Rectangular Concrete-filled Steel Tube Research Articles

A Simple Method to Evaluate the Bearing Capacity of Concrete-Filled Steel Tubes with Rectangular and Circular Sections: Beams, Columns, and Beam–Columns

This study investigates the behavior and capacity of concrete-filled steel tubes (CFTs) with rectangular and circular sections under various loading conditions: axial loads, pure-bending, and combined axial load-bending moments. A finite element-based numerical model is developed and validated against existing experimental data. Using an extensive databank generated from finite element analysis, this research proposes analytical empirical relations for determining the bearing capacity of rectangular and circular composite beams, columns, and beam–columns. These relations provide a direct, concise, and efficient method for calculating the ultimate strength of CFT members, making them valuable for engineering design. Comparisons between the proposed analytical results and previous experimental studies demonstrate the high accuracy of this method in analyzing rectangular and circular CFT member behavior. The findings contribute to a better understanding of CFT structural performance and offer practical tools for designers working with these composite elements.

Experimental investigation on axial compressive performance of rectangular multi-cell stocky concrete-filled steel tubes stiffened with PBL

An experimental investigation on the structural performance of rectangular multi-cell stocky concrete-filled steel tubes (CFSTs) stocky stiffened with perfobond leiste (PBL) under compression. Compression tests were conducted on 12 stocky CFSTs, varying concrete strengths, number of cells, and cross-section shapes. The tests discussed the failure process, load-deformation behaviours, section capacities, ductility factors, and core concrete enhancement factors of the specimens. It was found that all the 12 tested CFSTs experienced local bucking, and owing to the inclusion of PBL, the short sides of the steel tubes exhibited double-wave bulging, while the long sides showed multiple-wave bulging. With the enhancement of concrete strength from 29.4 to 65.1MPa, the section capacity exhibited a significant increase of 18–30%. As the cell number increased from 1 to 3, the section capacity increased by 1.35–1.59 times. When the cross-section of triple-cell CFSTs changed from the I-shape to the L-shape, the section capacity only increased by 3–9%. Moreover, the enhancement factor of the core concrete and the confinement factor showed a significant correlation. The comparison between test capacities and predicted capacities using the methods given in design codes ANSI/AISC 360-16, EN 1994-1-1, and GB 50936-2014, as well as proposed by Zhang, revealed that the capacity ratios of predicted values to experimental values ranged from 0.63 to 0.89, indicating an overly conservative prediction. Considering the confinement factor, a modified design method, based on Zhang’s method was proposed, to more accurately predict the section compressive capacity of rectangular multi-cell stocky CFSTs stiffened with PBL.

Post fire behavior of square and rectangular concrete filled steel tubes with granulated blast furnace slag fine aggregate concrete

AbstractThe present study investigated the behavior of concrete‐filled steel tubes (CFST) and concrete‐filled double‐skin steel tubes (CFDST) of square and rectangular shapes after exposure to elevated temperatures. The infill concrete was prepared with granulated blast furnace slag (GBS) as fine aggregate, and no natural fine aggregate was used. A total of 20 CFST and CFDST specimens of both square and rectangular shapes were prepared. The specimens were heated at 200, 400, 600, and 800°C temperatures for 2 h and allowed to cool inside the furnace after heating. Axial load was applied to the specimens to check their behavior after exposure to fire. The reduction in the load‐carrying capacity was insignificant for the specimens heated at 200, 400, and 600°C for both square and rectangular CFST and CFDST conditions. The decrease in load‐carrying capacity was slightly higher in the case of CFDST specimens compared to CFST specimens. A three‐dimensional finite element model using ABAQUS software was proposed for predicting the behavior of the tested specimens. The proposed model could predict the behavior of both unheated and heated specimens with acceptable accuracy.

Advancements in light-gauge steel rectangular CFST columns: A comprehensive experimental study

This research examines the structural performance of rectangular Concrete-Filled Steel Tube (CFST) columns produced from light-gauge steel tubes. The study aimed at improving their strength, stiffness, and ductility via a combination of external confinement, internal stiffeners, and hybrid fiber-reinforced concrete (HFRC) infill. An axial compression test was carried out on a total of 18 samples, comprising of unconfined hollow steel tubes, bracing-confined tubes, ring-confined tubes, unconfined CFST, bracing-confined CFST, and ring-confined CFST columns. To restrict lateral expansion, external restraints including bracing and ring-type steel rods, were spot-welded to the outer steel tube. To optimize the column’s load carrying capacity and mitigate buckling effects, the spacing of the confinements were systematically designed. HFRC infill and alterations in the inner profile with and without vertical strips and studs, were also taken into consideration. The experimental results plus the failu re modes, axial load-deflections and load-deflection curves were analyzed to understand the behavior of the CFST columns. Performance indicators such as strength and stiffness ratios, and confinement effect ratio, were assessed for the various sample types. This research accentuates the efficiency of external confinement techniques in improving strength and ductility. Existing design codes were adopted for the theoretical estimations of the axial compression capacity, highlighting variations in predictions. This study significantly contributed beneficial understandings of the structural performance of rectangular CFST columns, stressing the importance of both internal and external confinements and HFRC infill.

Experimental Study on the Detection of the Existence and Location of Mimicked and Unexpected Interface Debonding Defects in an Existing Rectangular CFST Column with PZT Materials.

Interface bonding conditions between concrete and steel materials play key roles in ensuring the composite effect and load-carrying capacity of concrete-steel composite structures such as concrete-filled steel tube (CFST) members in practice. A method using both surface wave and electromechanical impedance (EMI) measurement for detecting the existence and the location of inaccessible interface debonding defects between the concrete core and steel tube in CFST members using piezoelectric lead zirconate titanate (PZT) patches as actuators and sensors is proposed. A rectangular CFST specimen with two artificially mimicked interface debonding defects was experimentally verified using PZT patches as the actuator and sensor. By comparing the surface wave measurement of PZT sensors at different surface wave travelling paths under both a continuous sinusoidal signal and a 10-period sinusoidal windowed signal, three potential interface debonding defects are quickly identified. Furthermore, the accurate locations of the three detected potential interface debonding defects are determined with the help of EMI measurements from a number of additional PZT sensors around the three potential interface debonding defects. Finally, the accuracy of the proposed interface debonding detection method is verified with a destructive observation by removing the local steel tube at the three detected interface debonding locations. The observation results show that the three detected interface debonding defects are two mimicked interface debonding defects, and an unexpected debonding defect occurred spontaneously due to concrete shrinkage in the past one and a half years before conducting the test. Results in this study indicate that the proposed method can be an efficient and accurate approach for the detection of unknown interface debonding defects in existing CFST members.

Hybrid particle swarm optimization and group method of data handling for the prediction of ultimate strength of concrete-filled steel tube columns

This study presents a hybrid model coupling particle swarm optimization (PSO) with group method of data handling (GMDH) for predicting the ultimate strength of rectangular concrete-filled steel tube (RCFST) columns. A large database of 490 data samples collected from the existing literature was used to construct the model. Compared with the optimal model among the nine existing models, the coefficient of variation (COV), mean absolute percentage error (MAPE) and root relative squared error (RRSE) values of all datasets of the PSO-GMDH model were decreased by 58.38 %, 69.22 % and 64.27 %, respectively; while the coefficient of determination (R2) and a20-index values were increased by 34.32 % and 8.65 %, respectively. The results show that the predicted results of PSO-GMDH model are in good agreement with the experimental results and can accurately predict the ultimate strength of rectangular RCFST columns. In addition, a graphical user interface (GUI) has been developed to facilitate the application of the PSO-GMDH model.

Flexural Strength and Ductility of a Concrete Filled Steel Tube Beam with Different Layouts

Concrete-filled steel tube (CFST) is a composite member consisting of a steel tube filled with concrete, resulting in an enhanced structural element used in various types of construction. This research investigates the flexural strength of CFST members with varying steel tube thicknesses of 1.5 mm and 2.0 mm and different shapes: square, rectangular, and circular. The study aims to determine the flexural strength of each shape. Fifteen beams with different cross-sections and plate thicknesses were tested experimentally in the lab. The results indicated that 2.0 mm thick CFSTs, regardless of shape, exhibited superior strength and deformation resistance compared to thinner and hollow beams. This underscores the significance of using thicker plates and concrete to enhance structural integrity and durability. Notably, rectangular CFSTs demonstrated a 91.84% increase in strength, while circular beams showed greater deflection resistance, highlighting the importance of careful material selection and design choices in structural engineering to optimize performance and resilience under stress.

Behaviour of rectangular concrete-filled steel tube beams under monotonic and cyclic loadings

Concrete filled steel tube (CFST) has been extensively explored for columns but limitedly explored for beams. This current study investigates the behaviour of rectangular CFST beams under monotonic and cyclic loadings. Experiments were conducted for 12 CFST beams with depth-to-thickness (D/t) ratios of 66.7–111.1, followed by theoretical analyses. The experimental results indicated that tensile yielding and compressive local buckling of steel tubes governed the plastic behaviour of the tested CFST beams. The buckling significantly degraded the strength of CFST beams. When the D/t ratio decreased from 111.1 to 66.7, the stiffness, yield load, and ultimate load increased by 33.2%, 49.4%, and 40.0%, respectively, but the ultimate deflection was reduced by ∼19.5%. The effect of cyclic loading induced a degradation of stiffness of 0.85–2.85%/cycle, depending on the increment of the peak cycle deflection. The buckling negatively affected the ultimate state, significantly reducing the ductility. Investigations into solutions to delay the buckling of steel tubes should be encouraged. Three approaches based on concepts of composite sections, fully plastic sections of steel tubes, and the proposed decoupling were applied to compute the ultimate strengths of the tested beams. The calculation results indicated that the model of fully plastic sections of steel tubes exhibited the best agreement with the test results. The fully plastic and proposed decoupling models provided reasonable results, while the composite model slightly overestimated the ultimate load of CFST beams. The results provide some technical information for structural engineers in designing rectangular CFST beams.

Resilience-based seismic design and cyclic behavior of assembled joints between self-compacting concrete-filled rectangular steel tube frame columns and H-shaped steel beams

The overall stability of prefabricated steel structures depends significantly on the strong seismic resilience exhibited by the connections between beams and columns. This paper introduces a novel beam–column connection approach, referred to as the welded upper and lower flanges and two diagonal web plates (WULF-TDWP). Unlike conventional methods, this approach replaces bolted connections with butt-welded joints between steel beams and employs short cantilever beams to achieve plastic hinge displacement. The steel-column cross-section was designed with a larger aspect ratio to better absorb and distribute energy. Six full-scale specimens were subjected to cyclic loading tests to investigate the seismic performance of the WULF-TDWP system. The main test parameters included the axial load ratio, welding configuration in the node region, and presence of reinforcement plates. The specimens exhibited two distinct failure modes: plate buckling deformation and beam–column end weld tearing. The experimental results included the hysteresis curves, skeleton curves, ductility coefficients, stiffness degradation curves, and strength degradation curves of the specimens. The experimental findings highlighted the favorable hysteresis performance, load-carrying capacity, and deformation capacity of all the nodes. Additionally, the plastic hinges were observed to shift, thereby delaying the premature failure of the node region. Notably, the omission of welding between the cantilever short beam flange and steel column significantly reduced the initial stiffness of the node. Through finite element analysis, the seismic performance of the beam-column joints with upper and lower flange welded connections and cantilever short beams was elucidated. The reliability of the finite element model for assessing the seismic performance of the nodes was confirmed through validation using experimental findings. Furthermore, this paper categorizes the nodes and introduces a simplified calculation model based on the moment–rotation method.

Axial compressive behavior of T-shaped welded multi-partition composite members

T-shaped welded multi-partition composite members, which are made of several rectangular concrete-filled steel tubes, are proposed to speed up the fabrication procedure. Seven half-scale T-shaped specimens were tested by considering the section height-to-width ratio and slenderness ratio. In the test, a slight torsion angle was measured when the instability failure along the asymmetric axis occurred, indicating the specimens had good torsion resistance. When the relative slenderness ratio of the specimen was larger than 0.44, the specimens failed due to the instability along the asymmetric axis. Parametric numerical analysis is conducted by considering the slenderness ratio, cross-section dimension, steel ratio, and material strength. The results show that the strength of concrete negatively impacts the ductility of the specimens, leading to a decrease of 43%, while the strength of the material positively influences the stability of the specimens. The formulas from different traditional codes are verified by the parametric numerical analysis results, indicating most codes can conservatively predict the sectional bearing capacity, but overestimate the stability coefficient of the specimens by neglecting the reduction effect of the excessive height-to-depth ratio. Recommendations are provided for calculating the stability coefficient under axial compression applicable to T-shaped welded multi-partition composite members.

Behavior of eccentrically loaded rectangular CFST components for shear walls using double horizontally-corrugated steel plates

The utilization of corrugated steel plates in concrete filled steel tube (CFST) structures has shown advantageous performance and considerable economy due to their high out-of-plane stiffness and local buckling resistance. A novel composite shear wall composed of multiple CFST components using double horizontally-corrugated steel plates and connected using pure corrugated steel plates with large wave heights was proposed. Fifteen CFST components with double horizontally-corrugated steel plates were designed and statically tested to evaluate the eccentric compression performance. Parameters including nominal eccentricity ratios, nominal sectional aspect ratios, steel plate thicknesses, and diameters of reinforced longitudinal reinforcements were considered. The bearing capacity, stiffness, and ductility of the CFST component with double horizontally-corrugated steel plates were investigated. In addition, the non-uniformities of confinement along with cross-sectional depth was studied through the analysis of measured strains and finite element simulations. Moreover, two capacity models of the eccentrically loaded components were proposed based on eccentricity reduction coefficient and stress balance of the cross-section, respectively. Both models effectively predicted the experimental and simulated results.

Experimental study and design method of embedded concrete-filled rectangular steel tube column base under cyclic load

Embedded column base has been widely used in concrete-filled steel tube (CFST) structures due to its high rigidity and good seismic performance. However, the strength analysis of the embedded CFST column base was not yet clear since there was little experimental research on it. In this paper, the experimental investigations of six embedded concrete-filled rectangular steel tube (CFRST) column bases under constant axial load and cyclic load were carried out to study the effects of embedded depth, improvement measures and axial compression ratios on the seismic performance of the column bases. The experimental results indicated that setting stiffeners, increasing the embedded depth or axial compression ratios could improve the seismic performance of the column base. In this experiment, the critical embedded depths of the columns with or without stiffeners were 0.7 and 1.5 times the column width B respectively. When the embedded depth was 0.7B, the contribution of anchor bolts to the moment resistance capacity of the column bases could reach up to 14.2%. Based on the analysis of the force transmission mechanism between the column and the concrete foundation in the embedded CFRST column base, a design method considering the contribution of different components to the moment resistance capacity of the CFRST column bases is proposed. The prediction results are in good agreement with the tested results and collected data, within ± 15% error. The parameter analysis based on the design method has revealed the influence patterns of various parameters on the moment resistance capacity of the column bases.

Flexural performance of rectangular CFST composite T-beams: Experimental, numerical, and theoretical investigation

Steel-concrete composite beams find extensive application in bridge construction, offering adaptability to complex terrains and structural advantages. Nevertheless, a persistent challenge lies in local instability, especially in steel beams with large aspect ratios. This study proposes stirrup-confined concrete-filled steel tube (CFST) composite beams as a solution to enhance structural performance by mitigating local instability. The research comprises comparative tests, numerical simulations, and theoretical examinations of rectangular CFST composite beams. Results demonstrate a significant improvement, with a 40% increase in flexural stiffness and a 10% increase in ultimate bearing capacity compared to traditional composite beams. Stirrup confinement effectively limits cross-section slip between the steel tube and infilled concrete, resulting in slip measurements of 0.72 mm at the end of loading. Examination of aspect ratios reveals substantial enhancements, showing a 65.6% increase in flexural stiffness and a 54.7% increase in ultimate bearing capacity as aspect ratios increase. Concrete strength grade exhibits minor effects, with slight improvements as the grade increases. Steel yield strength significantly influences ultimate bearing capacity, with a maximum 24.4% increase in higher-strength steel. Moreover, the steel content ratio enhances both flexural stiffness (up to 40.2%) and ultimate bearing capacity (up to 34.6%) with an increased steel ratio. Increased concrete slab thickness leads to improvements of up to 18.3% in flexural stiffness and up to 10.1% in ultimate bearing capacity. Formulas for predicting the flexural stiffness and bearing capacity of rectangular CFST composite T-beams are developed, offering practical guidance for optimizing their performance in structural engineering applications.

Stability of Steel Columns with Concrete-Filled Thin-Walled Rectangular Profiles

This paper provides a numerical and experimental analysis of global stability of axially compressed columns made of thin-walled rectangular concrete-filled steel tubes (CFSTs), with the consideration of initial geometric imperfections. The presented work introduces the theory of stability and strength of composite structural members subjected to axial compressive force. Moreover, a numerical calculation method for the determination of column resistance under axial load is presented, taking into account the influence of second-order effects that are considered in the European standard for the design of such members. This paper also presents the method of creating 3D models using the ABAQUS software, numerical analysis, and comparison of the obtained numerical results with experimental tests. In addition to the actual boundary and load conditions, the real properties of the used materials were also taken into account during the creation of 3D models. The actual properties of the used materials were obtained experimentally. Based on the obtained results and their comparison, several new findings and proven facts about the design and assessment of axially compressed columns made of thin-walled rectangular steel tubes filled with concrete are presented in the conclusions of the paper.

Reconsideration of shear strength expressions for CFSTs: Rectangular tubes

Concrete filled steel tubes (CFSTs) are typically circular or rectangular. Circular CFSTs are mostly used as vertical components of deep foundation systems; rectangular sections are more commonly used in building construction such as square CFSTs for columns. Prior work has focused on circular CFSTs with far fewer studies on square or rectangular sections. In addition to being more limited, prior research on square CFST sections has focused on flexural and axial response; there have been far fewerstudies on the shear response. As such, the accuracy of shear-strength equations is uncertain. A research study was undertaken to understand and improve design expressions for the shear design of rectangular CFSTs. First, the research team collectedexperimental data on shear resistance of rectangularCFSTs. Selected experimental data was used to develop and validate an advanced nonlinear finite element model (FEM) to predict the measured response and observed damage of rectangular CFSTs controlled by shear behavior. The validated model was then used to conduct parameter studies to investigate important design parameters of rectangular CFSTs responding primarily in shear including: 1) concrete and steel material properties, 2) cross-sectional aspect ratio, and 3) impact of enhanced bond capacity/composite action through the introduction of a single shear key at each end of the member. The results were used to better understand the importance of each parameter on the shear response and strength. A database was assembled, combining the experimental data with the strength predicted by each FEM, to evaluate existing design equations. The shortcomings of the existing equations included (1) only accounting for the steel or the concrete fill contribution, and (2) overestimating the total shear strength because the behavior of the CFST in shear is not well understood. This paper provides a new approach to assessing the shear strength as the individual contributions of the steel tube and the concrete fill are computed for each model to better understand their interaction. This also permits the development of a new design equation to remedy the shortcomings of existing codified models. In particular, the proposed model accurately estimates the individual contributions of steel tube and concrete fill to the shear resistance for salient design parameters.

Predicting compressive strength of RCFST columns under different loading scenarios using machine learning optimization

Accurate bearing capacity assessment under load conditions is essential for the design of concrete-filled steel tube (CFST) columns. This paper presents an optimization-based machine learning method to estimate the ultimate compressive strength of rectangular concrete-filled steel tube (RCFST) columns. A hybrid model, GS-SVR, was developed based on support vector machine regression (SVR) optimized by the grid search (GS) algorithm. The model was built based on a sample of 1003 axially loaded and 401 eccentrically loaded test data sets. The predictive performance of the proposed model is compared with two commonly used machine learning models and two design codes. The results obtained for the axial loading dataset with R2 of 0.983, MAE of 177.062, RMSE of 240.963, and MAPE of 12.209%, and for the eccentric loading dataset with R2 of 0.984, MAE of 93.234, RMSE of 124.924, and MAPE of 10.032% show that GS-SVR is the best model for predicting the compressive strength of RCFST columns under axial and eccentric loadings. It is an effective alternative method that can be used to assist and guide the design of RCFST columns to save time and cost of some laboratory experiments. Additionally, the impact of input parameters on the output was investigated.

Confinement mechanism of rectangular CFST components using double horizontally-corrugated steel plates

This paper presents experimental and analytical investigations on the confinement mechanism of a novel rectangular concrete-filled steel tube (CFST) component for use in composite shear walls. The CFST component consists of a steel tube made by welding double horizontally corrugated steel plates and double flat steel plates, and infilled with concrete. Tests of eight components and finite element analysis of twenty-three components under uniform compression were conducted to explore confinement mechanism of the novel tube to core concrete. The impacts of several factors such as steel plate thickness, nominal sectional aspect ratios, slenderness ratios, and the strength of the steel and concrete on the confinement mechanism were analyzed. The non-uniform confinement mechanism of horizontally corrugated steel plates was investigated based on their vertical and horizontal strain responses at the wave crests, middles, and troughs. The test results and numerical simulations demonstrate that the proposed CFST components exhibited desirable axial compressive behavior with ductile failure modes. The tested specimens with nominal sectional aspect ratios ranging from 1.2 to 2.39 had strength indexes greater than 1.17. Even with a width-thickness ratio of 325.33, the horizontally corrugated steel plates effectively confined the core concrete. Furthermore, this research proposed a design strength model that considered the confinement effects of corrugated plates. The model accurately predicted the experimental and numerical results.

High-strength rectangular concrete-filled steel tube long columns: Parametric studies and design

High-strength steel and concrete materials (i.e., steel with yield stress Fy > 525 MPa and concrete with compressive strength f'c > 70 MPa) have been applied in various types of structures because they can increase the resistance and space efficiency of the structure. However, the AISC Specification (AISC 360-16) does not permit the use of high-strength materials in concrete-filled steel tube (CFT) members due to a lack of adequate research. This paper aims at investigating the behavior of high-strength CFT long columns and evaluating the applicability of current design equations for high-strength rectangular CFT long columns. Firstly, an experimental database including 74 tests of high-strength rectangular CFT long columns was compiled and gaps in the database were identified. Then, finite element (FE) models were developed and benchmarked for parametric studies. The effects of width-to-thickness ratio of the steel tube, yield stress of steel, compressive strength of concrete, and length-to-depth ratio of the member were investigated. Finally, new design equations for high-strength rectangular CFT long columns were proposed based on the modified slenderness reduction factor in AISC 360-16.

Flexural behavior and reliability analysis of rectangular concrete-filled cold-formed steel tabular beams

Concrete-filled steel tube (CFST) has been widely investigated for columns, whereas it has been less explored for beams. This study investigates the behavior and reliability of CFST beams under bending, both experimentally and theoretically. Experiments were performed on nine rectangular CFST beams and three steel tube (ST) beams under bending. The experimental results showed that local buckling was the failure of both ST and CFST beams. The load−deflection behavior of CFST beams was significantly better than that of ST beams. Load-carrying capacity and stiffness of CFST beams was found to be approximately 3.0 and 1.29 times those of ST beams, respectively. The mechanical properties of steel were much more efficiently exploited in CFST beams than in ST beams. The mean ductility of 8.19 classified CFST beams to be highly ductile. The average plastic hinge length approximately equals the height of CFST beams. An available model was used to predict the moment capacity of CFST beams, and the results confirmed the accuracy of the model. Results of reliability analyses showed that mean moment capacity was independent on any individual variable or a combination of variables. In contrast, the standard deviations heavily depended on the considered variables. Consequently, the reliability index due to variable of steel thickness is the highest at 32.2, followed that due to the steel strength at 24.5, whereas those due to other variables varied from 8.0 to 9.3.

A prediction of axial capacity of rectangular concrete filled steel tube columns using neural network

A prediction of axial capacity of rectangular concrete filled steel tube columns using neural network