Glass Fiber-reinforced Polymer Spirals Research Articles

Strain Behavior of Short Concrete Columns Reinforced with GFRP Spirals

This paper presents a comprehensive study focused on evaluating the strain generated within short concrete columns reinforced with glass-fiber-reinforced polymer (GFRP) bars and spirals under concentric compressive axial loads. This research was motivated by the lack of sufficient data in the literature regarding strain in such columns. Five full-scale RC columns were cast and tested, comprising four strengthened with GFRP reinforcement and one reference column reinforced with steel bars and spirals. This study thoroughly examined the influence of various test parameters, such as the reinforcement type, longitudinal reinforcement ratio, and spacing of spiral reinforcement, on the strain in concrete, GFRP bars, and spirals. The experimental results showed that GFRP–RC columns exhibited similar strain behavior to steel–RC columns up to 85% of their peak loads. The study also highlighted that the bearing capacity of the columns increased by up to 25% with optimized reinforcement ratios and spiral spacing, while the failure mode transitioned from a ductile to a more brittle nature as the reinforcement ratio increased. Additionally, it is preferable to limit the compressive strain in GFRP bars to less than 20% of their ultimate tensile strain and the strain in GFRP spirals to less than 12% of their ultimate strain to ensure the safe and reliable use of these materials in RC columns. This research also considers the prediction of the axial load capacities using established design standards permitting the use of FRP bars in compressive members, namely ACI 440.11-22, CSA-S806-12, and JSCE-97, and underscores their limitations in accurately predicting GFRP–RC columns’ failure capacities. This study proposes an equation to enhance the prediction accuracy for GFRP–RC columns, considering the contributions of concrete, spiral confinement, and the axial stiffness of longitudinal GFRP bars. This equation addresses the shortcomings of existing design standards and provides a more accurate assessment of the axial load capacities for GFRP–RC columns. The proposed equation outperformed numerous other equations suggested by various researchers when employed to estimate the strength of 42 columns gathered from the literature.

Axial and bending behavior of GFRP bar‐reinforced hollow‐core polypropylene fiber concrete columns

AbstractThis study reported the axial (concentric and eccentric) and bending (four‐point bending) loadings behavior of glass fiber‐reinforced polymer (GFRP) bar‐reinforced hollow‐core polypropylene fiber concrete (HC‐GFRP‐PFC) columns. The confinement effect of HC‐GFRP‐PFC columns with different center‐to‐center (c/c) spacing of GFRP spirals was also investigated. Twelve hollow‐core circular specimens with an outer diameter of 214 mm and an inner (circular hole) diameter of 56 mm were experimentally investigated. Four reference specimens were cast with nonfibrous (normal) concrete, whereas the remaining eight specimens were cast with polypropylene fiber (0.15% by volume of concrete) concrete. It was found that, with a similar ratio of reinforcement, the HC‐GFRP‐PFC specimens gained 2%–4% higher maximum load (PMaximum) and 9%–19% higher ductility (μ) than the GFRP bar‐reinforced hollow‐core nonfibrous concrete (HC‐GFRP‐NFC) specimens under concentric axial loading and four‐point bending. The HC‐GFRP‐PFC specimens with a 30 mm c/c spacing of the GFRP spiral gained 6%–36% higher PMaximum and 4%–59% higher μ than the HC‐GFRP‐PFC specimens with a 60 mm c/c spacing of the GFRP spirals under different loading conditions.

Seismic column-to-footing connections reinforced with steel/GFRP bars and GFRP spirals

Hybrid reinforcement is explored for column-to-footing connections in seismic regions constructed with grouted duct connections as an accelerated bridge construction method. Two 38% scale precast concrete column-to-footing specimens were built; the first column was reinforced with hybrid reinforcement using a combination of mild steel and glass fiber reinforced polymer (GFRP) longitudinal bars, and the second with all-steel longitudinal bars. Double layers of GFRP spirals were used to provide improved concrete confinement for both columns; GFRP spirals exert higher levels of confining pressure on the column concrete core as deformation increases due to their elastic nature compared to steel spirals that yield. An equation was developed for the cross sectional area and pitch of a GFRP spiral to provide the same confining pressure as a steel spiral. The purpose of the cyclic load tests was to show that the column reinforced with hybrid reinforcement could reduce residual displacements using the elastic nature of GFRP bars. Pull-out tests of GFRP bars inside grouted ducts were carried out to determine the minimum embedment depth to achieve GFRP bar tensile strength. The seismic performance of both specimens was examined under quasi-static cyclic loads. The hybrid column reached a drift ratio of 9.0% drift ratio when a GFRP longitudinal bar fractured in compression; the all-steel column reached a drift ratio of 11.0% when two longitudinal steel bars fractured in tension. The elastic nature of the GFRP longitudinal bars provided substantial self-centering ability and reduced the residual displacement of the hybrid column compared to the all-steel column, thus enhancing its seismic resilience.

Behavior of high-strength concrete (HSC) box girders reinforced with GFRP bars, ties, and spirals under torsion

To date, the torsional behavior of high-strength concrete (HSC) box girders reinforced with glass fiber-reinforced polymer (GFRP) reinforcement has not been investigated. This study reports on the experimental results of HSC box girders reinforced with GFRP bars, ties, and spirals under pure torsion. Seven full-scale reinforced concrete (RC) box girders with a total length of 4,000 mm, width of 380 mm, height of 380 mm, and wall thickness of 100 mm were examined over a clear span of 2,000 mm. The test parameters included the type, configuration, and amount of the web reinforcement and the concrete type. All specimens have the same longitudinal reinforcement ratio. The test specimens comprised three box girders reinforced with GFRP bars and individual ties, three specimens reinforced with GFRP bars and continuous spirals, and one box girder entirely reinforced with steel reinforcement as a reference specimen. Two girders were fabricated with normal-strength concrete (NSC)—one reinforced transversally with GFRP spirals; the other reinforced with ties—to investigate the influence of concrete type on torsional behavior. The test findings indicate that, at the same web reinforcement ratio and reinforcement configuration, the HSC specimens achieved higher pre- and post-cracking torsional strength and stiffness than their counterpart NSC specimens. The continuous spiral configuration instead of individual ties improved the overall torsional performance of the tested box girders. Moreover, the stirrup's capacity strongly influenced the torsional strength of the GFRP- and steel-reinforced concrete box girders, but the stirrup stiffness did not affect the ultimate torque.

Investigation of Circular Hollow Concrete Columns Reinforced with GFRP Bars and Spirals

Glass fiber-reinforced polymer (GFRP) reinforcements are useful alternatives to traditional steel bars in concrete structures, particularly in vertical structural elements such as columns, as they are less prone to corrosion, and impart increasing strength and endurance of buildings. There is limited research on the finite element analysis (FEA) of the structural behavior of hollow glass fiber-reinforced polymer reinforced concrete (GFRPRC) columns. The hollow portion can be used for the service duct and for reducing the self-weight of the members. Numerical analysis of the compressive response of circular hollow concrete columns reinforced with GFRP bars and spirals is performed in this study. This article aims to investigate the axial behavior of hollow GFRP concrete columns and compare it with that of solid steel reinforced concrete (RC) columns as well as hollow steel RC columns. The Abaqus software is used to construct finite element models. After calibration of modeling using an experimental test result as a control model, a parametric study is conducted. The columns with the same geometry, loading, and boundary conditions are analyzed in the parametric study. It is resulted that the hollow GFRP concrete columns provide a greater confinement effect than the solid steel RC columns. The average variation in the ultimate axial load-carrying capacities of the experimental results, from that of the FEA values, is noted to be only 3.87%, while the average difference in the corresponding deformations is 7.08%. Moreover, the hollow GFRP concrete columns possess greater axial load and deformation capacities compared with the solid steel RC columns.

Seismic Behavior of Concrete Bridge Piers Reinforced with Steel or GFRP Bars

This paper evaluates the seismic behavior of eight one-third-scale concrete bridge piers reinforced with various configurations of steel or glass fiber–reinforced polymer (GFRP) bars. Each specimen was tested under a constant axial gravity load, combined with reversed quasistatic cyclic lateral loading. The behavior of the piers was assessed and compared in terms of strength, stiffness, deformability, energy dissipation, and damage. The results indicate that well-detailed hybrid configurations with steel longitudinal bars and GFRP spirals offer a ductile seismic response with reduced postpeak strength degradation. The GFRP spirals were effective in confining the concrete core and restraining longitudinal bar buckling. Piers reinforced with GFRP longitudinal and transverse bars exhibit a stable and deformable seismic response with little residual displacement or strength degradation. However, this behavior was accompanied by a reduction in effective stiffness exceeding 40% and approximately half the hysteretic energy dissipation at an equivalent drift level. All piers reinforced with GFRP bars or spirals exceeded lateral drift requirements set by North American codes.

Confinement model for circular concrete columns transversely reinforced with GFRP spirals and hoops

In many applications, bars made of Glass-Fiber-Reinforced-Polymer (GFRP) have successfully replaced steel rebars and become a practical substitute for shear and flexural reinforcement in reinforced concrete (RC) members. Nevertheless, the behavior of GFRP-RC columns may differ considerably from steel-RC columns because of the variations in the mechanical properties of the two types of reinforcement. In this study, a database of 95 experimentally tested circular columns is collected and utilized to assess the confined strength of GFRP-RC columns. The database has been filtered based on the slenderness ratio to avoid the slenderness effect in the analysis. The filtered database has been used to assess the prediction accuracy of several widely adopted confinement models in terms of and to develop a new proposed model. The influence of all factors affecting the peak stress in confined concrete is considered in this study. The analysis shows a linear relationship between lateral confinement and the increase in axial stress. The proposed confined compressive stress model provides the highest statistical correlation to the experimental data. In addition, the trend line obtained through regression analysis of the concrete strain is in good agreement with the experimental results.

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.

Durability assessment and behavior under axial load of circular GFRP-RC piles conditioned in severe simulated marine environment

This study concerns the feasibility of using innovative glass fiber-reinforced polymer (GFRP) bars, spirals, and hoops in constructing sustainable marine reinforced concrete structures. The experimental investigation aimed at assessing the durability and structural performance of GFRP-reinforced concrete (RC) circular piles exposed to two simulated marine environments in the laboratory. A total of 15 GFRP-RC circular piles measuring 304 mm in diameter and 1000 mm in height were longitudinally reinforced with GFRP bars and transversely with GFRP spirals or hoops. Five specimens were fabricated as references (unconditioned). The remaining 10 specimens were continuously immersed in simulated marine environments (conditioned) for 12 months: five were kept in seawater at room temperature (22 °C), while the other five were stored in a large chamber that produced hot waves at high temperature (60 °C). After conditioning, all the specimens were tested under axial compression loads. Two structural variables were considered: the transverse reinforcement configuration (spirals versus hoops) and the confinement level (spiral spacing). The durability assessment included microstructure examinations (i.e., differential scanning calorimetry (DSC) and scanning electron microscopy (SEM)) were performed on GFRP bars and spirals taken from the conditioned piles. Furthermore, the bond between concrete and bars or spirals was checked by optical microscopy (OM). The microanalysis observations indicate no visible damage in the contact surface between concrete and GFRP bars or individual fibers and the resin matrix. The compressive test results pointed out that the GFRP-RC piles subjected to severe marine environments experienced 19% enhancement in their axial capacities compared to their reference counterparts. The GFRP spirals and hoops performed well in severe marine environments. The nominal axial capacities of the columns were predicted with the available design equations and are presented and discussed herein.

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

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

Concentrically loaded recycled aggregate geopolymer concrete columns reinforced with GFRP bars and spirals

The increased quantity of construction and demolition waste and the high carbon footprint of cement production is creating significant environmental problems. This study explored the use of recycled coarse aggregates (RCA) in geopolymer concrete (GPC) and reinforced with glass fiber reinforced polymer (GFRP) bars and spirals to fabricate novel and structural GRAGC columns. A total of 9 GRAGC columns with 1150 mm in height and 250 mm in diameter were tested to failure under axial compression. The influence of a different number of longitudinal GFRP bars and spiral spacing on the cracking behaviour, ductility, and axial load-carrying capacity (LCC) were investigated. A nonlinear finite element model (FEM) was implemented to predict the axial compressive response of GRAGC columns. The experimental results depicted that an improvement in the ductility and lateral confinement was observed by decreasing the spacing of GFRP spirals. GRAGC columns with eight longitudinal GFRP bars portrayed the highest LCC. All tested GRAGC columns portrayed similar failure modes with the damage at the central region of the specimens. The theoretical model suggested over a database of 225 GFRP reinforced columns showed a high accuracy compared with the previous models. The present study suggests an efficient and environmental-friendly compression member.

Axial performance of GFRP composite bars and spirals in circular hollow concrete columns

The fiber reinforced polymer (FRP) bars are used in hollow concrete columns (HCCs) to alleviate the steel-reinforcement corrosion problem and to make an efficient and lightweight structure. The presented study has endeavored to numerically and theoretically explore the structural behavior of hollow concrete columns (HCCs) reinforced with glass fiber reinforced polymer (GFRP) bars and spirals. Six HCCs were simulated in a commercial finite element software ABAQUS 6.14. The control finite element model (FEM) was calibrated for various variables of HCCs using the previous experimental testing results. The complex nonlinear behavior of concrete was defined using the concrete damaged plastic model (CDPM) and the behavior of GFRP bars was considered as linear elastic. The proposed FEM portrayed a close correlation with the testing results of HCCs. Moreover, the different empirical models were proposed for predicting the two-peak loading behavior of FRP-reinforced HCCs based on a large database constructed from the previous research.

Experimental and theoretical study of GFRP hoops and spirals in hybrid fiber reinforced concrete short columns

Literature is deficient in exploring the structural behavior of concrete columns reinforced with glass fiber reinforced polymer (GFRP) bars and hybrid fibers. In the present study, the hybrid fiber reinforced concrete (HFRC) consisted of steel fibers and polypropylene fibers. A total of twelve GFRP reinforced HFRC (GHC) columns (250 mm in diameter and 1150 mm in height) were fabricated using longitudinal GFRP bars and transverse GFRP hoops/spirals and tested to failure under different loading conditions. The testing results concluded that all the GHC columns presented similar failure modes with the rupture of GFRP bars and GFRP hoops/spirals. The decrease in the spacing of GFRP transverse reinforcement resulted in an improvement in the axial strength (AS) and ductility of GHC columns. The eccentricity of loading resulted in a significant reduction in the AS of GHC columns. The proposed empirical model based on an experimental database of 270 fiber reinforced polymer reinforced concrete columns presented a good behavior for the experimental results. The comparative investigation solidly verifies the accuracy of the newly proposed empirical model for predicting the AS of GHC columns by assuming the compressive involvement of GFRP bars and the lateral confining pressure due to transverse GFRP reinforcement.

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.

Behavior of axially loaded low strength concrete columns reinforced with GFRP bars and spirals

This paper investigates the behavior of circular concrete columns reinforced with glass fiber reinforced polymer (GFRP) bars and spirals under axial load. Nine circular low strength concrete columns of 230 mm diameter and 1500 mm height were constructed and tested. The test parameters included reinforcement type (GFRP and steel), longitudinal reinforcement ratio, and spacing of spirals. Most tested columns showed two peak loads. Test results revealed that the GFRP-RC columns behaved similarly to the steel-RC counterparts. However, the GFRP-RC columns gave a slightly lower first peak load compared to their counterparts reinforced with steel. Increasing the GFRP reinforcement ratio slightly enhanced the capacity of the columns. Highly confined columns showed better ductile failure and significantly increased the second peak load of the columns. Design equations that predict the capacity of FRP-RC columns were evaluated using the experimental data of this study. The results showed that the Canadian Standard Association equation was conservative especially for columns with high reinforcement ratios. In addition, three different confinement models were used to predict the maximum confined concrete strength and they gave reasonable predictions compared to the experimental ones. Furthermore, an existing analytical model was used to predict the load-axial displacement of the tested columns and it showed reasonable correlation with the experimental ones up to the first peak loads. However, significant deviations were observed at the post-peak stages.

Circular Concrete Columns and Beams Reinforced with GFRP Bars and Spirals under Axial, Eccentric, and Flexural Loading

Abstract Glass fiber-reinforced polymer (GFRP) reinforcement has been considered as a replacement for the traditional steel reinforcement, mainly due to its corrosion resistance. In this paper, a t...

A New Design-Oriented Model of Glass Fiber-Reinforced Polymer-Reinforced Hollow Concrete Columns

Hollow concrete columns (HCCs) reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals are considered an effective design solution for bridge piers, electric poles, and ground piles because they use less material and maximize the strength-toweight ratio. HCC behavior is affected by critical design parameters such as inner-to-outer diameter ratio, reinforcement and volumetric ratios, and concrete compressive strength. This paper proposes a new design-oriented model based on the plasticity theory of concrete and considering the critical design parameters to accurately describe the compressive load-strain behavior of GFRP-reinforced HCCs under monotonic and concentric loading. The validity of the proposed model was evaluated against experimental test results for 14 full-scale hollow concrete columns reinforced with GFRP bars and spirals. The results demonstrated that the proposed design-oriented model was accurate and yielded a very good agreement with the axial compressive load behavior of GFRP-reinforced hollow concrete columns.

Torsion in concrete beams reinforced with GFRP spirals

Abstract Current FRP guidelines do not have enough evidence on the torsional performance of beams reinforced with glass fiber-reinforced polymer (GFRP) reinforcement due to the lack of research and complexity of the problem. A review of the past work was presented in the state-of-the-art section to stand on mile-stone prospective considering the variety and development of GFRP manufacturing. This study examined the rectangular spirals and rectilinear stirrups to reinforce concrete beams in the transverse direction under pure torsion loading. The test parameters included four levels of transverse reinforcement ratio and the type of transverse reinforcement in terms of rectilinear stirrups vs. spirals. The test results demonstrated that rectangular GFRP spirals provided superior tensile resistance required to develop high ultimate torsional moments after cracking and hence can be effectively used. The failure of the tested beams was attributed to the rupture of GFRP rectangular spirals at bent portions. The test results of the spiraled specimens were discussed and compared with predictions from a developed analytical model and based on CSA equations. Two values of failure plane angle and stress levels were considered. The 45-degree inclination angle provided safe predictions with an average experimental-to-practiced result of 1.16 compared to 0.99 using the 37.5-degree. Design equations were proposed and validated for the ACI code for a probable future incorporation.

Compressive behavior of axially loaded circular hollow concrete columns reinforced with GFRP bars and spirals

This study explored the use glass-fiber-reinforced-polymer (GFRP) bars and spirals as reinforcing materials in hollow concrete columns in order to mitigate steel-related corrosion problems and understand the fundamental behavior of such construction system under the applied loads. Four concrete columns 250 mm in external diameter and reinforced longitudinally with six 15.9 mm diameter GFRP bars were cast with different inner diameters (0, 40, 65, and 90 mm) and tested under concentric axial loading. Based on the experimental results, increasing the inner-to-outer diameter ratio up to 0.36 in hollow GFRP reinforced columns changed the failure behavior from brittle to pseudo-ductile. Moreover, the hollow GFRP reinforced columns exhibited higher deformation capacity and higher confinement efficiency compared to the GFRP-reinforced solid columns and steel-reinforced hollow columns. A theoretical model considering the confined-concrete compressive strength and axial strain of 0.0025 in longitudinal GFRP bars can accurately predict the axial-load capacity of hollow concrete columns.