Concrete-filled Fiber-reinforced Polymer Tube Columns Research Articles

Experimental and analytical investigations of CFFT columns with and without FRP bars under concentric compression

This research study investigates experimentally and analytically the axial compressive behaviour of Concrete Filled Fiber Reinforced Polymer Tube (CFFT) columns with and without Fiber Reinforced Polymer (FRP) bars. The experimental program comprises five circular columns of 204-206 mm outer diameter and 800-812 mm height. All columns were tested under concentric axial compressive loads. It was found that CFFT columns with and without FRP bars achieved higher peak axial compressive loads and corresponding axial deformations than conventional steel reinforced concrete (RC) column. The contribution of FRP bars was about 12.1% of the axial compressive loads carried by CFFT columns reinforced with FRP bars. Axial load-axial deformation (P –

Behavior of FRP-confined high-strength concrete under eccentric compression: Tests on concrete-filled FRP tube columns

Accurate modeling of the complete stress-strain relationship of confined concrete is of vital importance in predicting the structural behavior of confined concrete columns under combined axial compression and bending. Although the axial stress-strain behavior of confined concrete under concentric loading is well established, the behavior under eccentric loading when axial and bending loads are combined is not well understood. This paper presents an experimental study on the behavior of carbon fiber-reinforced polymer (FRP)-confined high-strength concrete (HSC) columns under eccentric compression loading. 31 short concrete columns with circular and square cross-sections were tested under compression with different load eccentricities. The equivalent axial stress-strain curves of FRP-confined HSC under eccentric loading are obtained through sectional analysis conducted on the recorded experimental data. The results indicate that load eccentricity significantly affects the axial stress-strain behavior of FRP-confined HSC. In both circular and square cross-section specimens, an increase in the load eccentricity results in an increase in the ultimate axial strain but a decrease in the second branch slope of the axial stress-strain curve, which translated to a reduced ultimate axial stress in the specimens of the current study. The analysis of the results has shown that the ultimate axial strain increased and ultimate axial stress and second branch slope of the axial stress-strain curve decreased almost linearly with increasing eccentricity.

Axial Response of Concrete-Filled FRP Tube (CFFT) Columns with Internal Bars

This paper aims at investigating the general axial behavior of long circular concrete-filled, fiber-reinforced polymer (FRP) tube (CFFT) columns internally reinforced with different longitudinal rebars. A total of seven CFFT and three reinforced concrete (RC) columns served as control specimens for comparisons and were constructed and tested under cyclic axial loading until failure. The test parameters were: (1) internal reinforcement type (steel, glass fiber-reinforced polymer (GFRP) or carbon fiber-reinforced polymer (CFRP)) and amount; (2) GFRP tube thicknesses; and (3) nature of loading. All columns had 1900-mm in height and 213-mm in diameter. Examination of the test results has led to a number of significant conclusions in regards to the trend and ultimate condition of the axial stress-strain behavior, mode of failure of tested CFFT columns, and plastic strains. As expected, an increase in the FRP tube thickness (or stiffness) resulted in an increase in the strength and strain enhancement ratios. The validity of the available design provisions for predicting the ultimate load-carrying capacity of tested columns is also highlighted.

Experimental and numerical studies of CFRP tube and steel spiral dual-confined concrete composite columns under axial impact loading

Abstract Compared with conventional steel spiral reinforced concrete (SRC) or concrete filled fiber reinforced polymer tube (CFFT) columns, the fiber reinforced polymer (FRP) tube and inner steel spiral reinforcement (SR) dual-confined concrete hybrid columns (shortened as FRP-SR-concrete) showed higher load-bearing capacity and ductility in static compressive loading. In literature, very few studies have considered the dynamic behavior of FRP-SR-concrete columns under impact loading when using such hybrid structures under seismic-induced axial dynamic loading. This study investigated the axial impact behavior of carbon FRP-SR-concrete (CFRP-SR-concrete) columns subjected to a drop-weight impact test. The experimental parameters considered were CFRP tube thickness, the SR volumetric ratio, height and the weight of the impact hammer of the drop-weight test. The axial impact resistance of conventional CFFT and SRC columns was further used for a comparison. The test results showed that the CFRP-SR-concrete had higher dynamic impact load and better cracking resistance compared with the SRC or CFFT counterparts. The impact resistance of the CFRP-SR-concrete columns was enhanced with an increase in the CFRP tube thickness and the volumetric ratio of the SR. Additionally, numerical simulation was performed to predict the failure process and the impact resistance of the CFRP-SR-concrete columns.

Experimental investigation of bond and tube thickness effect on the flexural behavior of concrete-filled FPR tube under lateral cyclic loading

The effect of bond and tube thickness on the flexural behavior of concrete-filled fiber reinforced polymer tube (CFFT) are investigated experimentally in this research. Two different kinds of tubes were used in this research, pultruded tubes and filament winding tubes. Two full scale CFFT column specimens are tested under lateral cyclic load only to study the effect of bond between the concrete core and the tube internal surface under lateral cyclic load only. One of them was prepared with sand-coating on the internal surface of the tube and the other specimen was kept without sand-coating. The CFFT columns were embedded 500mm into a rigid square reinforced concrete footing with 1200mm side dimension and 800mm depth. The two specimens are pultruded FRP tubes having the same mechanical properties and 305mm exterior diameter. Another two full-scale CFFT columns were reinforced with steel reinforcement and were fabricated with tube thicknesses of 4mm and 8mm. These two column were tested to study the tube thickness effect. The columns were embedded 400mm into rigid reinforced concrete footings, which were anchored to the laboratory floor. The columns were loaded under a constant axial load and lateral cyclic load. These two columns are filament winding FRP tubes were manufactured in the Composite Material Reinforcement Laboratory of the Sherbrooke University with the same interior diameter 324mm and with two different thicknesses 4mm and 8mm. The results indicate a significant improvement in the full composite action of CFFT in terms of flexural capacity and stiffness due to the sand-coating. The increasing of the tube thickness delays the yielding of steel and increases the ultimate flexural capacity of the CFFT.

Predicting Strain Reduction Factor for Concrete-Filled FRP Tube Columns Incorporating Interface Gap and Prestress

This paper reports the findings from an analytical study into the influence of fiber reinforced polymer (FRP)-to-concrete interface gap and prestressed FRP tubes on strain reduction factor (kε) for concrete-filled FRP tube (CFFT) columns. A database that consists of a total of 45 aramid FRP- (AFRP) confined normal-and high-strength concrete (NSC and HSC) specimens with circular cross-sections is presented. All specimens were cylinders with a 152 mm diameter and 305 mm height, and their unconfined concrete strengths ranged from approximately 45 to 110 MPa. Analyses of the experimental databases that consisted of 22 specimens manufactured with FRP-to-concrete interface gap and a further 23 specimens prepared with lateral prestress is presented and discussed. Based on close examination of the hoop strain development on the FRP confining shell, expressions to predict strain reduction factors (kε) are proposed. The comparison of the proposed model predictions with the experimental test results of specimens prepared with an interface gap or prestressed FRP tubes shows good agreement.

Displacement-based model to predict lateral drift capacities of concrete-filled FRP tube columns

Abstract It has been shown over the past three decades that fiber reinforced polymer (FRP) composite tubes offer an attractive alternative to conventional confinement reinforcement to enhance strength and deformability of concrete columns. Concrete-filled FRP tube (CFFT) columns have been shown to exhibit highly ductile behavior under simulated seismic loading, making them suitable for use in earthquake-resistant construction. For the design of CFFT columns in new construction there is need for a rational procedure that enables the prediction of lateral drift capacities of these columns. This paper presents such a procedure for displacement-based design of circular and square CFFT columns. The approach incorporates influences of experimentally observed confinement parameters while also including axial load level and lateral drift capacity as design variables. The expression derived as part of the proposed design procedure has been validated using available experimental data, and it has been shown that the predicted capacities are in good agreement with the experimental results.

Lateral Strain-to-Axial Strain Model for Laterally Prestressed Concrete-Filled FRP Tubes

Concrete-filled FRP tube (CFFT) columns have recently gained significant research attention, with a number of experimental studies identifying significant benefits of using high-strength concrete (HSC) to produce high-performance CFFT columns. A recent experimental investigation revealed that prestressing the fibers in the fiber reinforced polymer (FRP) confining shell leads to significant improvements in the axial compressive behavior of HSC-CFFTs. This paper reports the findings from an analytical investigation into the lateral strain-to-axial strain relationship for prestressed HSC-CFFTs. This understanding of the lateral strain-to-axial strain relationship is of particular importance for prestressed CFFTs due to the influence of the additional lateral prestrain. Initially a database that consists of 23 aramid FRP- (AFRP) confined HSC cylindrical specimens with lateral prestress of up to 7.3 MPa is presented. Based on close examination of the experimentally recorded data, an expression to predict the lateral strain-to-axial strain relationship for prestressed HSC-CFFTs is proposed. The comparison of the proposed model predictions with the experimental test results for specimens prepared with prestressed FRP tubes shows good agreement.

Axial and flexural behavior of unreinforced and FRP bar reinforced circular concrete filled FRP tube columns

Fiber Reinforced Polymer (FRP) composites have emerged as a viable alternative of steel reinforcement due to higher ultimate tensile strength to weight ratio and corrosion resistance of FRP composites. Concrete Filled Fiber Reinforced Polymer Tube (CFFT) technique for new column construction has attracted significant research attention. This paper investigated the axial and flexural behavior of Concrete Filled Carbon FRP Tube (CFRP CFFT) columns with and without CFRP bar and concrete filled Glass FRP (GFRP) tube columns with and without GFRP bar. The test results of 16 circular CFFT and four steel Reinforced Concrete (RC) specimens of 203–205mm diameter and 800–812mm height have been reported in this paper. The test results showed a larger reduction in the confinement effectiveness of FRP tube than steel helices under increasing applied load eccentricity. FRP bar reinforced CFFT specimens exhibited higher axial loads, flexural loads, and deformations at peak loads than unreinforced CFFT and steel RC specimens. Experimental axial load-bending moment interaction curves of tested specimens also showed the improved performance of FRP bar reinforced CFFT specimens.