Concrete-filled Steel Tubular Stub Research Articles

Compressive Behaviour of Diagonally Stiffened Concrete Filled Steel Tubular Stub Columns with Reinforcement Stiffeners

Compressive Behaviour of Diagonally Stiffened Concrete Filled Steel Tubular Stub Columns with Reinforcement Stiffeners

Experimental study on axial compression properties of concrete filled steel tubular stub columns in varying ambient temperature

To better understand the mechanical property issues of in-service concrete-filled steel tube (CFST) bridges susceptible to natural environmental temperatures, 13 CFST stub columns were assessed under axial compression with different ambient temperatures and steel ratios, with the strength of the core concrete as the main parameters. The influence of ambient temperature on the peak strain and joint elastic modulus of the CFST stubs was investigated. The influence mechanism of steel content and core concrete strength on the residual toughness of the CFST at different ambient temperatures was revealed. In this study, we proposed a modified constitutive equation for CFST, taking into account the ambient temperature. We demonstrated that the peak strain, residual toughness ratio, and elastic modulus of the CFST stubs significantly decreased when the temperature decreased. The calculated values of the modified constitutive equation for CFST, taking into account the ambient temperature, were in good agreement with the test results and could be used to predict the trends in stress properties of the CFST stubs at different temperatures. The results could serve as a critical reference for the design and calculation of CFST structures in very cold regions.

Behavior of square geopolymer recycled brick aggregate concrete filled steel tubular stub columns under axial compression

Geopolymer recycled brick aggregate concrete filled steel tubes (GRBACFST) have the advantages of waste utilization, reducing carbon dioxide emission and overcoming concrete defects, which have broad potential applications in engineering structures. However, there is little relative research and regulations for this kind of structure with the innovative material. In this paper, 20 square GRBACFST stub columns were tested under axial compression to investigate the effects of concrete reference strength, replacement ratio of recycled brick aggregate (RBA) and thickness of steel tube. The failure mode, load–strain curve, ultimate strength, compressive stiffness and ductility were analyzed. Based on the material characteristics of geopolymer RBA concrete, the existing constitutive model of traditional core concrete confined by steel tube for finite element method was modified. Numerical data of 192 GRBACFST stub columns with different parameters under axial compression were generated and compared with the design methods for traditional concrete filled steel tubes. It can be found using the actual strength and elastic modulus of geopolymer RBA concrete, the existing formulas are capable of predicting the axial compressive ultimate strength and stiffness of square GRBACFST stub columns.

Confinement Effect and Efficiency of Concentrically Loaded RACFCST Stub Columns.

Recycled aggregate concrete-filled steel tubular (RACFST) columns are widely recognized as efficient structural members that can reduce the environmental impact of the building industry and improve the mechanical behavior of recycled aggregate concrete (RAC). The objective of this study is to investigate the behavior of recycled aggregate concrete-filled circular steel tubular (RACFCST) stub columns subjected to the axial loading. Three-dimensional finite element (FE) models were established using a triaxial plastic-damage constitutive model of RAC considering the replacement ratio of recycled aggregates. The FE analytical results revealed that the decreased ultimate bearing capacity of RACFCST stub columns compared with conventional concrete infilled steel tubular (CFST) columns was mainly due to the weakened confinement effect and efficiency. This trend will become more apparent with the larger replacement ratio of recycled aggregates. A practical design formula of the ultimate bearing capacity of RACFCST stub columns subjected to axial load was proposed on the basis of the reasonably simplified cross-sectional stress nephogram at the ultimate state. The derivation process incorporated the equilibrium condition and the superposition theory. The proposed equation was evaluated by comparing its accuracy and accessibility to some well-known design formulae proposed by other researchers and some widely used design codes.

Numerical Investigation of Composite Behavior and Strength of Rectangular Concrete-Filled Cold-Formed Steel Tubular Stub Columns.

The objective of this study was to investigate the composite behavior of rectangular concrete-filled cold-formed steel (CFS) tubular stub columns under axial compression. A fine finite 3D solid element model of rectangular concrete-filled cold-formed steel tubular stub column was established by ABAQUS, which utilized a constitutive model of cold-formed steel considering the cold-forming effect and a triaxial plastic-damage constitutive model of the infilled concrete. Good agreement was achieved and the average discrepancy between the experimental and FE results was less than 5%. Based on the verified models, a further parametric analysis was carried out to reveal the influence of various factors on the strength and behavior of the concrete-filled rectangular cold-formed steel tubular stub columns. The factors included constitutive models adopted for cold-formed steel, length over width ratio of the rectangular section, wall-thickness and width, and concrete strength and yield strength of the cold-formed steel. A total of 144 FE models were analyzed. The stress nephogram was reasonably simplified in accordance with the limit state and a theoretical formula considering confinement coefficient was proposed to estimate the ultimate bearing capacity of concrete-filled rectangular cold-formed steel tubular stub columns using the superposition method. The calculated results showed satisfactory agreement with both the experimental and FE results, which proved the validity and accuracy of the formula proposed in this paper. In the proposed formula, the confinement coefficient of square concrete-filled cold-formed steel tubular stub columns is larger than that of hot-rolled steel counterparts but smaller than that of the stainless steel counterparts.

Strength and behaviour assessment of axially loaded concrete filled steel tubular stub columns

As a result of the excellent performance under different loading conditions, concrete-filled steel tubular (CFST) stub columns are extensively used recently. The current study employs a 3D finite element analysis to assess the response of (CFST) stub columns when subjected to axial compression. The effect of some parameters of concrete and the confining steel tube where numerically investigated. The steel was considered as an elastic perfectly plastic material, whereas a damage plasticity behaviour was adopted for the concrete material. Analysis results suggested that the ultimate strength of concrete increases with the increase of its grade. On the other hand, increasing magnitudes of concrete grade caused a reduction in the ductility of the composite columns. Also, the increase in the steel yields stress, and the steel tube wall thickness contributes to an increase in the columns’ ultimate strength. However, they reduce the action of the concrete grade that increases the column’s ultimate strength. It was also noted that the ductility that the circular CFST stub columns showed is larger than that for square columns. Thus, the use of square CFST columns with high strength concrete, especially in seismically active areas, should be carefully considered.

Experimental investigation on recycled aggregate concrete filled steel tubular stub columns under axial compression

This paper presents an extensive experimental investigation of the circular recycled aggregate concrete filled steel tubes (RACFST) stub columns under to axial compression to assess their cross-section behaviour. Recycled aggregate concrete is a sustainable concrete produced with recycled coarse aggregate (RAC) from demolition wastes generally used to fabricate non-structural elements. When compared with natural coarse aggregate (NCA), the recycled coarse aggregate presents lower mechanical properties due to physical and chemical changes that occurred during the recycling process, and thus the resulting RAC possess lower strength than the conventional natural aggregate concrete. However, the confinement provided by the circular steel tube can increase the strength and ductility of RAC in recycled aggregate concrete filled steel tubes (RACFST) columns. The test programme presented in this paper comprised twenty-three composite columns with replacement ratios (the mass percentages of the NCA replaced by RCA in concrete) corresponding to 0% (nature coarse aggregate), 30 and 50% (recycled aggregate concrete), plus four steel columns used for comparison. The experiments have shown that, as anticipated, the concrete core enhances the composite section load-carrying capacity. However, the control over the contents of this concrete core influences the composite section's ductility. If the fill material presents a brittle behaviour, stress redistributions occur in both steel and concrete to compensate for this effect. Since the behaviour of natural aggregate concrete filled steel tubes (NACFST) and RACFST columns are similar, the present paper starts from a study based on a comparative assessment of the recommendations presented in ABNT NBR 8800, ABNT NBR 16239, AISC 360–16, Eurocode 4 and Australian/New Zealand AS/NZS 2327 design standards. These design recommendations proved to be consistent and in line with the performed experiments. Additionally, the results indicated that the cross-section slenderness ratio (D/t) and the confinement ratio directly influence the composite section response.

Reliability analysis of axial bearing capacity of concrete filled steel tubular stub columns with different cross sections

In this paper, Monte Carlo Simulation (MCS) and the simplified fourth-moment method based on cubic normal distribution are used to analyze the reliability of bearing capacity formula of concrete-filled steel tubular stub columns (CFST) under axial compression proposed by Ding Faxing, which considers the shape confinement coefficient of steel tube. The influence of different section shapes, different strengths of concrete and steel, two load combinations and different load ratios on the reliability index are considered. The results show: (1) the reliability index of MCS and simplified fourth-moment method are close, and the maximum difference is less than 5%; (2) the reliability of bearing capacity formulas of CFST with different cross sections meet the requirements of target reliability index 3.2; (3) When the ratio of office live load to dead load is 1.0, the lower the steel ratio and the higher the concrete strength, the greater the reliability index.

Experimental Study of Square CFST Stub Columns With a Low Steel Ratio Under Axial Loading

This paper presents an experimental and numerical study on large dimension concrete-filled square low steel ratio steel tubular (CFST) stub columns under axial loading. Four specimens were designed to investigate the effects of steel ratio on the confinement effect of square CFST stub columns with a low steel ratio. ABAQUS was used to establish 3D finite element (FE) models for simulation of square CFST stub columns with a low steel ratio under axial loading. Furthermore, based on the experimental verification, the definition of the confinement index (ϕ = fsAs/(fcAc)) was discussed and the effect of the grade of concrete and steel tube was also investigated. With the same cross-sectional dimensions, the confinement effect of the square CFST stub columns with a low steel ratio (less than 0.05) was better than the others. The stub columns with the yield strength of steel tube fs = 235 MPa (345, 420 MPa) and compressive cubic strength of concrete fcu = 40 MPa (60, 80 MPa) can give fully demonstrate the material performance and reflect the better confinement effect. Based on the experimental results and FE modeling, a practical calculation formula for the ultimate load-carrying capacity of square CFST stub columns with a low steel ratio was proposed. The formula calculation results presented in this paper show good agreement with the experimental results. Compared with the existing formulas, the proposed formula has better precision.

Mechanical behavior of outer square inner circular concrete-filled dual steel tubular stub columns

The mechanical behavior of the outer square inner circular concrete-filled dual steel tubular (SCCFT) stub columns under axial compression is investigated by means of experimental research, numerical analysis and theoretical investigation. Parameters such as diameter ratio, concrete strength and steel ratio were discussed to identify their influence on the mechanical properties of SCCFT short columns on the basis of the experimental investigation of seven SCCFT short columns. By establishing a finite element model, nonlinear analysis was performed to discuss the longitudinal and transverse stress of the dual steel tubes. The longitudinal stress characteristics of the core and sandwich concrete were also analyzed. Furthermore, the failure sequence was illustrated and the reasonable cross-section composition of SCCFT stub column was proposed. A formula to predict the axial load capacity of SCCFT stub column was advanced and verified by the results from experiment and the finite element.

Axial Loading Behaviour of Self-Compacting Concrete-Filled Thin-Walled Steel Tubular Stub Columns

This paper presents an experimental investigation on the mechanical behaviour of self-compacting concrete-filled thin-walled steel tubular (SCCFTST) stub columns loaded in axial compression to failure. Four specimens were tested to study the effect of diameter to wall thickness (D/t) ratios on the ultimate load, failure modes, and ductility of the columns. Confinement of the steel tube to concrete was also addressed. The failure modes, load versus displacement curves, and load versus strain curves were examined in detail. The experimental results showed that the ultimate state is reached when severe local buckling and rupture occurred on the steel tubes, and the concrete near the rupture has been crushed. The columns with larger D/t ratios appeared more local buckling, and its location is more close to the end of the columns. The SCCFTST stub columns with smaller D/t ratios show higher ultimate load and better ductility, and the steel tubes can exert higher confinement to the concrete.

Study on Rubberized Concrete-Filled Steel Tubular Stub Columns Under Axial Compression

In order to study the behavior of rubberized concrete-filled steel tubular (RuCFST) stub columns, an innovative composite member with steel tube and concrete filled with rubber particles was made. Twenty-four RuCFST stub columns were tested, in which six conventional CFST stub columns were prepared for comparison. The effects of changing rubber particle size (in the range of 1–2 mm and 2–5 mm) and rubber replacement ratio (0%, 10%, 20% replacement of sand) were made to discover the characteristics of the columns. The tested RuCFST stub columns displayed a local buckling similar to the conventional CFST stub columns. The tested results are compared with the predicted results of finite element analysis and the existing codes of CFST. Generally, the agreement between the predictions and results are reasonable.

Axial compression performance of thin-walled T-shaped concrete filled steel tubular columns under constant high temperature: Experimental and numerical study

This study investigates the effects of temperature and stiffener on the axial compression performance of thin-walled T-shaped concrete filled steel tubular (CFST) stub columns. Eight CFST columns with and without stiffener were fabricated and exposed to different elevated temperatures, then tested for axial compressive performance. The complete load-displacement curve of the specimens under axial compression, the failure pattern after test and the failure characteristics of concrete core are also discussed. The finite element analysis is then developed to establish the calculation model of temperature field and axial pressure field of thin-walled T-shaped concrete filled steel tubular stub columns with stiffeners at constant high temperature. The FE model presents a highly agreement with experimental data in term of load-displacement behavior, which enable to further investigate stress distribution and failure mechanism of the columns. In addition, parametric study is conducted showing that temperature, thickness of steel tube, yield strength of steel tube and compressive strength of concrete are the key factors in contributing to axial compressive performance of the CFST stub columns. Finally, to provide reference for practical application of engineering, a simplified calculation formula for ultimate bearing capacity and axial compression stiffness of CFST stub columns were obtained via the regression analysis based on results from the experimental and numerical analysis. The result shows that the relative errors between results calculated from simplified formulae and from FE models are within 10%, which indicates that the proposed formulae are able to provide the theoretical reference for the practical engineering applications.

Axial compressive behavior of recycled concrete filled steel tubular stub columns with the inclusion of crushed brick

In China, due to the extensive use of brick as the non-structural walls in the old concrete building, it is hard to exclude the waste brick from the waste concrete in the production of recycled coarse aggregates. This paper investigates the axially loaded recycled aggregate concrete filled steel tubes with the inclusion of crushed bricks as the coarse aggregates, which is called as the recycled brick aggregate concrete filled steel tubes (RBACFSTs). It was found that the compressive resistance only decreased by up to 3.8% when half of the recycled coarse aggregate was substituted by the crushed clay brick (CCB). The structural effects of the CCB replacement are much smaller than the corresponding effects in the material property tests, owing to the confinement effects. The stress states of the steel and the concrete infill were analyzed separately. Model equations to describe the stress–strain responses and the design recommendations for RBACFSTs were proposed.

Mechanical behavior of self‐stressing steel slag aggregate concrete filled steel tubular stub columns

AbstractThe mechanical behaviors of the self‐stressing steel slag aggregate concrete filled steel tubular (SSSACFST) stub column are investigated for practical structural applications. Twelve specimens under axial and eccentric compression are tested. The influences of different parameters, such as the eccentricity, the diameter–thickness ratio of the steel tube and the expansion rate of the steel slag aggregate concrete (SSAC) are studied. The experimental results show that the shear and the bending deformation dominate the failures of the specimens under axial and eccentric compression, respectively. The column with a high diameter–thickness ratio has a low ultimate bearing capacity and ultimate strain. The incremental range of the load capacity and the ultimate axial and circumferential strains of the specimens will be increased by raising the expansion rate of the SSAC. Based on the experimental results, the applicability of the current concrete filled steel tube design provisions for the SSSACFST stub columns is evaluated, and two analytical models for predicting the bearing capacity of the SSSACSFT stub columns under axial and eccentric compression are proposed.

Confinement coefficient of concrete-filled square stainless steel tubular stub columns

The objective of this paper is to investigate the confinement coefficient of concrete-filled square stainless steel tubular (CFSSST) stub columns under axial loading. A fine finite 3D solid element model was established, which utilized a constitutive model of stainless steel considering the strain-hardening characteristics and a triaxial plastic-damage constitutive model of concrete with features of the parameter certainty under axial compression. The finite element analysis results revealed that the increased ultimate bearing capacity of CFSSST stub columns compared with their carbon steel counterparts was mainly due to that the composite action of CFSSST stub columns is stronger than that of carbon steel counterparts. A further parametric study was carried out based on the verified model, and it was found that the stress contribution of the stainless steel tube is higher than the carbon steel tube. The stress nephogram was simplified reasonably in accordance with the limit state of core concrete and a theoretical formula was proposed to estimate the ultimate bearing capacity of square CFSSST stub columns using superposition method. The predicted results showed satisfactory agreement with both the experimental and FE results. Finally, the comparisons of the experimental and predicted results using the proposed formula and the existing codes were illustrated.

Axial compression analysis of square concrete-encased concrete filled steel tubular stub columns after fire exposure

Abstract This paper presents results from numerical studies on the effect of critical factors governing the axial compression mechanical properties on square cross-section concrete-encased concrete filled steel tubular (CFST) stub columns after fire exposure. A validated three dimensional finite element model is applied for evaluating axial compression mechanical properties of concrete-encased CFST stub columns after fire exposure under different factors. The factors varied in the parametric study include fire exposure time, steel tube area ratio, longitudinal bar ratio, compressive strength of concrete, yield strength of steel tube, and sectional core area ratio. Results from parametric studies show that axial compressive strength and axial stiffness of square concrete-encased CFST stub columns after fire decrease significantly. The decline of axial stiffness is higher than that of axial compression ultimate bearing capacity. Fire exposure time and sectional core area ratio have significant influence on the reduced level of axial compressive strength and axial stiffness of square concrete-encased CFST stub columns after fire exposure. Steel tube area ratio and reinforcement ratio have some influence on the reduced level. Compressive strength of concrete and yield strength of steel tube have limited influence on the reduced level.

Composite action of hollow concrete-filled circular steel tubular stub columns

To better understand the influence of hollow ratio on the hollow concrete-filled circular steel tubular (H-CFT) stub columns under axial compression and to propose the design formula of ultimate bearing capacity for H-CFT stub columns, 3D finite element analysis and laboratory experiments were completed to obtain the load-deformation curves and the failure modes of H-CFT stub columns. The changes of the confinement effect between core concrete and steel tube with different hollow ratios were discussed based on the finite element results. The result shows that the axial stress of concrete and hoop stress of steel tube in H-CFT stub columns are decreased with the increase of hollow ratio. After the yield of steel, the reduction rate of longitudinal stress and the increase rate of circumferential stress for the steel tube slowed down. The confinement effect from steel tube on concrete also weakened slowly with the increase of hollow ratio. Based on the limit equilibrium method, a simplified formula of ultimate bearing capacity for the axially loaded H-CFT stub columns was proposed. The predicted results showed satisfactory agreement with the experimental and numerical results.

08.17: Experimental behaviour of high‐strength thin‐walled concrete filled steel tubular stub columns

ABSTRACTDeveloped more than 80 years ago, the design procedure of concrete filled steel tubes (CFST) has several limitations that can still be found in most current international design standards. The two main limitations that present themselves are the lack of ability to achieve material enhancement when using high strength materials and restrictions on the geometry of the steel tube thickness to the overall column diameter. This geometric limitation is placed on the design to ensure that the steel tube remains ‘compact’. In complying with these constraints it is assumed in the design equations that local buckling of the steel tube will not take place before the ultimate global buckling load is achieved.With the introduction of higher strength materials, specifically when dealing with steel, the strength increase leads to the design of sections with increased slenderness. As the section becomes more slender, the ability to maintain the compact section limitations in the design codes becomes increasingly difficult. This paper looks at an experimental study on very thin‐walled steel tubes filled with high‐strength concrete and how localised buckling affects their compressive capacity.Adopting a diameter to thickness ratio of 200, 24 circular tubes were constructed using a high‐strength cold‐formed steel sheet, with yield stresses above 500MPa and filled with 100MPa concrete. Employing both thin‐walled sections and high strength materials, the effects of localised buckling in these composite members when subjected to compression has been studied. The experimental programme explored four main conditions; when both the steel and concrete were loaded and bonded together, when the concrete core inside the CFST was loaded, when the steel tube in the CFST was loaded and when the concrete core without the steel tube was tested.By studying the failure modes of both the concrete and the steel tube when acting compositely and individually, the experimental work shows that there is valid evidence to support the theory that even when using high strength materials in slender sections, confinement to the concrete core is provided. Finally, the results of the experimental work have been compared to the compressive design capacities predicted by current international design codes, showing that these provisions are conservative.

Axial Bearing Capacity of Elliptical Concrete Filled Steel Tubular Stub Columns

To study the axial bearing capacity of elliptical concrete filled steel tubular (ECFST) stub columns, the calculation theory and accuracy of existing formulas are analysed. The comparison of the calculation results of existing formulas and test results shows that the calculation precision is within the scope of engineering tolerance. Therefore, the existing formulas are proposed for practical project.