GFRP-reinforced Concrete Columns Research Articles

Analytical and Experimental Behaviour of GFRP-Reinforced Concrete Columns under Fire Loading

Fire engineering endeavours to mitigate injury or the loss of life in the event of a fire. This is achieved primarily through fire prevention, containment, and extinguishment measures. Should prevention fail, the structural integrity of buildings, coupled with effective evacuation strategies, becomes paramount. While glass fibre-reinforced polymer (GFRP) materials have demonstrated efficacy in reinforcing concrete elements, their performance under fire conditions, notably in comparison to steel, necessitates a deeper understanding for structural applications. This study experimentally and numerically investigates the fire performance of GFRP-reinforced concrete (RC) columns subjected to only fire load without additional external loads. The research aims to ascertain the fire resistance based on the thickness of the concrete coating and the ultimate tensile strength of GFRP rebars after 90 min of fire exposure. Four GFRP-RC columns were subjected to a standardized fire curve on all sides in the experimental program. In the analytical program, a theoretical model was developed using the heat transfer module of the COMSOL software. The results of both analyses were very close, indicating the reliability of the procedure used. Based on the findings, recommendations regarding the fire resistance of GFRP-RC columns were formulated for structural applications. Results from this research provide the civil engineering community with data that will help them continue using FRP materials as internal reinforcement for concrete.

Compressive and Bonding Performance of GFRP-Reinforced Concrete Columns

The use of glass-fiber-reinforced polymer (GFRP) bars as an alternative to steel bars for reinforcing concrete (RC) structures has gained increasing attention in recent years. GFRP bars offer several advantages over steel bars, such as corrosion resistance, lightweight, high tensile strength, and non-magnetic properties. However, there are also some challenges and uncertainties associated with the behavior and performance of GFRP-reinforced concrete (GFRP-RC) structures, especially under compression and bonding behavior. Therefore, there is a need for comprehensive experimental investigations to validate the effectiveness of GFRP bars in concrete columns. This paper presents a study that aims to address these issues by conducting experimental tests on GFRP-RC columns. The experimental tests examine the mechanical properties of GFRP bars and their bond behavior with concrete, as well as the axial compressive behavior of GFRP-RC columns with different reinforcement configurations, tie spacing, and bar sizes. The findings reveal that GFRP bars demonstrate a comparable, if not superior, compressive capacity to traditional steel bars, significantly contributing to the load-bearing capacity of concrete columns. The study concludes with a set of recommendations for further exploration, underscoring the potential of GFRP bars in revolutionizing the construction industry.

Effect of Confinement Level and Staggering on Seismic Performance of Lap-Spliced GFRP-Reinforced Concrete Columns

Effect of Confinement Level and Staggering on Seismic Performance of Lap-Spliced GFRP-Reinforced Concrete Columns

Effect of Transverse Reinforcement Ratios and Configurations on the Behavior of Hollow Circular Concrete Columns Reinforced with GFRP under Concentric Loading

Hollow concrete columns (HCCs) are an effective structural system for piles, electric poles, and bridge piers due to their low self-weight in conjunction with the high strength offered and reduced material use. This study investigated the behavior of concentrically loaded circular HCCs reinforced with glass fiber–reinforced polymer (GFRP) bars and spirals. Eleven hollow circular columns with outer/inner diameters of 305 and 113 mm and two solid specimens as controls were fabricated. All had a height of 1,500 mm. The investigated parameters included transverse GFRP reinforcement ratio in terms of the on-center spiral spacing and spiral diameter, configuration (spiral and hoops), and the influence of hollowness. The theoretical ultimate load-carrying capacity and the confined concrete strength of the tested hollow GFRP-reinforced concrete columns were evaluated and predicted using the available design equations and confinement models in the FRP design codes, standards, and literature. The test results indicate that either decreasing the spacing of the spiral/discrete hoops or increasing the spiral diameter could increase the ultimate carrying capacity as well as improve the confinement efficiency and ductility of HCCs.

Experimental investigation of concentrically and eccentrically loaded circular hollow concrete columns reinforced with GFRP bars and spirals

Hollow concrete columns (HCCs) constitute a structural system with low self-weight, reduced material use, and high strength-to-weight ratio. Limited studies, however, have focused on investigating the concentrically loaded behavior of circular HCCs reinforced with glass fiber-reinforced polymer (GFRP) reinforcement. Moreover, there appears to be no research on the behavior of such columns under eccentric loading. This study investigated the performance of 10 large-scale GFRP-reinforced HCCs measuring 1,500 mm in height with outer/inner diameters of 305/113 mm. The test parameters were the effect of two longitudinal reinforcement ratios (2.5 % and 3.8 %) and five different levels of eccentricity (0 %, 8.2 %, 16.4 %, 32.8 %, and 65.6 % eccentricity) on the compressive and flexural behavior of GFRP-reinforced circular hollow columns. The test results show that the behavior of these columns was more significantly affected by the level of applied eccentricity than the longitudinal reinforcement ratio. The failure of specimens loaded under low eccentricity levels was compression controlled due to spalling of the concrete cover, followed by fracturing of the GFRP bars, attributed to most of the cross section being subjected to high compressive stresses. Conversely, initiation of failure for the specimens tested under high eccentricity levels was flexural tension followed by tensile cracking, which caused a secondary compression failure in the concrete. It should be noted that the contribution of the second-order effect on the total moment capacity was minor, approximately 9 %, compared to the primary bending moment induced by the initial eccentricity of 91 % on average. Lastly, the ductility of the hollow GFRP-reinforced concrete columns was higher than that of solid columns under eccentric loading, which significantly improved the energy absorption ability, leading to a decrease in the strength decay beyond the peak load.

Performance of concrete columns longitudinally reinforced with steel and GFRP bars and confined with GFRP spirals and cross ties under reversed cyclic loading

This paper reports the comparative results of an experimental study performed on concrete columns reinforced entirely with glass fiber-reinforced polymer (GFRP) bars and with hybrid reinforcement (longitudinal steel bars and transverse GFRP spirals and cross ties) subjected to quasi-static cycling loading. Four full-scale bridge columns were constructed with longitudinal steel bars and confined with GFRP spirals and cross ties (hybrid-reinforced concrete columns). Four other columns were constructed solely with GFRP reinforcement (GFRP-reinforced concrete columns). The bridge columns had a cross section of 400 × 400 mm with a total height of 1850 mm. The columns were tested to failure under combined constant compressive axial load and quasi-static reversed lateral loading. The columns were investigated in terms of longitudinal bar type, longitudinal reinforcement ratio, and transverse reinforcement ratio. The results show that the longitudinal reinforcement type significantly affected column performance in terms of seismic parameters such as ductility and energy dissipation. The hybrid-reinforced concrete columns exhibited superior ductility and dissipated more energy than the GFRP-reinforced concrete columns. Furthermore, the GFRP-reinforced concrete columns experienced more gradual failure than the hybrid-reinforced concrete columns. Appropriately confined hybrid-reinforced concrete columns attained acceptable drift levels that meet the recommendations in most design codes. The transverse reinforcement ratio and longitudinal reinforcement ratio patently influenced column behavior. The lower elastic modulus of the GFRP bars compared to that of the steel bars had an impact on the theoretical lateral load capacity of the concrete columns.

Artificial Neural Network (ANN) and Finite Element (FEM) Models for GFRP-Reinforced Concrete Columns under Axial Compression

In reinforced concrete structures, the fiber-reinforced polymer (FRP) as reinforcing rebars have been widely used. The use of GFRP (glass fiber-reinforced polymer) bars to solve the steel reinforcement corrosion problem in various concrete structures is now well documented in many research studies. Hollow concrete-core columns (HCCs) are used to make a lightweight structure and reduce its cost. However, the use of FRP bars in HCCs has not yet gained an adequate level of confidence due to the lack of laboratory tests and standard design guidelines. Therefore, the present paper numerically and empirically explores the axial compressive behavior of GFRP-reinforced hollow concrete-core columns (HCCs). A total of 60 HCCs were simulated in the current version of Finite Element Analysis (FEA) ABAQUS. The reference finite element model (FEM) was built for a wide range of test variables of HCCs based on 17 specimens experimentally tested by the same group of researchers. All columns of 250 mm outer diameter, 0, 40, 45, 65, 90, 120 mm circular inner-hole diameter, and a height of 1000 mm were built and simulated. The effects of other parameters cover unconfined concrete strength from 21.2 to 44 MPa, the internal confinement (center to center spiral spacing = 50, 100, and 150 mm), and the amount of longitudinal GFRP bars (ρv = 1.78–4.02%). The complex column response was defined by the concrete damaged plastic model (CDPM) and the behavior of the GFRP reinforcement was modeled as a linear-elastic behavior up to failure. The proposed FEM showed an excellent agreement with the tested load-strain responses. Based on the database obtained from the ABAQUS and the laboratory test, different empirical formulas and artificial neural network (ANN) models were further proposed for predicting the softening and hardening behavior of GFRP-RC HCCs.

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.

SEISMIC PERFORMANCE OF GFRP-RC RECTANGULAR COLUMNS: NUMERICAL STUDY

Composite materials like glass fiber-reinforced polymer (GFRP) is becoming widely acceptable to be used as a reinforcing material due to its high ultimate tensile strength-to-weight ratio and excellent resistance to corrosion. However, the seismic behavior of GFRP-reinforced concrete columns has not been fully investigated yet. This paper presents the results of a numerical analysis of full-size GFRP-RC rectangular columns under cyclic loading. The simulated column depicts the lower part of a building column between the foundation and the point of contra-flexure at the mid-height of the column. GFRP reinforcement properties and concrete modeling based on fracture energy have been incorporated in the numerical model. Experimental validation has been used to examine the accuracy of the constructed finite element models (FEMs) using a commercially available software. The validated FEM was used to perform a parametric study, considering several concrete strength values and axial load levels, to study its influence on the performance of the GFRP-reinforced concrete columns under cyclic loading. It was concluded that the hysteretic dissipation capacity deteriorates under high axial load level due to severe softening of the concrete. The FE results showed a substantial improvement of the lateral load-carrying capacities by increasing concrete compressive strength.

Material Characterization of GFRP Bars in Compression Using a New Test Method

Abstract This article presents a new test method for determining the mechanical properties of glass fiber–reinforced polymer (GFRP) composite bars in compression, namely the compressive strength, compressive modulus of elasticity, ultimate crushing strain, and compressive stress-strain curves of the bars. The contribution of GFRP bars in compression is currently neglected by major design guidelines related to GFRP-reinforced concrete columns. However, the demand for using GFRP bars is increasing because multiple researchers have shown the effectiveness of the bars in concrete columns. Thus, the need for characterization of the mechanical properties of GFRP bars is increasing, while there is no standardized test method to evaluate the compressive properties of these bars. Therefore, in this article, a new test method is proposed for evaluating the compressive characteristics of GFRP bars. The proposed test method was examined through testing a total of 35 specimens. It was observed that the test method was able to evaluate the compressive characteristics of the GFRP bars successfully. Three different modes of compressive failure were observed, which were related to the crushing of GFRP bars in different locations in the bar, but no premature failure or bar buckling was observed. Moreover, a comparison between tensile and compression characteristics of the GFRP bars showed that the tensile test results are not sufficient to estimate the compressive characteristics, and performing a compression test is necessary.

Investigation of HFRC columns reinforced with GFRP bars and spirals under concentric and eccentric loadings

There is a lack of experiments and finite element analysis (FEA) on the structural behavior of glass fiber-reinforced polymer (GFRP) reinforced concrete columns with hybrid fibers. The main objective of the current study is to investigate and compare the structural performance of GFRP-reinforced concrete columns with hybrid fibers (GHC columns) and steel-reinforced concrete columns with hybrid fibers (SHC columns) confined with spirals and subjected to concentric and eccentric loading by performing experiments and the finite element modeling (FEM). Steel fibers (SF) and polypropylene fibers (PF) were used together to develop the hybrid fiber reinforced concrete (HFRC). Six GHC circular columns and six SHC circular columns were fabricated having a cross-sectional dimension of 250 mm and a height of 1150 mm. ABAQUS 6.14 was used for the FEA of the columns by using a modified concrete damage plastic (CDP) model for HFRC. The results from the present work depicted that both types of columns (GHC and SHC columns) show similar failure modes. The average axial strength of GHC columns was 91.32% of the axial strength of SHC columns. The GHC columns presented higher ductility (up to 19.71%) compared with SHC columns. The eccentric loading caused a significant reduction in the axial strength of columns. The newly developed theoretical equation performed well over the experimental results. The comparative study solidly substantiates the validity and applicability of the newly developed theoretical and FEA models for capturing the axial strength of GHC columns by considering the axial involvement of longitudinal GFRP bars and the confinement effect of transverse GFRP spirals.

Prediction of axial load-carrying capacity of GFRP-reinforced concrete columns through artificial neural networks

The present research aims to propose new models for predicting the axial load-carrying capacity of concrete columns reinforced with glass fiber reinforced polymer (GFRP) bars. Two different approaches i.e. Artificial Neural Networks (ANNs) and empirical modeling, were adopted for achieving the aim. A large database of 279 specimens of GFRP-reinforced concrete columns was developed from the literature. The proposed ANN model was calibrated for the different number of neurons in the hidden layers to achieve an optimized model. Furthermore, a preliminary evaluation of the previously proposed empirical models for predicting the axial capacity of GFRP-reinforced concrete columns was performed over the developed database to obtain a more general form of the model. The currently proposed ANN and empirical models presented a close agreement with the experimental database with R2 = 0.848 and R2 = 0.730, respectively. The comparative study of the predictions represents that the currently proposed models are more accurate than the previously proposed models for predicting the axial capacity of GFRP-reinforced concrete columns. Moreover, an extensive parametric study of 600 specimens was performed using the proposed empirical model to examine the effect of various material and geometric parameters of GFRP-reinforced concrete columns.

Structural Behavior of GFRP-Reinforced Circular HFRC Columns Under Concentric and Eccentric Loading

The previous research is rich in plain concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars, but it is deficient in GFRP-reinforced concrete columns incorporating hybrid fibers. The present study aims to explore and compare the structural behavior of steel and GFRP-reinforced concrete columns having hybrid fibers (SHFC and GHFC columns). Two types of fibers, i.e. steel fibers and polypropylene fibers, were used to develop the hybrid fiber-reinforced concrete. A total of 18 circular concrete columns (9 SHFC columns and 9 GHFC columns) having a height of 1150 mm and a diameter of 250 mm were constructed and tested under axial loading at various eccentricities. The test measurements portrayed that the SHFC columns presented a better performance in terms of axial strength (about 20% higher) and ultimate deflections. The GHFC columns presented higher ductility indices compared with SHFC columns. Both steel and GHFC columns showed similar failure modes and similar reductions in the axial strength when subjected to eccentricities. The newly developed empirical model for the prediction of the axial strength of GHFC columns showed a close agreement with the experimentation. Thus, the comparative study solidly substantiates the application of the proposed empirical model.

Inelastic Second-Order Analysis for Slender GFRP-Reinforced Concrete Columns: Experimental Investigations and Theoretical Study

Abstract Designing reinforced concrete (RC) columns reinforced entirely with fiber-reinforced polymer (FRP) bars requires an explicit definition of the slenderness upper and lower limits for use in...

Glass fiber-reinforced polymer-reinforced rectangular concrete columns under simulated seismic loads

This paper presents the results of nine concrete columns reinforced with longitudinal and transverse glass fiber-reinforced polymer (GFRP) bars and two concrete columns reinforced with longitudinal steel bars and transverse GFRP bars. These specimens were tested under lateral cyclic quasi-static loading while simultaneously subjected to constant axial load. The influence of the volumetric ratio of stirrups, the shear span ratio and the axial load level on the behavior of GFRP-reinforced concrete columns are discussed. The results showed that GFRP-reinforced concrete columns can have sufficient bearing capacity and achieve high levels of deformability. The lateral drift ratios of all the columns reached 4.08–5.06%, which meet seismic drift limitations in most building codes. The evaluation methodology of ductility coefficient may not assess the seismic deformability and resistance of GFRP-reinforced concrete columns objectively, while the integrated performance index can reflect the influence of the volumetric ratio of stirrups, the shear span ratio and the axial load on seismic performance comprehensively. The results further indicate that concrete columns reinforced with GFRP bars can be successfully designed and used in seismic engineering if confined well.

Design of GFRP-reinforced rectangular concrete columns under eccentric axial loading

The use of glass-fibre-reinforced polymer (GFRP) reinforcement as an alternative to steel for use in reinforced concrete (RC) structures has developed significantly in recent years. With excellent corrosion resistance, a high tensile strength to weight ratio and being non-magnetic and non-conductive, GFRP is an excellent solution for projects requiring improved corrosion resistance or reduced maintenance costs. However, despite a number of recent studies illustrating the effective use of GFRP rebars as longitudinal reinforcement for concrete compression members, the current international design codes do not recommend including GFRP reinforcement in the compression member capacity calculations. A test programme was thus carried involving the construction and testing of 17 rectangular concrete columns reinforced with steel or GFRP. This paper provides full derivations of the interaction diagrams for both steel- and GFRP-reinforced concrete columns. The interaction diagrams fitted the experimental data very well for both types of RC column. It was found that the GFRP-reinforced columns did not have a ‘balance point’ on the interaction diagram, and this was clearly shown for longitudinal reinforcement ratios above 3%. It was found that excluding the strength and stiffness of GFRP reinforcement from concrete compression calculations is conservative. Theoretical capacities better represent the experimental data when the strength and stiffness of GFRP reinforcement are included. The resulting factored interaction curves were exceeded by all experimental capacities.