Fiber Reinforced Polymer Bars Research Articles

Experimental study on the mechanical properties of FRP reinforced shotcrete lining of tunnel in extremely fractured surrounding rock

Tunnel excavation in the southwestern area of China encounters many difficulties caused by the large deformation of extremely fractured surrounding rock, which is the product of high plate tectonic stress. Improving the initial cracking strength and ductility of shotcrete layer is one of the most important means to reduce the frequency of support structure repair, which will improve tunnel construction efficiency and ensure personnel safety. In this case, this paper introduced fiber reinforced polymer (FRP) mesh to replace the steel mesh as reinforcement to optimize the support effect of shotcrete lining. Both large-scale model test and mechanical test are conducted to compare the reinforcement effect between FRP and steel mesh. Research results indicate that replacing steel mesh with FRP can increase the ultimate deformation capacity of tunnel lining by more than four times. The parametric analysis results indicate that increasing the lining thickness, the diameter of the FRP bars and the mesh density have different degrees of effect on improving the stiffness and strength of tunnel lining. The research results can provide reference for relevant projects.

Multiscale analysis of the flexural performance of FRP reinforced concrete structures

Based on existing experimental data and analysis, seven different fiber-reinforced polymer (FRP) bar models including carbon fiber-reinforced polymer (CFRP), basalt fiber-reinforced polymer (BFRP), aramid fiber-reinforced polymer (AFRP), glass fiber-reinforced polymer (GFRP), GFRP and CFRP combined (G–C), GFRP and AFRP combined (G–A), BFRP and CFRP combined (B–C), and BFRP and AFRP combined (B–A) were established. Finite element simulation analysis was conducted on seven different FRP bar combinations under static load bending tests. The flexural behavior of the specimens reinforced with different FRP bar combinations and their influencing factors were analyzed. The results showed that using AFRP as the reinforcement material for FRP composite bars in FRP reinforced concrete beams cannot effectively enhance the overall load-carrying capacity of the composite bars. The combination of CFRP with GFRP and BFRP bars significantly increases the stiffness of the FRP bar structure and improves the structural load-carrying capacity of the concrete beams.

Experimental Study on Flexural Behavior of RC Piles with Basalt Fiber-Reinforced Polymer Bars and Load Carrying Capacity Calculation

The practical application of BFRPB (Basalt Fiber-Reinforced Polymer Bars) as a support structure in foundation pit and slope engineering is relatively under-researched. The indoor tensile test presented in this paper is carried out on the bond between BFRPB and different labelled concrete. The mechanical characteristics of BFRPB, the failure characteristics, and the load-carrying capacity were analyzed. The results of this study demonstrate that the normal section stress of concrete cylindrical components with BFRP has a good linear relationship and supports the rationality of the flat section assumption. In circular reinforced concrete BFRP structures, the failure of the pile load occurs in four phases, and the cracking load is in the range of 51% to 67% of the normal yield load. The main bars increase in strain with load but become attenuated in the compression zone. The deformation of the main bars increases with the load but becomes muted in the compression zone. Based on the method of calculating the load-carrying capacity of GFRP-reinforced RC piles and the normal limit load-carrying moment obtained from in-door tests, the bending moment correction coefficient in the calculation formula for the load-carrying capacity of BFRP-reinforced RC piles was then obtained.

Comparative Performance Analysis of Small Concrete Beams Reinforced with Steel Bars and Non-Metallic Reinforcements

This research investigates the performance of small concrete beams that are reinforced with glass fiber-reinforced polymer (GFRP) bars, basalt fiber-reinforced polymer (BFRP) bars, and traditional steel bars. It addresses the limitations of traditional steel reinforcement, emphasizing the need for alternative strategies. Fiber-reinforced polymer (FRP) materials, including GFRP and BFRP, are examined for their mechanical characteristics compared to steel. The experimental program focuses on ultimate load-bearing capacity, deflection, deformation at different load levels, and failure modes. The concrete specimens, prepared according to Eurocode, consist of six small concrete beams measuring 80 × 120 × 1100 mm with varied reinforcements. The study reveals that GFRP-reinforced beams outperform BFRP and steel reinforcements in ultimate load-bearing capacity, showcasing enhanced structural performance. The GFRP-reinforced beams exhibit capacity and resilience characteristics surpassing those of both BFRP and steel, whereas the deflection observed was higher on both fiber-reinforced beams than on the steel-reinforced beams. The examination of failure modes reveals that the concrete beams that were reinforced with FRP bars showed a bending property before failure, while those reinforced with steel broke easily without bending much. This comprehensive research contributes to advancing our understanding of FRP materials’ application in concrete structures, paving the way for further optimization and overcoming limitations in reinforcement materials.

Effect of BFRP ties on the axial performance of RC columns reinforced with BFRP and GFRP rebars

The adoption of fiber-reinforced polymer (FRP) bars in lieu of traditional steel reinforcement for concrete structures has gained prominence. Nevertheless, prevailing international standards have not incorporated provisions to assess the significant contribution of FRP materials to the axial capacity and deformability of compression members. This study investigates the impact of Basalt (BFRP) ties on the axial performance of full-scale concrete columns reinforced with BFRP and Glass (GFRP) rebars, alongside traditional steel longitudinal rebars. Ten columns were subjected to concentric loading, with parameters including the type of longitudinal rebars (BFRP, GFRP, and steel), spacing of BFRP ties (180 mm, 120 mm, and 60 mm), and diameter of steel rebars (16 mm and 20 mm). Varied steel rebar diameters aimed to discern the influence of axial stiffness on column behavior. Results indicate an 18 % to 26 % higher axial load capacity in steel-reinforced concrete (RC) columns compared to FRP-RC columns. Both types of FRP rebars contributed approximately 12 % to the axial capacity. Reducing BFRP tie spacing from 180 mm to 60 mm significantly increased deformability by up to 250 % in FRP-RC columns and ductility by up to 14 % in steel-RC columns. The study highlights conservative predictions in existing design equations (ACI 440.11–22 and CSA S806-12) for the axial load capacity of BFRP and GFRP RC columns, underestimating by 14 % to 20 %, as they neglect the contribution of FRP rebars. Utilizing a concrete crushing strain of 3,000 µε and 3,500 µε as the ultimate FRP compressive strain produced predictions closest to the experimental axial load capacity.

Shear Behavior of Precast Concrete Box Culverts Reinforced with Glass Fiber-Reinforced Polymer Bars under Concentrated Load

Shear Behavior of Precast Concrete Box Culverts Reinforced with Glass Fiber-Reinforced Polymer Bars under Concentrated Load

Concrete Structures Reinforced with FRP BAR

Abstract: Fiber reinforced polymer (FRP) bars have been widely used in civil engineering used as a substitute for steel reinforcement because it has many advantages such as high strength-to-weight ratio, electromagnetic neutrality, light weight, ease of handling and no corrosion. Moreover, the productive technology becomes more and more mature and industrialized so that FRP has become one economic and competitive structure material. Based on the recent researches, this paper mainly introduces progress in the studies on concrete structures reinforced with FRP bars. These contents in this paper includes the bond performance of FRP bars in concrete, Compression Behavior, flexural behavior, and ductility of concrete structure reinforced with FRP bars in the past few years in the world .

Bond performance of NSM FRP–concrete interfaces with epoxy under chloride‐salt conditioned environments

AbstractConcrete in coastal areas is susceptible to structural damage caused by corrosion and expansion of reinforcement. Near‐surface mounted (NSM) fiber‐reinforced polymer (FRP) bars have become effective for strengthening damaged reinforced concrete structures. The bonding performance of NSM FRP bars in concrete is a key factor limiting their application and promotion in civil engineering. In this study, the influences of the conditioned environment, such as the chloride salt concentration, immersion time, and bond length of the FRP bar, on the bonding performance were investigated experimentally. First, material properties in a conditioned environment were studied. Subsequently, the failure mode, bond stress–slip curve, and bond strength of the NSM FRP bar in concrete were investigated. Finally, the microstructure and chemical composition of the materials were revealed using scanning electron microscopy and energy‐dispersive spectroscopy (EDS) images of the materials under environmental conditions. The transfer mechanism of NSM FRP bars in concrete with epoxy was revealed. The results showed that the failure modes of the pullout specimens can be divided into epoxy splitting failure and basalt fiber‐reinforced polymer (BFRP) pulling failure. The chloride‐salt concentration was a critical factor affecting the bond properties, and the longer the bond length, the lower the bond strength. The microstructure clearly shows that the degradation of the bonding behavior at the interface of the NSM FRP bar in concrete in a conditioned environment is attributable primarily to the resin damage of the epoxy, resulting in pit corrosion. There was no significant damage to the fibers in the FRP bar, and the degradation was primarily due to resin matrix damage and interfacial debonding. The EDS results showed that the degradation of the epoxy resin and BFRP bars was caused by CO bond and SiO bond fractures, respectively.

Comprehensive analysis of bond stress transfer mechanisms in glass fiber-reinforced polymer-reinforced concrete beams using acoustic emission monitoring

The present study investigates the critical bond characteristics between glass fiber-reinforced polymer (GFRP) bars, which is essential for the application bars as corrosion-resistant components in structural concrete. The interfacial bond deterioration and stress transfer mechanisms have been investigated in the present study by employing acoustic emission (AE) monitoring in hinged-type GFRP-reinforced concrete (GFRP-RC) beam specimens. The bond strength of the test specimens, governed by chemical adhesion, mechanical interlocking, and frictional resistance, has been intricately examined. Various AE signal parameters as well as historic and severity indices derived from the AE signal parameters have been meticulously evaluated and correlated with bond stress and rebar slip variations. The present study has also introduced an innovative approach of using the sentry function for the assessment of bond deterioration and associated mechanisms. The results of the present study demonstrate the reliability of AE parameters in monitoring debonding and bond strength variation, the effectiveness of the sentry function in evaluating damage progression, and the utility of historic and severity indices in capturing micro-mechanism transformations. The accurate localization of debonding and the qualitative distribution of bond stress have also been demonstrated by through correlations between cumulative AE parameters and rebar slip, Additionally, the present study also highlights the significance of peak frequency variations in AE signals, serving as a crucial tool for quantifying the mechanical interlocking and interfacial friction. The results contribute significantly to precise assessments and development of effective strategies for mitigating bond deterioration in GFRP-RC elements.

Study on the effect of strain rate on the bond performance between GFRP bars and ECC after seawater freeze-thaw cycles

With the increase in marine and coastal infrastructure in cold regions, freeze-thaw damage and dynamic loads will reduce structural performance. However, the dynamic bonding performance of seawater sea sand ECC and glass fiber-reinforced polymer (GFRP) bars after freeze-thaw cycles is still unclear. In this paper, the mass loss rate, dynamic elastic modulus, and compressive strength of seawater sea sand ECC were studied through freeze-thaw cycle tests. The bonding properties of seawater sea sand ECC and GFRP bars were examined under two freeze-thaw environments (Seawater environment, Freshwater environment), four freeze-thaw cycles (0, 50, 100, and 150), and four strain rates (2.63 × 10−5s−1, 2.63 × 10−4s−1, 2.63 × 10−3s−1, and1.32 × 10−2s−1) using pull-out tests. Additionally, the microstructure was analyzed using SEM. The results show that compared with the freshwater freeze-thaw cycle, the seawater freeze-thaw cycle deteriorates the surface peeling resistance and mechanical properties of seawater sea sand ECC. Compared with the non-freeze-thaw specimens, the failure mechanism after freeze-thaw cycles changed from the gradual increase of bond strength with the increase of strain rate to the gradual decrease. Compared with the dynamic elastic modulus, compressive strength, and bond strength freeze-thaw damage model based on the Weibull distribution, it was observed that the predicted life of compressive strength is overestimated, while the predicted life of bond strength is underestimated. The bond strength and slip calculation models for freeze-thaw cycles and strain rates have been established. This provides a theoretical foundation for predicting the structural service life and conducting durability research on ECC and GFRP bars in seawater and sea sand.

Parametric study, finite element analysis, and load capacity calculation for flexural behaviour of seawater and sea sand concrete beams reinforced with GFRP bars

This study sought to enhance the understanding of seawater sea sand concrete (SWSSC) structures reinforced with glass fiber-reinforced polymer (GFRP) bars. To achieve this, an experimental investigation was conducted involving the production and testing of 6 GFRP bar-reinforced SWSSC beams (GFRP beams) alongside 3 ordinary seawater sea sand concrete (OSWSSC) beams (Ordinary beams) to evaluate their flexural performance. Additionally, a subsequent analysis comprised the establishment of 11 full-scale finite element models aimed at parameter assessment on GFRP beams. The experimental and numerical findings revealed that an increase in sea sand replacement ratio in SWSSC beams, with a shear-span ratio of 2.2, led to varying degrees of shear-compression failure. Notably, owing to the superior crack resistance of SWSSC, the beams demonstrated outstanding structural coordination. Compared to OSWSSC beams, GFRP beams with a 100 % replacement ratio of sea sand or an increased in concrete strength to C55 had initial stiffness values that were 150 % and 106 % larger, respectively. Further investigation unveiled that a reduction in the shear-span ratio from 2.5 to 1.0 or an increase in the longitudinal reinforcement ratio from 1.27 % to 2.53 % significantly augmented the ultimate load-carrying capacity, resulting in increases of 88.0 % and 37.7 %, respectively. Based on these findings, several design recommendations are proposed: 1. Establish a deflection limit at l0/500 or implement more stringent measures for GFRP beams. 2. Consider reducing the diameter of GFRP bars while maintaining a 50 % sea sand replacement rate to mitigate crack formation. 3. An excessive longitudinal reinforcement ratio hampers the enhancement of specimen load-carrying capacity. 4. Consider utilizing Chinese specifications for flexural capacity calculations.

Behavior and design of eccentrically compressed hybrid steel and GFRP reinforced concrete columns at elevated temperature

AbstractThis study presents analytical model for the analysis of hybrid (steel and fiber reinforced polymers (FRP)) reinforced concrete (RC) columns at elevated temperature under eccentric compressive loads. The bending moment resistance of the (RC) columns at elevated temperature is formulated based on force equilibrium and strain compatibility of the concrete column section under combined bending moment and axial force. Deterioration the mechanical properties of concrete, steel, and FRP bars due to the rise of temperature has been taken into account using equations proposed by previous studies. Validating the suggested model was carried out by comparing the analytical results with corresponding experimental and numerical results in terms of axial load‐lateral displacement relationships, axial load‐bending resistance interaction diagrams, and failure modes. Validation results have shown the accuracy of the suggested analytical model. A parametric study has also been conducted using the proposed analytical model to investigate the effect of some parameters on the axial load‐bending resistance interaction diagrams of hybrid steel and FRP‐RC columns under elevated temperature. These parameters include the effect of higher temperature values, the effect of reinforcement material, and the effect of reinforcement configuration. Parametric study results have revealed some interesting conclusions that may be implemented in the design of hybrid RC columns at fire.

Numerical analysis of shear critical BFRP-reinforced concrete beams containing basalt fibers

Simulation models were developed for concrete beams reinforced with basalt fibers (BF) and basalt fiber-reinforced polymer (BFRP) bars. Experiments were conducted on physical concrete beams to validate predictions of the numerical models. The effect of replacement of natural aggregates (NA) by recycled concrete aggregates (RCA) and the inclusion of BF on shear response of BFRP-reinforced concrete beams was then investigated numerically. The shear capacity of the beam models with 30–100% RCA decreased by 10–28 % relative to that of a control beam model with NA. The inclusion of BF at a volume fraction (vf) of 0.5 % to beam models with 30 % and 60 % RCA fully restored the shear capacity of the control model. At 100 % RCA, a maximum of 93 % of the shear capacity of the control model was restored at vf= 1.5 %. Research findings would assist practitioners in proper modeling of BFRP-reinforced concrete beams containing nonmetallic fibers.

Physicochemical-mechanical simulation of the short- and long-term performance of FRP reinforced concrete beams under marine environments

To broaden the applications of fiber reinforced polymer (FRP) reinforced concrete structures under marine environments, it is crucial to gain a fundamental understanding of their short- and long-term performance. In this study, the effectiveness of the proposed multi-scale simulation platform, which incorporates the proposed degradation model of FRP bars, is quantitatively assessed via the comparison between the predicted results and experimental load-displacement curves under different marine conditions (continuous immersion, wet-dry cycling and subtropical marine atmosphere). The spatially physical, chemical and mechanical information, such as pH value, moisture, hydration degree, strength, porosity during the exposure was also revealed. Finally, the long-term structural performance of FRP-reinforced concrete beams exposed to the predefined environmental conditions over durations of 20, 50 and 100 years are assessed using the multi-scale simulation platform. After 50 years of exposure, the load-bearing capacity of GFRP-reinforced concrete beams was found to decrease by 35.8 % in immersion conditions and by 17.9 % in subtropical marine atmosphere. The degradation of the load-bearing capacity in the case of 100 years exposure to subtropical marine atmosphere was found to be less severe than that (23.1 %) in the case of 50-year immersion. These findings not only deepen our understanding of the material and structural properties of FRP-reinforced concrete beams under various environmental conditions, but also validate the effectiveness of the proposed multi-scale platform.

Numerical assessment of using FRP rebars as an alternative passive reinforcement in RC beams

AbstractRecent sustainable building strategies make the right decisions to be environmentally friendly and reduce carbon emissions. In some reinforced concrete (RC) elements, fiber-reinforced polymer (FRP) bars have been proposed as an alternative to conventional steel bars. The demand for using noncorrosive and/or nonmetallic reinforcing bars in various reinforced concrete projects has increased. Although these concrete elements are lightweight, have a long lifespan, and need little maintenance, their non-ductile nature and bond with the surrounding concrete create significant challenges. Several experimental investigations have been conducted to evaluate the behavior of RC elements, even with their high cost. This study aims to assess numerically the viability of using FRP bars instead of traditional steel ones in simply supported reinforced concrete beams (RCBs) as longitudinal reinforcement (passive reinforcement). Utilizing the three-dimensional (3D) nonlinear finite element analysis (FEA) software (ABAQUS), a total of eighteen models were carried out to validate the results available in reference case studies with FRP bars. The verification of the numerical results has been verified by comparing them with the reference experimental data. Next, in order to assess the rigidity of such RCBs with FRP bars, parametric research was carried out. The numerical results proved that RCBs with FRP bars have a positive impact on enhancing load-carrying capacities. But on the other hand, the strain energy of such RCBs with CFRP bars is reduced to about 75% of the strain energy of RCBs with steel bars, which leads to low beam ductility.

Experimental and numerical research on shear performance of GFRP bar reinforced seawater sea-sand concrete deep beams without stirrups

Using glass fibre-reinforced polymer (GFRP) bars to reinforce seawater sea-sand concrete (SWSSC) is a feasible way to replace traditional concrete structures. Thus, this paper aims to understand the shear response of GFRP bar-reinforced SWSSC (GFRP-SWSSC) deep beams. Experimental and numerical programs were carried out on four-point shear tests of GFRP-SWSSC deep beams without stirrups. Seventy specimens were tested to investigate the effects of key parameters on shear responses, including concrete categories, seashell content, section heights, and GFRP bar diameter. The test results indicated that the cracking strength of GFRP-SWSSC deep beams was slightly higher than ordinary concrete deep beams. The increased section height of GFRP-SWSSC deep beams and the decreased shell content remarkably enhanced the stiffness and shear ultimate strength. The corresponding finite element model (FEM) of GFRP-SWSSC specimens was established and validated by comparison with test results. Further, three guidelines predictions for the shear strength of GFRP-SWSSC beams were too conservative. The new design formulae derived from modified tension-compression theory were put forward to evaluate the shear strength of GFRP-SWSSC deep beams, and the comparisons demonstrated that the proposed design formulae achieved sufficient accurate predictions for practical engineering. Based on research on shear performance, the hybrid GFRP-SWSSC structure is a feasible solution to resource shortages, which provides a promising application prospect in marine engineering.

Strength reduction factor based on probabilistic analysis for hybrid reinforced concrete beams

The American Concrete Institute (ACI) developed ACI-318 and ACI-440 codes, providing design guidelines for concrete beams subject to flexure and reinforced with steel or Fiber-Reinforced Polymer (FRP) bars, respectively. Although using a hybrid reinforcing system that combines steel bars and FRP bars has gained significant attention, ACI codes have no design guidelines for this concept. The main objective of this study is to determine the appropriate strength reduction factor for hybrid steel/FRP RC beams (i.e., concrete beams reinforced with a hybrid system of FRP and steel bars) by conducting a comprehensive probabilistic analysis over a wide range of hybrid steel/FRP RC beams dataset. This factor is a crucial component of the design standards outlined by the American Concrete Institute (ACI). The reliability index of the beams dataset under consideration is determined within the framework of reliability analysis using the First Order Reliability Method (FORM). Furthermore, a sectional analysis is employed as a mechanical model initially verified using an experimental dataset of 95 specimens. This model is utilized to forecast the flexural capacity of beams.The study's findings indicate a substantial correlation between the strength reduction factor and the reinforcement and live-to-dead load ratios. For the objective of conservative design, a strength reduction factor of 0.65 is suggested.

Structural Behavior of Circular Concrete Columns Reinforced with Longitudinal GFRP Rebars under Axial Load

This paper presents experimental and theoretical assessments of the structural behavior of circular steel fiber-reinforced concrete (SFRC) columns reinforced with glass fiber-reinforced polymer (GFRP) bars subjected to a concentric axial compressive load. Laboratory experiments were planned to evaluate and compare the effect of different design parameters on the structural behavior of column specimens based on experiments and finite element (FE) analysis. The experimental variables were (i) concrete types, i.e., conventional concrete (CC) and fiber-reinforced concrete (FC), (ii) longitudinal reinforcement types, i.e., steel and GFRP bars, and (iii) transverse rebar configurations, i.e., tied and spiral with different pitches. Sixteen column specimens were fabricated and categorized into four groups with respect to rebar configurations and concrete types. The results showed that the failure modes and cracking patterns of those four column groups were comparable, particularly in the pre-peak branches of load-deflection curves. Even though the average ultimate load of the columns with longitudinal GFRP bars was 17.9% less than that with longitudinal steel bars, the ductility index (DI) was 10.2% greater than their counterpart on average. The addition of steel fibers (SF) to concrete increased the axial peak load by up to 3.1% and the DI by up to 6.6% compared to their counterpart CC columns without SFs. The DI of specimens was increased by higher volumetric ratios (up to 12%) and spiral types (up to 5.5%). The concrete damage plastic (CDP) model for FC columns was updated in the finite element software ABAQUS 6.14. Finally, a new simple equation was theoretically proposed to predict the axial capacity of specimens by considering the inclusion of longitudinal GFRP rebars, volumetric ratio, and steel spiral/hoop ties. Good agreement between the proposed model predictions and the experimental/numerical results was observed.

Precast CSA-based concrete tunnel lining segments reinforced with GFRP bars: Challenges and opportunities

This research study investigates the potential of using Calcium Sulfoaluminate (CSA) binder as a sustainable alternative to ordinary Portland cement (OPC) in the production of precast concrete tunnel lining (PCTL) segments. The effectiveness of CSA-based concrete, reinforced with Glass Fiber-Reinforced Polymer (GFRP) bars, was examined through an experimental program. Comparative analyses, including analytical, experimental, and Life Cycle Assessment (LCA) comparisons, were conducted with OPC-based segments reinforced with traditional steel. The results indicate that the proposed CSA/GFRP solution has the potential to improve sustainability in mechanized tunnelling and prefabrication. A case study is also presented to support these findings.

Bond behavior of the interface between concrete and basalt fiber reinforced polymer bar after freeze-thaw cycles

Bond behavior of the interface between concrete and basalt fiber reinforced polymer bar after freeze-thaw cycles