Polymer Rebars Research Articles

Mixture optimisation for cement-soil mixtures with embedded GFRP tendons

The glass fiber-reinforced polymer (GFRP) rebar reinforced cemented soil is widely employed to solve the weak foundation problem led by sludge particularly. The robustness of this structure is highly dependent on the interface bond strength between the GFRP tendon and cemented soils. However, its application is obstructed owing to the deficient studies on the influence factors. Therefore, this study investigates the effects of water content (Cw: 50%–90%), cement proportion (Cc: 6%–30%), and curing period (Tc: 28–90 days) on peak and residual interface bond strengths (Tp and Tt), as well as the unconfined compression strength (UCS). Results indicated that mechanical properties were positively responded to Tc and Cc, while negatively correlated to Cw. Besides, Random Forest (RF), one of the machine learning (ML) models, was developed with its hyperparameters tuned by the firefly algorithm (FA) based on the experimental dataset. The pullout strength was predicted by the ML model for the first time. High correlation coefficients and low root-mean-square errors verified the accuracy of established RF-FA models in this study. Subsequently, a coFA-based multi-objective optimisation firefly algorithm (MOFA) was introduced to optimise tri-objectives between UCS, Tp (or Tt), and cost. The Pareto fronts were successfully acquired for optimal mixture designs, which contributes to the application of GFRP tendon reinforced cemented soil in practice. In addition, the sensitivity of input variables was evaluated and ranked.

Flexural behaviour of geopolymer concrete beams reinforced with BFRP and GFRP polymer composites

The paper presents the experimental investigations on the flexural behaviour of geopolymer concrete beams reinforced with Basalt Fibre Reinforced Polymer (BFRP)/Glass Fibre Reinforced Polymer (GFRP) rebars and the effect of inclusion of the new adhesively bonded BFRP/GFRP stirrups. M30 grade geopolymer and conventional concrete beams with the dimension of 100 × 160 × 1700 mm were cast to investigae the flexural behaviour of BFRP/GFRP and steel bars. This study also examined the mode of failure, deflection behaviour, curvature moment capacity, crack width, pattern, propagation, strains and average crack width of the BFRP/GFRP bars with stirrups in the geopolymer concretes using a four-point static bending test. The results were compared to that of conventional steel-reinforced concrete, and it was found that the Basalt and Glass reinforced polymer beams demonstrated premature failure and sudden shear failure. Further, the FRP bars exhibited higher mid-span deflection, crack width and crack propagation than steel bars. Crack spacing of the FRP bars decreased with an increase in the number of cracks. The correlation between the load and the deflection behaviour of the beams was determined using statistical analysis of multi variables regression.

Flexural behavior of concrete beams reinforced with glass fiber reinforced polymer and steel bars

In this study, a comparative experimental analysis is performed between steel-reinforced concrete beams, which are dimensioned based on NBR 6118 (2014), and beams reinforced with glass fiber-reinforced polymer (GFRP) rebar, which are dimensioned based on ACI 440.1R (2015) after being subjected to a four-point bending test. The beams are dimensioned to resist the same force and to satisfy the service limit state (SLS). Results show that the two groups of beams exhibit similar vertical displacement behaviors until the SLS-DEF, whereas the GFRP beams exhibit larger deflections. At the ultimate load, the beams with fiberglass bars indicate a higher resistance by approximately 64% compared with those with metal bars.

Study of Geopolymer Concrete Beam with Glass Fibre Reinforced Polymer Rebars – A Review

Reinforced Concrete (RC) is a widely used composite material in construction. It is composed of concrete with high compressive strength and steel bars and stirrups of high tensile strength placed longitudinally and transversely, complementing each other in overcoming their weaknesses. Corrosion of steel reinforcement and cement sustainability are two main persistent issues creating great difficulty in the entire construction industry across the globe. Sincere efforts were also made to replace ordinary Portland cement with geopolymer cement, and steel reinforcements with fiber reinforcement for more than two decades. Different combinations were tried in using them for beams, slabs, columns, and combinations of the above. Though researchers have shown many leads in the research, no concrete proofs were made about the better combinations and the structural code for common usage. In this paper, available literature were reviewed in detail and summarized. A study was carried out for the intended purpose to identify focus areas for further research, and it is listed.

Performance of simply supported concrete beams reinforced with high-strength polymer re-bars under blast-induced impulsive loading

Performance of simply supported concrete beams reinforced with high-strength polymer re-bars under blast-induced impulsive loading

Tests of polypropylene macro synthetic fibers and GFRP reinforced concrete columns subjected to concentric and eccentric loading

Literature is deficient in exploring the structural efficiency of polypropylene macro synthetic structural fiber reinforced concrete (RC) columns (PMC columns) having glass fiber reinforced polymer (GFRP) rebars. The illustrated investigation aimed to study the axial compressive efficiency of GFRP-RC columns containing polypropylene macro synthetic structural fibers (GPMC columns) under different loading eccentricities. Eighteen (18) columns were manufactured having a height of 1200 mm and a diameter of 300 mm. Eight (8) samples were manufactured employing GFRP reinforcement and the other eight (8) samples consisted of steel rebars (SPMC columns). The axial strength (AS), failure modes, axial shortening, axial load-axial shortening curves , and cracking patterns were evaluated under different eccentricities. The testing results illustrated that the SPMC samples exhibited higher AS and less ductility than GPMC samples. Both GPMC and SPMC samples illustrated similar failure efficiency. The eccentric shortening resulted in similar drops in AS for both GPMC and SPMC samples. This investigation put forward a durable, lightweight, and corrosion-resistant concrete shortening structural member that can be employed in marine and coastal regions. • Eighteen GPMC and SPMC columns were manufactured. • Tests were performed under concentric and eccentric loading. • SPMC columns portrayed higher axial strength than GPMC columns. • Mostly the samples failed in the upper half region.

Structural evaluation of recycled aggregate concrete circular columns having FRP rebars and synthetic fibers

Large quantity of recycled aggregate concrete (RAC) obtained from concrete and demolition waste needs to be disposed of properly and sustainably. The present investigation aims to examine the axial compressive behavior of polypropylene macro synthetic fiber (PMF) reinforced RAC (MRC) columns containing glass fiber reinforced polymer (GFRP) rebars. Nine GFRP rebars reinforced columns (GMRC columns) and nine steel rebars reinforced columns (SMRC columns) with 1200 mm height and 300 mm diameter were tested under concentric and eccentric loading. The axial load-carrying capacity (LC), failure behavior, damaging modes, and compressive deformations were assessed. The results depicted that the SMRC columns had greater axial LC by 23.4% and lower ductility capacity by 16% than GMRC columns. Mostly, the failure mechanism of GMRC and SMRC columns was similar. The application of eccentricity resulted in similar declines in axial LC for both GMRC and SMRC specimens. 3D finite element modeling of GMRC specimens was performed using a modified damaging plastic model for MRC. The suggested finite element model estimated the efficiency of GMRC specimens with high accuracy for both axial LC and corresponding deformations of samples.

Experimental investigation on the flexural behaviour of basalt fibre reinforced polymer rebar concrete

This study experimentally explores the effects of applying various types of fibres to concrete mixes on the flexural behaviour of longitudinal structural members with basalt fibre reinforced polymer (BFRP) bars. The main objective is to research the viability of using new advanced fibres of basalt to enhance the concrete response. Basalt fibre and basalt fibre reinforced polymer rebar and compared with the conventional concrete and with a 40 MPa compressive strength target, eighteen beams were fabricated and tested; twelve with basalt fibre reinforced polymer rebar concrete and six with conventional concrete Basalt fibre lengths 30 mm with 15 µm and BFRP bar length of 800 mm with 8 mm diameter were taken into account. Flexural tests were done using a four-point test setup on both of the BFRP- conventional concrete (CC) beams. The test matrix would include BFRP bar reinforcing beams and conventional steel rebar for comparative purposes. Results showed that the application of basalt fibres to concrete enhanced the ductility of these beams' curvature. Due to the delay in the concrete failure in the compression zone, a significant improvement in bending ability was also reported, which supported the BFRP bars achieved a higher ultimate strength. The opening and deep formation of a crack have been effectively limited by the aggregate interlock of basalt fibres, which maintained the crack widths lower than in the 0.7 mm permissible maximum in service. Basalt fibres of 4%, 6%, and 8% were done. Compared to conventional concrete 6% basalt fibre at 28 days of the curing period, the maximum compressive strength was attained 52.38 N/mm2, tensile strength was attained 5.55 N/mm2, Flexural strength increases to 7.45 N/mm2. However, basalt fibre reinforced polymer rebar concrete was larger than conventional concrete beams.

Experimental Research on Material Behaviour of Glass Fiber Reinforced Polymer Bars in Tension

Glass Fiber Reinforced Polymer (GFRP) rebars have been widely used to solve the corrosion problem of steel bars in concrete structures. It has been produced as a lightweight and corrosion-resistant than steel reinforcement in many structural applications. They are regarded as a promising substitute for steel bars in concrete infrastructures. It is necessary to test GFRP bars to fully understand their material properties to ensure the safe and efficient use of the material. In this study, five specimens of each type of GFRP bars with a diameter of 6, 8, 10, 12, and 14 mm were tested under tension. Therefore, a total of 25 samples were examined from the same manufacturer. According to ASTM’s recommendations (D7205/D7205M-06) for tensile tests of GFRP bars, the diameter and thickness of the steel pipes for both ends were considered in the preparation of the test specimens to keep the GFRP bars consistent and aligned throughout the experiment. The experimental test results included the stress-strain curves, tensile strength, ultimate strain, and modulus of elasticity. The study showed an accurate result that indicated the tensile strength of the GFRP bars can be expressed by a linear distribution. For a bar diameter of 10mm, the length to diameter ratio L e /d b =8 showed a maximum tensile to compressive strength ratio. In the failure results of the test, there were two-mode failures of GFRP bars: fracture failure and pull-out failure of GFRP bars. Most of the specimens had GFRP bar fracture failures, only two specimens (GBT1-10-2 and GBT1-10-3) were damaged due to the pull-off of the GFRP bars which was not a typical failure mode. Keywords: GFRP Bars, Tensile Test, Stress-Strain Curve, Fracture Failure DOI: 10.7176/CER/13-5-05 Publication date: August 31 st 2021

Predicting the load-carrying capacity of GFRP-reinforced concrete columns using ANN and evolutionary strategy

Recently, glass fibre reinforced polymer (GFRP) rebars have been widely used by different researchers due to the high strength and deformability of polymer rebars. However, current concrete designing codes do not include design provisions for GFRP‐reinforced concrete columns, and neglect the contribution of GFRP bars when used as compression reinforcements. Therefore, this study intends to develop a new simple closed-form model to predict the load-bearing capacity of GFRP-reinforced concrete columns under an axial load considering the influence of longitudinal GFRP rebars and confinement conditions. This study was performed in two steps. In the first step, three artificial neural network (ANN) algorithms were used to predict the axial performance of GFRP-reinforced columns: radial basis function (RBF), support vector regression (SVR) and multilayer perceptron (MLP). Then, a sensitivity analysis was performed and the impact priority of each of the input parameters was examined. In the second step, a comparison between the obtained results and available models was performed, and a new highly accurate formula was proposed using the Covariance Matrix Adaptation- Evolution Strategy (CMA-ES) to predict the nominal compressive strength of GFRP-reinforced concrete columns. The results showed that the ultimate strength and strain of longitudinal and transverse rebars and their spacing were important parameters affecting the axial load-bearing capacity of GFRP-reinforced concrete columns and the previous models did not consider the influence of these parameters. Therefore, the presented ANN models in this study with high accuracy and low error could be used as beneficial tools to predict the axial performance of GFRP‐reinforced concrete columns. In addition, among the presented ANN methods, RBF showed the highest accuracy and efficiency. Also, the developed closed-form model with a high agreement with experimental results could be used as an efficient model to determine the nominal strength of GFRP-reinforced concrete columns.

The combined effect of crumb rubber aggregates and steel fibers on shear behavior of GFRP bar-reinforced high-strength concrete beams

To reduce reinforcement congestion in locations of high rebar concentration in a structure, fiber-reinforced polymer (FRP) rebar (replacing steel rebar) can be used in combination with steel fiber (replacing stirrups). Here, an extensive investigation was conducted for the first time in literature on the effect of steel fibers and crumb rubber (CR) aggregate on the shear behavior of high-strength concrete beams reinforced with glass FRP (GFRP) bars. Thirty beam specimens were manufactured and the effect of the key variables including the GFRP reinforcement ratio, shear span-to-depth ratio, CR content, and fiber content in volume on the shear performance of the beams was investigated. Parameters under investigation were the cracking pattern, manner of failure, load-midspan deflection performance, shear capacity, toughness, and post-cracking strength of the beams. The results indicate that when the fiber volume fraction, concrete compressive strength, and GFRP reinforcement ratio increased, the beam shear capacity increased. Conversely, increasing the shear span-to-depth ratio and CR content led to a decrease in the shear capacity. It was also found that the steel fibers were more efficient in improving the beam shear behavior at higher content of CR, such that they changed the cracking type and failure mode from shear to flexural. Finally, the analysis of variance (ANOVA) technique was used to perform statistical analysis of experimental data and calculate the contribution of different parameters to the experimental results.

Behavior of Structural Concrete Frames with Hybrid Reinforcement under Cyclic Loading

A substantial amount of work was carried out on the use of fiber-reinforced polymer (FRP) in reinforcing concrete structural elements, which demonstrated considerable inelasticity or deformity through monotonous and fatigue loads. Even so, the action of FRP bars in FRP-RC columns and frame structures has not yet been studied during reversed cyclic loading. In this research, reversed cyclic loading was conducted on three beam-column joint models using the finite element method with ANSYS software. The first model was for a joint designed with steel rebar for both the longitudinal reinforcement and stirrups. Glass fiber reinforced polymer (GFRP) rebar was used to reinforced the second joint model for both longitudinal reinforcement and steel stirrups, and the third joint model was designed with hybrid steel/GFRP reinforcement for the longitudinal reinforcement and steel stirrups. The performance of the three models under reversed cyclic loading, such as load vs. story drift and energy dissipation capacity, were compared. The GFRP-reinforced model displayed a predominantly elastic activity up to failure. Although its energy dissipation was weak, its performance in terms of total storey drift demand was satisfactory.

Seismic performance of fibre-reinforced polymer and steel double-reinforced bridge piers

The re-centring ability and durability of important bridges have been the main objectives in recent provisions of seismic design codes. To achieve better recoverability and durability for piers, this article presents a double-reinforced pier configuration, in which the outer layer is reinforced with fibre-reinforced polymer (FRP) rebar and the inner layer is reinforced with steel rebar. An equal flexural capacity design method was used to determine the double-reinforced configurations. The effects of the potentially influential design parameters on the seismic response of piers were studied and compared to those of conventional RC piers. The results show that the proposed design method can satisfy the ultimate capacity and durability demands. The double-reinforced piers had a better performance than conventional piers in terms of the ductility, post-yield stiffness and residual deformation. The maximum deformation and energy dissipation capacity of the double-reinforced piers were comparable to those of the conventional RC piers. The results also demonstrated that the proportion of steel reinforcement had a clear effect on the performance of double-reinforced piers. However, FRP reinforcement with a high modulus of elasticity should be avoided due to the adverse effect on ductility.

Influence of elevated temperatures on the bond behaviour of ribbed GFRP bars in concrete

FRP-reinforced concrete (RC) structures operating for several years in chemically aggressive environments have confirmed the good mechanical performance and durability of FRP reinforcement. However, the concerns and lack of knowledge about fire behaviour is still hampering its use in buildings; in fact, even moderately elevated temperatures are reported to cause premature loss of bond in overlapping rebars, potentially affecting the structural safety of load bearing members exposed to fire. This paper presents experimental and analytical investigations on the bond behaviour between glass fibre reinforced polymer (GFRP) rebars and concrete at moderately elevated temperatures. Steady-state tensile and pull-out tests were performed in two types of ribbed GFRP rebars, with different glass transition temperatures (Tg of 104 °C and 157 °C), from ambient temperature up to 300 °C. The results obtained were also compared with those of fibre wrapped-sand coated GFRP rebars (Tg of 98 °C) previously investigated by the authors. As expected, the tensile strength and elastic modulus of the ribbed GFRP rebars and especially the strength and stiffness of the GFRP-concrete interface were severely degraded with temperature. This study highlighted that the key parameters governing the bond to concrete at elevated temperatures are the surface finish and Tg of the rebars – at 100 °C, bond strength reductions between 20% and 34% were obtained for the ribbed rebars, while in the sand coated rebars such reduction had been 81%; most of the reduction of the GFRP-concrete interaction in the ribbed rebars occurred for temperatures above the rebars Tg, contrary to the sand coated rebars in which bond had been almost completely degraded below its Tg. Based on the test results, for each temperature, local bond stress vs. slip models were numerically calibrated for the specific ribbed GFRP rebars used in the experiments. These laws can be used in advanced numerical models to simulate the fire behaviour of GFRP-RC members.

Development length of glass fibre reinforced polymer (GFRP) rebar based on non-uniform bond stress

Due to the assumption of uniform bond stress, the development length of fibre reinforced polymer (FRP) bars by design standards can be unnecessarily long and difficult to provide in practice. Hence, the bond stress distribution and required development length of a glass fibre reinforced polymer (GFRP) rebar is investigated. Four beam-bond specimens, two following RILEM specifications and two based on a procedure by ACI are tested to evaluate the effect of test method on bond strength. Ten pullout tests are also performed using the same bar. The two test methods yield similar results, but the ACI test is easier to perform. The bond stress distribution in the beams is highly nonlinear but in the pullout tests approaches uniformity. The actual development length is found to be 50% to 250% less than that required by the aforementioned standards. Consequently, a new equation is proposed based on the logistic growth function to model the non-uniform bond stress distribution and estimate the required development length.

Strength Profile Pattern of FRP-Reinforced Concrete Structures: A Performance Analysis through Finite Element Analysis and Empirical Modeling Technique.

Limited research work is available in the literature for the theoretical estimates of axial compressive strength of columns reinforced with fiber reinforced polymer (FRP) rebars. In the present work, an experimental database of 278 FRP-reinforced concrete (RC) compression members was established from the literature to recommend an empirical model that can accurately predict the axial strength (AS) of GFRP-RC specimens. An initial assessment of 13 different previously anticipated empirical models was executed to achieve a general form of the AS model. Finally, a new empirical equation for forecasting the AS of GFRP-RC short columns was proposed using the curve fitting and regression analysis technique. The performance of the proposed empirical model over the previous experimental database represented its higher accuracy as related to that of other models. For the further justification of the anticipated model, a numerical model of GFRP-RC columns was simulated using ABAQUS and a wide parametric study of 600 GFRP-RC samples was executed to generate a numerical database and investigate the influence of various parameters using numerical and empirical models. The comparison between theoretical and numerical predictions with R2 = 0.77 indicted that the anticipated empirical model is accurate enough to apprehend the AS of FRP-RC specimens.

Moment Redistribution in Continuous Externally CFRP Prestressed Beams with Steel and FRP Rebars.

This paper assesses the impact of adopting carbon- or glass-fiber-reinforced polymer (CFRP or GFRP) instead of steel rebars on the redistribution of moments in prestressed concrete beams (PCBs) with external CFRP tendons. A numerical program is introduced, and numerical simulations are performed on two-span continuous beams with steel, CFRP or GFRP rebars of various areas, i.e., Ar2 = 360–3560 mm2, and Ar1/Ar2 = 1.5, where Ar1 and Ar2 are areas of tensile rebars over the positive and negative moment zones, respectively. The results show the moment redistribution is contributed by concrete cracking only for the beams with fiber-reinforced polymer (FRP) rebars, and by concrete cracking and steel yielding for the beams with steel rebars. As a result, the use of FRP rebars leads to a substantially lower moment redistribution than in steel rebars. It is also demonstrated that Eurocode 2, CSA A23.3-04 and ACI 318-19 fail to reflect the rebar influence on moment redistribution in PCBs with external tendons. A simplified equation for the quantification of moment redistribution in externally PCBs with steel and FRP rebars is recommended, which yields accurate and conservative predictions.

Experimental fire testing of large‐scale glass fibre‐reinforced polymer‐reinforced concrete beams with mid‐span straight‐end bar lap splices

SummaryAdopting glass fibre‐reinforced polymer (GFRP) rebars as a replacement of conventional steel reinforcement in different infrastructure applications is mainly attributed to its corrosion resistance and considerable lightweight‐to‐high strength ratio. However, the use of FRP rebars in construction is still limited due to the degradation of its mechanical properties at elevated temperatures. The experimental work presented in this paper aimed to investigate the structural fire behaviour of concrete beams reinforced with GFRP bars having lap splices at the beam mid‐span. Four identical 2750‐mm long concrete beams with cross‐sectional dimensions of 300 mm × 350 mm were experimentally examined under four‐point flexure bending. A 60‐mm thick concrete cover was used on the bottom, front and back sides of all beams. Two beams were tested as control specimens in ambient condition, while the other two beams were exposed to standard fire while subjected to a transverse load equivalent to 40% of the beam ultimate design moment. Experimental results show that concrete beams sustained the applied loads for a minimum of 53 minutes in standard fire conditions. Also, both test beams failed due to slippage of the spliced bars when the temperature measured at the top of the middle bar approached its glass transition temperature.

Bayesian optimization algorithm based support vector regression analysis for estimation of shear capacity of FRP reinforced concrete members

The use of fiber-reinforced polymer (FRP) rebars in lieu of steel rebars has led to some deviations in the shear behavior of concrete members. Several methods have been proposed to forecast the shear capacity of such members. Nonetheless, there are differences in the methods of considering the various parameters affecting shear capacity, and some of them provide widely scattered and conservative results. This paper presents a hybrid of the Bayesian optimization algorithm (BOA) and support vector regression (SVR) as a novel modeling tool for the prediction of the shear capacity of FRP-reinforced members with no stirrups. For this purpose, a large dataset of simply supported beams and unidirectional slabs reinforced with FRP were utilized. The model performance was assessed using several statistical performance indicators and compared with the Japan Society of Civil Engineers (JSCE), British Institution of Structural Engineers (BISE), Canadian Standard Association (CSA), and American Concrete Institute (ACI) design codes and guidelines, as well as some other artificial intelligence (AI) models. For development of the model, all the hyperparameters, i.e., kernel function type, epsilon, box constraint, and kernel scale, were optimized using the BOA technique. The k-fold cross validation approach was utilized to avoid overfitting of the model. It was found that the mean, median, standard deviation, minimum, maximum, and interquartile range of the developed hybrid model predictions are very close to the experimental results. The predicted results overlap the experimental data with a coefficient of determination of 95.5%. The plot of relative deviations and residual plots are scattered around the zero reference line with low deviation, which indicates that the model is reliable and valid. The error terms (e.g., mean absolute error, root mean square error) obtained for all specimens were 4.85 and 11.03, which are very low values. The correlation coefficient (R) and fractional bias (FB) were found to be 0.977 and 0.0033, which are very close to 1 and 0, respectively, thus implying a reliable prediction. The comparative investigations with other codes and guidelines show that the hybrid BOA–SVR model predictions are more accurate and robust than those of the other models.

Flexural and Shear Behavior of Beams Reinforced with GFRP Rebars

A new inexperienced constructing material is glass fibre reinforced polymer (GFRP) rebar. GFRP rebars are non-corrosive, non-conductive, light-weight substances and have an excessive longitudinal tensile capacity that is beneficial for use in civil infrastructure applications. In this analysis, the overall performance of GFRP rebar-reinforced concrete beams was assessed. Full scale exams had been conducted underneath four-point bending on eight one hundred fifty x 250 x 1500 mm beams to inspect the influence of GFRP specimens reinforced through both GFRP or metal rebars with flexural reinforcement ratios (ρf) ranging from 0.53 to 1.45 times the balanced ratio (ρfb). In phrases of crack pattern, load deflection behaviour, load strain conduct and peak capacity, the check facts used to be analysed to decide the flexure and shear conduct of GFRP RC beams. The find out about confirmed that the ultimate load capacity of beams is immediately proportional to the flexural reinforcement ratio, and for steel bolstered specimens, cracking moments had been greater, relative to GFRP. For GFRP RC beams, the peak carrying ability is extra than steel beams. GFRP beams confirmed greater deflections than bolstered beams of steel. The findings additionally confirmed that the building of GFRP bolstered beams in concrete with GFRP stirrups can be influenced by means of shear failures. The reinforcement ratio and shear design of GFRP bolstered concrete beams is affected by way of their behaviour.