naturally, and inevitably pose a significant challenge to environmental protection, resulting in the recycling of waste FRP bars is of great significance. Compared to chemical recycling and thermal recycling, mechanical recycling processes are more economical and environmental. In this study, the waste Hybrid FRP (HFRP) bars were mechanically recycled into fiber clusters for reinforcing concrete, and the influences of the fiber clusters on the mechanical properties of concrete were studied through compression test, splitting tensile test and four-point bending test. Meanwhile, Fourier transform infrared (FT-IR) spectroscopy and Scanning electron microscopy (SEM) were used to observe the interaction between the fiber clusters and the concrete, and acoustic emission (AE) technique was utilized to monitor the fracture characteristics inside the concrete. Results showed that the performance of mechanically recycled fiber clusters was retained to a certain extent and the alkaline environment of concrete produced slight damage to the fiber clusters. The addition of fiber clusters could obviously improve the mechanical properties of concrete, especially its energy absorption capacity under the splitting tensile and flexural loads. The absorbed energy EH/50 and peak flexural toughness of concrete with 2% fiber clusters were 97.24% and 126.47% higher than those of conventional concrete, respectively, and its flexural toughness index TP,150 was 163.16% higher than that of concrete containing 0.5% fiber clusters. As the volume fraction of fiber clusters increased, the number of AE event localization points and shear cracks mainly caused by fiber clusters pull-out and sliding increased. This study can bring enlightenment for the mechanical recycling of FRP bars into fiber clusters for concrete.

Study on the bond-slip performance of glass fiber reinforced polymer bars and marine concrete under repeated loading

The bond property between glass fiber reinforced polymer (GFRP) bars and concrete under repeated loading is critical in determining the suitability of GFRP bars for marine engineering. This study investigates the bond strength and slip between GFRP bars and marine concrete under repeated loads using a beam-type test. The 16 groups of beam specimens are fabricated, and 50 repeated loads are applied to them. The influences of loading level and loading times on bond strength, slip process, slippage, and residual slippage are analyzed. The loss rate of bond strength exceeds 50%, and irrecoverable cracks in the steel hinge of beam specimens are observed when the repeated load level is 65% of the ultimate load. The slippages rise as the loading level increases. When the number of repeated loadings reaches about 8, the slippage is 50% of the entire slippage, and then the slip difference gradually decreases, and slippages no longer increase. Residual slippages increase with the loading level, but they increase initially and then stabilize with the loading times. The fitting curves agree well with the experimental results, indicating that they could be employed to describe the bond property of GFRP bars in marine concrete under repeated loading.

Experimental and numerical investigation of the flexural behavior of one–way RC slabs strengthened with near–surface mounted and externally bonded systems

This study investigated the flexural performance of one-way reinforced concrete (RC) slabs strengthened with two distinct strengthening systems: near–surface mounted (NSM) bars and externally bonded (EB) carbon fiber-reinforced polymer (FRP) strips. The NSM bars comprised four types: carbon FRP (CFRP), basalt FRP (BFRP), glass FRP (GFRP), and stainless–steel (SS) bars. The NSM–strengthened slabs showcased substantial enhancements in yield and ultimate load capacity, ranging from 20 % to 55 % and 59–123 %, respectively. In comparison, those strengthened with EB–CFRP strips displayed increases from 46 % to 107 % and 45–177 %, respectively, depending on the axial stiffness ratio of the strengthening system provided. Furthermore, the slabs reinforced with NSM–BFRP bars showed an 11–25 % improvement in their ductility indices. In contrast, the slabs reinforced with EB experienced a decrease in ductility ranging from 38 % to 50 %. This reduction was attributed to the differences in the modes of failure observed in both strengthening systems. The rupture of the NSM–FRP bars and the strain readings associated at the end of testing confirmed that the tensile strength of the NSM–FRP bars was fully exploited whereas the EB–CFRP strips utilized only 29–36 % of their ultimate tensile strain due to debonding. A finite element (FE) model was formulated to anticipate the behavior of the strengthened slabs. A strong correlation between the numerical predictions and the experimental outcomes was observed. The experimental–to–numerical ratios of the ultimate load ranged between 1.0 and 1.08 for the NSM–strengthened slabs and between 0.98 and 1.38 for the EB–strengthened slabs. This validated the FE models’ ability to capture the nonlinear performance of the strengthened slabs.

Flexural Performance and Stress Calculation of External Prestressed Fiber-Reinforced Polymer-Bar-Strengthened One-Way Concrete Slabs.

External prestressing is widely employed in structural strengthening engineering due to its numerous advantages. However, external prestressed steel bars are prone to corrosion when exposed to the service environment. This paper is dedicated to examining the use of fiber-reinforced polymer (FRP) bars as external prestressing materials to strengthen one-way concrete slabs. Five one-way concrete slabs were strengthened with externally prestressed FRP bars with different prestress levels and different amounts of FRP bars, while one non-strengthened slab was used for comparison. The effects of strengthening on the flexural behavior, specifically the cracking load, ultimate load, stiffness and failure mode, were analyzed systematically. Moreover, the ductility and cost-benefit optimizing properties of the reinforcing design were discussed. The results show that external prestressed FRP bars significantly improve the cracking load, ultimate load and stiffness of one-way concrete slabs. The absence of a bond between the concrete and FRP bars overcomes the brittleness of the FRP bars, while the strengthened slabs exhibit satisfactory ductility and a higher post-yield stiffness and bearing capacity. Additionally, the cost/benefit ratio is optimized by increasing the prestress level, while a higher number of prestressed FRP bars is beneficial to ductility. Finally, a method for calculating the stress in prestressed FRP bars at ultimate loads was proposed. Irrespective of the prestressing material, this method is applicable to both strengthened beams and one-way slabs.

Compression performance of FRP bar-reinforced seawater sea-sand concrete encased FRP-wrapped steel tube columns

This paper developed a new type of composite column made of fibre-reinforced polymer (FRP) bar-reinforced seawater sea-sand concrete (SWSSC)-encased FRP-wrapped steel tubes, which is suitable for maritime engineering. In this composite form, the inner steel tube was isolated to the chloride ions by wrapping with an FRP sheet, and FRP bars were employed to reinforce the exterior SWSSC. To avoid/delay the occurrence of internal steel tube buckling, two measures were implemented, that is, filling with ordinary concrete, and bundling and welding using four hollow small-sized steel tubes. The compression performance was explored by axial compression and eccentric compression tests, and three experimental variables were set, including the steel tube thickness (2.5 mm and 5 mm), number of steel tubes (0, 1 and 4), and eccentricity (20 mm, 40 mm and 60 mm). The test results showed that increasing the thickness of the steel tube could improve the bearing capacity and lateral deformation of specimens (e.g., from 32.66 MPa to 36.99 MPa), whereas the number of steel tubes had a minor positive effect on the specimens. Meanwhile, the bearing capacity of the specimens decreased with increasing eccentricity of the eccentric compression test from 41.51 MPa to 36.99 MPa. Finally, a calculation method was proposed to predict the peak eccentric strength of specimens, which can provide a reference for the design of this kind of composite column.

Flexural behaviour of reinforced concrete beams reinforced with Glass Fibre Reinforced Polymer (GFRP) bars: experimental and analytical study

Flexural behaviour of reinforced concrete beams reinforced with Glass Fibre Reinforced Polymer (GFRP) bars: experimental and analytical study

Effect of Rebar Harsh Storage Conditions on the Flexural Behavior of Glass FRP Concrete

Nowadays, fiber-reinforced polymer (FRP) has become a widely accepted alternative reinforcement to steel bars in concrete members due to its many sustainability traits, as represented by its high strength-to-weight ratio, corrosion resistance, non-conductive properties, and electromagnet neutrality. However, FRP bar exposure for an extended period of time to harsh environmental conditions and chemicals can have an adverse effect on their mechanical properties. In this investigation, glass FRP bars were exposed to indoor controlled temperature, outdoor direct sunlight, outdoor shade, seawater, and alkaline solution for six months prior to using them as reinforcement in concrete flexural members. This research involves the fabrication and testing of five pairs of 3 m-long concrete beams with 200 mm by 300 mm cross-sections embedded in the tension zone with the exposed GFRP bars. The 10 beams were instrumented with strain gauges and tested following a four-point loading scheme using a hydraulic jack attached to a rigid steel frame. Crack width records from the tests showed the inferior serviceability of the beams that contained rebars stored in an outdoor environment relative to the control beams. GFRP bar exposure to an alkaline solution or outdoor direct sunlight slightly affected the cracking and ultimate moment capacities, reducing them by 5% and 3% in terms of the same parameters as the controlled indoor exposure, respectively. The influence of GFRP bar exposure to open-air shade or sunlight decreased the pre-cracking stiffness by 25% and flexural ductility by 10–20% when compared with the control specimens. The predicted ultimate flexural strength using the ACI 440 provisions gave comparable results to the experimentally obtained values. A simple mathematical equation that envelops the moment–deflection relationship for GFRP over-reinforced concrete beams and only requires information about initial cracking and ultimate flexural conditions is proposed.

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.