Basalt Fibre Reinforced Polymer Reinforcement Research Articles

Flexural behaviour of BFRP grid/bar reinforced UHPC beams and slabs

This study investigates the integration of Basalt Fiber Reinforced Polymer (BFRP) and Ultra-High Performance Concrete (UHPC), which exhibit significant potential for a durable and sustainable solution in marine and offshore infrastructure. An experimental program of BFRP grid/bar-reinforced UHPC beams and slabs subjected to four-point bending is presented. A total of nine beams and ten slabs were prepared and tested to investigate the effect of BFRP reinforcement ratio (0 %–3.33 %), type of reinforcement (grid and bar), and steel fiber content of UHPC (0 %, 1 %, 2 % and 3 %). The results revealed that the inclusion of BFRP reinforcement, even at a small reinforcement ratio, is feasible to enhance structural ductility due to the large rupture strain and superior strength characteristics of BFRP material. Moreover, the steel fibers played a crucial role in preventing shear failures of UHPC and creep failures of BFRP reinforcement. Within a range of 0–2 %, the steel fiber content not only benefited the load-resistance and deformation capacity but also effectively improved the cracking load. However, high fiber content (3 %) had a minimal contribution to load-bearing capacity and negatively affected ductility. A theoretical model based on the deflection method was employed to forecast the general behaviour of the flexural members. Comparisons between experimental results and numerical predictions confirm its accuracy.

Data-driven predicting of bond strength in corroded BFRP concrete structures

The mechanical properties of basalt fiber-reinforced polymer (BFRP) concrete structures in corrosive environments are largely dependent on the bonding performance between the BFRP reinforcement and concrete. An accurate and convenient method for calculating the bonding strength is crucial for engineering design. However, experimental methods and existing empirical models are insufficient to encompass the intricate interdependencies among the bonding factors. This study proposed a machine learning (ML)-based bonding strength prediction method, which utilizes random forests (RF) and adaptive boosting (AdaBoost) algorithms to predict the interfacial bond strength of BFRP reinforcement in corroded concrete. The model was trained on a dataset of 355 samples, effectively quantifying the relationships between the BFRP reinforcement parameters, concrete parameters, corrosion factors, and bonding strength. The performance of the two algorithms was evaluated using R2, RMSE, and MAE indicators, and the prediction results were explained using the SHAP method. The results show that the predicted results of the machine learning model are highly consistent with the experimental results, with the AdaBoost model achieving an R2 of 0.925 on the test set, demonstrating high predictive performance. Among the various factors, the corrosion factor has the most significant impact on bonding strength, followed by concrete compressive strength and BFRP bar yield strength. Ultimately, the model was juxtaposed against traditional empirical formulas, affirming its efficacy and dependability. The research presents a novel approach to predicting bond strength in corroded BFRP bar-concrete systems.

Flexural behavior of BFRP bar–hybrid steel fiber reinforced UHPC beams

Ultra-high-performance concrete (UHPC) has the potential to overcome the durability limitations of conventional concrete. Basalt Fiber Reinforced Polymer (BFRP) bars can mitigate the corrosion effects of steel bars and fully exploit the properties of UHPC. Industrial Steel Fibers (ISF) are a widely used component in the preparation of UHPC. To reduce environmental pollution and costs, this study proposes using recycled tire steel fibers (RTSF) instead of ISF in the production of UHPC. RTSF will be combined with BFRP bars to prepare hybrid steel fiber UHPC beams. The study investigates the effects of RTSF substitution for ISF and BFRP reinforcement ratio on the flexural performance of UHPC beams. The study indicates that the beam's bending failure modes include concrete crushing, equilibrium, and BFRP bar tensile failure. The replacement rate of RTSF has a dual effect on the flexural performance. As the RTSF replacement rate increases from 0 % to 100 %, the cracking load and ultimate capacity of the beams decrease by 2.86 % and 10.38 %, respectively, while the mid-span deflection of the beam increases by 7.94 mm when it reaches failure. When the replacement rate of RTSF is 60 %, the beams exhibit optimal bending performance, and their ultimate capacity can be increased by 2.95 % compared to the capacity when the replacement rate is 0 %. The failure mode of the beams is significantly influenced by the reinforcement ratio of the BFRP bars. Increasing the BFRP reinforcement ratio from 1.12 % to 7.12 % resulted in a 65.8 % decrease in maximum crack width and a 57.6 % decrease in mid-span deflection, while the ultimate load is increased by 78.6 %. The proposed theoretical calculation formula can effectively predict the flexural capacity of BFRP bar hybrid steel fiber UHPC beams, providing a theoretical basis for the application of FRP reinforced hybrid steel fiber UHPC beams.

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.

Evaluation of BFRP strengthening and repairing effects on concrete beams using DIC and YOLO-v5 object detection algorithm

In this study the effectiveness of using Basalt Fiber Reinforced Polymer (BFRP) for strengthening and repairing concrete beams after pre-damage was investigated. Four-point bending tests were conducted on concrete beams, and their strain nephograms were analyzed using 3D-DIC (Digital Image Correlation) to assess the BFRP reinforcement and repair effects on concrete. A damage indicator model based on stress-displacement curves was proposed to quantify concrete damage and evaluate the BFRP strengthening effect. Additionally, the YOLO-v5 object detection algorithm was employed to detect surface damage on concrete specimens, and its results were cross-verified with the damage indicator. The study reveals that BFRP reinforcement primarily affects the concrete beams beyond the elastic limit, enhancing their load-bearing capacity by 37.91% and improving ductility. The proposed damage indicator proves successful in quantifying damage in BFRP-reinforced concrete beams, distinguishing the transition points between elastic, cracking, and failure stages. The YOLO-v5 algorithm accurately detects damage in strain nephograms, providing sensitive and timely identification of concrete damage. Results proves that the offset ratio between the damage identification results of YOLO-v5 and the experimental stress-displacement curve data is between − 3.03% and 8.66%. The proposed damage indicator and YOLO-v5 detection offer valuable tools for evaluating damage and monitoring the health of concrete structures in engineering applications.

Effects of pre-cracked width and seawater erosion on the cracking behavior of SFRC beams with BFRP bars subjected to cyclic loading

This study aims to explore the effects of various pre-cracked widths, seawater erosion and BFRP reinforcement ratios on the cracking behavior of steel fiber reinforced concrete (SFRC) beams with Basalt Fiber Reinforced Polymer (BFRP) bars subjected to cyclic loading. Pre-cracked beams were made by applying loads to obtain a predetermined crack width, such as 0.02 mm, 0.2 mm, and 0.4 mm crack widths. Eleven beams were poured and tested by a four-point bending load under cyclic loading. The crack pattern and load-crack width curves of beams were drawn and analyzed. The effects of pre-cracked width, seawater erosion, and BFRP reinforcement ratio on crack behaviors of beams were investigated and discussed. The results showed that the tensile strength of BFRP bars degenerated after seawater corrosion, and its degradation rates increased with the increase of diameter. The failure mode of beams after seawater erosion may transform from concrete crushing failure to BFRP tensile failure; The maximum crack width of all beams under service load was less than 0.5 mm. Increasing the BFRP reinforcement ratio can significantly improve the crack resistance of beams, but pre-cracked width and seawater erosion had adverse effects on the crack behavior. Existing codes overestimated the crack width of SFRC beams reinforced with BFRP bars. Finally, a new calculation model of crack width of SFRC beams with BFRP bars after seawater corrosion was proposed, and its results were closer to the experimental results.

Behavior of Shear-Critical Recycled Aggregate Concrete Beams Containing BFRP Reinforcement

The shear performance of recycled aggregates beams reinforced with basalt fiber-reinforced polymer (BFRP) bars is evaluated and compared with that of similar beams made with natural aggregates (NA). Six beams with a shear span-to-effective depth ratio (a/d) of 3.0 were tested to failure. Test variables consisted of the recycled concrete aggregate (RCA) replacement percentage (60 and 100%) and the presence of BFRP stirrups in the shear span. Experimental results showed that a RCA replacement of 60% marginally reduced (5%) the shear capacity. However, the reduction in the shear capacity was more pronounced (17%) for the specimen made with 100% RCA. The contribution of BFRP stirrups to the shear capacity decreased with an increase in the RCA replacement percentage. The width of the major shear crack at a given value of load was higher for the beams with RCA. The deflection values at the ultimate load were greater for beams made with RCA. A codified analytical approach as well as a model published in the literature were employed to predict the shear capacity of the tested beams. Predictions of the codified analytical approach were very conservative. The analytical model published in the literature provided a more reasonable prediction for the shear capacity of the tested beams than that of the codified analytical approach.

Strength of Hybrid Steel-BFRP Reinforced Concrete Beams with Openings in the D-Region Strengthened Internally and Externally

The opened beams always confused the designers due to the guidelines missing. In this research, six hybrid beams reinforced with mixed steel and basalt fiber-reinforced polymer (BFRP) bars and having constant cross-sections of 150 mm × 300 mm and a clear span of 1800 mm were cast and tested under a four-point loading setup. Generally, five beams had symmetrical rectangular openings with dimensions of 150 mm × 250 mm located at a distance of 250 mm (equivalent to the beam effective depth) from the beam support, while an additional solid beam served as a control. The studied parameters included the effect of using internal reinforcement (steel or BFRP bars) provided adjacent to the opening sides or by incorporating an external BFRP sheet around the opening corners. Also, double enhancement with internal steel reinforcement bars together with external strengthening BFRP sheet was investigated. The relevant results showed that the opened beam without enhancement lost 75% of the maximum load compared with the solid beam. Placing internal steel or BFRP bars around the openings increased the maximum load by 62% and 60%, respectively, compared to the non-enhanced opened beams. Using an external BFRP sheet to strengthen the opening corners of the beam enhanced the maximum load by 76% compared with the non-enhanced opened beam. Consequently, by combining both the internal steel reinforcement and external BFRP sheet around the openings, the maximum load increased by 137% compared with the non-enhanced opened beam. Ultimately, a numerical analysis of the three-dimensional finite element model was performed to confirm the experimental findings, and the relevant results showed compatibility correlations with the experimental ones. Also, the effect of various parameters such as BFRP reinforcement ratio and number of BFRP sheet layers around the openings was investigated by adapting the validated numerical model.

Precast segmental beams made of fibre-reinforced geopolymer concrete and FRP tendons against impact loads

In the open literature, there is no investigation into the impact behaviour of prefabricated segmental concrete beams (PSCBs) cast with low CO2-emission fibre-reinforced geopolymer concrete (GPC), reinforced with non-corrodible basalt fibre-reinforced polymer (BFRP) reinforcement, and post-tensioned with carbon FRP (CFRP) tendons. This research, hence, aims to close this existing gap of knowledge. The primary goals are to investigate the effect of dispersed fibres on the impact response of PSCBs and to compare the performance of CFRP versus steel tendons. The experimental results reveal that the PSCBs fail due to excessive joint openings that lead to concrete spalling and flying concrete debris. The inclusion of dispersed fibres in the concrete postpones crack development, reduces reinforcement strain, and effectively mitigates concrete spalling and stiffness degradation of the beams. While fibres show limited influence on the deflection response of PSCBs, as the deformation of segmental beams is predominantly governed by joint openings with no fibres bridging across the joints, they play a crucial role in preventing severe damage during impact events. The impact response of beams post-tensioned with CFRP tendons is analogous to those with steel tendons. Notably, both the CFRP tendon and BFRP reinforcement remain intact even when the beam fails under impact loads. This implies that CFRP tendons and BFRP reinforcement can be successfully employed in constructing durable and sustainable segmental GPC beams capable of withstanding impact loading. A high-fidelity numerical model of PSCBs made of GPC and FRP tendons and reinforcement subjected to impact loads is also developed, for the first time, to supplement the discussions of experimental findings.

Flexural performance and damage evaluation on basalt fiber reinforced polymer (BFRP) sheet reinforced concrete

Basalt fiber reinforced polymer (BFRP) is a promising composite material for concrete restoration as an external sheet reinforcement. This work aims to propose a methodology that can effectively monitor and evaluate the damage of external BFRP sheet reinforced concrete during its industrial service life. For better understanding of flexural performance and damage evaluation on BFRP sheet reinforced concrete, four-point bending tests were conducted on specimens produced with different bonding conditions (bonding BFRP sheet at 0%, 80%, 90%, and 95% of failure load) to explore suitable repair strategies for engineering. Multi-view digital image correlation technique is used to analyze the deformation on concrete part and BFRP sheet simultaneously. Such a non-contact measurement makes it possible to observe crack development and evaluate damage degree of concrete beams during loading process and could be applied in industrial measurement. In addition, crack development could be characterized by length and width, which is calculated by strain distribution of both concrete part and BFRP sheet. Results reveal that BFRP sheet could improve about 78.56% of flexural strength and 304.38% of ductility. Besides, it is found that the growth of damage degree is steadier in BFRP reinforced specimens. According to the early warning levels proposed in this work, it is suggested that BFRP reinforcement should be adopted before concrete is loaded to 90% of failure load to allow for timely repair and facilitate subsequent health monitoring.

Flexural and compressive performance of BFRP-reinforced geopolymer sea-sand concrete beams and columns: Experimental and analytical investigation

The combination of geopolymer sea-sand concrete (GSSC) and basalt fiber reinforced polymer (BFRP) reinforcement has the potential to optimally exploit the advantages of both materials, resulting in superior structural durability and environmental friendliness. The resulting structure is called a BFRP-reinforced GSSC structure, which has broad application prospects in marine engineering construction. This paper presents a recent experimental and analytical investigation into the flexural and compressive performance of BFRP-reinforced GSSC structures to verify the expected benefits of such a material combination. In particular, a type of GSSC that uses MgO as an expansion agent to reduce concrete shrinkage was used in this study. The results of four-point bending tests on nine rectangular beams, where longitudinal reinforcement ratios and reinforcement types were key parameters, and monotonic axial compression tests on seven columns, where concrete types and transverse reinforcement ratios were key parameters, are reported in this paper. The test results initially confirmed the advantages of using GSSC in combination with BFRP reinforcement and showed that: (1) the ultimate carrying capacity of BFRP-reinforced GSSC beams and columns was higher than that of conventional steel-reinforced counterparts for the same reinforcement configurations; (2) the flexural and compressive capacity of BFRP-reinforced concrete beams and columns could be enhanced by an appropriate increase in reinforcement ratio and the addition of expansion agents. Finally, this paper presents design equations for the flexural and compressive capacity of BFRP-reinforced GSSC structures.

Theoretical and experimental investigation of the time‐dependent relaxation rates of GFRP and BFRP reinforcement bars

AbstractCracked concrete members with fiber‐reinforced polymer (FRP) reinforcement generally suffer from increased deflections compared to steel‐reinforced members due to FRP reinforcements' lower modulus of elasticity. An approach to counteract this problem can be the prestressing of the FRP reinforcement, which can significantly reduce member deflections. However, time‐dependent prestress losses occur due creep and shrinkage of the concrete and relaxation of the prestressing tendons. Within the first part of this article, mathematical approaches to determine relaxation rates from creep tests are introduced. Subsequently, short‐term and long‐term tensile tests under sustained load on glass and basalt FRP reinforcement bars are presented. Based on the experimental data and the mathematical model, relaxation rates for the investigated specimens are derived. In addition, using an approach based on logarithmic extrapolation, the relaxation rates at 1 million hours (end of service life) are calculated, and the experimentally determined residual tensile properties are evaluated.

Punching Shear Behavior of Fibrous High Strength Concrete Slabs Reinforced with BFRP Bars

Abstract This study offers test findings from research work conducted to investigate the punching shear behavior of fibrous high strength concrete flat slabs reinforced with Basalt fiber-reinforced polymer (BFRP) bars. Eleven two-way concrete slabs were tested until they failed under central concentrated force. BFRP bars were employed to reinforce ten of the eleven slabs for flexural reinforcement, while steel bars were used to reinforce one slab for comparison. Each slab measured 1000 × 1000 × 70 mm with a 60 × 60 mm steel column at the center of the slab. The flexural-reinforcement type, flexural-reinforcement ratio, and steel fibers content were the test parameters. According to the test findings, raising the BFRP reinforcement ratio improved the slabs’ punching shear capability and load-deflection response. In comparison to slabs with a lower reinforcing ratio, these slabs also showed fewer, narrower cracks. Steel fibers were added, which improved the failure mode from brittle, unexpected failure to ductile failure. The experimental findings are compared to a shear strength equation offered by several concrete design codes, including ACI 440.1R-15, CAN/CSA S806-12, and JSCE.

Experimental investigation into the behaviour of continuous concrete beams reinforced with basalt FRP

The durability of reinforced concrete structures is an ongoing challenge for engineers, particularly in harsh environments such as industrial or marine settings. This paper is concerned with continuous concrete beams which are reinforced with basalt fibre reinforced polymer (BFRP) reinforcing bars, rather than traditional steel rebars, to improve the durability. Continuous concrete members are commonly used in bridges and carparks and therefore may be susceptible to corrosion by being a harsh environment or through exposure to de-icing salts. There are increasing levels of interest in structural solutions that offer durability as well as mechanical performance, and in this context, BFRP reinforcement can provide an effective, sustainable, and durable solution. This paper describes an experimental programme comprising four, two-span continuous reinforced concrete beams, containing BFRP rebars and stirrups. The test results are analysed in the paper, with particular focus given to the cracking behaviour, bending capacity, moment redistribution and deflections. The test results are compared with American and Canadian design codes. It is found that both design codes overestimate the cracking moment and sagging bending moment capacity but underestimate the deflections. Furthermore, this research found that BFRP RC continuous beams exhibited at least 20% moment redistribution. The findings from this research suggest that the RC continuous beams can be entirely reinforced with BFRP rebars and stirrups to achieve corrosion free concrete element.

Structural behavior of FRP connector enabled precast geopolymer concrete sandwich panels subjected to one-side fire exposure

Precast concrete sandwich panel (PCSPs), consisting of two reinforced concrete (RC) wythes (i.e., interior and exterior), a core insulation layer and connectors, can help to improve the building energy efficiency. This study is concerned with the fire and post-fire residual performance of an innovative PCSP system, in which fiber-reinforced polymer (FRP) reinforced geopolymer concrete is used as the two wythes and FRP tubes are used as the connectors. Six PCSP specimens were fabricated and five of them were tested under one-side fire exposure. The experimental parameters included the concrete type (geopolymer and conventional concrete), the reinforcement type (basalt FRP reinforcement and steel reinforcement), the connector type (plate-type and hexagonal tubular type), and the RC wythe thickness. After the fire exposure, all the specimens were tested under concentric loading to evaluate their residual axial load capacity. In addition, numerical analysis was conducted to facilitate a better understanding on the experienced temperature field of the PCSPs. It was found that the PCSPs with geopolymer concrete exhibited a decrease of the axial load capacity by 88.5% after 4 h one-side fire exposure while they performed better than that with conventional concrete. Besides, the reinforcement type, RC wythe thickness and the connector type are key factors influencing the post-fire structural performance of the PCSPs.

Experimental and finite element studies on the structural behavior of BFRC continuous beams reinforced with BFRP bars

This study presents an experimental and numerical study on the structural behavior and moment redistribution of basalt fiber-reinforced concrete (BFRC) continuous beams with basalt fiber-reinforced polymer (BFRP) bars. A total of seven BFRP-BFRC two-span continuous beams were tested to failure under a five-point test setup. Three parameters were investigated: volume fractions (Vf) of basalt macro-fibers (BMF), BFRP reinforcement ratio, and stirrups spacing. Test results indicated that compared to stirrups spacing, reinforcement ratio and Vf of BMF were more significant in improving the structural performance and moment redistribution of the tested beams. Furthermore, nonlinear 2D finite element (FE) models were developed using the commercial ABAQUS software to predict the behavior of the tested beams. The FE analysis accounted for the tensile cracking and compressive crushing of concrete using the built-in concrete damaged plasticity model. Ayub’s analytical model was employed to simulate the nonlinearity of BFRC in compression. The accuracy of the FE models was validated using the experimental load-deflection responses and crack patterns at failure. Good agreement was obtained between the experimental and numerical results with the experimental-to-predicted mean, standard deviation, and coefficient of variance values of 1.036, 0.041, and 3.95% for the ultimate loads and 0.993, 0.046, and 4.68% for the deflections, respectively.

The impact of percentage content of basalt fiber-reinforced polymer and steel reinforcement on the strength indicators of experimental beams with hybrid reinforcement

The use of composite reinforcement in the structures subject to bending is limited due to their excessive deformation. One way to overcome this shortcoming is to use hybrid reinforcement where steel and composite reinforcement are used in combination. The effectiveness of this approach has been proven by previous studies. There are no studies on the establishment of the effective ratio between steel and composite elements. This paper presents the results of tests of prototype beams with hybrid reinforcement made of basalt fiber-reinforced polymer (BFRP) and steel. A total of 12 series of samples of beams, three beams in each series, were studied. The percentage of both types of reinforcement was variable; it varied from a ratio of 100% / 0% to 0% / 100% in increments of ~ 20% (the numerator of the fraction corresponds to the percentage of steel reinforcement, and the denominator – to the percentage of BFRP reinforcement). According to the results of tests of beams by static loading, it was found that the use of hybrid reinforcement allowed to increase the bearing capacity of the samples by 33% – 74%, depending on the percentage of reinforcement in the cross section, compared with the beams of the control series. Based on the nature of breaks and load-bearing capacity, the most optimal ratio of steel and BFRP reinforcement was 60% – 40%. The optimal percentage of cross section reinforcement is 1.07%.

Axial load–moment interaction diagram of full-scale circular LWSCC columns reinforced with BFRP and GFRP bars and spirals: Experimental and theoretical investigations

No research has yet been reported on the behavior of lightweight-aggregate self-consolidating concrete (LWSCC) columns reinforced with fiber-reinforced polymer (FRP) bars. LWSCC can be of great interest for reducing dead loads, section dimensions, and project costs, especially for precast elements. This paper presents, for the first time, the test results of a study conducted on 12 circular LWSCC columns reinforced with two types of FRP bars: basalt FRP (BFRP) and glass FRP (GFRP). In addition, columns with steel reinforcement were introduced into the test matrix as references. A mix design for the LWSCC with an equilibrium density of 1,807 kg/m3 and compressive strength of 52 MPa was developed and used to cast the columns. The columns were tested under concentric and eccentric loading. The test variables were the eccentricity-to-diameter ratio, and the type of reinforcement (steel versus GFRP and BFRP). The study was conducted to investigate whether the type of concrete and reinforcement affect the column performance and to develop the experimental load–moment interaction diagram. The load–strain behavior for the concrete, bars, and spirals; the load-deformation curves (axial and lateral); and the experimental P–M interaction diagrams are presented. An analytical study was conducted to predict the axial–flexural capacity. The effect of concrete density was considered in the analysis based on parameters in the codes for conventional and modified rectangular stress blocks. The test results indicate that the LWSCC columns with BFRP and GFRP reinforcement had behavior and strength comparable to their steel-reinforced counterparts when tested under different levels of eccentricity. The analytical results show that the column capacity was sensitive to variations in the rectangular stress-block parameters. Lastly, this study demonstrated the effectiveness of integrating GFRP and BFRP reinforcement into lightweight-aggregate concrete would play a role in producing lighter and more durable concrete members for precast applications.

Flexural behavior of seawater sea-sand concrete beams reinforced with BFRP bars/grids and BFRP-wrapped steel tubes

This paper presents an investigation of a new type of seawater sea-sand concrete (SWSSC) beam which consists of BFRP bars/grids and BFRP-wrapped steel tubes (BWST). The transversally placed basalt fiber-reinforced polymer (BFRP) grid units act as shear stirrups, while the longitudinal BWST near the bottom area is used to improve the tension resistance. The flexural behavior of the hybrid SWSSC beams under different BFRP reinforcement ratios with or without the BWST were experimentally tested and compared. In addition, a finite element model (FEM) was established and a parametric study was conducted to show the influence of key parameters. The results showed that the placement of the BWST could significantly improve the mechanical properties of the hybrid beams, especially in terms of improving the flexural stiffness and reducing crack width. In addition, the full-length embedded BWST could shorten the height of the vertical cracks developed along the FRP grids, and denser diagonal cracks developed in the shear span.

Experimental study on cracking behavior of steel fiber-reinforced concrete beams with BFRP bars under repeated loading

This study aimed to investigate the feasibility of using steel fibers to control crack spacing and width for concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) bars under repeated loading. Four-point bending tests were performed on 11 concrete beams reinforced with BFRP bars having various concrete strength grades, BFRP reinforcement ratios, steel fiber volume ratios, and steel fiber shapes. The flexural strength, cracking moment, crack propagation, crack spacing, and crack width of the beams were obtained from experiment, among which the cracking moment, crack spacing, and crack width were compared with their counterpart predicted from analytical models in various codes and literature. Compared with concrete beams reinforced with BFRP bars but without steel fibers, steel fiber-reinforced concrete (SFRC) beams with BFRP bars exhibited a higher cracking resistance, higher cracking moment and flexural strength, and smaller crack spacing and width. The use of high-strength concrete increased cracking moment and reduced crack width and spacing; however, the BFRP reinforcement ratio only affected crack width and spacing but does not affect cracking moment. The ACI 400.1R-15, CAS S806-12, and Chinese national standard GB 50608-2010 codes all underestimated the cracking moment of SFRC beams with BFRP bars but overestimated the crack width. Finally, a series of new analytical models based on the tensile constitutive law of SFRC were developed for the cracking moment, crack spacing, and crack width and validated by experimental results that they performed better than their counterparts in ACI 400.1R-15 and CAS S806-12 codes.