Resistance model for confined circular reinforced concrete columns under eccentric loads

GFRP was employed in constructions as an alternative to steel, which has many advantages like lightweight, large tensile strength and resist corrosion. Existing researches are insufficient in studying the influence of hybrid reinforced concrete composite columns encased by GFRP I-section (RCCCEG) and I-section steel (RCCCES). In this study twenty one (RC) specimens of a cross-section of 130 mm × 160 mm, with different length (long 1600 mm and short 750 mm) were encased by using I-section (steel and GFRP) and tested under various loading (concentric, eccentric and flexural loads). The test was focused on the influence of many parameters; load-carrying capacity, mode of failure, deformation and drawing an interaction diagram (N-M) for columns. The research explores the feasibility and effectiveness of the employing GFRP and steel sections. The test results concluded that all the composite columns with I-section steel presented similar failure modes to I-section GFRP composite column. Increasing in strength and ductility in short and slender reinforced concrete composite columns related to reinforced concrete columns. The eccentric load has a significant reduction in column strength, especially in slender column. The 3D FE models of (RCCC) were established by ABAQUS. (RCCC) was studied in terms of failure mode, deformation and bearing capacity also an analytical study was employed to obtain analytical results for short specimens subjected to flexural load and employing these outcomes for drawing interaction diagram (N-M) for short columns. Based on the verification of FE analysis, the experimental and theoretical results showed a good agreement.

Behavior of RC columns and those strengthened with FRP composite under an innovative reversing cyclic eccentric axial loading

In this study, high-strength steel (HSS) reinforcement with a yield stress of about 600 MPa was used in reinforced concrete columns to reduce both the reinforcing bar congestion and the construction costs. For this purpose, 16 square concrete columns reinforced with either the conventional normal-strength steel (NSS) or HSS rebars were subjected to axial and eccentric compression loads. The primary test variables included longitudinal reinforcement with two strength grades, axial load eccentricities, two different concrete compressive strengths, and different longitudinal reinforcement ratios. The structural response of the columns reinforced with reduced HSS rebars (Grade 600) was compared with that of the columns reinforced with grade 420 MPa rebars in terms of their load-carrying capacity, failure mechanism, axial force-bending moment (P-M) interaction, and ductility. Experimental results showed that although the amount of longitudinal steel reinforcement was reduced by about 34% in columns containing grade 600 MPa rebars, their load-carrying capacity and P–M interaction diagrams were comparable to those of the reference columns containing conventional NSS rebars. It was also concluded that simultaneous use of high-strength rebars and high-strength concrete below a balanced point would lead to slightly higher values of ductility index (by up to 4%) than when normal concrete strength and conventional reinforcement steel rebars of Grade 420 MPa are used.

Fiber-reinforced concrete increasingly is being used for structural members. This study investigates the compressive behavior of reinforced concrete columns with and without steel fibers under axial and eccentric loads. The 16 confined columns had a concrete core 165 x 165 mm (6.49 x 6.49 in.) at the midsection and were hunched at the ends to apply eccentric loading and prevent boundary effects. The specimens were tested to failure at different strain rates under two loading schemes: concentric compression and eccentric compression with a constant eccentricity. The axial load and axial strains were obtained to evaluate the effects of the presence of steel fibers, the thickness of the cover concrete, and the eccentricity of the applied axial load. A comparative analysis of the experimental results showed that the presence of steel fibers delayed the spalling of concrete cover and increased the strain capacity and ductility. The eccentricity of the applied axial load caused substantial variation in the peak load, ultimate strength, and failure modes. The structural response of cross sections of normal concrete and steel fiber-reinforced concrete columns subjected to compressive concentric and eccentric loading was numerically modeled to compare the experimental results. Adequate reproduction of experimental results was obtained using a suitable choice of constitutive laws for concrete and reinforcing steel bars and a reasonable calibration criterion of the model. Directions for future research are discussed.

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

Eccentric compressive behavior of steel fiber-reinforced RC columns strengthened with CFRP wraps: Experimental investigation and analytical modeling

This study performs the test with full-scaled models for each diameter to evaluate the behavior of the reinforced concrete columns using the spiral wire rope as a lateral reinforcement of the circular columns. This study performs the quasi-static test which induced binding shear destruction to review circular concrete columns bound with high strength wire rope. Three specimens of concrete columns with 700 and 800 mm diameter each were manufactured to evaluate the movement of reinforced circular columns with the wire rope. A hoop reinforced column and 2 spiral reinforced columns were manufactured to compare the bending history and the ductility reinforced with the wire rope to existing reinforced concrete columns. The peak strain of the longitudinal reinforcements is occurred at approximately 0.75 D from the bottom of the column. The spirally confined concrete columns with high-strength wire ropes showed that improve 2.5 % of the shear strength.KeywordsWire ropesSpiralDuctilityColumnsLateral reinforcements

Tall building columns are subjected to high axial loads particularly at lower levels. In zones of high seismicity, these columns have to maintain their axial load carrying capacity during an earthquake. Conventional ordinary reinforced concrete, structural steel and concrete filled tube columns are not as effective as steel confined concrete columns. Steel tubed concrete columns are more ductile and have higher lateral resistance even under high axial compressive loads. In this paper, the seismic behavior of steel confined reinforced concrete columns is presented. Results were compared with those of ordinary reinforced concrete columns. The test results suggest that steel confined reinforced concrete columns are more ductile and have better seismic performance than ordinary reinforced concrete columns. © 1998 John Wiley & Sons, Ltd.

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 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.

This paper investigates the behavior of reinforced concrete (RC) circular columns under combined loading including torsion. The main variables considered in this study are the ratio of torsional moment to bending moment (T/M) and the level of detailing for moderate and high seismicity (low and high transverse reinforcement/spiral ratio). This paper presents the results of tests on seven columns subjected to cyclic bending and shear, cyclic torsion, and various levels of combined cyclic bending, shear, and torsion. Columns under combined loading were tested at T/M ratios of 0.2 and 0.4. These columns were reinforced with two spiral reinforcement ratios of 0.73% and 1.32%. Similarly, the columns subjected to pure torsion were tested with two spiral reinforcement ratios of 0.73% and 1.32%. This study examined the significance of proper detailing, and spiral reinforcement ratio and its effect on the torsional resistance under combined loading. The test results demonstrate that both the flexural and torsional capacities are decreased due to the effect of combined loading. Furthermore, they show a significant change in the failure mode and deformation characteristics depending on the spiral reinforcement ratio. The increase in spiral reinforcement ratio also led to significant improvement in strength and ductility.

Axial behaviour of circular steel tubed concrete stub columns confined by CFRP materials

The spiral reinforcement is a very common technique used for reinforcing columns in active seismic regions due to its high ductility and high ability of energy absorption. This paper presents a nonlinear finite element analysis of high-strength concrete confined with opposing circular spiral reinforcements. The results are compared with tested scaled concrete columns made with opposing spirals under monotonic axial loads. The developed model is used to investigate the effect of spiral spacing, γ (ratio of the core diameter to the whole cross section diameter) and compressive strength on behaviour of circular spiral reinforced concrete column confined with opposing spiral reinforcements. The results of the parametric study demonstrated that for the same spacing between spirals and same strength of concrete, increasing γ will result into increasing the failure load of the column. It is also concluded that the ductility of the studied columns is not affected by changing the value of γ.

Eccentric compression behavior of seawater and sea sand concrete columns reinforced with GFRP and stainless steel bars

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