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

This research explores the use of Glass Fiber Reinforced Polymer (GFRP) bars and GFRP circular sections as longitudinal reinforcement in Reinforced Concrete (RC) columns, specifically to mitigate corrosion issues in harsh coastal environments. Twelve concrete specimens were prepared and tested under various loading conditions to evaluate the performance of GFRP as a substitute for conventional steel reinforcement. The experimental findings indicated that GFRP-RC columns displayed slightly lower axial load and bending moment capacities compared to steel-RC columns, though the ductility of both types was found to be similar. The study also highlights the significance of considering the role of GFRP bars in compression, supported by experimental results. This research offers valuable insights into the behavior and performance of both steel and GFRP-reinforced concrete columns, particularly in environments vulnerable to corrosion, with assessments conducted at 28 and 60-day intervals. A comparison of the outcomes from these timeframes reveals the effectiveness of GFRP as a reinforcement option in corrosive conditions

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

Concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars have been greatly interesting recently. The distinct properties of GFRP bars, such as high tensile strength and low modulus of elasticity compared to steel bars, as well as the linear stress-strain behavior, make the study of GFRP-reinforced concrete (FRP-RC) columns important. This paper investigates the structural behavior of column specimens reinforced by fully and partially GFRP bars subjected to concentric and eccentrically applied Compressive loads. 12 columns were reinforced by (36%, 64%, and 100%) of the GFRP bars ratio, and the control specimen was reinforced by conventional steel rebars; all specimens were tested under different eccentric ratios (e/h) 0, 0.66, and 1. The failure mode, the relation between the axial load and the average axial displacement, and a comparison between the experimental results and the theoretical interaction diagram for columns were presented and discussed. The results show that most of the failure in specimens occurs as a compressive failure, and it fails in the weakest region by crushing concrete, as well as kinking in GFRP bars. Using GFRP bars significantly increases the axial displacement values compared to the steel rebars in longitudinal reinforcement and decreases the failure load for specimens with an increase in the ratio of GFRP bars. The average axial displacement value for columns specimens tested under eccentric load at e/h equal to 0.66 and 1 decreases by 75% and 94.4% compared with the control specimen.

The behavior of fiber-reinforced polymer (FRP) bars under compression is not fully understood yet due to the limited research in this area. However, the long-term durability, weathering resistance, and exceptional mechanical properties of FRP bars justify the need for their use in compression members. The main objectives of this study are to evaluate the mechanical properties of glass FRP (GFRP) and basalt FRP (BFRP) bars under compression and examine their performances as main longitudinal reinforcements in reinforced concrete (RC) columns. In the first part of this research, a series of static compression tests were conducted on GFRP and BFRP bars of different diameters. The second part of this research numerically investigated the behavior of FRP-RC columns under concentric and eccentric loading using the mechanical properties of the FRP bars obtained experimentally. Nonlinear finite element models were developed to simulate the compressive behavior of the concrete columns reinforced with GFRP and BFRP bars. The FE models were verified with the experimental results conducted previously. The verified FE models are then utilized to conduct a parametric analysis considering two different column geometries and cross-sections, five reinforcement ratios, two concrete compressive strengths, three types of ties materials, and several loading eccentricities to develop a set of interaction diagrams that may provide valuable data for design purposes. The results indicated that the FRP bars could have a significant contribution to the overall capacity of FRP-RC columns by up to 35% of the total force at failure, depending on the reinforcement ratio. The performance of both the GFRP- and BFRP-RC columns was almost similar in terms of capacity, deflection, and bar strength contribution.

Structural assessment of eccentrically loaded GFRP reinforced circular concrete columns: Experiments and finite element analysis

The bond performance of glass fibre reinforced polymer (GFRP) bars and that of steel bars embedded in Alkali Activated Cement (AAC) concrete are analysed and compared using pull-out specimens. The bond failure modes, the average bond strength and the free end bond stress-slip curves are used for comparison. Tepfer’s concrete ring model is used to further analyse the splitting failure in ribbed steel bar and GFRP bar specimens. The angle the bond forces make with the bar axis was calculated and used for comparing bond behaviour of ribbed steel bar and GFRP bars in AAC concrete. The results showed that bond failure mode plays a significant role in the comparison of the average bond stress of the specimens at failure. In case of pull-out failure mode, specimens with ribbed steel bars showed a higher bond strength while specimens with GFRP bars showed a higher bond stress in case of splitting failure mode. Comparison of the bond stress-slip curves of ribbed steel bars and GFRP bars depicted that the constant bond stress region at the peak is much smaller in case of GFRP bars than ribbed steel bars indicating a basic bond mechanism difference in GFRP and ribbed steel bars.

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.

This study aims to examine the behavior of reinforced concrete (RC) circular columns retrofitted with ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) jackets and fiber‐reinforced polymer (FRP) wraps under concentric and eccentric loading. In the present study, for the first time, UHPFRC jackets containing synthetic macro fibers (barchip) were used. The results were then compared with those obtained by UHPFRC containing steel fibers. Moreover, to improve the effect of concrete jacketing on the column behavior under eccentric loading, the innovative interface treatment of the longitudinal grooving method (GM) was applied. For these purposes, 15 such circular columns, 120 mm in diameter and 500 mm in height, were subjected to load eccentricities of 0, 30, and 60 mm. Thus, six columns were retrofitted with UHPFRC jackets 15 mm in thickness that included both steel and synthetic macro fibers (barchip) while another six were strengthened with UHPFRC jackets and intermittent glass FRP (GFRP) warps. The experimental results revealed that load‐carrying capacity raised with the increase of the load eccentricity, as evidenced by enhancements of 283%, 303%, and 401% in the loading capacity of the specimens strengthened with UHPFRC jackets containing both GFRP warps and steel fibers for eccentricities of zero, 30, and 60 mm, respectively, relative to those of the control. In addition, enhancements of 198% and 530% were recorded respectively for ductility and energy dissipation under a loading eccentricity of zero mm in specimens retrofitted with UHPFRC jackets including steel fiber and GFRP warps when compared with the same parameters in the corresponding control specimens. Finally, a previous theoretical model was adopted to derive the axial loading‐bending moment (P–M) interaction diagrams whereby the results of the present study were satisfactorily verified.

Hollow-core concrete columns are widely used as structural members to reduce the cost and self-weight of concrete structures. This study investigates the axial load–axial deformation behavior of glass fiber-reinforced polymer (GFRP) bar- and helix-reinforced hollow-core circular concrete columns. Four specimens of 214-mm outer diameter and 56-mm circular inner hole diameter with a height of 850 mm were tested under axial compression. One specimen was reinforced with steel bars and steel helices, and the remaining three specimens were reinforced with GFRP bars and GFRP helices. It was found that, for a similar amount of longitudinal and transverse reinforcements, the GFRP bar-reinforced specimen achieved 15% and 4% higher effectiveness of confinement reinforcement and ductility, respectively, than the steel bar-reinforced specimen. The effectiveness of confinement reinforcement and ductility of the GFRP bar-reinforced specimen was higher for the smaller pitch of GFRP helices. The GFRP bar-reinforced specimen with helices of 30 mm pitch achieved 46% and 66% higher effectiveness of confinement reinforcement and ductility, respectively, than the GFRP bar-reinforced specimen with helices of 90 mm pitch.

Concrete is the most widely used construction material because of its specialty of being cast into any desired shape. The main requirements of earthquake resistant structures are good ductility and energy absorption capacity. Fiber reinforced concrete possesses high flexural and tensile strength, improved ductility, and high energy absorption over the conventional concrete in sustaining dynamic loads. The aim of this paper is to compare the properties of concrete beams in which three types of fibers are added individually. Steel fibers, polypropylene fibers and hybrid fibers were added to concrete in the weight ratio of four percentages in the preparation of four beam specimens. The fourth specimen did not contain fibers and acted as a control specimen. The dimensions of the beam specimens were 150 mm × 150 mm × 700 mm. The reinforced concrete beams of M30 grade concrete were prepared for casting and testing. Various parameters such as load carrying capacity, stiffness degradation, ductility characteristics and energy absorption capacity of FRC beams were compared with that of RC beams. The companion specimens were cast and tested to study strength properties and then the results were compared. All the beams were tested under three point bending under Universal Testing Machine (UTM). The results were evaluated with respect to modulus of elasticity, first crack load, ultimate load, and ultimate deflection. The test result shows that use of hybrid fiber improves the flexural performance of the reinforced concrete beams. The flexural behavior and stiffness of the tested beams were calculated, and compared with respect to their load carrying capacities. Comparison was also made with theoretical calculations in order to determine the load-deflection curves of the tested beams. Results of the experimental programme were compared with theoretical predictions. Based on the results of the experimental programme, it can be concluded that the addition of steel, polypropylene and hybrid fibers by 4% by weight of cement (but 2.14 % by volume of cement) had the best effect on the stiffness and energy absorption capacity of the beams.

The behavior of eccentrically loaded RC columns strengthened by NSM steel and glass fiber reinforced polymer (GFRP) rebars is investigated in this study. A total of six RC column specimens have been cast in this study with dimensions of (150×150×1200) mm (width × height × length). Two column specimens are unstrengthened and considered as controls, while the other specimens are strengthened by the NSM method using steel bars and hybrid steel and GFRP rebars. All column specimens have been tested under concentric and eccentric loads with an eccentricity of 75mm up to failure. Experimental results in terms of crack patterns, modes of failure, and load-displacement curves are all monitored, recorded, and assessed. The experimental results have shown an improvement in the ultimate load capacity for all strengthened column specimens. Further, results have demonstrated that, under concentric load, the almost similar enhancement in the strength of NSM-strengthened RC column specimens using steel bars only and hybrid steel and GFRP bars. However, at eccentric load, the ultimate load capacity of the strengthened RC column was increased by 62% and 79.45% compared to the control column using NSM steel and hybrid steel, and GFRP, respectively. Finally, this study found that at e/h = 0.5 using GFRP in the tension zone increased the ultimate load by about 11% when compared to steel.

This paper presents the experimental results of nine large-scale circular concrete columns reinforced with longitudinal and transverse glass fiber-reinforced polymer (GFRP) bars. These specimens were tested under lateral cyclic quasi-static loading while simultaneously subjected to constant axial load. Based on the measured hysteretic loops of moment-versus-curvature and shear-versus-tip deflection relationships, a series of parameters related to ductility, energy dissipation capacity, and flexural strength are used to evaluate the seismic behavior of each column. The results showed that concrete columns reinforced with GFRP bars and spirals can behave in a manner that has stable post-peak response and achieve high levels of deformability. The results indicate that, as a relatively new material with excellent corrosion resistance and high strength-weight ratio, GFRP bars can be successfully used as internal reinforcement in ductile concrete columns.

Experimental study on cyclic flexural behaviour of GFRP-reinforced seawater sea-sand concrete slabs with synthetic fibres

The modern research is aimed to enhance the tensile properties of concrete so that its performance should be made better in various reinforced concrete structures. In the current study, twenty hybrid-fiber-reinforced concrete (HFRC) columns and one plain concrete column were cast to examine the effect of hybrid fibers on the axial capacity, load-deflection response and cracking patterns of columns under axial concentric loading. All specimens were square in cross section having a side length of 150 mm and a height of 1200 mm. Two different types of fibers were used; one is steel fibers (SF) and second is polypropylene fibers (PPF). Four different volumetric ratios of SF (0.7%, 0.8%, 0.9%, 1.0%) and five different ratios of PPF (0.1%, 0.3%, 0.5%, 0.7%, 0.9%) were used in the current study. The results indicate that the combination of 0.8% SF and 0.5% PPF performed well for load-carrying capacity and a combination of 0.9% SF and 0.3% PPF presented the best performance for the ductility of HFRC columns. Moreover, a constitutive finite element model (FEM) was proposed using concrete damaged plastic (CDP) model in ABAQUS for predicting the axial behavior and crack patterns of HFRC columns under concentric loading. A close agreement was observed between the experimental measurements and FE predictions. Finally, a detailed comparison of theoretical axial capacities of HFRC columns was performed using the predictions of various codes and proposed equations.

Efficiency of glass-fiber reinforced-polymer (GFRP) discrete hoops and bars in concrete columns under combined axial and flexural loads