FRP-reinforced Concrete Beams Research Articles

Experimental Investigation of Ductility in GFRP RC Beams by Confining the Compression Zone

Nowadays, building structures in corrosive environments requires some considerations. Being lightweight, high tensile strength, and corrosion resistance are the features that make fiber-reinforced plastic (FRP) bars an alternative component for longitudinal steel reinforcement of concrete. On the other hand, the linear elastic behavior of FRP bars, alongside the brittle behavior of concrete, makes brittle members without considerable ductility. In this paper, the effect of compression region confinement with CFRP sheets on the FRP-reinforced concrete beams was experimentally investigated. Eight GFRP reinforced beams with 2 m length, including one reference beam and seven confined beams, were constructed and tested under a four-point bending test. Based on the type of confinement, specimens are categorized into four groups. Flexural behavior improvements, including load carry capacity, energy dissipation capacity, and ductility, were observed in at least one specimen of each confined group. According to the results, the specimen that was spirally confined with a 30 mm ribbon width and angle of 10° had the best total energy absorption up to about 110% improvement in comparison to the unconfined specimen. On the other hand, vertically confined specimens with 50 mm ribbon width showed the highest improvement in ductility indices and load carrying capacity up to 60% and 11% in comparison to unconfined specimens, respectively. Due to concrete compression zone fractures in flexural failure mode, the over-reinforce method is considered the design philosophy. Results indicate that regardless of the confinement type (discrete vertical, discrete spiral, or continuous spiral confinement), there is an optimal amount for width, blank space between ribbons, and depth of confinement to achieve the best flexural behavior.

Shear strength model of FRP-reinforced concrete beams without shear reinforcement

The current design codes for evaluating the shear strength of concrete beams reinforced with fiber-reinforced polymer (FRP) bars predominantly rely on a semi-empirical approach through test data calibration without a robust theoretical background. This approach may lead to either overestimation or underestimation, resulting in significant scattering in strength predictions. This study proposed a modified approach to enhance the existing unified shear-strength model developed for steel-reinforced concrete (RC) beams based on the compression zone failure mechanism, for predicting the shear strength of FRP-RC beams without shear reinforcement. The proposed model integrates strain and stress approaches, accounting for the distinctive characteristics associated with FRP reinforcement. Additionally, the overall shear resistance capacity of the FRP-RC beam is considered as the sum of contributions from the intact concrete of the compression zone and the aggregate interlock mechanism. The reliability of the proposed model is verified by comparing its predictions with a comprehensive database comprising 264 FRP-RC beam specimens without shear reinforcement reported by 41 research groups. Furthermore, the accuracy of the proposed model was assessed through a comparative analysis with existing evaluation methods, encompassing machine learning-based models, empirical models, theoretical models, and design codes. The results indicate that the proposed model satisfactorily predicts the shear strength of FRP-RC beams within a wide range of design parameters. In comparison with machine learning-based models, the proposed theoretical model exhibits a similar level of accuracy in terms of the mean shear strength ratio and coefficient of determination (R2) values but with less scattering, indicated by lower coefficient of variation (COV) and root mean square error (RMSE) values. In addition, the proposed model outperforms existing empirical and theoretical models, as well as current design codes, by significantly enhancing prediction accuracy, demonstrated by lower COV, RMSE, and higher R2 values. Finally, a parametric study was conducted to investigate the effects of the key parameters on the shear strength of FRP-RC beams using both the proposed model and representative existing evaluation methods.

Transient state analysis of rehabilitated RC beams using finite element modelling and prediction using an artificial neural network

The present research develops and verifies a simpler numerical approach for analyzing the thermal transient state of rehabilitated concrete beams reinforced with various types of FRP (fiber-reinforced polymer) subjected to high temperatures and specifically built as under-reinforced concrete beams. This approach offers a straightforward, efficient, and exact instrument for numerical analysis. The proposed analytical technique has been validated by load-displacement curves and cross-section temperature data, indicating its dependability and practicality. Subsequently, the validated approach was used to examine the impact of significant variables on the outcome and restoration of FRP-reinforced concrete beams at high temperatures. The methodology gives the Comparing conventional and CFRP, GFRP, AFRP reinforced beams using beam, truss, and shell elements. Thermal and UDL loads were applied, mesh at 25 mm × 25 mm. Transient analysis contrasts performance via displacement and temperature. The temperature versus displacement curve shows the FRP comparisons. Identifying the critical temperature before failure is crucial, emphasizing the curve’s significance in assessing structural performance and potential failure points. Nodal temperatures ranged 939 °C–963 °C (rehabilitated) versus 958 °C (conventional). 200 °C difference affects thermal boundary conditions for structural analysis and Conventional peaks at 320 °C, while AFRP, GFRP, and CFRP reach 358 °C, 385 °C, and 390 °C respectively. CFRP lasts 2400 min. Neural network models demonstrate effective generalizability, enabling satisfactory predictions of RC beam rehabilitation with CFRP laminates within the study’s parameter range.

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.

Rational prediction of moment redistribution in continuous concrete beams reinforced with FRP bars

In continuous fiber reinforced polymer (FRP) reinforced concrete (RC) beams, moment redistribution is typically not allowed in the design owing to the lack of ductility of FRP bars. However, this simplification cannot be justified as moment redistribution depends primarily upon the difference in stiffness along the beam length. This study aims at improving the current state-of-the-art redistribution quantification in continuous FRP RC beams. Redistribution behavior against neutral axis depth (c/d) of continuous FRP RC beams are numerically assessed, focusing on the impact of ρr1/ρr2 (ρr1, ρr2= tensile reinforcement ratios at positive, negative moment zones). It is shown that continuous FRP RC beams may experience marked positive or negative redistribution of moments, depending on ρr1/ρr2. However, the importance of ρr1/ρr2 is neglected in c/d-based code models (EC2, BSI and CSA). A modified BSI model is proposed to estimate the moment redistribution in continuous FRP RC beams. By introducing ρr1/ρr2, the proposed simplified model accounts for the structural characteristic and demonstrates a rational prediction of moment redistribution in these beams.

Experimental and Analytical Investigation of FRP Reinforced Concrete Beams in Flexure

Experimental and Analytical Investigation of FRP Reinforced Concrete Beams in Flexure

Experimental Investigation into the Flexural Behaviour of Basalt FRP Reinforced Concrete Beams

This study involved conducting four-point bending tests on three types of rebar-reinforced concrete beam: those reinforced with steel bars, those reinforced using basalt fiber-reinforced polymer rods, and hybrid reinforced concrete beams that used both Basalt fiber-reinforced plastic and reinforcing steel. Various reinforcement ratios and configurations were used to analyze mid-span deflection, flexural capacity, fracture distribution, and Basalt FRP bars strain. The results suggest that using a hybrid reinforcement system that combines Basalt fiber-reinforced plastic and reinforcing steel can improve the transverse rupture strength of rebar-reinforced concrete beam, reduce deflection and cracking, and use the high-strength characteristics of Basalt FRP bars.

Impact response analysis and prediction of FRP-RC beams with varying flexural stiffness: Numerical simulation and modified two-DOF calculation

The damage behavior and simplified calculation of fiber-reinforced polymer reinforced concrete (FRP-RC) beams subjected to impact loading have attracted substantial attention. In this study, a finite element model incorporating strain rate was employed. Based on the model, the progressive damage behavior and nonlinear impact response of FRP-RC beams with varying stiffness under hammer-to-beam mass ratios were examined. The results indicate that in the investigated conditions, the damage mode of FRP-RC beams does not vary with the changes in the tension reinforcement ratio, but is affected by the hammer-to-beam mass ratio. Due to the absence of a yielding stage for FRP bars, a nonlinear alteration occurred in the rebound of the FRP bars’ strain and the beam’s displacement with a redistribution of stress. When the reinforcement ratio varies from 0.32% to 3.37%, the peak displacements, reaction and impact forces vary by 25%-49%, 53%-78%, and 0.1%-1% under different mass ratios, respectively. The reinforcement ratio does not change the relationship between the mass ratio and the curve shape of the impact force time history. Additionally, an improved two-degree-of-freedom model considering the FRP’s elastic brittleness effect and modified contact stiffness scaling factor was developed, their accuracy was verified. However, there are still many inconveniences to applying the two-DOF model in engineering. Consequently, based on the above two-DOF model, explicit formulas considering contact stiffness, bending stiffness, impactor velocity and mass for displacement and impact force response of impacted FRP reinforcement concrete beams were proposed, which greatly facilitates engineering calculations.

Fracture behaviour characterisation of FRP-reinforced concrete based on digital image correlation and acoustic emission technology

In order to identify the dynamic fracture characteristics of fibre-reinforced polymer (FRP)-reinforced concrete, three-point bending fracture tests of FRP-reinforced concrete with five different strain loading rates (10−1/s, 10−2/s, 10−3/s, 10−4/s and 10−5/s) are carried out. The fracture behaviour of FRP-reinforced concrete is analysed using digital image correlation (DIC) and acoustic emission (AE) techniques. Crack propagation in FRP-reinforced concrete beams during the fracture process is observed and a quantitative relationship is established between the AE parameters and the load level before the ultimate load is reached. Test results on the variation of the AE parameters can characterise the internal damage behaviour of the FRP-reinforced concrete beams and monitor the distribution characteristics of any cracks. The crack propagation trajectory of the FRP-reinforced concrete beams can be observed using the DIC technique and quantitative analysis of the crack opening displacement (COD) can be achieved.

Deformation-based design of hollow coarse-aggregate ultra-high-performance-concrete beams reinforced with CFRP bars

This study aims to develop a novel type of beams strengthened with carbon fiber-reinforced polymer (CFRP) bars and cast using ultra-high-performance concrete (UHPC) with coarse aggregates (CA-UHPC) to address issues such as poor ductility, extensive cracking, and significant deflection observed in FRP-reinforced concrete (FRP-RC) beams. Six hollow beams were fabricated and tested via a four-point-bending test under cycle loading to study the effects of parameters, including CFRP reinforcement ratios, hollow shapes, and hollow ratio on the deformation performances of the beams. The results show that the deformation of all hollow beams under service loads met the requirements of the GB50610 code for deformation. Increasing hollow ratio had a negative impact on the flexural behaviors of beams, and this effect was more pronounced in beams with higher hollow ratios than in beams with lower hollow ratios. The flexural performances of square hollow beams were better than that of circular hollow beams with the same hollow ratio. Compared to other hollow beams, square hollow beams with a hollow ratio of 44.44% demonstrated superior flexural performance and optimal cost-effectiveness. Ultimately, leveraging the computational framework for steel fiber reinforcement and residual deflection, predictive models for deflection were formulated for CFRP-CA-UHPC beams with various hollow configurations under both static and cyclic loading conditions.

Development of Prediction Models for Shear Strength of FRP Reinforced Fibrous Concrete Beams without Stirrups Using ANN and Nonlinear Regression

ABSTRACT The shear behaviour of fibre-reinforced polymer reinforced concrete (FRP-RC) beams without web reinforcement suffers from low strength, low stiffness, more brittleness and wide and quick propagated cracks. Fortunately, the addition of various types of fibres could improve most of these weaknesses. On the other hand, the shear strength prediction of FRP-RC beams with various types of fibres is one of the most complex cases in structural engineering applications. Developing generalised, precise and consistent prediction models are necessary and very limited. This paper investigates the impacts of various types of fibres on shear strength and presents proposing four new prediction models, utilising artificial neural networks and empirical nonlinear regression analysis, and modifying the combination of available models based on a collected database of 49 shear test results of FRP-RC members with various types of fibres. The comparison of the developed models with the available equations from the literature indicates that the developed models yielded excellent performance, great efficiency and a high level of accuracy over all other existing models. Additionally, the parametric study confirmed that all the developed models have great abilities to accurately predict the actual response of each parameter, in spite of its complexity, on the shear strength of FRP-reinforced fibrous concrete beams without stirrups.

Flexural property and design method evaluation of BFRP and steel bars hybrid reinforced concrete beams

AbstractFiber reinforced polymer (FRP) bars have been widely used as a replacement for steel bars in civil engineering due to their high strength and superior durability. However, compared to steel reinforced concrete (RC) beams, FRP RC beams have insufficient ductility and are more expensive. Therefore, a hybrid beam reinforced with steel and FRP bars has been proposed recently. In this study, the flexural properties of steel bar RC beam, basalt FRP (BFRP) bar RC beam, and BFRP steel bars hybrid RC beams were studied based on numerical simulation. The effect of As/Af on the stress of longitudinal reinforcements, load–midspan curves, ductility, and overall performance of the hybrid RC beams is analyzed. Results indicated that the hybrid RC beams exhibited a second‐order stiffness after the steel bars yielded owing to the contribution of the BFRP bars. As As/Af increases, the ductility of the hybrid RC beam and the strength utilization of BFRP bars increase, and a preferable ductility and overall performance can be achieved when As/Af was close to 1.0. The theoretical calculation results of hybrid RC beams based on ACI, CSA, and GB codes are compared with the simulation results, and the accuracy of the ultimate flexural strength of the prediction results is verified. In addition, equations for predicting the deflection of hybrid RC beams are proposed, and they exhibit higher prediction accuracy compared to the prediction models based on the ACI code.

Metaheuristic Optimization of Random Forest for Predicting Punch Shear Strength of FRP-Reinforced Concrete Beams.

Predicting the punching shear strength (PSS) of fiber-reinforced polymer reinforced concrete (FRP-RC) beams is a critical task in the design and assessment of reinforced concrete structures. This study utilized three meta-heuristic optimization algorithms, namely ant lion optimizer (ALO), moth flame optimizer (MFO), and salp swarm algorithm (SSA), to select the optimal hyperparameters of the random forest (RF) model for predicting the punching shear strength (PSS) of FRP-RC beams. Seven features of FRP-RC beams were considered as inputs parameters, including types of column section (TCS), cross-sectional area of the column (CAC), slab's effective depth (SED), span-depth ratio (SDR), compressive strength of concrete (CSC), yield strength of reinforcement (YSR), and reinforcement ratio (RR). The results indicate that the ALO-RF model with a population size of 100 has the best prediction performance among all models, with MAE of 25.0525, MAPE of 6.5696, R2 of 0.9820, and RMSE of 59.9677 in the training phase, and MAE of 52.5601, MAPE of 15.5083, R2 of 0.941, and RMSE of 101.6494 in the testing phase. The slab's effective depth (SED) has the largest contribution to predicting the PSS, which means that adjusting SED can effectively control the PSS. Furthermore, the hybrid machine learning model optimized by metaheuristic algorithms outperforms traditional models in terms of prediction accuracy and error control.

Flexural behaviour of steel–basalt fibre composite bar-reinforced concrete beams

The utilisation of steel–basalt fibre composite bars (SBFCBs) can effectively solve the corrosion problem of steel-reinforced concrete beams and avoid the poor ductility problem of pure FRP-reinforced concrete beams. However, the research on flexural performance of SBFCB-reinforced concrete beams is still rare. Eleven beams with different reinforcement methods were tested to study the flexural behaviour of SBFCB-reinforced concrete beams and provide reference for its design and application. The failure mode, ultimate bearing capacity and strain of concrete and reinforcement, as well as the crack distribution during loading, were studied. The effects of different reinforcement methods and equivalent reinforcement ratios on the flexural performance of the beams was discussed. In addition, the equivalent reinforcement ratio range of under-reinforced failure was determined, and the theoretical calculation formulas of the yield load and ultimate bearing capacity of the beams were deduced. Results demonstrated that the failure mode of SBFCB-reinforced concrete beams was affected by the equivalent reinforcement ratio; the cracking load values of the beams were close to each other, and the yield load and ultimate load increased with the increase in equivalent reinforcement ratio. The SBFCB-reinforced concrete beams have obvious secondary stiffness. Furthermore, the deflection of the beams at the late loading stage increased faster than that before the yield of the steel bar, which indicates that the beams have good ductility. Moreover, increasing the equivalent reinforcement ratio increased the crack number in the pure bending section of beams, reduced the average crack spacing and reduced the maximum crack width. The ultimate bearing capacity calculated by the deduced formulas were in good agreement with the measured values. The maximum strain of SBFCBs is recommended to be limited to 0.75 times the ultimate strain to prevent sudden brittle failure.

Feasibility Study on the Effect of FRP Shear Reinforcements on the Behaviour of FRP-Reinforced Concrete Deep Beams

Unlike steel reinforcements in concrete, Fiber Reinforced Polymer (FRP) materials are light and free from corrosion. Therefore, FRP materials are increasingly being used in structural engineering as a replacement for steel reinforcements. While the use of FRP bars as longitudinal reinforcements in concrete deep beams has been studied somewhat widely, their use and effectiveness as web reinforcements are not well studied. In this study, the effect of the FRP web reinforcements on the behaviour and strength of FRP-reinforced concrete deep beams were investigated in an experimental study. Four glass fiber-reinforced concrete (RC) simply supported deep beam specimens were tested under a concentrated load with different shear span-to-depth ratios and web reinforcement ratios. The behaviour of the deep beams was described in terms of load–deflection behaviour, crack developments, strain in FRP reinforcements, and failure modes. The experimental investigation emphasized the significance of web reinforcements in determining the reinforced concrete deep beam behaviour, such as mid-span deflection, crack breadth, failure modes, and ultimate strengths. Furthermore, to predict the behavior of deep beams, numerical Finite Element models using Abaqus software were created. The present test results were compared to those predicted using the Finite Element models. This investigation shows that web reinforcement is quite important for FRP-RC deep beams to achieve a robust behaviour by enhancing its capacity and deformability.

Performance of Compression Yielded FRP-Reinforced Concrete Beams with T Sections

Concrete structures reinforced with fiber-reinforced polymer (FRP) reinforcement have been increasingly applied in civil engineering construction to improve several structural performances of bridges and buildings. However, the major weakness of these structures is that they typically suffer from poor ductility and brittle failure. An innovative mechanism called compression yielding (CY) has recently been proposed to enhance the ductility of FRP-reinforced concrete beams. In this study, the moment capacity and ductility of CY beams with T sections are analyzed based on a layered approach. The key variables in the design of a CY beam with a T section are identified and their importance is comprehensively investigated based on the elementary effects method and a parametric study. It is found that the ductility performance can be effectively improved by using a CY material with postmodulus ratio close to 0, and the moment capacity can be enhanced significantly by increasing the CY material strength. The most effective measure for simultaneously improving the moment capacity and ductility performance is to increase the CY block height.

Shear Strength Prediction of Slender Concrete Beams Reinforced with FRP Rebar Using Data-Driven Machine Learning Algorithms

Estimating the shear strength of a fiber-reinforced polymer (FRP)–reinforced-concrete (RC) beam is a complex task that depends on multiple design variables. The use of FRP bars has emerged as a promising alternative to diminish the corrosion problems that are associated with steel reinforcement in adverse environments; however, an accurate and reliable method of shear strength prediction is needed to ensure the economical use of materials and robust designs. Several optimized design equations are available in the literature; however, when utilizing these equations a substantial difference is observed between the predicted outcome (Vpred) and the experimental shear strength (Vexp) result. Therefore, this paper presented a novel approach toward implementing machine learning (ML) algorithms to accurately estimate the shear strength of FRP–RC beams. A large database that consisted of 302 shear test results on FRP-reinforced slender concrete beams without stirrup was collected from the literature to formulate the most efficient prediction model. The performance of each ML algorithm model was compared with the existing design provisions and models. The model interpretation was performed through feature importance analysis to explain the model output compared with a black box. The proposed data-driven ML models demonstrated a high level of accuracy and excellent performance and were superior to the existing shear strength models. In addition, a simple graphical user interface (GUI) was developed to aid practicing engineers when estimating shear strength without the need for complicated design procedures.

Shear and flexure of FRP-reinforced concrete beams and slabs – A review

The article reviews structural response of flexural members reinforced with fiber-reinforced polymer (FRP) as a sustainable alternative to conventional carbon steel. It overviews experimental studies and code-based models that characterize shear and flexural response of concrete beams and slabs reinforced with FRP bars. Discussion on lower resistance to fire being key limitation of FRP bars is also included. The most commonly used fibers to manufacture FRP bars include carbon, glass, basalt, aramid, or combinations of these materials. Consequently, each material plays its role in contributing to shear and flexure differently. Basalt FRP are characterized by higher tensile capacity and resistance to corrosion, carbon FRP bars can withstand exposure to harsh environments; glass FRP bars possess lower modulus of elasticity that may cause large deflection and wider cracks. FRP bars are generally preferred over carbon steel for use in concrete elements where exposure to chlorides or chemicals is expected, or places where non-magnetic properties are essential. Beams and slabs reinforced with FRP bars are likely to undergo larger deflections due to lower stiffness of FRP bars. The dominant failure mode of FRP-reinforced concrete flexural members is discussed in comparison to conventional steel-reinforced members. The article identifies increasing interest and research in using green concrete reinforced with FRP bars that helps to make construction serviceable and sustainable. However, premature de-bonding of bars remains a concern with more research needed to avoid deterioration of mechanical properties by underutilization of materials. Although concrete is practically fire-resistant, FRP is likely to undergo damage of resin due to the presence of combustible organic polymers. The bulk of research implies that the thermal instability of the resin in FRP reinforcing bars is not a disadvantage that outweighs the possible benefits of its usage in the construction industry.

Firefly Algorithm-Based Artificial Neural Network to Predict the Shear Strength in FRP-Reinforced Concrete Beams

The shear strength of fiber-reinforced polymer (FRP) reinforced concrete beams is often given a large safety margin by current construction requirements. Six characteristics are utilized as inputs to compute the shear strength of FRP-reinforced concrete beams. This study uses 198 samples from the literature to predict the shear strength of 139 training samples and 59 testing samples. Additionally, the ANN structure is optimized with the firefly algorithm. The FA-ANN model is also compared to ACI-440, CSA-S806, and BISE-99 codes, and the optimized model by Nehdi et al. Findings show that regarding the shear strength of FRP-reinforced concrete beams, the firefly algorithm-optimized model performs better than the other four models. Concerning accuracy, the coefficient of correlation, R2, was calculated as 0.961, while the average absolute error (AAE) is 0.22 for the shear strength of FRP-reinforced beams.

Experimental and numerical study on the effect of fibers on shear strength of basalt FRP-reinforced concrete beams without stirrup

Experimental and numerical study on the effect of fibers on shear strength of basalt FRP-reinforced concrete beams without stirrup