Fiber Reinforced Polymer Bars Research Articles

Glass Fiber-Reinforced Polymer Bars as Shear-Friction Reinforcement for Concrete Cold Joints

Glass Fiber-Reinforced Polymer Bars as Shear-Friction Reinforcement for Concrete Cold Joints

Influence of seawater sea sand concrete environment on the long‐term tensile properties of pultruded basalt and basalt‐carbon‐hybrid fiber reinforced polymer profiles

AbstractTo reveal the durability of fiber‐reinforced polymer (FRP) profiles, which differ from FRP bars due to the clear variations in the internal structure of the fibers. This study experimentally investigated the tensile properties of FRP profiles in the seawater sea sand concrete (SSC) environment at 25, 45, and 60°C. Unidirectional basalt FRP profiles, multidirectional basalt FRP profiles, and basalt and carbon hybrid FRP profiles were considered. SEM analysis was performed to evaluate the corrosion mechanism. Results show that the strength degradation of FRP profiles accelerated with rising ambient temperature due to resin corrosion in hyperthermia. After 63 days of immersion in the SSC environment solution, multidirectional basalt FRP (BFRP) profiles exhibited more severe corrosion than unidirectional BFRP profiles (82.5% and 88.2%, respectively). The hybrid FRP profiles exhibited a strength retention of 86.4%, which was higher than that of multidirectional BFRP profiles due to the superior alkali resistance of carbon fibers compared to basalt fibers. In addition, prediction models of FRP profiles based on the Arrhenius relation were proposed with a high correlation coefficient of R2.Highlights Durability of FRP profiles in SSC environment was studied. Basalt and carbon fibers hybrid reinforced multidirectional polymer profiles. Corrosion mechanism of FRP profiles was revealed. Tensile property prediction model of FRPs in SSC environment was proposed.

Performance assessment of LC3 concrete structures considering life-cycle cost and environmental impacts

Developing green materials for infrastructure construction is of vital importance for sustainable development. Limestone calcined clay cement (LC3) is an appropriate alternative for the reduction of CO2 emissions and resource consumption in the cement industry. Recycled concrete aggregate (RCA), seawater and sea sand are potentially advantageous from a sustainability perspective, especially in coastal regions. Fiber-reinforced polymer (FRP) bars with excellent corrosion resistance are ideal alternative materials for steel bars in a corrosive environment. In this paper, a new type of green concrete structure incorporating LC3, seawater, sea sand, RCA, and FRP bars was investigated, and the performance was assessed to verify the considerable sustainable advantages while considering life cycle cost and environmental impacts. The results showed that the proposed LC3 concrete exhibited lower environmental impacts: compared with traditional concrete, and the CO2 and energy consumption of LC3 concrete were reduced by 32%–41.7% and 23.3%–28%, respectively. Although the initial cost was higher for LC3 and CFRP bars, this disadvantage could be offset by their longer service life and lower maintenance costs during their life cycle. Compared with traditional RC structures, the total cost, CO2 and energy consumption in the life cycle were reduced by 39%, 30.5%–65.4%, and 18.5%–58.9% for the LC3 concrete structure, respectively. In contrast to the life cycle cost, the LC3 replacement ratio had a negative effect on the environmental indices for the LC3 concrete and structure. Considering the promising advantages in economy and environmental impact, the proposed LC3 concrete and structure provides an effective approach for the sustainable development of the construction industry.

Flexural behaviour of GFRP-reinforced concrete pontoon decks under static four-point and uniform loads

Concrete pontoon decks are subject to flexural loading actions under concentrated and uniform loads caused by self-weight, live loads, and wave actions. This study investigated the structural behaviour of concrete pontoon decks reinforced with glass fiber-reinforced polymer (GFRP) bars under static four-point and uniform loading conditions. Five large-scale GFRP-reinforced concrete decks with a length of 2400 mm, width of 1500 mm, and thickness of 125 mm were tested to evaluate their moment capacity, strain behaviour, cracking propagation, and failure mechanism. The effects of the loading configurations, reinforcement arrangement, and cutout simulating the piles' location were evaluated. The edge cut-out initiated flexural-shear cracks, causing the pontoon decks to fail at an effective bending stress 10% lower than the solid decks. Decreasing the span-to-depth ratio from 5.6 to 4.0 increased the induced shear stress of a section and caused the deck to fail by shear compression. Uniform loading resulted in an even load distribution and minimized the stress concentration around the cutout. An increase in the effective depth improved all deck flexural characteristics. The equations in ACI 4401. R-15 and CSA S806–12 provided an accurate prediction for solid decks but overestimated the ultimate flexural strength of the GFRP-reinforced concrete decks with a cutout.

Investigations on geopolymer-based seawater sea-sand high performance concrete slabs reinforced with basalt FRP bars under direct contact explosions

Adopting locally available raw materials like seawater and sea-sand in coastal areas and oceanic islands has facilitated meeting the demands of marine engineering. However, these raw materials contain corrosive elements that could threaten the steel reinforcement in concrete structures, thus non-corrosive fibre-reinforced polymer (FRP) bars are proposed. In the present study, the geopolymer-based seawater sea-sand high performance concrete (G-SHPC) slab reinforced with basalt FRP bars was designed to preliminarily evaluate its dynamic behaviour under contact explosions. Tests were conducted on three large-sized slabs with different TNT charge weights, including 0.8 kg, 1.6 kg and 2.2 kg. To complement the experimental investigation, a numerical simulation was then performed in ANSYS-DYNA. A Continuous Surface Cap (CSC) model was developed to accommodate the unique characteristics of G-SHPC. Two different blast modelling methods, including the Arbitrary Lagrangian-Eulerian (ALE) algorithm and a hybrid Finite-Element (FE) and Smooth Particle Hydrodynamics (SPH) algorithm, were examined to faithfully reproduce the contact explosion phenomena. The structural models considered the bond-slip behaviour, and three bond-slip models were compared. The numerical results obtained through the ALE algorithm and the beam-in-solid bond-slip model exhibited fair agreement with the test results, with a maximum error of less than 6.3%. A parametric study was further conducted to establish the damage identification diagram. Formulas based on empirical data were formulated to anticipate the damage degrees of G-SHPC slabs exposed to contact explosions.

Experimental investigation of concrete frames reinforced with GFRP bars under reversed cyclic loading

Fiber reinforced polymers (FRP) have been widely investigated and successfully used as internal reinforcement in new reinforced concrete (RC) members and structures such as slabs, beams, bridges, multi-storey car parks and others as means to overcome the corrosion problem of steel. The linear-elastic behaviour, brittle failure and low modulus of elasticity are some of the significant mechanical characteristics of FRP rebars which raise concerns on their capability to allow structural members to dissipate energy in seismic zones and thus limit their use in earthquake resistant RC structures (such as moment resisting frames). The behaviour of concrete frames reinforced with FRP bars is still in its early stages of research and development with only a few researchers exploring such structures under in-place cyclic loading (seismic loading). As a result, design codes do not provide guidance for RC moment frames internally reinforced with FRP. This study attempts to partially fill the gap by investigating the behaviour of glass fiber reinforced polymers (GFRP) RC frames under in-plane loading. Six 1/3 scaled RC frames were constructed and tested under reversed cyclic loading to simulate seismic loading conditions. Three were reinforced with GFRP bent bars and three (their counterparts) with conventional steel. The testing was conducted in displacement-controlled mode with the loading history according to ACI 374.1–05. Test parameters included longitudinal reinforcement ratio and arrangement in the columns and presence of links in the joints. The experimental results are presented as hysteretic curves, lateral load / drift graphs, stiffness degradation and cumulative energy dissipated with the overall indication of the feasibility of GFRP RC frames in seismic regions. All GFRP specimens successfully reached 2.75% loading drifts. The energy dissipation of GFRP specimens was lower at initial drifts compared to the steel reinforced samples, but it become greater at final drift. GFRP frames had approximately the same load bearing capacity as their counterparts and even greater in one case. Ultimate loads for G frames were reached at higher level of displacement than for S frames.

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Bond strength prediction of FRP bars to seawater sea sand concrete based on ensemble learning models

The bond strength between fiber-reinforced polymer (FRP) bars and seawater sea sand concrete (SWSSC) is a critical factor in structural design and applications. To address the inherent nonlinear problem, where bond strength is closely tied to constitutes of concrete and properties of FRP bar, this paper presented a novel approach to predict the bond strength using ensemble learning models and investigated the effects of input parameters on bond strength. For this purpose, a dataset of tests of pullout failures was determined consisting of 13 input parameters. Based on the determined dataset, two prediction models were developed using ensemble learning algorithms Random Forest (RF) and XGBoost. Simultaneously, a bond strength equation for pullout failures was derived from the ACI 440.1R-15 database since the existing equation in the code was originally developed to address splitting failures. The developed models demonstrated commendable accuracy based on statistical evaluations. Given its superior prediction and comparable generalization performances compared to the XGBoost model, the RF model was chosen for bond strength prediction compared to the developed equation. Comparative results favored the RF model, which significantly outperformed the developed equation in bond strength prediction. Furthermore, the study investigated the effects of input parameters by analyzing SHAP (SHapley Additive exPlanations) values. The analysis unveiled the influential mechanisms of mechanical property and composition of SWSSC, along with the mechanical, geometric, and surface properties of FRP bar on bond strength. In conclusion, the developed models represent an effective approach for predicting the bond strength of pullout failures between FRP bars and SWSSC.

Effects of exposure in seawater sea-sand concrete pore solution on fatigue performance of carbon FRP bars

The study aims to propose a methodology to predict the fatigue performance of carbon fiber-reinforced polymer (CFRP) bars under the seawater sea-sand concrete (SWSSC) environment. The effects of exposure in SWSSC pore solution on the fatigue damage mechanisms and fatigue performance of CFRP bars are presented. Firstly, the tensile fatigue tests of reference CFRP bars were performed under various stress levels with a constant stress ratio of 0.1. Secondly, the tensile fatigue tests of exposed CFRP bars subject to the simulated SWSSC pore solution were carried out. The tensile failure modes and fatigue damage mechanisms corresponding to different stress levels, were identified using scanning electron microscopy (SEM). Besides, the relationship between fatigue life expectancy and underlying fatigue damage mechanisms was carefully analyzed. Finally, the effective stress level method (ESLM) was proposed to evaluate the residual fatigue life of exposed CFRP bars based on the benchmark S–N curve. Combined with the degradation models (chemical etching/diffusion models) proposed in our previous research, ESLM could bridge corrosion fatigue life prediction of the exposed CFRP bars and the benchmark fatigue data of the non-exposed CFRP reinforcement. The predicted results have good correlations with the experimental data. This method can also provide valuable insight for the corrosion fatigue life prediction of other types of FRP composites.

Bond Performance between Fiber-Wrapped Ribbed Basalt Fiber-Reinforced Polymer Bars and Seawater Sea-Sand Concrete

The high corrosion resistance of fiber-reinforced polymers (FRPs) and related concrete structures means that they are suitable for application in the marine environment. Therefore, the replacement of steel bars with fiber-reinforced polymer (FRP) bars enhances corrosion resistance in seawater sea-sand concrete (SSC) structures. Geometric parameters significantly influence the performance of the bond between ribbed FRP bars and SSC, thereby affecting the mechanical properties of the concrete structures. In this study, the performance of the bond between ribbed (i.e., with fiber wrapping) basalt-fiber-reinforced polymer (BFRP) bars and SSC was investigated through pull-out tests that considered rib geometry and SSC strength. The results demonstrated that an increase in rib and dent widths reduced the bond stiffness, while an increase in rib height and SSC strength gradually increased the bond stiffness and strength. Additionally, the bond stiffness and bond strength were relatively low because the surface fiber bundles buffered the mechanical interlocking force between the BFRP ribs and the concrete, resulting in plastic bond failure during the loading process. Furthermore, the adhesion of the fiber bundles to the surface of the BFRP bars also influenced bond performance, with higher adhesion leading to greater bond stiffness and strength.

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.

Applicability of available NDT methods for damage detection in concrete elements reinforced or strengthened with FRP

The application of Fiber Reinforced Polymer (FRP) materials in concrete structures has been rising due to their several advantages, including lightweight, high tensile strength, ease of installation, and corrosion resistance. They have been mostly implemented for strengthening and repairing existing structures in the form of an externally bonded system, i.e., sheet, jacket, near surface mounted. Furthermore, they have been recently utilized as internal reinforcement of concrete elements in the form of strands, bars, tendons, etc. Although higher durability and performance are associated with the FRP material in some aspects compared to steel, concerns remain regarding damages and defects in this material, many of which are related to their unique features. Importantly, debonding of FRP materials from a concrete surface or within a concrete element has always been an issue resulting in the premature failure of the structure. To this end, concrete elements strengthened or reinforced with FRP materials has to be inspected periodically to detect potential issues and hence prevent any premature failures. This study first determines all possible or potential damages and anomalies attributed to FRP reinforced/strengthened concrete (FRP-RSC) elements. It then investigates Non-Destructive Testing (NDT) methods that can be applicable to the inspection of FRP-RSC elements from a literature survey of past studies, applications, and research projects. Furthermore, this study evaluates the ability of two of the most commonly used NDT methods, Ground Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU), in detecting FRP bars/strands embedded in concrete elements. GPR and PAU tests were performed on two slab specimens reinforced with GFRP (Glass-FRP) bars, the most commonly used FRP bar, with variations in their depth, size and configuration, and a slab specimen with different types of available FRP reinforcements. The results of this study propose the most applicable methods for detecting FRP and their damage/defects in FRP-RSC elements. This study further investigates the feasibility of two new methods for improving the detectability of embedded FRP bars. By providing the inspection community with more clarity in the application of NDT to FRP, this study offers means for verifying the performance and, therefore, help the proliferation of FRP materials in concrete structures.

Degradation of mechanical properties and microstructure evolution of basalt-carbon based hybrid FRP bars in real seawater and sea-sand concrete

The degradation of basalt fibre-reinforced polymer (BFRP) bars induced by alkaline environments hinders their application in seawater and sea-sand concrete (SWSC). The use of carbon fibres (CFs) to partially replace basalt fibres in the preparation of hybrid-FRP (HFRP) bars is an effective method for enhancing the durability of BFRP-bar. To evaluate the effectiveness of using CFs to replace part of the basalt fibres in preparing HFRP bars to enhance the durability of BFRP-bar in real SWSC. The tensile and interlayer interface properties of HFRP bars with different CFs hybrid contents (VCF, %) and arrangements in the SWSC were tested after exposure to seawater at different temperatures. Digital microscopy, scanning electron microscopy, X-ray computed tomography and matrix digestion analysis were used to investigate the microstructural evolution of HFRP bars and SWSC after conditioning. The results showed that the VCF increasing to 10% or 25% significantly alleviated the interlaminar shear strength (ILSS) and tensile strength (TS) losses. The maximum enhancements in the ILSS and TS retention for the SWSC-embedded BFRP bar were 19.12% and 17.55%, respectively. The hybrid CFs changed the failure model of the BFRP-bar. Compared with HFRP bars with CFs in the core, HFRP bars are more likely to deteriorate when the CFs are dispersed circumferentially. The hybrid CFs improved the environmental reduction coefficients (ERC) of TS and ILSS of the HFRP bars. Compared with the SWSC, the ERC of the HFRP bars in the normal concrete was significantly improved.

Shear behavior of reinforced beams with basalt fiber reinforced polymer bars: Review, comparative analysis, and experimental validation

In recent years, there has been a growing trend in the construction industry towards utilizing basalt fiber reinforced polymer BFRP bars. This study aimed to provide a comprehensive analysis of BFRP beams by collecting a vast dataset consisting of approximately 130 experimental data. The first part of the study involved a concise review of the shear behavior of BFRP beams, focusing on eight key parameters. Subsequently, an extensive analysis was conducted using ten different shear models and seven code provisions to predict the shear strength of BFRP beams, both with and without shear reinforcement. Based on the collected data from various studies, an equation was proposed to accurately estimate the shear strength of BFRP beams. The performance of this equation was evaluated during both the training and testing phases. The results indicated that the proposed equation was suitable for predicting the precise shear strength of BFRP beams. Furthermore, to validate the behavior and shear capacity of BFRP beams, four beams were experimentally tested, including one small beam and three larger ones. These beams were designed to consider various parameters such as reinforcement ratio, presence of stirrups, and size effects. The experimental results not only confirmed the knowledge obtained from the review regarding the cracking and stiffness behavior, but also supported the findings of the extensive analysis. Moreover, the proposed equation demonstrated good performance in accurately predicting the shear strength of tested BFRP beams.

Experimental study to evaluate the flexural behavior of concrete beams reinforced with CFRP grid

Fiber reinforced polymer (FRP) is evaluated as an excellent material to replace rebar in reinforced concrete due to its advantages such as high tensile strength-to-weight ratio and high corrosion resistance. Many studies have been conducted to use FRP as substitutes for steel rebar. However, most of these studies were conducted using FRP bars, and research on using FRP grids in the construction field is focused on the field of repair and strengthening. Therefore, this study reports the results of an experimental study to evaluate the flexural behavior of concrete beam with Carbon FRP (CFRP) grid tensile reinforcements as a basic study to evaluate the feasibility of using FRP grid as a as substitutes for steel reinforcement. Thirteen test specimens were prepared for the experiments. The CFRP grids were applied to the specimens as tensile reinforcement. The concrete cover thickness, layers of the CFRP grid and the spacing between the CFRP grids were considered as test variables. The experiment results showed that the specimens without spacing between the CFRP grids were destroyed by side CFRP grid fracture. Also, as the CFRP grid layer increased, the ultimate load increased by 53% to 94%, and when the cover thickness decreased by 10 mm, the ultimate load decreased about 10%. The ratios of the nominal flexural strengths calculated according to the CSA S806–12 and ACI 440.1R-15 standards were 1.004 and 1.09, respectively. Thus, the use of the CSA S806–12 standard enables a relatively accurate prediction of the nominal flexural strength of concrete beams reinforced with CFRP grids.

Deterioration of bond performance between BFRP bars and coral aggregate concrete incorporating slag-based geopolymers under seawater corrosion environments

The utilization of durable geopolymers instead of ordinary Portland cement (OPC) for developing geopolymer-based seawater coral aggregated concrete (GPCAC) in coastal constructions contributed to the improved marine resource utilization and the reduced CO2 emissions and construction costs. Thus, this study investigated the durability of GPCAC and its bond performance with basalt fiber-reinforced polymer (BFRP) bars under seawater drying-wetting cycles, and cement-based CAC was also selected as a comparison. The bond characteristics and degradation mechanisms of slag-based GPCAC and cement-based CAC specimens were compared and analyzed under different seawater exposure condition. Experimental results revealed that both GPCAC and CAC specimens demonstrated various degrees of degradation in bond strength, whereas their initial bond stiffness exhibited a slight increase owing to the hygroscopic expansion of the superficial epoxy resin of BFRP bars, after being exposed to seawater environmental attacks. This degraded bond strength was primarily attributed to the existence of corrosive ions (i.e., SO42-, Mg2+, and Cl-) in seawater and free OH- in concrete capillary pores. These compounds chemically reacted with the slurry hydration products and the resin matrix, which resulted in the decreasing of concrete strength, the hydrolysis of the resin matrix, the deterioration of fibers, and fiber-resin interface debonding. Compared with CAC specimens, GPCAC specimens achieved better resistance to seawater attacks owing to the more dense and stable reaction products formed by geopolymers compared to OPC. After being subjected to 60 °C seawater attacks for 12 months, approximately 4.9% and 12.0% reductions in the bond strength were reported for GPCAC and CAC specimens, respectively. Finally, the residual bond strength of both GPCAC and CAC specimens was predicted after being served in seawater erosion conditions for 50 years.

The effect of type of mechanical anchors on bond behavior of ribbed-surface GFRP bars embedded in concrete

The deficiency in the bond between concrete and fiber-reinforced polymer (FRP) bars is a major hindrance to their widespread use in concrete structures. One effective solution to this problem is to use mechanical anchors along the bar. This research investigates the effect of mechanical anchors on the bond behavior of glass fiber-reinforced polymer (GFRP) bars embedded in concrete. In the first phase, eight beam specimens were constructed and tested in flexure, in which the FRP bars contained no anchors or anchors made of polyethylene, aluminum, or steel. The increase in maximum tensile stress in the bar was 43 %, 17 %, and 12 % for specimens with steel, aluminum, and polyethylene anchors, respectively. Steel anchors were identified as the most effective option with the greatest maximum stress and greatest initial stiffness in the stress-slip curve. In the study's second phase, an additional set of 16 beam specimens was tested to investigate the effect of the number of steel anchors. The results showed that the tensile stress developed in the GFRP bar increases at a higher rate with a greater number of steel anchors. Compared to the specimen without anchors, the bar stresses increased by 20–25 % for one and 52–59 % for two steel anchors.

Bond and Cracking Characteristics of PVA-Fiber-Reinforced Cementitious Composite Reinforced with Braided AFRP Bars

Easy maintenance and high durability are expected in structures made with fiber-reinforced cementitious composite (FRCC) reinforced with fiber-reinforced polymer (FRP) bars. In this study, we focused on the bond and cracking characteristics of polyvinyl alcohol (PVA)-FRCC reinforced with braided AFRP bars (AFRP/PVA-FRCC). Pullout tests on specimens with varying bond lengths were conducted. Beam specimens were also subjected to four-point bending tests. In the pullout tests, experimental parameters included the cross-sectional dimensions and the fiber volume fractions of PVA-FRCC. A trilinear model for the bond constitutive law (bond stress–loaded-end slip relationship) was proposed. In the pullout bond test with specimens of long bond length, bond strength was found to increase with increases in both the fiber volume fraction and the cross-sectional dimension of the specimens. Bond behavior in specimens of long bond length was analyzed numerically using the proposed bond constitutive law. The calculated average bond stress–loaded-end slip relationships favorably fitted the test results. In bending tests with AFRP/PVA-FRCC beam specimens, high ductility was indicated by the bridging effect of fibers. The number of cracks increased with increases in the fiber volume fraction of PVA-FRCC. In specimens with a fiber volume fraction of 2%, the load reached its maximum value due to compression fracture of the FRCC. The crack width in PVA-FRCC calculated by the predicted formula, considering the bond constitutive law and the fiber bridging law, showed good agreement with the reinforcement strain–crack width relationship obtained from the tests.

Tests and modeling of hybrid fiber-reinforced geopolymer concrete elements having BFRP helix: An application for sustainable built environment

Due to the high quantity of carbon emissions from the cement industry, sustainable development for the built environment applications is required by utilizing geopolymers in concrete construction. Considering this problem, the structural efficiency of hybrid fiber-reinforced geopolymer concrete (HFGC) compressive elements made of basalt fiber-reinforced polymer (BFRP) bars is not well understood through experiments or numerical modeling in the literature. By conducting experiments and using finite element analysis (FEA) modeling, the primary goal of current research is to examine and compare the structural performance of BFRP-reinforced HFGC compressive elements (GHC) and steel-reinforced HFGC compressive elements (SHC), both of which are subjected to either concentric and or eccentric loading. The HFGC was created using a combination of steel and polypropylene fibers. Twelve circular compressive elements with a cross-sectional dimension of 300 mm and a height of 1200 mm were created i.e., six GHC and six SHC compressive elements. A parametric study was carried out using the proposed FEA model. The findings of the current research showed that the axial strength of GHC compressive elements was on average 91.8 % that of SHC compressive elements. Both types of elements depicted similar amounts of reduction in the axial strength when subjected to eccentric loads, for instance, 38.5 % and 144.2 % reductions were observed for GHC elements having helix spacing of 38 mm compared with the concentrically loaded counterparts. The recommended analytical relationship based on the database also performed well. The comparative study, which considers the axial involvement of main BFRP bars and the confinement effect of transverse BFRP helix, firmly supports the validity and applicability of the newly developed analytical and FEA models for capturing the axial strength of GHC compressive elements.

Experimental study on flexural behaviors of FRP and steel bars hybrid reinforced concrete beams

To investigate the flexural behaviors of Fiber-reinforced polymer (FRP) and steel bars hybrid reinforced concrete (Hybrid-RC) beams, twelve beams were designed and manufactured, including one steel bars reinforced concrete (Steel-RC) beam, one GFRP reinforced concrete (GFRP-RC) beam, and ten Hybrid-RC beams. The effects of FRP bars type, concrete strength, and effective reinforcement ratio on the flexural behaviors of Hybrid-RC beams were studied through experiments and compared with the predicted results of theoretical models. The research results indicated that when the reinforcement area and service load were the same, the crack width, deflection, ultimate bearing capacity, and ductility of Hybrid-RC beams were between Steel-RC and GFRP-RC beam. The flexural bearing capacity of Hybrid-RC beams might also be increased by using FRP bars with a higher elastic modulus or by increasing the effective reinforcement ratio; however, it would reduce the ductility of the beams. In contrast, increasing the concrete strength could simultaneously increase the Hybrid-RC beams’ flexural bearing capacity and ductility. The equation for calculating the stress of FRP bars in the ultimate state of Hybrid-RC beams was obtained by fitting regression based on the test results, and the equation’s predicted results and test results showed good agreement. In addition, the predicted results of the flexural behaviors of Hybrid-RC beams using the theoretical model agreed with the experimental results.