Concrete-filled Steel Tubular Columns Research Articles

Experimental and numerical study on self-compacting alkali-activated slag concrete-filled steel tubes

This study presents a comprehensive experimental and numerical investigation of axially loaded self-compacting alkali-activated slag concrete-filled steel tubular (ACFST) stub columns. Integrating alkali-activated slag concrete (AASC) with concrete-filled steel tubes (CFST) can yield a novel construction composite material that offers advantageous outcomes for both AASC and steel tube. AASC, an environmentally friendly alternative to traditional concrete, offers improved sustainability, while CFST can provide enhanced structural capabilities. To investigate the performance of ACFST columns, nine different AASC mixtures were designed, each varying in binder content, water-to-binder ratio, Na2O %, and activation modulus. In this study, eighteen ACFST specimens were tested under axial compression, evenly divided into nine circular and nine square CFST sections. A numerical model is developed to evaluate the stress-strain behaviour of confined AASC filled in circular and square steel tubes. The proposed numerical model is first applied to analyse ACFST specimens tested in this study and then used to analyse ACFST specimens tested by another researcher to verify its accuracy. The results, including ultimate load capacity, axial load-displacement graphs, and failure modes obtained from the proposed numerical model, have shown strong agreement with the test results. This suggests that the proposed model can be effectively utilized to predict the axial compressive behaviour of both circular and square ACFST columns.

Compressive behavior of CFDST columns: Effects of thin-walled inner steel tubes

Concrete-filled double skin steel tubular columns with large hollow ratios (LHR-CFDST), as quintessential elements within offshore wind turbine structures, have received significant attention in contemporary times. As the scale of this type of structure continues to expand, an effective strategy to reduce steel consumption involves elevating the diameter-to-thickness (D/t) ratios of the steel tubes. Presently, there is a dearth of studies that explore the performance of LHR-CFDST columns in the case of thin-walled inner steel tubes. Four LHR-CFDST columns with varying D/t ratios of the inner tubes and one double-skin hollow steel tubular column were produced and tested under axial compression. The study encompassed an investigation into failure modes, local buckling behaviors, and ductility characteristics. The local buckling performance index of specimens with varying D/t ratios differed by up to 16.9%. Furthermore, the verified finite element model was subsequently employed for mechanistic analyses pertaining to the sandwiched concrete's stress distributions, and so on. When the peak loads were attained, the maximum variation in the stress values of the concrete of the specimens with different D/t ratios reached 50.4%. Subsequently, a multi-parameter impact analysis was applied to give a reasonable limit on the D/t ratio (225) of the inner steel tube for engineering design. Finally, the prevailing ultimate strength formulas outlined in established specifications were adapted by integrating the characteristics uncovered through this investigation.

Study on restraint coefficient of the stirrups-stiffened square concrete filled double-skin steel tube axial compression stub columns

This paper proposes a novel structural design for stirrups-stiffened square concrete-filled double-skin steel tubular stub columns (SCFDST) that offers high capacity and superior advantages in terms of low consumption of concrete and steel, as well as economic efficiency. The study includes an axial pressure test on two sets of 8 SCFDST columns with varying hollow ratios and stirrup ratios, with a specific focus on the influence of stirrups on mechanical properties. Experimental results demonstrate that stirrups significantly enhance the mechanical properties of SCFDST columns with large hollow ratios, including stiffness, bearing capacity, and ductility, with a more pronounced effect observed as the stirrup ratio increases. A three-dimensional solid finite element (FE) model of the SCFDST columns is developed and validated using ABAQUS software and appropriate constitutive models. Parameter analysis is then conducted based on the FE model, revealing that the stirrups not only restrain the concrete itself but also provide additional restraint by limiting the deformation of the steel tube. This improvement effect was more significant in the middle of steel tubes section. When stirrup ratio was 0.015, the steel tube had the highest constraint efficiency on the concrete. The study introduces a constraint enhancement factor to represent the enhanced restraining effect of stirrups on the steel tube, which is incorporated into a fresh equation for determining the maximum bearing capacity (Nu) of SCFDST columns. The derived formula offers clear physical meaning and high accuracy, building upon the existing formula for CFDST columns.

Seismic behavior of polypropylene fiber reinforced rubber concrete-filled circular steel tubular columns

In this study, the seismic behavior of polypropylene fiber reinforced rubber concrete-filled circular steel tubular columns subjected to low cyclic loading was investigated. The effects of varying rubber content, slenderness ratio, axial compression ratio, and steel content on specimen damage were analyzed. Digital Image Correlation (DIC) and Acoustic Emission (AE) instruments were utilized to monitor the full-field strain on the surface of the specimens and the generation and development of internal concrete cracks. A fiber modeling method was developed for calculating the compression bending bearing capacity of the columns. The results indicated a uniform failure pattern, primarily located at the column base. Adding rubber powder decreased the bearing capacity of the specimen, yet enhanced their energy dissipation capacity and ductility. Higher axial compression ratio led to early failure in the steel tube, with the slenderness ratio significantly affecting seismic performance. The calculation methods according to GB 50936–2014 (CECS 254–2012) and DL T5085–1999 showed higher accuracy than other codes, with average values of 0.558 and 0.576, and standard deviations of 0.067 and 0.089, respectively. The variation coefficient for the calculation method in GB 50936–2014(CECS 254–2012) was 12.02%, lower than that of DL T5085–1999. The proposed fiber modeling method demonstrated superior calculation accuracy, with an average value of 0.957, a standard deviation of 0.032, and a variation coefficient of 3.29%.

Test, simulation and design of square concrete-filled steel tubular stub columns fabricated with high-strength materials under biaxial eccentric loading

This work aims to determine the biaxial eccentric performance of high-strength concrete-filled steel tubular (HCFST) stub columns. Ten specimens were tested under combined axial load and biaxial moment to evaluate the failure process, with the parameters of eccentricity ratio and steel ratio varied in the tests. Numerical studies were carried out to explore the working mechanism of the column, and parametric investigations were implemented to confirm the key factors affecting the behavior of the biaxially loaded columns. Codes AISC 360 and GB 50936 were adopted to examine the load-bearing capacities of the column, and a new design model was further proposed, together with the reliability analysis. The results showed that the biaxially loaded HCFST stub column failure exhibits concave regional yielding and concrete crushing. The concave regional longitudinal stress enhances with the eccentricity ratio, while the transverse stress presents an opposite trend before the concave yielding. Furthermore, it is numerically identified that enhancing the steel contribution is beneficial to the high e/B' ratio case. Based on the ultimate load capacity predictions from AISC 360 and GB 50936, it is noted that both codes provide conservative estimations, while the proposed model exhibits a closer prediction with the test results and thus being recommended for design of biaxially loaded HCFST stub columns.

Experimental investigation on residual capacity of steel-reinforced concrete-filled thin-walled steel tubular columns subjected to combined loading and temperature

Steel-reinforced concrete-filled thin-walled steel tube (SRCFST) is gaining popularity in construction, primarily due to its superior structural performance. However, there is still a scarcity of studies investigating the residual capacity of SRCFST columns subjected to a full-range fire. A comprehensive research was conducted in this, involving both experimental testing and numerical simulation, to investigate the residual capacity of SRCFST columns. Six SRCFST columns were tested under combined loading and temperature to achieve the temperature distribution, failure modes, residual strength, and structural response within the cross-section. The developed finite element (FE) model was used to validate the test results. Three different paths, including after exposure to fire and without initial load, the full-range fire, and the actual path in the current test, were considered toevaluate the influence of different time-load-temperature paths on the mechanical properties of SRCFST columns. Results reveal that the region comprised of profiled steel and surrounded concrete forms a composite constrained region, with little loss of strength and stiffness occurring in the core region. The initial load level and heating time ratio were found to have a significant negative influence on the residual load-carrying capacity and ductility of SRCFST columns. In contrast, circular SRCFST columns are more resistant to the effects of fire than square SRCFST columns. Finally, the existing design methods were used and extended to evaluate the residual load-carrying capacity of SRCFST columns subjected to a complete temperature-load-time process.

CatBoost algorithms to predict the load-bearing capacity of centrally compressed short CFST columns of circular cross-section

The article investigates the use of regression models, GradientBoostingRegressor and RandomForestRegressor, to predict the load-bearing capacity of centrally compressed short concrete filled steel tubular columns. The work is based on experimental data covering a wide range of column geometric characteristics and material strength characteristics. An important part of the analysis was to deter-mine the influence of various parameters on the model predictions. The importance of features, assessment of the quality of models (MSE, MAE, MAPE) were considered , and visualization of actual and predicted values was carried out to compare the results. The results showed that both models success-fully cope with the task of predicting the load-bearing capacity of structures under given conditions. Analysis of the importance of features revealed the most significant parameters affecting the load-bearing capacity of columns. Visualization of forecasts and analysis of residuals confirmed the adequacy of the models. Additionally, a process of tuning model parameters using cross-validation was carried out to optimize their performance. The results of the study can be used in engineering applications such as the design of reinforced concrete structures to predict load-bearing capacity.

Axial compressive bearing capacity of high-strength concrete-filled Q690 square steel tubular stub column

Concrete-filled high-strength steel tubular (CFHSST) column is a kind of composite structure that uses high-strength steel instead of ordinary steel to strengthen the transverse restraint of concrete. In this work, in order to investigated the axial bearing capacity of CFHSST square column, a series of 22 CFHSST square stub columns were prepared by using two kinds of Q690 high-strength steel plates with different thickness of 3 mm and 6 mm with the strength of 741–749 MPa and 819–871 MPa, respectively. The static axial compression tests were carried out to understand the confinement effect of high-strength steel tube on concrete of different strength under static axial pressure and the influence of local buckling on the specimen. The axial compressive performances of CFHSST square stub columns are analyzed, including the failure mode, the relationship between load and deformation, and the stress-strain relationship. The test results show that the core concrete strength and area are major factors which have affected on bearing capacity of CFHSST square stub columns. Furthermore, width-to-thickness ratio exhibits significantly improving the failure mode and ductility of CFHSST square stub columns, while width-to-thickness ratio, the ratio of steel or the coefficient of hoop determine confinement effect. Q690 steel tube has good confinement effects, but the confinement effects on low strength concrete is small, especially for the specimen with relatively small width-to-thickness ratio. Finally, the calculation method of the ultimate bearing capacity of CFHSST square stub columns under axial compression is proposed, which can effectively evaluate the ultimate bearing capacity of CFHSST square stub columns.

Numerical investigation and design of UHPC-encased CFST stub columns under axial compression

Reinforced ultra-high-performance concrete (RUHPC)-encased concrete-filled steel tubular (CFST) columns in composite construction have exceptional fire and corrosion resistance, superior load-bearing capacity, and enhanced ductility compared to standalone RUHPC and CFST columns. However, research on their behavior is limited. This paper presents a 3D finite element (FE) simulation model for accurately predicting the behavior of axially loaded RUHPC-encased CFST short columns. The model accounts for the effects of the concrete confinement provided by the steel reinforcement and circular steel tube. The existing experimental data is used to validate the FE model. The validated model is then utilized to investigate the performance of RUHPC-encased CFST columns with various geometric and material properties. The range analysis technique is applied to an orthogonal design to assess the relative significance of the factors affecting the structural behavior. The findings reveal that RUHPC-encased CFST columns have high ultimate strength and ductility. The range analysis identifies the importance order of parameters as: the compressive strength of UHPC, the steel fiber concentration, tube diameter, stirrup spacing, tube thickness, and confined concrete’s compressive strength. Lastly, a simplified design model is developed to estimate the compressive capacity of RUHPC-encased CFST stub columns, providing accurate results that are verified by tests and numerical analysis.

A review on the performance of concrete filled tubular columns under axial compression: Emphasis on geometrical parameters and various concrete infills and encasings

SummaryThis paper summarizes the literature available on the behavior of concrete‐filled steel tubular (CFST) columns to evaluate the effect of geometrical properties such as shape of cross‐section, diameter‐to‐thickness ratio, and length‐to‐diameter ratio of CFST columns under axial loading. Then, the impact of different material composition for core concrete and encasing material is concluded for columns under axial loading. The performance of CFST is evaluated in terms of failure modes, ductility, stiffness, and axial compressive strength. For encasing tube, carbon steel, stainless steel, and aluminum are studied while for core, various concretes such as Normal (NSC) and high strength concrete (HSC), light weight concrete (LWC), recycled aggregate concrete (RAC), expansive concrete (EC), rubber crumb concrete(RuCC), and steel slag concrete (SSC) are covered for review in this paper. Material limitations as provided by various codes for design of composite structures is also mentioned for both tube and core concrete. Failure modes of concrete‐filled tubular(CFT) columns are most affected by geometric properties columns while materials used for concrete and encasing tube do not cause much difference. Though, ductility, axial compressive strength, and stiffness are affected by both geometric and material properties.

Performance of eccentrically loaded ultra-high-strength concrete-filled Q770 steel tubular columns with varying slenderness ratios: Experimental and numerical investigations

This study conducts experimental and numerical investigations into the response of ultra-high-strength (UHS) concrete-filled ultra-high-strength steel tubular (UHSCFST) columns under eccentric loading, varying the slenderness ratio, to develop effective design guidelines for engineering applications. A series of eccentric compression tests were conducted on twelve UHSCFST columns with varying slenderness ratios to identify failure mechanisms and load-bearing characteristics. In the experimental program, critical influencing factors, including load eccentricity ratio, slenderness ratio, and UHS steel strength, were considered. Finite element models of eccentrically loaded UHSCFST columns were developed using ABAQUS and validated through a comparison of tested and simulated results to analyze load-sharing ratios and stress distribution for each column component. The findings indicated that UHSCFST column failure modes were characterized by compression-controlled and flexure-dominated damage under the combined effects of slenderness ratio and load eccentricity ratio. UHS concrete played a dominant role in bearing the eccentric load, and a judicious selection of UHS steel yield strength can improve column capacity and resistance. Additionally, these validated models were employed to conduct parametric studies that evaluated the effects of design and load parameters on the eccentric load capacity of UHSCFST columns. Design equations were developed based on tested and simulated results to predict the ultimate load capacity of UHSCFST column with varying slenderness ratios under eccentric loading conditions.

Axial compression performance of high-temperature-exposed concrete-filled steel tubular columns repaired with carbon fiber reinforced polymer

Axial compression tests were conducted on high-temperature-exposed round concrete-filled steel tube (CFST) short columns repaired with carbon fiber reinforced polymer (CFRP) to test the influence of temperature, CFRP-wrapped layers and concrete strength on compressive performance. The experimental data were plotted as load–displacement and load–hoop strain curves, and the variation laws of the curves were analyzed. The load–displacement curves contain elastic, elastoplastic, and plastic strengthening phases. A finite element model of a high-temperature-exposed CFST column repaired with CFRP was established to analyze the stress changes in the CFRP, steel tube, and concrete. CFRP improves the bearing capacity, stiffness and ductility of CFST columns that were damaged by high temperatures. As the number of CFRP layers increased, the bearing capacity of the repaired columns improved, and deformation was delayed. Taking into account the damage of temperature and the restraint effect of CFRP, an equation was developed to evaluate the axial compression bearing capacity of high-temperature-exposed CFST columns repaired with CFRP.

Numerical analysis of circular steel–reinforced concrete-filled steel tubular stub columns

This paper presents a computational model for determining the axial responses of short circular steel–reinforced concrete-filled steel tubular (SRCFST) columns. A novel confinement model is formulated for the concrete core, which is effectively confined by the external circular steel tube and the embedded steel section. The modelling scheme of the confinement is programmed using a mathematical model that utilises fibre-element discretisation of column cross-sections. The numerical predictions are verified by experimental measurements and results obtained from finite-element analysis, demonstrating the accuracy of the modelling technology. In addition, existing concrete confinement models for concrete in circular concrete-filled steel tubular columns are assessed. The new confinement model is shown to be superior in replicating the responses of SRCFST columns. The influences of the design parameters on the column's performance are numerically investigated and ranked in order of importance through a sensitivity analysis. In this study, not only is the validity of current design standards in determining the axial load capacity of SRCFST columns examined but a new design formula is also proposed. The proposed confinement model can be employed in numerical procedures for the inelastic simulation of SRCFST columns; the design formula is suitable for use in practical design.

Erratum to: Experimental Behavior of Recycled Aggregate Concrete Filled Steel Tubular Columns

Erratum to: Experimental Behavior of Recycled Aggregate Concrete Filled Steel Tubular Columns

Predicting axial compression capacity of CFDST columns and design optimization using advanced machine learning techniques

Concrete-filled double-skin steel tubular (CFDST) columns are fundamental in civil engineering, known for their exceptional mechanical properties. Their load-bearing capacity, influenced by factors such as geometry, material properties, and loading conditions, is a critical aspect of CFDST column design. This study introduces an innovative approach that leverages the synergy between gradient-boosting regression (GBR) and three metaheuristic optimization algorithms: sine-cosine-based swarm optimization (SCSO), grey wolf optimization combined with whale optimization (GWO_WOA), and artificial rabbits optimization (ARO). Its primary aim is to accurately predict the axial compression capacity (ACC) of CFDST columns for optimal design. Using a comprehensive database of 153 empirical results from CFDST columns subjected to axial loads, the proposed model is rigorously compared with eight alternative machine learning models, three established design standards, and two empirical equations to validate its robustness. The results highlight the superiority of the finely tuned GBR model, optimized with the ARO algorithm, over peer models and conventional benchmarks. This framework also serves as the foundation for optimizing the CFDST column design by identifying the optimal dimensions that maximize ACC while meeting the design constraints. Clearly, this model can significantly improve CFDST column design, thereby benefiting structural engineers and designers striving to enhance the safety and efficiency of CFDST structures.

Seismic Behavior of T-Shaped Concrete-Filled Steel Tubular Column to Steel Beam Joints with Side Plates

This study investigates the seismic behavior of the T-shaped concrete-filled steel tubular (CFST) column to steel beam joints, aimed at expanding their applicability in areas with high-seismic fortification intensity. A construction form of T-shaped CFST column to steel beam joint with side plates is presented. The variables studied in these experiments include the side plate length, the axial compression ratio, the presence of side plates, and the presence of binding bars. The force mechanism, failure modes, load–displacement curves, strength, stiffness, ductility, and energy dissipation capacity of seven specimens were evaluated under low-cycle reciprocating load. The experimental results demonstrate that the joints of side plates show a full hysteresis curve, with the ductility coefficient ranging from 1.67 to 2.49, and the equivalent viscous damping coefficient between 0.147 and 0.234. The joint panel zone displays strong deformation and energy dissipation capacity. The inclusion of side plates and binding bars improves the seismic behavior of the joint. The setting of side plates enables the formation of a plastic hinge on the steel beam, creating a beam hinge failure mechanism and satisfying the seismic design principle of “strong column and weak beam, strong joint and weak member” as required by the building structures.

Performance of round-ended CFST columns under combined actions of eccentric compression and impact loads

Round-ended concrete-filled steel tubular (RECFST) columns are gaining increasing usage in bridge structures. During their service life, RECFST columns under eccentric compression may suffer from impact loading. This study conducted test and numerical investigations to assess the performance of RECFST columns under the coupled actions of compression, bending and lateral impact loads. Fourteen columns were fabricated and tested, considering the influences of axial-load ratio, bending moment and impact energy. The damage mode and the time histories of impact force and displacement were accessed and analyzed. The experimental findings revealed that the initial bending moment negatively affected the impact resistance of RECFSTs. In addition, finite element model was established in ABAQUS and calibrated against the test results. The calibrated model was then employed to conduct the failure mechanism analysis and parametric study. Finally, a single-degree-of-freedom (SDOF) analysis was conducted to predict the mid-height deflection of RECFST columns under combined action of compression, bending and lateral impact loads, by incorporating the influences of pre-axial load and initial bending moment.

Behaviour of ultra-high strength concrete-filled dual-stiffened steel tubular slender columns

This paper is concerned with the behaviour of square concrete-filled dual-stiffened steel tubular (CFDSST) slender columns with a concentrically-placed inner circular steel tube. Previous studies have illustrated that these columns have greater structural performance in terms of load-carrying capacity compared with conventional concrete-filled stiffened steel tubular (CFSST) columns. However, the behaviour of CFDSST slender columns filled with ultra-high strength concrete (UHSC) has not been investigated and current design codes do not include provisions for UHSC, although it is increasingly popular owing to demands for structures to be lighter and more sustainable. Accordingly, the current paper fills that gap in existing knowledge and explores the behaviour of CFDSST slender columns using finite element (FE) analysis. The available test results from previous studies were collated and are employed to validate the numerical model. The validated FE model is then employed to investigate the axial load versus deflection responses for a wide variety of UHS-CFDSST slender columns. The behaviour of both intermediate-length and long columns is assessed through parametric analyses. The results of these studies show that the strength of the concrete sandwiched between the two steel sections, the yield strength of outer steel tube, and the outer tube slenderness ratio have a significant effect on the axial resistance of UHS-CFDSST intermediate-length columns, while the capacity of long columns is most affected by the sandwiched concrete strength. The ultimate resistances are compared with different available design methods, and AISC 360–16 code is recommended for predicting the ultimate resistance of UHS-CFDSST slender columns with modifications proposed to account for the different components forming this innovative cross-section.

Data-driven prediction and optimization of axial compressive strength for FRP-reinforced CFST columns using synthetic data augmentation

Fiber-reinforced polymer (FRP) sheets can be used as additional confinement to improve the load-bearing capacity and durability of concrete-filled steel tubular (CFST) columns. This study presents a data-driven approach aimed at accurately predicting the strength and optimizing the design of FRP-CFST columns under axial compressive loading. To overcome the limited database size (only 287 samples), a synthetic data augmentation technique was developed with recourse to the tabular generative adversarial networks (TGAN). Four machine learning (ML) models were rigorously trained using two distinct schemes “Trained with synthetic - Tested with real” (TSTR) and “Trained with real - Tested with real” (TRTR) to seek out the best strength prediction model. Then the winner model was integrated with the metaheuristic optimization algorithm—nondominated sorting genetic algorithm II (NSGA-II), to optimize both the axial strength and material cost of FRP-CFST columns. This fusion enabled a dual-objective optimization via generating the Pareto front, providing designers with a spectrum of optimal design solutions. It turned out that the categorical gradient boosting model trained with the TSTR mode (CATB-Syn) showed superior performance than the other ML models. Its accuracy also surpassed that of existing design equations. The combination of CATB-Syn with NSGA-II provided a reliable Pareto front, and the interpretability of CATB-Syn was also verified. Thus, the proposed framework opens a new avenue for the efficient design of such double-jacketed columns.

Investigation of cyclic behavior of partially concrete-filled steel tubular columns

A partially concrete-filled steel tubular (CFST) member is formed by partially filling concrete into a steel hollow section (SHS). Partially CFST members are mainly used as bridge piers and frame columns due to the improved structural performance, since the potential plastic hinge is expected to occur at the composite section when subjected to an earthquake. In practice, the shear transfer between the upper SHS and the lower CFST part of a partially CFST column needs careful consideration, sometimes leading to complex details. In this study, two types of shear connectors, namely bolted shear connectors and diagonal-rib shear connectors were proposed and arranged below the concrete-filling interface. Five square partially CFST specimens and a reference steel tubular column were designed and tested under combined constant axial compression and cyclic lateral loading. The test variables included the concrete-filling ratio, types of shear connectors, and strength of shear connectors. The results demonstrated the effectiveness of the two types of shear connectors, and the specimens with diagonal-rib shear connectors showed excellent performance. The method and corresponding formulas about the full shear connection were proposed to calculate the resistance of square partially CFST columns under combined compression and flexure.