Filled Steel Tubular Stub Columns 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.

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.

Tests and analysis on circular UHPFRC-filled steel tubular stub columns under eccentric compression

This paper developed the circular ultra-high performance fiber-reinforced concrete (UHPFRC)-filled steel tubular stub columns (CUFTSCs) for buildings and bridge piers. Eccentric-compression behaviours of CUFTSCs were studied through a 16-test program, and the studied key influencing parameters were eccentricity ratio (e/r = 0.0, 0.30, 0.68, and 0.98) and thickness of steel tube (ts). Under eccentric compression, the CUFTSCs failed in flexure-governed mode and exhibited linear, nonlinear, and recession working stages. The nonlinearities of CUFTSCs under eccentric compression were mainly contributed by nonlinear mechanical behaviours of compression steel tube and UHPFRC and minor steel-tube local buckling. UHPFRC crushing and major steel-tube local buckling occurred to the peak load point and recession branch of N-Δ/N-δ curves of CUFTSCs, respectively. As the eccentricity ratio increases the failure mode of CUFTSCs gradually changed from the compression-governed mode to flexural-bending-governed mode. The ductility of CUFTSCs is significantly improved through using thick steel tube. The code equations in EC4, AISC and GB50936 were conservative on predicting Nu-Mu interaction curves of CUFTSCs due to the ignorance of tensile strength of UHPFRC. The developed analytical models offer the most accurate estimations on Nu-Mu interaction curves of CUFTSCs.

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.

Axial compressive behavior of square ice filled steel tubular stub columns

Concrete has many limitations in the building construction in cold areas. However, there is abundant ice in those regions. Therefore, using ice as a substitute for concrete has been explored by researchers. Inspired by the idea of square concrete filled steel tube (CFT), a new column form termed square ice filled steel tubular (IFT) column is proposed in this study. It consists of a square outer steel tube with the inner space filled with ice. A total of eighteen stub columns were made and tested under axial compression, including three circular plain ice specimens, nine square IFT specimens and six hollow square steel tubes, to demonstrate the advantages of the composite column. The width-to-thickness (B/t) ratio of the steel tubes varies from 39.5 to 77. The test results confirmed that the ice core is effectively confined by the steel tube, and the inward local buckling of the steel tube is suppressed by the inner ice, leading to higher strength and better ductility of the square IFT specimens compared with hollow steel tubes and plain ice columns. A simplified axial bearing capacity equation for square IFT stub columns is proposed and it provides reasonable and accurate predictions of the test results.

Behavior of innovative circular ice filled steel tubular stub columns under axial compression

The use of conventional building materials has many limitations in cold regions. Inspired by the idea of concrete filled steel tube (CFT), a new form of construction component named ice filled steel tube (IFT), which effectively combines the advantages of both ice and steel tube, was innovatively proposed in this study. This paper presents an experimental study on circular IFT stub columns under axial compression. The main parameter of the test specimens is the diameter-to-thickness (D/t) ratio of the steel tube. A total of 12 specimens including 3 plain ice columns and 9 circular IFT columns were divided into four series and tested under axial compression. The test results showed that the development of cracks in ice was delayed by the steel tube. As a result, both the ultimate bearing capacity and the ductility of the ice column were improved due to the confinement from the steel tube. The local bucking at the bottom of the steel tube was also delayed by the ice core. Therefore, the circular IFT column has good potential to serve as a structural component in cold regions.

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.

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.

Study on Cross-shaped Concrete Filled Steel Tubular Stub Columns Subjected to Axial Compression: Experiments and Design Method

Despite its wide application prospect, researches on the cross-shaped concrete filled steel tubular (CFT) columns are scarce, and no design method can be used. This paper concerns with the axial load behavior of cross-shaped CFT stub columns. Five specimens were tested to examine the influences of three parameters on the characteristics of failure, the bearing capacity and deformability. The parameters include the width-thickness ratios of steel plates, the yield strengths of steel and the sectional dimensions. Experimental results demonstrate that the global outward bulge of steel tube near the concave corners is significant, so that the stresses on the steel tube distribute unevenly and the confinement effects on the concrete are inferior to the rectangular CFT columns. By decreasing the width-thickness ratio of each steel plate, the global outward bulge near the concave corners was smaller, but the ductility could be improved only when it decreased by 2.08 times. By increasing the yield strength of steel to 1.47 times, the bearing capacity and deformation were inversely smaller, but the ductility was increased. By increasing the length-width ratio of each leg to 2.25 times, the global outward bulge was increased and local buckling occurred earlier. Then the application scopes for evaluating the maximum strength of specimens by the methods in design codes are provided. A new method is also proposed by considering the confinement effects of concrete and the strength loss of steel tube. The results predicted by the proposed method show good agreement with the experimental ones.

Nonlinear Finite Element Analysis to the Circular CFST Stub Columns

The circular concrete filled steel tubular stub columns have been widely used especially when the need to high load carrying capacity structures is the utmost concern. Fulfilling this need, many studies were performed to analyze these structures.This paper presents finite element analysis using the software ABAQUS to thecircular CFST stub columns. The produced FE model is verified by comparing its results, failure load and axial load-shortening curves, to the experimental results. It has been found that results of the FE model are in excellent agreement with the experimental data.

Study on Behavior of RPC Filled Steel Tubular Stub Columns Under Axial Compression

Reactive powder concrete (RPC) with compressive strength higher than 170 MPa was prepared by using ordinary Portland cement, silica fume, ground granulated blast-furnace slag or fly ash. RPC shows high strength, constant Poisson’s ratio, high compressive peak strain but post-peak brittle failure. Based on the RPC mechanical behavior study, investigation of the interaction between steel tubes and core RPC was performed, in view of its effect on the bearing capacity and deformability of RPC filled steel tubular (RPCFT) stub columns subjected to axial loading. RPCFT stub columns have very high ductility and alleviate the RPC disadvantage of brittle failure. However, the confinement effect of steel tubes on RPC is lower than that of normal strength concrete and thus, it can be neglected during the design process for convenience and safety.

STUDY OF BEARING CAPACITY AND COMPLETE STRESS-STAIN CURVES FOR CONCRETE FILLED SQUARE STEEL TUBE COLUMNS

Based on data from 266 tests of concrete filled steel tubular stub columns gathered from literature, the design equations for axial load capacities according to domestic and international codes and specifications are examined. It is found that the equations of AISC, CECS and AIJ specifications are most conservative. The EC specifications provide statistically closer but slightly conservative predictions to the test results. The average predictions by DL and GJB specifications are slightly higher than the test data. The paper also characterizes the load-deformation relationships, and statistically evaluates several stress-strain models proposed by different researchers. It was found that they coincided with test results in the elastic stage, but for the description of the decline and strengthening stages, each model is quite different and has different applicable scope.

Testing and analysis of axially loaded normal-strength recycled aggregate concrete filled steel tubular stub columns

Thirty-nine stub columns were tested to failure to investigate the compressive behaviour of normal-strength recycled aggregate concrete filled steel tubular (RACFST) stub columns under axial loading. Study parameters included recycled coarse aggregate (RCA) substitution level, source of RCA, compressive strength of recycled aggregate concrete (RAC) core and ratio of steel area over concrete area. Experimental results showed that the scatter in the mechanical properties of RACFST stub columns is smaller than that in RACs due to the contribution of steel tubes. The source of RCA had little effect on the compressive behaviour of axially loaded RACFST stub columns within the parameter range adopted in the tested specimens. A reduction of less than 10% was measured in the compressive strength of RACFSTs due to the incorporation of RCA, which is smaller than that for RAC samples in material tests. As part of the work, confinement effects of the steel tubes to the RAC cores during the whole loading process were investigated based on the strain gauge measurements. Model equations were then proposed to predict the longitudinal stress–strain relationships for both steel tubes and RAC cores. Current CFST design provisions are compared with the RACFST stub columns test results, and the design recommendations are presented.