Circular Concrete-filled Steel Research Articles

Experimental behavior of circular concrete-filled steel tabular columns under near-fault cyclic loadings

This study investigated the behavior of concrete-filled steel tabular (CFST) columns under near-fault cyclic loading experimentally. Ten CFST columns were tested: one under monotonic loading, one under conventional cyclic loading, and other eight under near-fault cyclic loadings. The results indicated that slow local buckling occurred at plastic hinges after 4%-drift cycles, resulted in slow strength degradation and pinching. These became more pronounced as the cycle amplitude increased. Load-carrying and deformation capacities marginally decreased by the effect of cyclic loading. Secant stiffness sharply dropped by the pulses of 4%-drift amplitude. The earlier arrival of the pulses caused higher drops of secant stiffness. Near-fault pulses imposed a considerable large amount of energy to columns, which resulted in slow local buckling, slow strength degradation, but significant stiffness degradation. Shifting the pulse cycles to the cycle five of a conventional cyclic loading history was proposed for testing structural components under near-fault earthquakes.

Axial compressive behavior of circular concrete-filled steel tube stub columns with steel slag coarse aggregate

Steel slag, an industrial waste by-product, has been used as an alternative sustainable aggregate material in construction applications to attempt to manage solid waste. In this context, this work conducts axial compression tests on 5 groups of 10 circular steel slag concrete-filled steel tube (SSCFST) stub columns to study the feasibility of using steel slag coarse aggregate in concrete-filled steel tubes. The failure mode, load–strain curve, axial bearing capacity, initial axial stiffness, critical strain, and lateral deformation coefficient of the columns are analyzed. Further, the effects of the steel slag replacement ratio and cross-section dimension on the axial compressive properties of the specimens are quantified. These test results are employed to verify the reliability of a finite element model of the circular SSCFST stub columns established using Abaqus software. Then, a parametric analysis is performed to investigate the factors influencing the axial compressive performance of circular SSCFST stub columns. Moreover, the prediction accuracy of the existing design methods for the axial bearing capacity of circular SSCFST stub columns is evaluated. The results show that the replacement ratio of steel slag influences the axial compressive properties of concrete-filled steel tubes negligibly: the axial bearing capacity and initial axial stiffness of the columns decrease only by 1.4% and 2.4% respectively, at a steel slag replacement ratio of 100%. Increasing the cross-section diameter from 160 mm to 180 and 200 mm improves the axial bearing capacity of the columns by 25.6% and 54.6% respectively and reduces the critical strain by 12.4% and 21.7% respectively. The confinement factor is still critical to affecting the axial compressive performance of circular SSCFST stub columns. Finally, the formulas proposed in standards GB 50936–2014 and AIJ-2008 can be employed to calculate the axial bearing capacity of SSCFST stub columns.

Dispersion characteristics of surface wave in SCCS: theoretical analysis, numerical simulation and MASW-based NDT

To fully validate the feasibility of multichannel analysis of surface waves (MASW)-based interfacial debonding detection for steel–concrete composite structures (SCCS), dispersion characteristics of surface waves in SCCS are systematically investigated using theoretical analysis and elaborate 3D numerical simulations. First, the influences of material strength and thickness of concrete core, steel plate thickness on the dispersion figures are analyzed based on the theoretical dispersion characteristic of Rayleigh wave. Scientific layering strategy, including single steel plate, double-layer, and three-layer medium assumptions, is investigated using the theoretical dispersion analysis of Lamb wave. Besides, the dispersion characteristics of surface wave in circular steel pipes are calculated to determine the appropriate theoretical dispersion curves for MASW measurement. Finally, the stress wave propagation processes in SCCSs with various internal structures, including stiffeners, studs, and diaphragms, as well as the debonding width, are simulated using 3D numerical simulation to validate the research finding of theoretical analysis and detectability of MASW-based non-destructive testing on interfacial debonding defects in rectangular and circular concrete-filled steel tubulars. Finally, the dispersion characteristics corresponding to displacement, velocity, and acceleration of surface waves are comparatively discussed. The research findings of this study are the cornerstone of experimental study and essential theoretical support for identifying interfacial debonding and bond-slip damage of SCCS components utilizing MASW method.

Circular concrete-filled double skin steel tubes under concentric compression: Tests and FEA parametric study

Circular concrete-filled double skin steel tubes under concentric compression: Tests and FEA parametric study

Experimental Study on Ultrasonic Tomographic Method to Detect Compactness of Concrete filled Steel Tube

When the concrete filled steel tube member is poured, due to the large volume, the internal concrete is difficult to vibrate, easy to produce defects, not easy to observe, and the internal defects will have a non-negligible impact on its mechanical properties, therefore, it is particularly important to detect the internal defects of the concrete filled steel tube column. In this paper, the internal defects of CFST are studied based on the principle that acoustic wave propagates along the shortest acoustic path in CFST. For square concrete-filled steel tubular column, when the measurement method is adopted, the theoretical sound time calculation and sound velocity distribution map imaging are carried out for different measurement point densities. It is found that the defect identification effect is better when the number of measurement points is 5.For circular concrete-filled steel tubular column, when the measurement point spacing is determined to be 30° arc length, the measurement point arrangement method in the specification cannot be combined with CT imaging method, so the measurement point arrangement method of one-point emission and five-point receiving is proposed, and it is found that it has good identification effect on internal defects.

Seismic Performance of Concrete Column Connection with Square-Upper-Circular-Lower Steel Tube for Antique Buildings

The antique building combines traditional design with contemporary technology, making it an important structural style. Columns, as a crucial structural component, directly affect how well the building functions as a whole. This paper proposes a new connection form with the upper square concrete-filled steel tube-lower circular concrete-filled steel tube (USCFST-LCCFST). This study investigates the seismic performance of the proposed connection form of the columns. First, the finite element software ABAQUS-2021 is used to simulate and analyze the connection forms of the upper square concrete-filled steel tube and lower circular reinforced concrete (USCFST-LCRC) and the upper square steel reinforced concrete and lower circular reinforced concrete (USSRC-LCRC) above the antique building, respectively, which confirms the rationality of the modeling method explored in this paper. Then, geometric modeling of the USCFST-LCCFST connection is performed using ABAQUS. Simulation results demonstrate the superior seismic performance of the proposed connection form. In addition, the influence law of steel tube yield strength and the ratio of upper and lower column linear stiffness on its seismic performance are analyzed and determined through the variational parameter analysis of the USCFST-LCCFST connection form. The steel tube yield strength of USCFST-LCCFST column connection components is recommended to be 355–420 MPa and the ratio of upper and lower column linear stiffness should be no less than 0.063. In order to ensure the good seismic performance of the connection, the steel tube yield strength and the ratio of upper and lower column stiffness should be efficiently controlled in the design of antique buildings’ USCFST-LCCFST column connection components.

Simulation modeling and design of circular concrete-filled double-skin tubular slender beam-columns with outer stainless-steel tube

The stainless-steel tube has been used to construct Concrete-Filled Steel Tubular (CFST) columns because it has a high resistance to fire and corrosion, good durability, and aesthetic appearance compared to the carbon steel tube. However, there is very little published research on eccentrically loaded circular Concrete-Filled Double-skin Steel Tubular (CFDST) slender beam-columns composed of an outer stainless-steel tube and an inner carbon-steel tube. In line with this, this paper presents a fiber-based simulation model for predicting the structural performance of CFDST slender columns with external circular stainless-steel tube under eccentric compression. The simulation modeling of load-deflection curves and load-moment interaction diagrams for slender CFDST beam-columns is developed and verified by the experimental results. The verified simulation model is then used to study the effects of geometric and material properties on structural performance. The range analysis is applied to the orthogonal design to identify the relative significance of the factors that influence the structural response. The orthogonal design covers CFDST beam-columns with a hollow ratio ranging from 0.1 to 0.8. The results indicate that the column slenderness ratio is the most significant factor, followed by the loading eccentricity ratio, the outer tube thickness, stainless steel proof stress, concrete strength, and carbon steel yield strength. The accuracy of the design method specified in Australian standard AS/NZS 2327, and the proposed design methods are evaluated. The proposed equation provides accurate strength predictions of CFDST slender columns where the external skin is made of stainless steel.

Cyclic behavior and ultimate bearing capacity of circular concrete-filled double skin steel tube members subjected to combined compression and torsion

This paper presents a pseudo-static test investigation and finite element analysis on the behavior of circular concrete-filled double skin steel tube (CFDST) members under axial compression and torsion. The hollow ratio (χ) and axial compression ratio (n) are considered in the test study. The ductility, hysteretic behavior, failure modes, and compression–torsion correlation of circular CFDST members are discussed. The comparison results show that the validated finite element model is capable to capture the behavior of circular CFDST members under compression and torsion. The effect of loading paths and various parameters on the compression–torsion correlation of circular CFDST members are analyzed. Parametric analyses are carried out to investigate the effect of key parameters, such as material properties, nominal steel ratio, the wall thickness of inner steel tube, and hollow ratio on the compression–torsion correlation of circular CFDST members. It can be seen that the circular CFDST members under compression and torsion possess good load-bearing capacity, energy dissipation, and ductility properties. The loading paths, yield strength of inner and outer steel tubes, nominal steel ratio, and the wall thickness of inner steel tubes have little effect on the compression–torsion correlation of the composite members. When the axial compression ratio is less than 0.2, the axial compression load can slightly improve the torque capacity of circular CFDST members. Finally, the compression–torsion correlation equation of these members was proposed by regression analysis, and design formulas with good accuracy for predicting the torque capacity of circular CFDST members under compression and torsion were proposed.

Optimal design of circular concrete-filled steel tubular columns based on a combination of artificial neural network, balancing composite motion algorithm and a large experimental database

This article proposes a novel design methodology for circular concrete-filled steel tubular (CFST) columns, combining a large experimental database, an artificial neural network, and the balancing-composite-motion-optimization algorithm. First, the experimental database consisting of 1245 compression tests was compiled from the available literature, involving five input parameters: cross-sectional outer diameter, thickness of steel tube, length of column, yield strength of steel and cylindrical compressive strength of concrete, and one output variable: the measured axial capacity of columns. Second, the artificial neural network model was trained and validated using that database, in combination with various error measurement criteria: mean-squared-error, mean-absolute-error, and coefficient of determination. The optimization problem to find the optimal design of circular CFST columns was then formulated as a function of material cost and the geometrical parameters of the cross-section. Finally, balancing-composite-motion-optimization was employed to solve the aforementioned nonlinear optimization problem. The proposed model’s performance was compared with the widely used standards EC4, AISC, and DBJ, especially for scenarios exceeding the limitations of individual material strengths. Results showed that the proposed equation exhibited the best predictive performance. For practical application, we have derived an explicit prediction equation and implemented it in Excel, a user-friendly interface (the Excel file is appended to this paper). Thus, the proposed method in this study can assist existing codes in finding the optimal design of CFST columns, as the current standards have limitations as to the characteristic strength of the materials.

Axial compression behaviour of circular concrete-filled double-skin steel tubular columns with bolted shear studs: Numerical investigation and design

The concrete-filled double-skin steel tubular (CFDST) columns have recently attracted significant attention for practical engineering constructions. The axial resistance behaviour of CFSDTs can be greatly enhanced by installing bolted shear studs as pin supports for the outer. This is a companion paper that expands on the authors' work [1]. The previous paper concentrated on full-scale experimental testing to ascertain the influence of bolted shear studs on the axial resistance of CFSDT columns, while this study focused on finite element (FE) analysis and a simplified design approach for such composite structural members. A three-dimensional FE model for predicting the axial behaviour of circular CFDST columns without and with shear studs was developed and validated using the test results of the specimens' typical failure mechanisms and load-displacement responses. The model was then employed to perform structural analysis by comparing the axial load-displacement curve, internal force distribution, longitudinal stress distribution over the sandwiched concrete, and confinement mechanism of a circular column with bolted shear studs with that of its counterpart without bolted shear studs. Parametric studies were carried out to examine the effects of bolt longitudinal spacing, diameter, length, and yield strength. It was found that the spacing of the bolts-to-width (bs/Do) ratio had significant effects on the axial resistance and ductile performance of columns. Also, a bolt spacing corresponding to bs/Do<0.44 was suggested to attain an acceptable ductile performance in practical application. Verification of the design model revealed that it led to satisfactory predictions of the ultimate strengths of circular CFDST columns without and with shear studs.

Seismic performance of circular concrete-filled steel tube columns reinforced with inner latticed steel angles

The seismic behavior of circular concrete-filled steel tube (CFST) columns with inner latticed steel angles under combined axial load and reversed cyclic horizontal load was studied in this paper. A total of 8 specimens was tested, including two CFST specimens and six latticed steel angles reinforced CFST specimens. The main parameters studied were the diameter-to-thickness ratio of steel tube, the cross-sectional area of inner latticed steel angles and the axial compression ratio. Firstly, the load-displacement curves and load-strain curves were obtained experimentally; secondly, the failure modes, hysteretic behavior, skeleton curves, stiffness degradation, ductility index, hysteretic energy dissipation capacity were analyzed; thirdly, the seismic performance of the tested specimens were simulated by the established finite element (FE) models, and parametric studies were subsequently performed; finally, the modified calculation method for the horizontal bearing capacity was proposed. The research results showed that the failure of the composite columns was caused by the local buckling of the latticed steel angles and steel tube, and the latticed steel angles could effectively participate in the overall loading process. It was also found that latticed steel angles are able to improve the energy dissipation capacity.

Test on compressive performance of hollow concrete filled circular steel tube connected by thread through inner lining tube

A method of lengthening the steel tube of concrete-filled circular steel tube by inner lining tube and threaded connection is proposed. Taking the length, depth and position of the thread as the basic parameters, 12 hollow concrete-filled circular steel tube specimens connected by thread through inner lining tube are designed, and the axial compression test is carried out. The axial compressive loading-longitudinal compressive displacement curves, axial compressive loading -strain of steel tube curves and failure mode of the specimens are analyzed, and the effects of different parameters on the axial compressive bearing capacity and stiffness of the specimens are studied. The results show that the axial compressive loading-displacement curves of the specimen can be divided into linear elastic stage, elasto-plastic stage and descending stage. The bearing capacity and stiffness of the specimens connected by thread through inner lining tube are basically the same as those of the unconnected specimen or the specimen connected by weld. In the range of parameters studied of this paper, bearing capacity and stiffness of the specimens connected at end section by thread through inner lining tube are higher than those of the specimens connected at middle section by thread through inner lining tube, and the axial compressive bearing capacity and stiffness of the specimen increase with the increase of thread length and depth. Based on the comparison between the calculation results calculated by existing formulas of the axial compression bearing capacity of hollow concrete-filled circular steel tube and the test results of specimens connected by thread through inner lining tube, the calculation method of the bearing capacity of hollow concrete-filled circular steel tubes connected by thread through inner lining tube are suggested.

Mechanical properties of cross-shaped built-in lattice circular CFST short columns after fire

This paper describes four short built-in lattice circular concrete-filled steel tube (LCCFST) columns and four cross-shaped equal-strength reinforced concrete (ESRC) short columns. The initial stiffness, load-bearing capacity, ductility, and energy dissipation capacity of the specimens after different heating times (0 min, 60 min, 90 min, and 120 min) were analyzed. The results showed that both types of specimens exposed to fire after water spray cooling failed in the same way as the specimens unexposed to fire, i.e., by oblique shear failure. By extending the heating time, the load-bearing capacity of both specimens decreased constantly. The ductility and initial axial compression stiffness of the cross-shaped LCCFST short columns tended to initially increase and then decrease, while those of the cross-shaped ESRC short columns tended to decrease continuously. All specimens showed an increase in energy dissipation after exposure to fire, and the cross-shaped LCCFST short columns in particular performed better during the transition from the peak load to the failure load. Then, a strength reduction factor of concrete outside the steel tubes after water spray cooling was introduced and a load-bearing capacity formula of short cross-shaped lattice CFST columns was put forward.

Combining Artificial Neural Network and Seeker Optimization Algorithm for Predicting Compression Capacity of Concrete-Filled Steel Tube Columns

Accurate and reliable estimation of the axial compression capacity can assist engineers toward an efficient design of circular concrete-filled steel tube (CCFST) columns, which are gaining popularity in diverse structural applications. This study proposes a novel methodology based on computational intelligence for estimating the compression capacity of CCFST. Accordingly, a conventional artificial neural network (ANN) is hybridized with a metaheuristic algorithm called the seeker optimization algorithm (SOA). Utilizing information such as the column’s length, compressive strength of ultra-high-strength concrete, and the diameter, thickness, yield stress, and ultimate stress of the steel tube, the capacity of the column is predicted through non-linear calculations. In addition to the SOA, the future search algorithm (FSA) and social ski driver (SSD) are used as comparative benchmarks. The prediction results showed that the SOA-ANN can learn and predict the compression capacity pattern with high accuracy (relative error &lt; 2.5% and correlation &gt; 0.99). Also, this model outperformed both benchmark hybrids (i.e., FSA-ANN and SSD-ANN). Apart from accuracy, the configuration of the SOA-ANN is simpler owing to the smaller population recruited for the optimization task. An explicit formula for the proposed model is developed, which, owing to its observed efficiency, can be reliably applied to CCFST columns for the early estimation of the compression capacity.

Seismic behavior of steel-plate encased concrete shear wall with paralleled circular CFST columns: Laboratory test and numerical simulation

Aiming to improve the structural behavior of high-rise buildings, a steel-plate encased concrete shear wall with parallel circular concrete-filled steel tube columns (P-CFST-SCSW) is proposed and investigated by experiments and numerical studies in this study. All seven specimens were conducted and tested under reversed cyclic force to explore the influences of different design parameters, including axial compression ratios, steel tube thicknesses, spacing-thickness ratios, and shear span ratios. The failure modes, hysteresis behavior, strength and stiffness degradation, energy dissipation were thoroughly recorded and compared in detail. Results indicated that all specimens have experienced the failure process of boundary steel tubes buckling, steel plates buckling and concrete crushing. Results also showed that the bearing capacity and deformation capacity of proposed composite walls was excellent. The peak force and initial stiffness of P-CFST-SCSWs were improved by reducing the shear span ratio and increasing the axial compression ratio, while the stiffness degradation and ductility quickly deteriorated. The increased thickness of circular steel tubes considerably improves the seismic behavior of P-CFST-SCSWs. Finally, the numerical model was established to further investigate the effect of the concrete strength, steel yielding strength, and circular CFST columns number on lateral behavior of P-CFST-SCSWs.

Static strength of CFRP-strengthened preloaded circular concrete-filled steel tube stub column columns – Part II: Theoretical and numerical analysis

Carbon fiber reinforced polymer (CFRP) has high strength and is lightweight, and it can be used to strengthen circular concrete-filled steel tubes (CFSTs). For CFSTs in service, they are usually subjected to preloading. By considering the strain lag of CFRP, a theoretical model for analyzing CFRP-strengthened preloaded CFST stub columns is presented, and corresponding equations are derived for calculating the yield strength and the ultimate strength. Using the death and birth technique of CFRP element, finite element (FE) modeling is also presented to simulate the failure process of a CFRP-strengthened preloaded CFST stub column. The reliability and the accuracy of both theoretical equations and the FE model are evaluated by comparing the predicted results with experimental results reported in Part I. Finally, the CFRP-strengthening efficiency for the yield strength and the ultimate strength is assessed through the parametric study on 48 models. The effects of CFRP layers and preloading percentage on the strength of CFRP-strengthened preloaded CFST stub columns are also discussed.

Static strength of CFRP-strengthened preloaded circular concrete-filled steel tube stub columns, Part I: Experimental test

In the process of strengthening circular concrete-filled steel tube (CFST) stub columns in servicing period with carbon fiber reinforced polymer (CFRP), the CFST stub columns are generally preloaded. This study concerns the efficiency of CFRP in strengthening preloaded CFST stub columns. Thirteen specimens are designed and tested under axial compression, including two un-strengthened CFST specimens, four circular CFRP-strengthened concrete-filled steel tube (CFRP-CFST) specimens without preloading and seven preloaded CFRP-CFST specimens. The failure process, the failure mechanism, and the static strengths of the specimens, including yield strength and ultimate strength, are analyzed based on the experimental results. Improvement of the static strengths of the CFRP-strengthened specimens is discussed. The effect of preloading and CFRP layers on the static strength is investigated. The results show that preloading has certain effect on the yield strength. However, its effect on the ultimate strength is very little and it can be ignored. Increasing CFRP layers can improve the strengths of the preloaded CFST specimens effectively.

New Fuzzy-Heuristic Methodology for Analyzing Compression Load Capacity of Composite Columns

Predicting the mechanical strength of structural elements is a crucial task for the efficient design of buildings. Considering the shortcomings of experimental and empirical approaches, there is growing interest in using artificial intelligence techniques to develop data-driven tools for this purpose. In this research, empowered machine learning was employed to analyze the axial compression capacity (CC) of circular concrete-filled steel tube (CCFST) composite columns. Accordingly, the adaptive neuro-fuzzy inference system (ANFIS) was trained using four metaheuristic techniques, namely earthworm algorithm (EWA), particle swarm optimization (PSO), salp swarm algorithm (SSA), and teaching learning-based optimization (TLBO). The models were first applied to capture the relationship between the CC and column characteristics. Subsequently, they were requested to predict the CC for new column conditions. According to the results of both phases, all four models could achieve dependable accuracy. However, the PSO-ANFIS was tangibly more efficient than the other models in terms of computational time and accuracy and could attain more accurate predictions for extreme conditions. This model could predict the CC with a relative error below 2% and a correlation exceeding 99%. The PSO-ANFIS is therefore recommended as an effective tool for practical applications in analyzing the behavior of the CCFST columns.

Confinement-based direct design of circular concrete-filled double-skin normal and high strength steel short columns

By emphasising on the axial compressive resistance of circular concrete-filled double-skin carbon steel short (CFDST) columns, this paper proposes a direct design that takes into account the confinement effect of both outer and inner tubes. First, available test results of axially-loaded CFDST short columns were collected from the literature. Then, the results obtained from available resistance models, including design specifications, were compared with the test results. The comparisons revealed that most design models are conservative, some being too conservative, and all of them do not own the same accuracy along the entire slenderness range of the circular tubes, a fact attributed to the absence of confinement effect provided by the inner tube. Accordingly, the test resistances were used to obtain the lateral pressure (frp) due to the confinement effect provided not only by the outer tube (as in the previous studies) but rather by both outer and inner tubes of CFDST short columns with circular–circular and circular–square configurations. The calibrated formulae for frp were used to propose a design resistance formula for axially-loaded CFDST short columns. The results showed that these formulae provide much better resistances than the available predictors for any tube slenderness and for columns manufactured from different grades of steel and concrete materials.

Elastoplastic Analysis of Circular Steel Tube of CFT Stub Columns under Axial Compression.

Composite action between the components of the concrete-filled steel tube (CFT) is complex and it is difficult to accurately obtain the experimental relationship between the steel tube and the core concrete of CFT columns. The triaxially stressed core concrete has been studied by hydrostatic test in past research, while little research has been focused on the mechanical behavior of steel tube of CFT columns. It is difficult to obtain the experimental constitutive relationship of the steel tube of CFT columns to reflect the real-time influence of biaxial stress state and local buckling of steel plate on the steel tube. To clarify the mechanical behavior of the steel tube of CFT columns, this paper proposed an elastoplastic analytical method considering biaxial stress state and local buckling of steel tube to obtain the stress-strain curve of the steel tube. This method applied the Hook's law and the plasticity theory to interpret the information conveyed by the measured vertical and hoop strain histories of the steel tube. To verify its effectiveness, 11 circular concrete-filled steel tube stub columns were fabricated and tested under axial compression. Superposition results of the axial load-strain of steel tube and core concrete were compared against the experimental curves. The widely used Sakino-Sun model of the confined concrete was adopted to calculate the axial load-strain curve of the core concrete. Satisfactory agreements between the calculated and experimental results confirmed the rationality of the proposed method in tracing the constitutive relation of the biaxially stressed steel tube even after the occurrence of the local buckling. The obtained stress-strain relationship is critical for establishment of mathematical constitutive model and finite element model of steel tube.