Steel-reinforced High-strength Concrete Columns Research Articles

Behavior and design of eccentrically-loaded slender tubed steel-reinforced high-strength concrete columns

This study experimentally and numerically investigated the behavior of eccentrically-loaded slender circular tubed steel-reinforced concrete (CTSRC) columns filled with high-strength concrete (HSC). Six specimens with the HSC of 81.4 MPa were tested considering the length-to-diameter ratio and load eccentricity; and their effects on the failure phenomenon, bearing capacity, and ductility were evaluated. A three-dimensional finite element model was established and validated for further investigating the column behavior. The study results indicate that all specimens fail in a flexural failure mode and show good ductility; and the shear studs and circular steel tube are found to ensure the composite behavior of CTSRC columns. Besides, increasing the tube thickness contributes more to the improvement of column ductility than the load capacity and the steel shape yields before the peak load, indicating the full utilization of steel strength. Based on the parametric study, a design method considering the second-order effect and the influence of unequal load eccentricities at both column ends is proposed to assist designers to determine the load capacity of slender CTSRC columns.

Axial compressive behavior of mega steel-reinforced high-strength concrete columns with different steel sections

Steel-reinforced concrete columns are the crucial vertical load-bearing members in the frame composite structures. Previous studies on steel-reinforced concrete columns primarily focus on simple H-shaped and cruciform steel sections; insufficient attention is paid to mega columns, which are frequently designed with complex steel sections and high-strength concrete. In this study, four scaled mega columns, including two open-shaped and two multicell-shaped steel-reinforced high-strength concrete columns with cross-sectional dimensions of 700 × 700 mm and different concrete strengths, were subjected to one-way repeated compression tests. The aforementioned tests were conducted to examine the damage evolution, load-axial deformation response, bearing capacity, strain development, stiffness degradation, ductility, and restoration capacity of the columns. The test results indicate that the multicell steel section effectively alleviates crack widening and concrete spalling, and improves the post-peak stiffness and ductility. With increasing concrete strength, the peak load, initial stiffness, and restoration capacity are improved, while the ductility is impaired, and more abrupt damage is recorded. Three existing codes were examined to calculate the bearing capacity with a conservative estimation, particularly the ACI 318-11, with a mean predicted result to test result ratio of 0.76. Hence, an analytical model considering the confinement provided by stirrups and steel sections was proposed to predict the load-axial displacement curve with desirable accuracy. Furthermore, a finite element model based on the division of different confined concrete was established to further explore the damage evolution and to conduct a parametric study.

Mechanical Property Analysis and Calculation Method Modification of Steel-Reinforced High-Strength Concrete Columns.

The existing studies lack research on the ductility of steel-reinforced high-strength concrete (SRHC) columns and current specifications restricted the use of high-strength concrete in steel-reinforced concrete (SRC) columns. To compensate for the shortcomings of the existing research and promote the application of high-strength concrete in SRC structures, we test six SRHC columns and one SRC column to examine the effects of the steel content, eccentric distance, and slenderness ratio on the ductility, bearing capacity, and failure mode of SRHC columns. Further, Abaqus finite element models are established to predict the influences of more parameters on post-peak ductility and analyze the relationship between strain development of the concrete and the decrease in bearing capacity of SRHC columns. The results show that the penetration of cracks into aggregate during failure is the primary reason for the poor ductility of the SRHC columns. Improving the confinement effect of the stirrups on concrete is the most effective measure to enhance the ductility of the SRHC columns. The decline in the stirrup spacing from 100 mm to 50 mm increased the ductility coefficient from 1.47 to 5.56. The effect of the steel content, stirrup strength, and slenderness ratio on the ductility coefficient of SRHC columns is less than 30%. After analyzing the reason for the error of current specifications, a modified formula with an error of less than 5% is developed.

Experimental and analytical research on steel reinforced high-strength concrete columns with different steel sections

Steel reinforced concrete columns are the key vertical load-bearing members in the frame composite structures of super high-rise buildings. The steel sections and steel ratios of these columns are the major factors affecting their seismic performance. In this paper, four large steel reinforced high-strength concrete (SRHC) columns were designed. The influences of closed and open steel sections on the seismic performance of SRHC columns with different steel ratios were analyzed. The test results show that the SRHC columns with closed steel sections had plumper hysteresis loops, a higher and more stable bearing capacity, and greater deformation and energy dissipation capacities than the columns with open steel sections. The influences of the steel ratio on the plumpness of the hysteresis loops, residual deformation and energy dissipation capacity of the columns with open steel sections were greater than those of the columns with closed steel sections. The fiber-based method was adopted to predict the F-Δ curves and N-M interaction curves of the SRHC columns with closed and open steel sections. The calculated results show good agreement with the test results, and the experimental results can provide evidence for the seismic design of SRHC columns with both closed and open steel sections.

Analysis of seismic performance and research of load capacity of steel reinforced high strength concrete columns with rectangular helical hoops

This paper mainly focused on the seismic performance and shear calculation method of steel reinforced high-strength concrete (SRHC) columns with rectangular helical hoops. An experimental investigation was performed in this paper. Eleven SRHC columns with rectangular helical hoops and one with ordinary hoops were constructed at the laboratory of Guangxi university. The failure modes, hysteresis loops, envelope curves, characteristic loads and displacements and cumulative damage analysis are presented and investigated. It can be seen from the test results that the failure modes of SRHC columns can be divided into three types with the shear span ratio increased, namely, shear baroclinic failure mode, flexure-shear failure mode and flexure failure mode. In addition, the specimens with rectangular helical hoops have plumper hysteretic loops. Shear span ratio is the main influencing factor of characteristic load; the axial compression ratio and concrete strength have less influence on characteristic load, while stirrup ratio has little effect on the characteristic load. Finally, a calculation method for shear capacity of SRHC columns under shear baroclinic failure and flexure-shear failure mode is proposed.

Behavior of eccentrically loaded circular CFRP-steel composite tubed steel-reinforced high-strength concrete columns

This paper investigates the behavior of circular CFRP-steel composite tubed steel-reinforced high-strength concrete columns under eccentric compression. The failure modes and load versus mid-span lateral displacement curves were analyzed comprehensively for the specimens with different test parameters. The experimental results show that the different continuities of the external steel tube has a great impact on failure patterns. The crushing of concrete and bulging of the steel tube in the compression side occurred near the 1/4 height of the specimens with grooves at 25 mm away from the end plates on the external tube, while, for the specimens with no gaps on the steel tube, local buckling was observed around the mid-height of the columns. However, the extent of bulging can be significantly alleviated with the increase of CFRP layers. Finite element (FE) analysis was conducted by using ABAQUS software in this study and the results show that good agreement can be achieved between the test observations and FE results. Based on the valid FE model, the parametric analysis was performed and a new model was proposed to predict the axial-flexural interaction behavior of the composite columns. It is evident that the theoretical predictions agree well with the FE results of the specimens in this paper with a certain safety margin (approximately 15%), which may provide a valuable guideline for the engineering design of CFRP-steel composite tubed steel-reinforced high-strength concrete columns.

Seismic resistance capacity of steel reinforced high-strength concrete columns with rectangular spiral stirrups

In this paper, several experimental investigations on seismic resistance capacity of steel reinforced high-strength concrete (SRHC) columns with rectangular spiral stirrups are presented. Tests were carried out on eleven SRHC columns with rectangular spiral stirrups and one comparative SRHC column with an ordinary stirrup arrangement under low reversed cyclic loading to investigate their failure patterns, characteristic loads and displacements, hysteresis loops, skeleton curves, inter-story drift ratios and ductility coefficients, energy dissipation capacities and stiffness degradation. Range analysis and variance analysis methods were used to analyze the data from the experiments. The results showed that the failure patterns of the test specimens changed from shear baroclinic failure to shear-bond and flexural failure, as the shear span ratio was increased. In addition, the shear span ratio is the main factor that had a significant effect on the carrying capacity of the test specimens. The carrying capacity of the SRHC specimens increased gradually, but their ductility decreased as the axial compression ratio was increased. The ductility coefficients of the SRHC specimens with the normal stirrup and the rectangular spiral stirrup were 3.01 and 3.27, respectively, indicating that the columns with the rectangular spiral stirrup had better deformation capacity. Furthermore, the inter-story drift ratios of all the columns with the rectangular spiral stirrup in elastic phase and elastic-plastic phase were in the range of 1/200 to 1/66 and 1/26 to 1/17, respectively, which are much larger than the limit value specified by the seismic design code. In addition, the SRHC columns with rectangular spiral stirrups exhibited plumper hysteresis curves and higher energy dissipation than the SRHC column with ordinary stirrup. Thus, the SRHC columns with rectangular spiral stirrups showed good seismic resistance capacity.

Experimental investigation of SRHSC columns under biaxial loading

The behavior of 8 steel reinforced high-strength concrete (SRHSC) columns, which comprised of four identical columns with cross-shaped steel and other four identical columns with square steel tube, was investigated experimentally under cyclic uniaxial and biaxial loading independently. The influence of steel configuration and loading path on the global behavior of SRHSC columns in terms of failure process, hysteretic characteristics, stiffness degradation and ductility were investigated and discussed, as well as stress level of the longitudinal and transverse reinforcing bars and steel. The research results indicate that with a same steel ratio deformation capacity of steel reinforced concrete columns with a square steel tube is better than the one with a cross-shaped steel. Loading path affects hysteretic characteristics of the specimens significantly. Under asymmetrical loading path, hysteretic characteristics of the specimens are also asymmetry. Compared with specimens under unidirectional loading, specimens subjected to bidirectional loading have poor carrying capacity, fast stiffness degradation, small yielding displacement, poor ductility and small ultimate failure drift. It also demonstrates that loading paths affect the deformation capacity or deformation performance significantly. Longitudinal reinforcement yielding occurs before the peak load is attained, while steel yielding occurs at the peak load. During later displacement loading, strain of longitudinal and transverse reinforcing bars and steel of specimens under biaxial loading increased faster than those of specimens subjected to unidirectional loading. Therefore, the bidirectional loading path has great influence on the seismic performance such as carrying capacity and deformation performance, which should be paid more attentions in structure design.

Mechanical performance of glass fiber–reinforced polymer tubes filled with steel-reinforced high-strength concrete subjected to eccentric compression

Glass fiber–reinforced polymer tubes filled with steel-reinforced high-strength concrete are proposed as glass fiber–reinforced polymer–steel-reinforced high-strength concrete composite members. Eccentric compression is a typical loading scenario for such column members in practice. Experimental investigation on eight glass fiber–reinforced polymer tubes filled with steel–reinforced high-strength concrete columns subjected to eccentric compression was conducted. The effects of fiber orientation, thickness of glass fiber–reinforced polymer tube, slenderness ratio of columns, and loading eccentricity were investigated. It was found that the compression bearing capacity of glass fiber–reinforced polymer–steel-reinforced high-strength concrete columns increased with the decrease in the fiber tangle angle and the increase in the thickness of the glass fiber–reinforced polymer tube but reduced with the increase in the eccentricity and the slenderness ratio. Corresponding formulas were developed based on the nonlinear full-process analysis theory to describe the compression behavior of glass fiber–reinforced polymer–steel-reinforced high-strength concrete under eccentric loading. Good agreement was found through the comparison between the theoretical and the experimental results. The validated modeling approach was, therefore, employed to develop a parametric analysis that can be used to provide valuable guidance for practical application and further research on such structural members.

Experimental study on steel reinforced high-strength concrete columns under cyclic lateral force and constant axial load

This paper presents the results of an experimental study on the seismic behavior of steel reinforced high-strength concrete (SRHC) columns. A total of 21 SRHC columns were tested under simulated earthquake loading conditions, and the major experimental parameters were the axial load level, stirrup arrangement, structural steel details and studs. The effects of these parameters on the behavior of the SRHC columns were analyzed in detail. The test results showed that SRHC columns with multiple stirrups and commonly used structural steel ratios demonstrated excellent seismic behavior and were suitable for use in high-rise buildings in seismic regions. The axial load had a negative effect on the energy dissipation and deformation capacity. Stirrups exhibited little effect on the initial stiffness and lateral force at cover spalling, but had a positive effect on the energy dissipation and deformation capacity. The benefit of structural steel was more obvious when the effective confinement index was larger or the SRHC columns were subjected to a greater axial load. Structural steel also improved the positive effect of the stirrups. It is suggested that multiple stirrups should be adopted in SRHC columns to provide full play to structural steel; in addition, more structural steel should be adopted when significant axial loads are applied to SRHC columns. Studs did not significantly affect the performance of SRHC columns during the early loading stage. However, columns with studs exhibited better energy dissipation and deformation capacity along with slower stiffness degradation.

The Shear Capacity Calculation of Steel Reinforcement High-Strength Concrete Short Columns Restrained with FRP

This article aims to study the calculation for shear capacity of SRHC (Steel Reinforced High-Strength Concrete) members restrained with CFS (Carbon Fiber Sheet). Experimental study, theoretical analysis and calculation simulating are integrated in this article for the research of the shear failure characteristics and effect of various parameters on their behavior of SRHC members restrained with SFC on the basis of existed SRHC members tested results. The shear strength formula of steel reinforcement high-strength concrete short columns restrained with CFS is put forward, which based on the superposed strength method. This method on the basis of the load-deformation process of CFS is similar to hooping. The results indicate that the shear capacity of SRHC columns restrained with CFS is higher than SRHC columns. And, due to the axial compression ratio, shear span ratio and the amount of reinforcement influence the shear capacity of the FRP materials. So, these three kinds of factors are also the influencing factors of shear capacity of SRHC members restrained with CFS. The effect of the internal concrete restrained with CFS is good because of the function of CFS is equal to hooping and the strain of CFS is bigger than the strain of steel, so this simple calculation method is safe , which may be useful for further study and engineering design.

Nonlinear Analysis of Eccentric Compression of GFRP Tube Filled with SRHC Columns

The whole bearing compressive process under eccentric compression is analyzed for the further study of bearing compressive capacity of GFRP tube filled with SHC（steel-reinforced high-strength concrete）columns subjected to eccentric compression. Based on finite strip method from the plane cross-section assumption, the computation program of bearing eccentric compressive capacity of GFRP tube filled with SHC columns is formulated according to the existing retrofit theory and related technical procedures. The relation curves of load-deformation, as well as the effect curves of concrete strength, slenderness ratio, eccentricity and containing bone rate to load-deformation is obtained by means of this calculating program. Calculations show that the ultimate bearing compressive capacity of composite column decreases with the increase of slenderness ratio, elastic stage of component curve gradually shortens and stiffness gradually loses; The ultimate bearing compressive capacity of composite columns decreases with the increase of eccentricity; component ductility improves; the ultimate bearing compressive capacity of composite columns increases with the increase of concrete strength. The calculated results agree well with the experimental results and provides a basis for practical design

Loading Process Simulation of GFRP Tube Filled with Steel-Reinforced High-Strength Concrete Columns Subjected to Eccentric Compression

For the further study of bearing compressive capacity of GFRP tube filled with SHC（steel-reinforced high-strength concrete）columns subjected to eccentric compression, and analysis its whole bearing compressive process under eccentric compression. Based on the flat section assumption finite strip method, the calculating program of bearing eccentric compressive capacity of GFRP tube filled with SHC columns is proposed according to existing retrofit theory and related technical procedures. The relation curves of load-deformation is gotten using this calculating program, at the same time it can get the effect curves of concrete strength, slenderness ratio, eccentricity and containing bone rate to load-deformation. Calculations show that the ultimate bearing compressive capacity of composite column decreases with the increase of slenderness ratio, and elastic stage of component curve gradually shortens and stiffness gradually loses; The ultimate bearing compressive capacity of composite columns decreases with the increase of eccentricity; component ductility improves; the ultimate bearing compressive capacity of composite columns increases with the increase of concrete strength. The calculated results agree well with the experimental results and this study provides a basis for practical design.

Experimental Study on the Seismic Behavior of SRHSC Columns

Based on the experiments of 4 SRHSC (steel reinforced high strength concrete) column specimens, which were different in concrete strength, axial compression ratio and spacing of hoop reinforcement, this paper investigates the seismic behavior and flexural strength of SRHSC columns under cyclic lateral loading which is controlled by the displacement. According to the date and phenomenon of experiment, adopting existed theory and foreign codes for composite columns, the failure mode, lateral load-deflection relationship, strength and stiffness deterioration, ductility capacity and energy dissipation capacity of SRHSC columns is analyzed.