Steel Tubular Columns Research Articles

Coupled behavior and seismic performance assessment of square-over-round RCFDST column with reinforced ribs to steel beam joints under cyclic loading

The cyclic loading test study and finite element analysis (FEA) were conducted to investigate the seismic performance of five square-over-round recycled concrete-filled double skin steel tubular (RCFDST) columns with reinforced ribs to steel beam joints varying parameters such as the length of ribs, hollow ratio, axial compression ratio, the ratio of beam-column flexural linear stiffness and strength of the recycled concrete. It was found that a larger the displacement resulted in a lower the strength degradation. Moreover, the structures with two types of concrete showed similarities in strength degradation. In the experiment, compared to the cases without reinforced ribs, the specimens with reinforced ribs exhibited a larger value of stiffness and related rigidity degeneration primarily, and then showed a slow trend in rigidity degeneration laterally. The ductility of the cases with recycled concrete is twice that of the cases with normal concrete. In addition, the FEA model with optimal β of 0.5 agreed with the experimental results in both their damage patterns and horizontal load-displacement hysteresis curves. According the ratio of performance to cost, the optimal ratio of beam-column flexural line stiffness (km) is found in a range from 1.0 to 1.5. In a whole, the joints with reinforced ribs show generally excellent seismic performance.

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

Finite Element Analysis of Axial Compression Behavior of L-Shaped Concrete-Filled Steel Tubular Columns with Different Combinations

L-shaped concrete-filled steel tubular (CFST) columns, a kind of structural member appropriate for high-rise buildings, not only avoid the defect of conventional square columns protruding from the wall but also have the green and low-carbon properties of steel structures appropriate for fabricated construction. To learn more about their axial compression behavior, refined 3D finite element models were established using the general finite element software ABAQUS. The reliability of the models was subsequently verified based on failure tests and load–displacement relation tests on eight L-shaped specimens. The axial compression mechanism of L-shaped CFST columns was investigated using the verified finite element models. Further systematic parameter analysis was carried out to investigate the influence of parameters such as steel strength, concrete strength, length ratio of long limb to short limb, the angle between the two limbs, and combination methods on the axial compression behavior of L-shaped CFST columns. The results demonstrate that the angle between the two limbs has a significant impact on the stress distribution of concrete and steel pipes. The corner effect increases as the angle between the two limbs decreases. The combination of F-type specimens can better exert the constraint effect of steel pipes on concrete, while the triangular cavity of unequal-limb specimens and specimens with an included angle of 60° cannot effectively trigger the interaction between steel pipes and concrete. The initial stiffness of L-shaped CFST columns increases with an increase in concrete strength and a decrease in limb length ratio, which is not sensitive to changes in steel strength and the included angle. The peak bearing capacity of the specimens increases with increases in steel strength and concrete strength and a decrease in the limb length ratio. Compared to C-type and Z-type specimens, the initial stiffness of F-type specimens is slightly higher, and the peak bearing capacity is significantly increased.

Seismic behavior of an improved drilled flange connection for I-beam to CFST column

The use of cold-formed steel tubes in the concrete-filled steel tubular (CFST) columns makes the design of the moment connections between beams and CFST columns much more challenging. This is because setting the internal diaphragms in the CFST column to transfer the bending moment of the beam end becomes impossible, and thus new joints are needed. A novel joint was proposed in a previous study by the authors, where two end plates were used for the force transmission between CFST columns and beam flanges. Moreover, to satisfy the “weak member strong joint” requirement, the I-beams were reduced by drilling a series of circular holes in their flanges. However, most of the tested specimens failed by the unexpected rupture of the complete joint penetration (CJP) groove welds between the beam flanges and end plates. In this paper, three specimens are redesigned and tested, where modifications are made to improve their behaviors under the seismic load. In this test, the local buckling of beam flanges at the drilled sections was observed in all specimens, and two specimens failed due to the fracture at the drilled sections, while CJP weld fracture and significant bending of beam flanges both occurred at the failure of the rest specimen. The hysteresis curves of all specimens are fusiform, indicating their good energy dissipations (the maximum equivalent viscous damping coefficients between 0.35 and 0.40). The failure rotation angles are about 2.44–3.01, and the ductility coefficients are between 2.26 and 2.66. According to EC3, all specimens can be classified into the rigid and full-strength joints. Subsequently, the parametric analyses using the validated finite element model are carried out, where the effects of main parameters are investigated on the seismic behavior of the presented joint. This study brings insights into the moment connections between the steel beam and CFST column with the outer cold-formed section.

Global stability design of concrete-filled corrugated steel tubular columns

In recent years, various types of concrete-filled steel tubular (CFST) columns were proposed and they have been widely used in engineering practice. Considering the great confinement effect of corrugated steel plate on the concrete, a novel type of CFST column called concrete-filled corrugated steel tubular (CFCST) column was proposed. The CFCST column consists of horizontally corrugated steel plates, corner steel bars and infilled concrete. In this paper, the stability performance of CFCST columns is studied. Firstly, a finite element (FE) model was developed for numerical simulation. The ultimate resistances, load-displacement curves and failure modes obtained from the FE models were compared with previous test results to verify the validity of the FE model. Subsequently, seven sets of numerical examples were analyzed to investigate the impact of key parameters on the global stability performance of CFCST columns. These examples involved variations in geometric dimensions, corrugation shapes and material strengths. Finally, the stability coefficients φ of CFCST columns obtained from FE numerical simulation were compared to several existing stability curves. On this basis, a new stability curve was proposed for predicting the global stability resistance of CFCST columns with good accuracy and reasonable redundancy.

Experimental study of concrete-filled stainless steel tubular stub columns with circular and square cross-sections subjected to combined compression and bending

This paper presents an experimental study into the structural behaviour and strength of concrete-filled stainless steel tubular stub columns with circular and square cross-sections subjected to combined compression and bending moment. A total of sixteen concrete-filled stainless steel tubular (CFSST) stub columns were tested, including two section types (circular and square hollow sections), two grades of concrete infill (C30 and C60), two thicknesses of tube wall for each cross-section (6 and 10 mm), and five loading eccentricity ratios (0, 0.2, 0.3, 0.4 and 0.5). The CFSST stub column specimens were loaded in compression, with different loading eccentricities applied to achieve a wide range of axial load-to-bending moment ratios. This research provides a comprehensive report on the experimental methodology and subsequent observations, including the failure modes, load-deformation curves, axial load-bending moment curves, strain development at the key locations and values of ductility index. It can be observed that for circular CFSST columns, ultimate load decreased by roughly 70% with an increase in loading eccentricity ratios from 0 to 0.5, while for square columns, the reduction was about 50% under same conditions. The experimental results were used to evaluate if the existing design provisions for carbon steel-concrete composite structures is capable of designing the investigated CFSST stub columns. It was found that the mean ultimate load to predicted failure load ratios are 1.25, 1.32, and 1.36, with coefficients of variations (COV) equal to 0.08, 0.09 and 0.11, for the European, American, and Chinese codes, respectively. Consequently, the design approach specified in the Chinese code led to the most conservative and scattered strength predictions among the three codified design approaches. In contrast, the European code provides the most precise predictions of the test results, though there still remains scope for improvements in the ultimate resistance predictions of CFSST stub columns subjected to combined compression and bending.

Investigation on behavior of concrete-filled double steel tubular columns infilled with nanomaterial-based concrete subjected to axial compression

Nanotechnology has been applied in construction to enhance the mechanical properties of concrete by using nanomaterials. A new stiffening scheme called catty-cornered propped concrete-filled steel tube (CFDST) column was proposed and analyzed under axial compression. The steel tube of CFDST specimens was filled with normal and nano material-based concrete, including nano-silica (NS), carbon nanotubes (CNT), and nano-titanium dioxide (NT). The study collected data on ultimate capacity, load vs strain behavior, and load vs deformation response, as well as ductility index (DI), secant stiffness, composite interaction, and confining effect variation. The results showed that the proposed stiffening scheme increased the ultimate capacity of unstiffened CFDST by approximately 14%, and the use of nanomaterials in CFDST infill concrete resulted in an approximately 7% increase in load capacity. Increasing the number of stiffening bars improved the ductility and stiffness of the column section, while the inclusion of nanomaterials decreased the ductility index and improved the stiffness of the section. The proposed stiffening scheme resulted in better composite interaction and increased confinement. The study concluded that the utilization of nanomaterial-based concrete as an infill in the stiffened CFDST column could enhance its performance under axial compression loading.

Axial Compression Load Capacity of Tubular Steel Columns with Polygon Cross-Sections

Axial Compression Load Capacity of Tubular Steel Columns with Polygon Cross-Sections

Mechanical performances of thin-walled high-strength concrete-filled steel tube square columns with high-strength reinforced cages under biaxial eccentric compression

In the current research that both steel tube and concrete use high-strength materials, there are few studies on the small wall thickness of steel tube exceeding the standard. In order to make full use of the mechanical properties of high-strength steel and enhance its restraint ability on concrete, this paper designs a steel cage dominated by transverse steel bars. A total of 15 square high-strength steel tube high-strength concrete medium-long column test pieces are tested and studied. The main parameters of the specimens are slenderness ratio, loading eccentricity and the form of internal steel reinforcement cage. After the loading test, according to the test results, the failure mode of the specimen is obtained and the mechanical properties of middle-long concrete-filled steel tubular columns are analyzed. The research results show that the ultra-thin high-strength steel pipe can restrain concrete well, but with the increase of eccentricity, its restraint capacity is slightly insufficient; the built-in steel cage can slow down the bulging of the specimen and help the steel pipe to further strengthen the restraint on concrete, but the steel cage as an indirect constraint cannot avoid the final bulging damage. Due to the existing formula overestimating the effect of ultra-thin steel tubes, this paper proposes a calculation formula for the axial compression of thin-walled high-strength concrete-filled steel tubes with steel cage short columns. Based on this method, the bearing capacity of medium-long columns under biaxial eccentric compression is calculated with good accuracy.

Influences of structural size and confinement effect on the axial compressive behavior of SCFST columns

In this study, the mechanical behavior of geometrically similar square concrete filled steel tubular (SCFST) columns under axial compression was investigated using numerical modeling. The effects of the confinement effect and structural size on the axial compressive behavior of the SCFST column were studied. A 3D mesoscale model of the SCFST column under axial compression was established and verified using available test results. The failure mode and the nominal axial stress-axial strain curve were then presented and analyzed. The effects of the steel ratio and section size on the failure mode of the SCFST column were not obvious. As the section size of the SCFST column increases, the peak axial stress and corresponding peak axial strain show a descending trend. Specifically, as the section size changes from 100 mm to 800 mm, the peak axial stress decreases by 46.2% and 23.8% corresponding to the steel ratios of 0.0 and 0.21. With an increase in the steel ratio increases and enhanced confinement effect, the influence of the size effect on the peak axial stress decreases. For the outer steel tube, the vertical stress increases and the hoop stress decreases with the increasing section size, leading to the weakened confinement effect. Subsequently, an empirical formula considering the size effect was proposed to calculate the axial bearing capacity of SCFST columns with different structural sizes and confinement effects. The proposed empirical equation was validated using collected test results. This equation can be applied to predict the axial load bearing capacity of SCFST columns with different structural sizes and steel ratios, especially for large structural sizes.

Influence of corrosion on loading capacity of circular concrete-filled steel tubular column

Concrete-filled steel tubular (CFST) columns are commonly used in engineering, especially in load-bearing structures. This study conducts an in-depth examination of how the axial resistance of CFST columns varies with random corrosion. A finite element model for circular CFST columns is developed and its accuracy is verified using available experimental data. The interaction between the outer steel tube and the concrete column is explored, along with the introduction of a strength reduction coefficient concept. Additionally, the concept of an axial load-bearing capacity reduction coefficient is introduced to illustrate variations in the axial resistance of circular CFST columns during different corrosion stages. The degradation patterns of reduction coefficients for uniform and random corrosion depths in the steel tube and CFST columns with varying mass loss rates are analyzed, and formulas are provided to predict the axial resistance in different corrosion stages. Furthermore, the study investigates the influence of variables such as material strength, component dimensions, and the thickness of the external steel tube, resulting in adjustments to the original expressions for various conditions.

Flexural performance of round-ended concrete-filled steel tubular specimens

Round-ended concrete-filled steel tubular (CFST) columns have numerous benefits, including easy construction, aesthetic appearance, and variable section arrangement. This study experimentally and numerically investigated the flexural behavior of round-ended CFST columns. The six testing results showed that as the aspect ratio increased from 1.38 to 1.86, the flexural resistance and stiffness increased by 82.0% and 159.9%, respectively. Every round-ended CFST specimen had excellent ductility. Concrete can be adequately confined by the round-ended steel tube. Mechanistic and parametric analyses were carried out using a finite element model. Mechanistic analysis demonstrated that the round segment of the steel tube can effectively confine the concrete, resulting in a considerable strength gain near the edge of the compression zone. The parametric analyses showed that as the concrete strength increased from 24 to 110 MPa, the flexural resistance increased by average 20.4%; as the steel strength improved from 235 to 700 MPa, the flexural resistance increased by average 155.4%; as the steel ratio enhanced from 0.05 to 0.2, the flexural resistance increased by average 179.7%; and as the aspect ratio increased from 1 to 3, the flexural resistance of the major (minor) axis increased (decreased) by about 59.9% (36.5%). The analysis showed that the flexural stiffness of this composite specimen can be accurately predicted by AISC 360–2016. Finally, a simplified model was proposed for estimating the flexural resistance of the round-ended CFST specimens.

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.

Tapered RAC-filled high-strength double-skin steel tubular stub columns: Tests and numerical analysis

This study experimentally and numerically explores the axial-compression behaviours of tapered recycled aggregate concrete-filled high-strength double skin steel tubular (RAC-FHDST) stub column. Twelve specimens were fabricated and tested, considering the effects of tapered angle, hollow ratio and replacement level of coarse recycled aggregate (CRA). The experimental results, consisting of deformation patterns, axial load versus strain responses and confining effect from external high-strength steel tube were obtained and analyzed. Failure mode showed that all stub columns exhibited good ductile behaviour. The elastic stiffness and ultimate strength of RAC-FHDSTs decreased with rising tapered angles, while the ductile index increased. As the replacement levels of CRA varied from 0% to 100%, the elastic stiffness and ductility index obviously reduced. Larger confining effect from outer steel tube to RAC occurred close to the top section of specimens, and the occurrence of confinement was advanced with decreasing hollow ratio and increasing CRA content. Additionally, detailed numerical models were constructed and validated using experiment results. The validated finite element (FE) models were then employed to analyze the working mechanism of specimen, encompassing the load distributions and the interaction between the sandwiched RAC and steel tubes. Afterwards, a parametric study was performed to reveal the influences of essential parameters on the axial compressive performance. Finally, the existing design approaches to normal CFST and CFDST stub columns were employed to assess their applicability for estimating the ultimate strengths of tapered RAC-FHDSTs.

Prediction of the axial compression capacity of stub CFST columns using machine learning techniques.

Concrete-filled steel tubular (CFST) columns have extensive applications in structural engineering due to their exceptional load-bearing capability and ductility. However, existing design code standards often yield different design capacities for the same column properties, introducing uncertainty for engineering designers. Moreover, conventional regression analysis fails to accurately predict the intricate relationship between column properties and compressive strength. To address these issues, this study proposes the use of two machine learning (ML) models-Gaussian process regression (GPR) and symbolic regression (SR). These models accept a variety of input variables, encompassing geometric and material properties of stub CFST columns, to estimate their strength. An experimental database of 1316 specimens was compiled from various research papers, including circular, rectangular, and double-skin stub CFST columns. In addition, a dimensionless output variable, referred to as the strength index, is introduced to enhance model performance. To validate the efficiency of the introduced models, predictions from these models are compared with those from two established standard codes and various ML algorithms, including support vector regression optimized with particle swarm optimization (PSVR), artificial neural networks, XGBoost (XGB), CatBoost (CATB), Random Forest, and LightGBM models. Through performance metrics, the CATB, GPR, PSVR and XGB models emerge as the most accurate and reliable models from the evaluation results. In addition, simple and practical design equations for the different types of CFST columns have been proposed based on the SR model. The developed ML models and proposed equations can predict the compressive strength of stub CFST columns with reliable and accurate results, making them valuable tools for structural engineering. Furthermore, the Shapley additive interpretation (SHAP) technique is employed for feature analysis. The results of the feature analysis reveal that section slenderness ratio and concrete strength parameters negatively impact the compressive strength index.

Artificial Neural Network Models for Determining the Load-Bearing Capacity of Eccentrically Compressed Short Concrete-Filled Steel Tubular Columns

Artificial neural networks (ANN) have a great promise in predicting the load-bearing capacity of building structures. The purpose of this work was to develop ANN models to determine the ultimate load of eccentrically compressed concrete-filled steel tubular (CFST) columns of circular cross-sections, which operated on the widest possible range of input parameters. Short columns were considered for which the amount of deflection does not affect the bending moment. A feedforward network was selected as the neural network type. The input parameters of the neural networks were the outer diameter of the columns, the thickness of the pipe wall, the yield strength of steel, the compressive strength of concrete and the relative eccentricity. Artificial neural networks were trained on synthetic data generated based on a theoretical model of the limit equilibrium of CFST columns. Two ANN models were created. When training the first model, the ultimate loads were determined at a given eccentricity of the axial force without taking into account additional random eccentricity. When training the second model, additional random eccentricity was taken into account. The total volume of the training dataset was 179,025 samples. Such a large training dataset size has never been used before. The training dataset covers a wide range of changes in the characteristics of the pipe metal and concrete of the core, pipe diameters and wall thicknesses, as well as eccentricities of the axial force. The trained models are characterized by high mean square error (MSE) scores. The correlation coefficients between the predicted and target values are very close to 1. The ANN models were tested on experimental data for 81 eccentrically compressed samples presented in five different works and 265 centrally compressed samples presented in twenty-six papers.

An innovative multi-objective optimization approach for compact concrete-filled steel tubular (CFST) column design utilizing lightweight high-strength concrete

Incorporating sustainability into Concrete-Filled Steel Tubular (CFST) columns' optimization can enhance efficiency and sustainability in construction. Discrepancies in international standards for ultimate load capacity computation in compact CFST columns under eccentric loading, particularly with lightweight high-strength concrete, pose challenges. This research compile a dataset of compact CFST columns, evaluating design codes (AISC 360-16, Eurocode 4) against experimental results. Besides, a comprehensive finite-element model predicts compact CFST column performance, investigating axial force-moment (P-M) interaction behavior with respect to the material strength ratio (fy/fc′). In the second phase of the study, an ANN model, incorporating input parameters, estimates axial load capacity, facilitating multi-objective optimization for optimal CFST column geometry. The results confirmed that Eurocode 4 outperforms AISC 360-16 in experimental axial capacity predictions (Nuc/Nuc,theoretical) where, the mean and standard deviation for Eurocode 4 were estimated at 1.07 and 0.22, respectively, compared to 1.21 and 0.29 for AISC 360-16. Besides, statistical metrics confirm the precision of the ANN model, particularly with high-strength concrete, promising efficiency in future computational intelligence-based structural design platforms.

Effect of imperfection on behaviour of axial loaded square and rectangular concrete-filled steel tubular columns

Axial compressive strength of Concrete Filled Steel Tubular (CFST) columns is significantly improved owing to lateral confinement and the interaction between steel tube and concrete core. Occasionally there exists an initial gap between the concrete core and steel tube which may occur due to improper compaction, shrinkage in concrete, lack of curing of concrete core, etc., consequently, the compressive strength of the column is reduced. Present study shows that the presence of a gap between the concrete core and steel tube reduces the axial strength of CFST column to some extent; however, it results in an enormous fall in the ductility of column. A total of 22 specimens, including 2 hollow steel tube subjected to axial compressive loading, were tested. The main parameters of these tests were the circumferential gap. The influence of gap on the failure mode and ultimate strength of the CFST specimens were investigated. The results show close agreement between calculated and experimental results in terms of load-deformation response and ultimate strength. The behavior of CFST columns with a gap is analyzed, to investigate the impact of different parameters on ultimate strength. A maximum limit of 1.4 to 5.9 gap ratio is proposed, and a simplified formula is suggested to estimate the effect of a gap on ultimate strength.

Numerical Study on Steel Reinforced Concrete Filled Steel Tubular Columns of Circular and Square Sections Exposed to Fire

Numerical Study on Steel Reinforced Concrete Filled Steel Tubular Columns of Circular and Square Sections Exposed to Fire

Seismic behavior of prefabricated frame with special‐shaped concrete‐filled steel tubular columns and H‐shaped steel beams

AbstractTo realize the prefabricated structure of special‐shaped concrete‐filled steel tubular (CFST) column frame and enhance the level of indoor room utilization, this paper proposed a novel prefabricated frame with special‐shaped CFST columns and H‐shape steel beams connection with side plate. To investigate seismic behavior of this prefabricated frame structure, a 2‐story and 2‐bay CFST frame specimen was fabricated and tested under reversed cyclic loading. The failure mode, hysteresis behavior, degradation of lateral stiffness and bearing capacity, ductility and energy dissipation were analyzed. Experiment results indicated that failure mode presented strong columns and weak beams. Hysteresis curve of frame showed fully shuttle‐shaped. The mean story drift angle was 1/36 at ultimate stage. Equivalent viscous damping coefficient was 0.038–0.464. The bearing capacity degradation was relatively gentle, but the overall stiffness degradation was more obvious. It suggested that the frame had proper seismic and energy dissipation property. After the test, the seismic property of test frame was further investigated through the numerical simulation approach. The failure mode and skeleton curve obtained from the simulation were nearly consistent with test results, indicating that numerical analysis results were precise and with high reference meaning.