Axial load-axial deformation behaviour of circular concrete columns reinforced with GFRP bars and helices

Fibre Reinforced Polymer (FRP) bars has attracted a significant amount of research attention in the last three decades to overcome the problems associated with the corrosion of steel reinforcing bars in reinforced concrete members. A limited number of studies, however, have investigated the behaviour of concrete columns reinforced with FRP bars. Also, available design standards either ignore the contribution of or do not recommend the use of GFRP bars in compression members. This study reports the results of experimental investigations of concrete specimens reinforced with GFRP bars and GFRP helices as longitudinal and transverse reinforcement, respectively. A total of five circular concrete columns of 205 mm in diameter and 800 mm in height were cast and tested under axial compression. The experimental results showed that reducing the spacing of the GFRP helices or confining the specimens with CFRP sheet led to improvements in the strength and ductility of the specimens. Also, an analytical model has been developed for the axial load-axial deformation behaviour of the circular concrete columns reinforced with GFRP bars and helices. The model has been validated with the experimental results

Axial load-axial deformation behaviour of circular concrete columns reinforced with GFRP bars and helices

Fibre Reinforced Polymer (FRP) bars has attracted a significant amount of research attention in the last three decades to overcome the problems associated with the corrosion of steel reinforcing bars in reinforced concrete members. A limited number of studies, however, have investigated the behaviour of concrete columns reinforced with FRP bars. Also, available design standards either ignore the contribution of or do not recommend the use of GFRP bars in compression members. This study reports the results of experimental investigations of concrete specimens reinforced with GFRP bars and GFRP helices as longitudinal and transverse reinforcement, respectively. A total of five circular concrete columns of 205 mm in diameter and 800 mm in height were cast and tested under axial compression. The experimental results showed that reducing the spacing of the GFRP helices or confining the specimens with CFRP sheet led to improvements in the strength and ductility of the specimens. Also, an analytical model has been developed for the axial load-axial deformation behaviour of the circular concrete columns reinforced with GFRP bars and helices. The model has been validated with the experimental results

Behaviour of circular concrete columns reinforced with GFRP bars and GFRP helices

Glass Fibre Reinforced Polymer (GFRP) bar has emerged as a preferable alternative to steel bar in Reinforced Concrete (RC) members in harsh, corrosive, and coastal environments. This is particularly because steel bars may corrode in such environments and may cause damage and deterioration of RC members. FRP bars are noncorrosive and possess high tensile strength to weight ratio. In spite of their high tensile strength, FRP bars are not recommended to reinforce concrete columns because of their low compressive strength and low modulus of elasticity in comparison to the steel bars. The behaviour of FRP bar reinforced concrete (FRPRC) columns under axial compression and particularly under eccentric axial loads was not addressed adequately in the previous studies. Moreover, the effects of FRP wrapping on the behaviour of FRP-RC columns was not investigated in the previous studies. This study aims to investigate experimentally and analytically the behaviour and performance of GFRP bar reinforced concrete (GFRP-RC) circular columns under different loading conditions. A total of 18 circular concrete specimens with 205 mm in diameter and 800 mm in height were cast and tested. The influences of reinforcing materials (steel and GFRP bars), helix pitches (30 mm and 60 mm), loading conditions (concentric, 25 mm eccentric, 50 mm eccentric and flexural loadings) and wrapping with CFRP sheets were investigated. In addition to the experimental works, analytical studies were conducted for the axial load-bending moment interactions of FRP-RC columns. The developed analytical model well predicted the axial load-axial deformation and moment-curvature behaviours of FRP-RC columns with reasonable agreements to the experimental results. The experimental and analytical results showed that GFRP bars can be used as longitudinal reinforcements to improve the performance of RC specimens in terms of axial load carrying capacity and bending moment. Also, the GFRP helices considerably confined the concrete core to sustain loads. In addition, well confined GFRP-RC columns can obtain two peak loads where the first peak load represents the capacity of unconfined cross-section and the second peak load represents the capacity of confined concrete core of the column

Load and moment interaction diagram for circular concrete columns reinforced with GFRP bars and GFRP helices

This paper presents analytical and experimental studies on the axial load-bending moment behavior of glass fiber-reinforced polymer (GFRP) bars and helices RC columns. The nominal axial load and bending moment of the columns were analyzed based on the stress-strain behavior of the cross-sectional components. A numerical integration method was used to determine the compressive force of concrete in the compression region. The analytical results were verified with experimental results of 12 circular specimens reinforced with GFRP bars and GFRP helices. Out of these 12 specimens, eight specimens were taken from available literature and four specimens were tested in this study. The influences of different parameters such as loading conditions, spacing of the GFRP helices, and wrapping the specimens with carbon fiber-reinforced polymer (CFRP) sheets on the behavior of GFRP-RC specimens were investigated. A parametric study was also carried out to investigate the effects of longitudinal and transverse GFRP reinforcement ratio and slenderness ratio on the axial load-bending moment diagrams of GFRP-RC columns. It was found that the slenderness effect is more pronounced on the confined cross sections under eccentric loads at the ultimate state condition

Experimental investigations on circular concrete columns reinforced with GFRP bars and helices under different loading conditions

Glass-fiber-reinforced polymer (GFRP) bar has emerged as a preferable alternative to steel bar in reinforced concrete (RC) members in harsh, corrosive, coastal environments in order to eliminate corrosion problems. However, only limited experimental studies are available on the performance and behavior of concrete columns reinforced with GFRP bars under different loading conditions. This study investigates the use of GFRP bars and GFRP helices (spirals) as longitudinal and transversal reinforcement, respectively, in RC columns. A total of 12 circular concrete specimens with 205-mm diameter and 800-mm height were cast and tested under different loading conditions. The effect of replacing steel with GFRP reinforcement and changing the spacing of the GFRP helices on the behavior of the specimens was investigated. The experimental results show that the axial load and bending moment capacity of the GFRP-RC columns are smaller than those of the conventional steel-RC columns. However, the ductility of the GFRP-RC columns was very close to the ductility of the steel-RC columns. It is concluded that ignoring the contribution of the GFRP bars in compression leads to a considerable difference between analytical and experimental results

Strength and ductility behavior of circular concrete columns reinforced with GFRP bars and helices

Long-term durability is a concern for Reinforced Concrete (RC) structures. Instances of premature deterioration of concrete structures due to corrosion of steel reinforcement are increasing. The use of Glass Fiber Reinforced Polymer (GFRP) bars as an alternative to traditional steel reinforcement in RC structures may resist premature deterioration. Although RC building and bridge columns in coastal areas are susceptible to significant deterioration, studies on concrete columns reinforced with GFRP bars and helices are limited. Also, design codes do not recommend the use of GFRP bars in compression members. This study investigates the use of GFRP bars and helices as longitudinal and lateral reinforcement, respectively, in concrete columns. Five circular normal strength RC columns with 205 mm in diameter and 800 mm in height were cast and tested under concentric loads. The influence of the longitudinal GFRP reinforcement and the spacing of the GFRP helices on the strength and ductility capacity of the columns were investigated. The experimental results showed that the contribution of the longitudinal GFRP bars was lower than the contribution of longitudinal steel bars to the load carrying capacity of the columns. Also, the load carrying capacity of the GFRP-RC columns was smaller than that of steel-RC columns. However, the ductility capacity of the columns was not affected by the use of GFRP helix instead of steel helix

Longitudinal reinforcement limits for fibre-reinforced polymer reinforced concrete members

Adequate ductility is an important issue for fiber-reinforced polymer (FRP) reinforced concrete (RC) members because of the brittle behavior of FRP bars and concrete. FRP reinforcement in the tension side needs to be sufficient to prevent the brittle rupture of the FRP bars and attain the ultimate compressive strain in concrete in the compression side. Also, the maximum amount of FRP reinforcement should be within a certain limit to ensure the FRP-RC members that fail by crushing of concrete undergo a considerable deformation. In this study, analytical calculations were carried out to develop equations for limiting minimum and maximum FRP reinforcement ratios in the FRP-RC flexural members. Different arrangements of FRP reinforcing bars and different cross-sectional geometries were considered in this study. The minimum FRP reinforcement ratio can be selected either to prevent rupture of FRP bars or to control the crack width. Also, the maximum FRP reinforcement ratio can be selected to obtain a required deformability

Fracture mechanics modeling of reinforced concrete joints strengthened by CFRP sheets

Nowadays, fracture mechanics modeling for strengthening structural members is a challenging issue for structural engineers. The developed fracture mechanics modeling was applicable for identifying propagation of a crack in concrete structural members such as beam-column connections. In the present paper, a numerical model derived from nonlinear fracture mechanics is developed to simulate the propagation of a crack in Carbon Fiber Reinforced Polymers (CFRP)-strengthened the connection. To validate the proposed model, two beam-column connections were made and tested. By using the proposed model, the outputs of the CFRP-strengthened connections show good agreement with the experimental results (8–12 %). It was also observed that propagation of the crack in the beam was prevented by the CFRP sheets. The average decrease was 36.9 % of the crack length compared with the control connection. The findings revealed that cracks formed in the connection area in the control specimen while extensive cracks appeared in the beam in the specimen strengthened by CFRP sheets

Crack propagation modeling of strengthening reinforced concrete deep beams with CFRP plates

Fracture analysis of reinforced concrete deep beam strengthened with carbon fiber-reinforced polymer (CFRP) plates was carried out. The present research aimed to discover whether crack propagation in a strengthened deep beam follows linear elastic fracture mechanics (LEFM) theory or nonlinear fracture mechanics theory. To do so, a new energy release rate based on nonlinear fracture mechanics theory was formulated on the finite element method and the discrete cohesive zone model (DCZM) was developed in deep beams. To validate and compare with numerical models, three deep beams with rectangular cross-sections were tested. The code results based on nonlinear fracture mechanics models were compared with the experimental results and the ABAQUS results carried out based on LEFM. The predicted values of initial stiffness, yielding point and failure load, energy absorption, and compressive strain in the concrete obtained by the proposed model were very close to the experimental results. However, the ABAQUS software results displayed greater differences from the experimental results. For instance, the predicted failure load for the shear-strengthened deep beam using the proposed model only had a 6.3% difference from the experimental result. However, the predicted failure load using ABAQUS software based on LEFM indicated greater differences (25.1%) compared to the experimental result

Moment-Curvature Behavior of Glass Fiber-Reinforced Polymer Bar-Reinforced Normal-Strength Concrete and High-Strength Concrete Columns

A numerical integration approach was developed to investigate the moment-curvature behavior of glass fiber-reinforced polymer (GFRP) bar-reinforced circular normal-strength concrete (NSC) and high-strength concrete (HSC) columns. The results obtained from the developed integration approach were validated with the experimental results of eight GFRP bar-reinforced circular concrete column specimens. Out of these eight specimens, four specimens were cast with NSC having a compressive strength of 37 MPa and four specimens were cast with HSC having a compressive strength of 85 MPa. A parametric study was carried out to investigate the effect of concrete compressive strength and GFRP longitudinal and transverse reinforcement ratios on the moment-curvature behavior of the GFRP bar-reinforced NSC and HSC circular columns under combined axial and flexural loads. The results of the parametric study indicate that increasing the concrete compressive strength or GFRP longitudinal reinforcement ratio leads to an increase in the bending moment capacity and a decrease in the ductility of GFRP bar-reinforced concrete columns. The confinement provided by the GFRP helixes (transverse reinforcement) improves both the bending moment capacity and the ductility of the GFRP bar-reinforced circular concrete columns. The improvement in the performance (bending moment and ductility) due to increasing the GFRP transverse reinforcement ratio was greater in the GFRP bar-reinforced NSC columns than in the GFRP bar-reinforced HSC columns