Circular Steel Tube Research Articles

Experimental study of steel single skin, double skin and dual tubes stub columns filled with rubberized concrete

This experimental study investigates the performance of rubberized concrete-filled dual steel tubular (RuCFDST) short columns under concentric compression, addressing a gap in existing literature. While previous studies focused on single- and double-skin circular steel tube stub columns, the specific behavior of RuCFDST columns remains largely unexplored. The study compares RuCFDST columns with rubberized concrete-filled steel tubes (RuCFST) and rubberized concrete-filled double-skin steel tubes (RuCFDSST). A total of eighteen specimens were experimentally tested, which consisted of three single-tube configuration, three double-skin configuration, and twelve dual tube configuration. The investigation covers rubberized concrete preparation, material testing, precise measurements, test setup, and result analysis. Key parameters include rubberized ratio (0 %, 10 %, 20 %, and 30 %) and concrete mix variations. The results provide insights into failure modes, load-shortening behavior, ductility, and strength index, with comparisons to the design predictions based on the European standard EC4. The inclusion of rubberized concrete enhances ductility, while RuCFDST columns show promise in combining sustainability and strength. The study also evaluates design predictions, revealing good agreement for lower rubberized content but indicating deviations for higher ratios, suggesting the need for refined design approaches in such cases.

Experimental study on the interfacial bond behavior of UHPC filled circular stainless steel tubes

As the interfacial bond property is of great significance to derive the composite action between stainless steel tube and UHPC for the Ultra-High Performance Concrete Filled Stainless Steel Tubular (UHPCFSST) columns, the push-out tests were conducted in this program, which includes 8 specimens having different stainless steel tube diameter and tube thickness. Based on the test results, the damage patterns and the full range load-slip curves are analyzed in detail, and the interfacial bond stress constitutes at different loading stages were also identified and evaluated. On top of that, the longitudinal strain of the stainless steel tube was analyzed based on elastic theory to derive the non-dimensional bond stress distribution law along the steel-concrete interface. The comparison between test results and the predictions from current code specification or the available empirical formulas indicate a large discrepancy and inconsistency. Therefore, the bond strength and corresponding slippage value of UHPCFSST columns were predicted by a new equation based on regression analysis. The research discovery obtained from this study provides theoretical significance and practical value for improving the design theory and application of UHPCFSST columns in practical engineering.

Study on eccentric compressive performance of circular double skin concrete filled steel tube connected by thread through inside lining tube

Connection method of lengthening the steel tube of circular hollow sandwich concrete-filled steel tube by inside lining tube and thread is proposed. Twelve circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube are designed and fabricated using the length of the thread along the axial direction, the working height of the thread, and the position of the thread as parameters; In addition, one unconnected specimen and two welded specimens also are designed and fabricated to conduct controlled experimental research. The test phenomena and failure modes, axial compressive load-compression curve, axial compressive load-lateral deflection curve, and axial compressive load-strain in steel tube curve, as well as bearing capacity, strength reservation, deflection curve shape, lateral stiffness, ductility and plane section assumption are analyzed. The research results indicate that, within the parameter range studied, the thread connection through inside lining tube is reliable before tripping, and the experimental phenomenon of specimens connected by thread is basically consistent with that of the unconnected specimens. The axial compressive load-compression curve and axial compressive load-lateral deflection curve of all specimens can be approximately divided into elastic stage, elasto-plastic stage, and descending stage. The peak load of all specimens is relatively close, while although experiencing almost the same loading process, the strength reserve of the specimens connected by thread is insufficient. During the entire loading process, the shape of the deflection curve of all specimens is close to the sine half wave curve, and the distribution of longitudinal strain in the steel tube along the height of the middle cross-section basically conforms to the plane section assumption. Calculation method for bearing capacity of circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube is suggested.

Numerical analysis of axially loaded concrete-filled steel tubular columns strengthened with CFRP grid-reinforced ECC

Carbon fiber-reinforced polymer (CFRP) and engineered cementitious composites (ECC) are commonly used to reinforce structural elements, with proven effectiveness in enhancing the performance of concrete-filled steel tube (CFST) columns as shown in prior experimental studies. However, the complex interaction among the components of the reinforced columns, including CFRP, ECC, the steel tube, and the concrete core, as well as the underlying mechanical mechanisms, remain insufficiently understood. This research aims to fill these gaps by developing a 3D finite element (FE) model of circular CFST short columns reinforced with CFRP grid-reinforced ECC for comprehensive numerical analysis. Sensitivity analyses are conducted to determine the governing parameters in the numerical simulation, including mesh size and critical plasticity parameters for the concrete damage model, such as the ratio of the second stress invariant on the tensile meridian to that on the compressive meridian (Kc), and the dilation angle (ψ) for both the concrete core and ECC. The model also accounts for the effects of concrete confinement provided by the CFRP grid-reinforced ECC layer and the circular steel tube. The accuracy of the FE model is validated against existing experimental data, and the model is subsequently used to investigate the behavior of reinforced CFST columns under varying geometric and material properties. The study examines failure modes, axial load-displacement responses, stress distributions, and the contribution of each material component to the load-bearing capacity of the strengthened columns. The results indicate an increase in ultimate axial strength ranging from 13% to 20% for the reinforced CFST columns. While the compressive strength of the ECC has a moderate effect on axial resistance, increasing ECC thickness, concrete strength, and steel tube yield strength significantly enhances the columns’ load-bearing capacity. Finally, a novel design model is proposed and validated, which accounts for the confinement effects provided by the CFRP grid and ECC on the concrete core.

Global buckling and residual capacities of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) columns after exposure to fire

The post-fire flexural buckling behaviour and capacities of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) columns are studied in this paper, underpinned by testing and numerical modelling. A testing programme was firstly conducted on twelve column specimens designed with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), including nine column specimens after exposure to the ISO 834 standard fire for 15 min, 30 min and 45 min and three reference column specimens at ambient temperature. The test failure modes, load–mid-height lateral deflection curves and failure loads were reported in detail. The influences of heating durations and recycled coarse aggregate replacement ratios on failure loads and mid-height lateral deflections at failure loads of circular RACFSST column specimens were discussed and their lateral deflection distributions were analysed. The testing programme was followed by a numerical modelling programme, where thermal and mechanical finite element models were developed to repeat the experimental results and afterwards used to carry out parametric studies to generate a numerical data pool over a wide range of cross-section dimensions and member lengths. Based on the test and numerical data, the relevant design rules for circular natural aggregate concrete-filled carbon steel tube columns at ambient temperature, as specified in the European code, Australian/New Zealand standard and American specification, were evaluated, using post-fire material properties, for their applicability to circular RACFSST columns after exposure to fire. It was revealed from the evaluation results that the three design codes led to overall acceptable levels of accuracy and consistency in predicting post-fire flexural buckling capacities of circular RACFSST columns, but with some unsafe predictions.

Seismic Performance of Precast Concrete Bridge Piers with Built-In Steel Tube Connection Key

Investigating the seismic behavior of precast concrete bridge piers is crucial in the design process due to the complex stress distribution in the connecting components. To demonstrate the seismic behavior of precast concrete bridge piers with hybrid joint connections, three bridge piers were designed with a scaling ratio of 1:8 and then tested under low cyclic loading conditions. The tests involved varying shapes of steel tube connection keys as parameters. This study involved examining failure modes and crack development, as well as analyzing the hysteretic performance, deformation capacity, energy dissipation, and stiffness degradation of the specimens. Furthermore, a finite element model was developed using ABAQUS, and the validity of the modeling approach suggested in this study was confirmed through tests. The results indicate that the precast piers exhibit reduced concrete damage at the joints. The enhanced strength of the joints is attributed to the incorporation of steel tube connection keys. The circular steel tube connection key integrated into the precast bridge pier offers a superior bearing capacity, energy dissipation, and stiffness degradation compared to the cross-shaped steel tube connection key. The presence of the built-in circular steel tube connection key in the precast bridge pier suggests that it complies with the seismic structural measures and is consistent with the design principle of “strong joint and weak member”.

Study on Bearing Mechanism of Steel Screw Pile

In order to study the bearing mechanism of a steel screw pile (SSP), a 3D-FEM of “SSP-stratum” was established based on the large-scale general finite element analysis platform ABAQUS. Secondly, the real friction coefficient between pile and soil was determined by comparing it with the field bearing test data of screw piles. Finally, the bearing mechanism and failure criterion of the SSP was revealed. The research showed that the pile-soil friction coefficient was about 0.6 under the condition of this stratum, and the screw pile was in the elastic working stage under the conditions of compression and tension load, which had a large bearing reserve. The magnitude of Young’s modulus was inversely correlated with the settlement value and the extreme value of principal stress. The increase in the Young’s modulus of the stratum was helpful in improving the bearing capacity of the screw pile. The compressive capacity of circular steel tube + screw pile (CST + SP) was about 2 times higher than CST, and the compressive capacity of circular steel tube + large blade + screw pile (CST + LB + SP) was about 2.4 times higher than CST. The tensile capacity of CST + SP was about 3.4 times higher than CST, and the tensile capacity of CST + LB + SP was about 4.9 times higher than CST. The arrangement of large blades better bore the load of the screw part and optimized the stress distribution of the structure. Based on the mechanical analysis in the vertical direction, the bearing mechanism of the SSP under compression and tension conditions was elaborated. The bearing failure criterion of the SSP was summarized from the aspects of mechanics and displacement. The bearing design of the SSP should meet the control of mechanics and deformation at the same time. The research work could provide a useful reference for the design and construction of SSPs.

Flexural behavior of circular concrete-filled steel tube members reinforced with annular stiffener

This paper presents a study on the flexural performance of a novel concrete-filled steel tube (CFST) member reinforced with an internal annular stiffener. The annular stiffener is composed of curved steel plates, and the circumferential plate serves as the interface connector. Four-point bending tests were conducted on the four new composite beams and two traditional CFST counterparts to investigate the flexural performance of the composite members. The failure modes, deflection distribution, flexural strength, strain distribution, and moment-curvature relationship were analyzed. The test results showed that the new composite members exhibited higher bending capacity and stiffness than their CFST counterparts. Then, a finite element (FE) model was established and validated using the test results to numerically investigate flexural behavior. The available design models for predicting the flexural capacities of the composite beams was compared. Design formulae considering the stiffener contributions were deduced to calculate the flexural strength of the composite beams based on the plastic-stress distribution method. It was demonstrated that the developed FE modeling appropriately simulated the structural behavior of the composite members. Parametric studies indicated that the use of high-strength concrete was inefficient. In addition, the comparison results indicated that the proposed design formulae were feasible for predicting the bending capacity of composite members.

Experimental Study on Axial Compression of Circular Steel Tube Reinforced by Self-Tapping Cable and Sleeve Tube

Experimental Study on Axial Compression of Circular Steel Tube Reinforced by Self-Tapping Cable and Sleeve Tube

Waste rubber recycling in concrete-filled steel tube members: Mechanical performance, reliability and life cycle assessment

This paper focuses on the axial compression mechanical performance, reliability analysis and environmental impact of rubber concrete-filled circular steel tube (RuCFST) columns. Initially, the research of the axial compression performance reveals that enhancing the wall-thickness or yield strength of steel tubes variably increases the yield, peak, and ultimate loads of RuCFST columns. The degree of enhancement of each characteristic point by growing the wall thickness of the steel tube is 5 %–44 %, 6 %–44 %, and 9 %–44 %, respectively; while the degree of enforcement is 5 %–55 %, 23 %–53 %, and 24 %–61 %, respectively, upon yield strength increase. Reliability analysis indicates that higher concrete grades decrease the probability of axial compression failure in RuCFST columns. Raising the yield strength and wall-thickness of steel tubes leads to a reduction in the reliability index. Both larger and smaller live-to-dead load effect ratios adversely impact the reliability index. In addition, the life cycle assessment method was used to evaluate the environmental impact of RuCFST columns, and the analysis was made after considering the superposition effect of waste rubber incineration and recycling into rubber aggregates.

Time-dependent responses and modeling of circular steel tube confined reinforced concrete (STCRC) accounting for partial exposure condition

Circular steel tube confined reinforced concrete (STCRC) columns are becoming increasingly popular in high-rise buildings in China due to their high compressive strength, excellent seismic performance, and high fire resistance. However, the time-dependent behavior has not been well studied for these columns. The time-dependent behavior of STCRC columns is particular, due to the longitudinally partial exposure condition for the concrete core, which is different from either fully exposed members or fully sealed ones. To investigate this difference, long-term experiments with a test duration of 1465 days were conducted on partially exposed circular STCRC columns and the test results were compared against those from fully exposed and fully sealed specimens. With the partial exposure condition accounted for by modifying the notional size h0 of the concrete core, a mathematical expression was then theoretically developed and benchmarked against the test data. Investigation shows that: (1) significant differences exist in the time-dependent deformation between partially exposed, fully exposed, and fully sealed columns; (2) with the modified notional size (defined as the longest path length for the water diffusion), the EC2 model can well predict the time-dependent deformation of partially exposed circular STCRC columns, with a maximum deviation of 7.6 %. The Mean Stress (MS) method is suggested for the conceptual design to achieve safer results.

Experimental and numerical study on behavior of UHPC-filled circular stainless steel tube stub columns under eccentric compression

Ultra-high performance concrete (UHPC) filled stainless steel tube (UFSST) is a newly proposed composite structure specifically designed to withstand harsh natural environments. To study the behavior of the UFSST column, 3 axial compression and 9 eccentric compression UFSST stub columns were tested respectively. And a comprehensive parametric analysis was conducted by employing a refine finite element model validated by the test data. The results show that the thickness (t) of stainless steel tubes is a key parameter affecting the eccentric compression performance of UFSST stub column. The increase in t can significantly improve the performance of UFSST stub columns, including the ultimate bearing capacity (Nu), ultimate bending moment (Mu), and ductility (DI). Finally, a modified computational model for the bearing capacity of UFST and UFSST stub columns under eccentric compression was proposed and showed a higher prediction accuracy. For UFST and UFSST stub columns, the prediction model yielded mean values of 0.99 and 1.00 for the ratio of predicted to experimental results, with standard deviations of 0.06 and 0.08, respectively.

Lateral impact performance of pitting corroded CFST columns for offshore applications

This study investigates the lateral impact performance of circular concrete-filled steel tube (CFST) columns with pitting corrosion. A comprehensive set of 15 CFST specimens was meticulously constructed, including 3 non-corroded specimens used as controls and 12 specimens subjected to varying pitting corrosion conditions. These conditions included different depths, numbers of corrosion pits, and pitting corrosion distributions. Additionally, an extensive Finite Element Analysis (FEA) was conducted to gain detailed insights into the instantaneous dynamic responses of CFST columns with pitting corrosion under lateral impact. The FEA included failure mechanism investigation, stress and strain analyses, bending moment responses, strain rate changes, and energy transformations. The experimental and FEA results reveal that pitting corrosion significantly affects the dynamic behavior of CFST columns, demonstrating reductions in impact force and flexural capacity due to pitting corrosion, and highlighting the influence of corrosion depth, number of pits, and distribution on column behavior. Finally, a simplified model incorporating the effects of pitting corrosion was proposed to estimate the dynamic flexural strength of pitting corroded CFST columns. The results provide valuable insights for designing and assessing the structural integrity of CFST members in marine environments.

Structural behavior of partially confined circular CFST columns under lateral cyclic loading

The seismic performance of concrete-filled steel tubular (CFST) columns is severely influenced by the failure at the potential plastic hinge zone. This paper proposes a novel confinement technique at the potential plastic hinge region using an inner circular steel tube for the circular CFST columns named partially confined concrete-filled steel tubular (PCCFST) columns. This confinement technique strengthens the plastic hinge region, and hence, the overall structural performance of the columns is enhanced. To verify the effectiveness of the proposed technique, a total of 7 columns: 6 PCCFST and 1 counterpart CFST have been tested under lateral cyclic loadings while subjected to constant axial load. Failure mode, hysteretic behavior, flexural capacity, ductility, and energy dissipation ability of the PCCFST specimens were investigated by varying the diameter and height of the inner circular steel tube. It was seen that the height of the circular inner steel tube has an obvious effect on the cyclic performance of the columns. For the PCCFST columns considered, the maximum lateral strength, ductility, and energy dissipation ability were enhanced by a maximum of ∼ 16 %, 24 %, and 14 %, respectively, when compared with the counterpart CFST column. A new design guideline has been proposed based on the Eurocode and limited experimental data obtained from the present study. A comparison between the experimentally determined maximum lateral strength and the proposed guideline has been made and is found to be in good agreement.

Research on the Gap Effect of Circular Concrete-Filled Steel Tubes Using the Improved Cohesive Zone Model

Understanding the influence of gap distribution characteristics on the mechanical properties of circular concrete-filled steel tubes (CCFSTs) under bending load is important for stability and support design in engineering projects. In this study, the improved cohesive zone model considering friction was used to describe the mechanical behavior of mortar interfaces. Meanwhile, the concrete damage plastic model and isotropic elastoplastic model were applied for core concrete and steel tubes. The improved cohesive zone model has a unified potential function that governs the Mode I and Mode II failure processes of mortar interfaces to realize the mechanical interaction between concrete and steel. A smooth frictional function was utilized in the elastic stage to calculate the accurate frictional effect. Furthermore, the capability of the model in addressing unloading and reloading was verified, and the fracture energy varied accordingly during the cyclic loading. Then, the mechanical response of CCFSTs was investigated under bending loads by setting different gap sizes and angles between the gap and loading direction. The results show that under three-point bending, the equivalent plastic strains at the middle part of CCFSTs are much larger and the peak bearing forces are much lower than the other degrees when the angles between the coronal gap axis and loading direction equal 0° and 180°. In addition, the order of the peak bearing forces, from highest to lowest, is when the height of the coronal-cap gap increases from 0.0 mm to 2.5 mm, 5.0 mm, and 7.5 mm. The significant effect makes it inappropriate to ignore the weakening of the structural performance caused by coronal gaps in structural design.

Axial compressive capacity prediction and optimal design of circular UHPC-filled steel tube based on Hybrid Symbolic Regression - Neural Network model

This study presents two methodologies for estimating the ultimate bearing capacity of ultra-high-performance concrete-filled circular steel tube (UHPCFST) columns and offers design optimization guidance: one employing a Symbolic Regression algorithm and the other a Hybrid Symbolic Regression - Neural Network (SR-NN) model. The models were trained, tested, and validated using experimental data from 498 samples sourced from existing literature. The optimal model, SR-NN_14_6, was identified from a pool of 480 models using a trial-and-error approach. The formula and model exhibited enhanced stability and precision, as indicated by their mean absolute error of 8.601 % and 8.051 %, respectively, marking an improvement exceeding 30 % relative to the best existing AIJ code. Using the validated model, a parametric analysis was conducted to assess the influence of the confinement effect coefficient (ξ) and steel ratio (α) on the strength index (SI) of UHPCFST members, leading to the identification of two optimal parameter ranges. The optimal ranges of ξ and α were determined to be 0.84 to 1.29 % and 20 % to 30 %, respectively, offering valuable guidelines for the design of UHPCFST members.

Research on eccentric-compressive behavior of steel stub columns with localized corrosion

To explore the impact of localized corrosion on the mechanical properties of hollow steel columns under eccentric loads, a specialized localized immersion-accelerated corrosion apparatus was developed. This device facilitated the creation of 17 locally corroded specimens, all subjected to eccentric loading. A systematic examination was conducted on various corrosion parameters including corrosion length, corrosion angle, localized corrosion rate, and corrosion location as well as loading conditions, which encompassed eccentricity and loading angle. Surface corrosion morphology and statistical parameters of the specimens were obtained using a 3D scanner. Subsequently, a nonuniform corrosion model, based on element displacement, was formulated through finite element analysis. Both experimental findings and numerical simulations indicate that localized corrosion does not alter the failure mode of locally corroded circular steel tubes (LCCSTs), which predominantly undergo local buckling in the compressed region. However, it was noted that localized corrosion leads to the elimination of the ascending segment in the load-displacement curve of the LCCSTs, thereby reducing both the ultimate load and ductility. Interestingly, the ultimate load of the LCCSTs was found to be relatively unaffected by variations in corrosion length and location but significantly influenced by factors such as localized corrosion rate, corrosion angle, eccentricity, and loading angle. Furthermore, through a comparative analysis of existing calculation models for the ultimate load of LCCSTs in major specifications, a practical model that accounts for localized corrosion is proposed. This model demonstrates high accuracy and is expected to enhance the understanding and prediction of the ultimate load capacity of LCCSTs in real-world applications.

Experimental study on bond performance of recycled coarse aggregates concrete with circular steel tubes after freeze–thaw cycling

AbstractExtrusion tests were conducted on recycled coarse aggregate concrete with circular steel tubes (RCCST, 100% replacement of recycled coarse aggregate) to investigate the impact of freeze–thaw cycles on bond properties. RCCST samples were subjected to 0, 25, 50, 75, 100, 125 and 150 freeze–thaw cycles and their bond properties were then compared with those of natural coarse aggregate concrete with circular steel tubes (NCCST) after 0, 100 and 150 freeze–thaw cycles. The experimental results indicate that freeze–thaw cycling damages the internal structure of RCCST, causing a significant decrease in interfacial bond strength with an increase in the number of freeze–thaw cycles. Freeze–thaw RCCST exhibits lower peak load and higher peak slip compared to NCCST, with increases of 25.2%, 73.2%, and 70.3% after 0, 100, and 150 freeze–thaw cycles, respectively. Regression analysis was used to derive an exponential equation that describes the relationship between longitudinal strain and strain gauge position. Additionally, a segmented fitting method was employed to obtain an expression for the bond slip of the freeze–thaw RCCST with a circular steel pipe.

Behavior of circular ultra-high-strength concrete-filled steel tube columns subjected to combined high-axial and cyclic lateral loads

The present study examined the seismic performance of circular concrete-filled steel tube (CFST) columns infilled with ultra-high-strength concrete (UHSC >100 MPa) as well as the beneficial effect of embedded spiral confining (SC) reinforcement at high axial load ratios (0.53–0.70) in order to enhance the safety and structural integrity of high-rise buildings. Seven specimens, including four CFST columns and three SC-CFST columns, were investigated under combined high axial and quasi-static cyclic lateral loads. The test parameters included axial load ratio (0.53–0.70), concrete compressive strength (64–111 MPa), embedded spiral confining reinforcement (pitch of 30 mm and 60 mm), and concrete vibration state. The test results demonstrated that adding spiral reinforcement improved the deformation capacity of CFST columns, which was reduced by the increased concrete strength. By embedding spiral confining reinforcement (volumetric ratio 3.3 %), the SC-CFST columns attained a deformation capacity comparable to that of CFST columns with normal concrete (64 MPa) for an axial load ratio of 0.53. The higher axial load ratio and concrete strength of composite columns led to a significant P-Delta moment effect, resulting in a substantial drop in columns' lateral load capacity. Composite columns with UHSC showed a larger contribution from the column base rotation to the specimen's lateral deformation when compared to composite columns with normal-strength concrete because the rigidity offered by UHSC made the column more rigid and reduced its flexural deformation. The unvibrated core concrete of the CFST column did not influence the initial stiffness and energy dissipation capacity. However, during the later stages of loading, the damage in core concrete rapidly accumulated, resulting in instant degradation of the load capacity and stiffness, considerable axial shortening, and poor deformation capacity. The experimental investigation offered a reliable reference on the performance of CFST columns constructed under high-axial load ratios (0.53–0.7) using ultra-high-strength concrete (>100 MPa) and spiral confining reinforcement so as to promote their application in practical engineering.

Experimental and numerical investigations of post-fire behaviour of circular steel tube confined steel-reinforced concrete columns under eccentric loading

Experimental and numerical analysis were conducted to investigate the post-fire behaviour of circular steel tube confined steel reinforced concrete (STCSRC) columns. A total of fifteen circular STCSRC columns, including five stub specimens and ten slender specimens, were tested under eccentric loading after heating following the ISO-834 standard fire curve. The test findings, such as cross-sectional temperature, failure modes, column deformation, residual load-bearing capacity, strains of steel tubes, etc., were all discussed in detail. A sequential thermal-stress coupling finite element (FE) model, including a heat transfer FE model and a mechanical FE model, was then developed using ABAQUS software and verified using the test results. To obtain further numerical data over a wide range of parameters, a parametric analysis was carried out using the established FE models. A simplified calculation method was presented to estimate the residual load-bearing capability of circular STCSRC columns subjected to eccentrical compression after ISO-834 fire exposure.