Tube Columns Research Articles

Axial load-carrying capacity of concrete-filled steel tube columns: a comparative analysis of various modeling techniques

Limited research is available in the literature to investigate the presentation of normal strength concrete-filled steel tube (CFST) circular compression elements under compression loading by considering various material and geometric coefficients. Thus, the present study investigates the mechanical behavior of CFST compression elements employing nonlinear finite element analysis (NLFEA), empirical/theoretical modeling, and a newly developed Artificial Neural Network (ANN) model, based on a large experimental database of 1223 samples. The NLFEA modeling is performed in ABAQUS (6.14) with an improved concrete damaged plasticity model for laterally restrained concrete. Various geometric and material properties are considered, for parametric NLFEA estimates preliminary validated toward the available experimental database. A new ANN model for the load-carrying capacity of CFST circular elements was also offered by employing the experimental database. The comparison between the calculations of the NLFEA model, empirical model, and ANN model displayed a close agreement with the database results.

Behavior of partial-length stiffened and full-length stiffened CFDST columns under axial load

Purpose Concrete-filled double skin tube (CFDST) columns are considered one of the most effective steel-concrete composite sections owing to the higher load carrying capacity as compared to its counterpart concrete-filled tube (CFT) columns. This paper aims to numerically investigate the performance of axially loaded, circular CFDST short columns, with the innovative strengthening technique of providing stiffeners in outer tubes. Circular steel hollow sections have been adopted for inner as well as outer tubes, while varying the length of rectangular steel stiffeners, fixed inside the outer tubes only, to check the effect of stiffeners in partially and full-length stiffened CFDST columns. Design/methodology/approach The behaviour of these CFDST columns is investigated numerically by using a verified finite element analysis (FEA) model from the ABAQUS. The behaviour of 20-unstiffened, 80-partially stiffened and 20-full-length stiffened CFDST columns is studied, while varying the strength of steel (fyo = 250–750 MPa) and concrete (30–90 MPa). Findings The FEA results are verified by comparing them with the previous test results. FEA study has exhibited that, there is a 7%–25% and 39%–49% increase in peak-loads in partially stiffened and full-length stiffened CFDST columns, respectively, compared to unstiffened CFDST columns. Originality/value Enhanced strength has been observed in partially stiffened and full-length stiffened CFDST columns as compared to unstiffened CFDST columns. Also, a significant effect of strength of concrete has not been observed as compared to the strength of steel.

Mechanical properties of CFSST with steel reinforcement cage under biaxial eccentric compression

To study the biaxial eccentric compression mechanical properties of high-strength concrete-filled square steel tube (CFSST) columns (high-strength materials are used for both steel tube and concrete) with steel reinforcement cage, twelve high-strength CFSST columns with the same cross-sectional dimensions were designed and fabricated with the form of the steel reinforcement cage, eccentricity, and the steel tube width-to-thickness ratio as the main parameters. The constraint enhancement mechanism of the concrete by the steel reinforcement cage and the effect of different parameters on the biaxial eccentric ultimate bearing capacity of column specimens was further analyzed by combining with ABAQUS simulation. The results show that the bearing capacity of the specimens decreases sharply with the increase of eccentricity and steel tube width-to-thickness ratio; the steel reinforcement cage can improve the bearing capacity and ductility of the specimen but has little effect on the stiffness; the arrangement of double orthogonal horizontal steel reinforcement can enhance the constraint effect of the steel tube in the middle of the cross-section edge length on the concrete of the specimens within a certain height range and weaken the constraint effect of the corner within the same height range; the enhancement effect of the steel reinforcement cage on the biaxial eccentric ultimate bearing capacity of the column specimens gradually decreases with the increase of eccentricity; when the eccentricity is constant, the effect of the steel reinforcement cage on the improvement of the biaxial eccentric ultimate bearing capacity of the column specimens with different width-to-thickness ratios is basically the same.

Confinement effectiveness of bamboo scrimber-filled steel tube columns under axial compression

Bamboo scrimber-filled steel tube (BSFST) columns, consisting of external steel tubes and inner bamboo scrimber, are expected to improve the strength and deformation ability of bamboo scrimber while maintaining excellent performance characteristics, such as light weight, high strength and environmental friendliness. Thirty bamboo scrimber columns and thirty BSFST columns were tested under axial compression to investigate the confinement effectiveness of BSFST columns. During the test, only the core bamboo scrimber bears the axial compression, and the main parameters to be considered are specimen size and steel tube thickness. The results show that the stress‒strain relation curve of the BSFSTs can be divided into an elastic stage and an elastic‒plastic stage, and the BSFSTs showed obvious stress hardening behavior in the elastoplastic stage. With increasing steel tube thickness, the bearing capacity, ultimate stress and ultimate strain of the specimens increase greatly. Finally, the calculation equations for the ultimate stress and ultimate strain of BSFST and the complete stress‒strain curve models of BSFST were proposed. The proposed model can accurately predict the complete stress‒strain behavior for BSFST columns.

Seismic Performance of an Exterior Joint between a Square Steel Tube Column and an H-Shape Steel Beam

This study developed a 1:2 scale model using T-shape steel with one-side bolts to connect a square steel tube column to an H-shape steel beam for a quasi-static test to investigate the mechanical properties and seismic behavior of semi-rigid joints. Within the study context, the joint’s failure characteristics, hysteresis characteristics, and strain tendency under cyclic load were determined. In addition, this research analyzed the force characteristics and seismic performance of such joints based on the test outcomes. In order to further study the seismic performance of such joints, ABAQUS finite element software was used to establish a numerical model and perform parametric analysis. The findings indicated that the force on both sides of the joint is inconsistent, resulting in different seismic performances on both sides of the joint. Selecting a T-shape steel connector significantly affects the seismic capacity of beam–column joints. The seismic capacity of joints can be improved by increasing the size of the T-shape steel. The stability of one-side bolts under repeated load is good, and their strain value rises steadily. Hence, this type of one-side bolt is suitable for connecting closed steel tube columns and other components. In general, the seismic performance of square steel tube column–H-shape steel beam joints with one-side bolts and a T-shape steel connection is good and is recommended for practical engineering.

Analytical Model for Steel Fibre-Reinforced Concrete-Filled Tubular Columns Exposed to Fire

This study proposes an analytical model for the evaluation of the mechanical behaviour of circular hollow section columns infilled with steel fibre-reinforced concrete when exposed to elevated temperatures in a fire situation. This work includes the discussion of the results from a sensitivity analysis conducted through numerical simulation and the development of an analytical model based on the prEN1994-1-2:2021 European standard for the design of reinforced concrete structures exposed to fire. The sensitivity analysis aims to compare the fire resistance of centrally and eccentrically loaded circular hollow section columns infilled with plain and steel fibre-reinforced concrete. The proposed analytical model for determining the design buckling load of composite steel fibre-reinforced concrete-filled tube columns in a ?re situation is ready to serve as an annexe or supplementary technical document to the EN1994-1-2:202x standard.

Behavior of Concrete-Filled U-Shaped Steel Beam to CFSST Column Connections

Two new types of connection between concrete-filled U-shaped steel (CFUS) beams and concrete-filled square steel tube (CFSST) columns were presented in this study, including rebar-sleeve with internal diaphragm connection and rebar-through with internal diaphragm connection. Based on the experiments of the rebar-plate with internal diaphragm connections between CFUS beams and CFSST columns under cyclic loading, the nonlinear finite element models of the tested specimens were developed and validated by comparing them with the experimental results. The numerical results were in agreement with the experimental results in terms of failure modes, stress distribution, and load-displacement skeleton curves. Based on the FEA results, the mechanical behavior of the two new types of connection were comprehensively discussed and compared. Furthermore, this parametric study was conducted for the rebar-sleeve with internal diaphragm connection to investigate the effect of specific parameters on the capacity of the connection. The parameters included: The thickness of U-shaped steel, the ratio of longitudinal reinforcement in the concrete slab, the strength of concrete in the beam, the strength of the U-shaped steel, and the thickness of the internal diaphragm. The results indicate that the thickness of the U-shaped steel (tb), the ratio of the longitudinal reinforcement in concrete slab (ρ), and the strength of the U-shaped steel have significant effects on the loading capacity of the connection—the loading capacity increases by about 20% when tb increases from 6 mm to 8 mm, increases by about 45% when ρ increases from 1.5% to 4.8% under negative P, and increases by about 20% when the steel yield strength (fy) increases from 235 Mpa to 420 Mpa.

Comparative Nonlinear Analysis of Composite Frames with Concrete Filled Steel Tube Columns Having Different Properties

In this study, the nonlinear analysis and seismic appraisal of composite frames having concrete filled steel tube columns (CFSTs) were investigated. The case study composite frames were made of the square columns surrounded by steel tube outside and infilled with concrete, and also steel I beams. These frames were taken as 4, 6 and 8 stories with three equal bays. Then, the nonlinear pushover analysis was applied to examine the influence of variation in the width-thickness ratio, slenderness ratio, yield strength of the steel tube and compressive strength of the concrete within the columns of each frame. Thus, a total of seventy-two different composite frame models with CFST columns and steel beams were examined in accordance with the response parameter of the base shear-top displacement. The obtained results were discussed comparatively as per the lateral capacity and initial stiffness. It was observed that the material and dimensional properties of the CFST columns influenced significantly the seismic behavior of the composite frames.

Unified compressive strength model for axially loaded circular composite short columns

Composite columns are widely used in modern structures owing primarily to their excellent structural performance, but they usually have very different ultimate axial compressive strength prediction models, which may lead to confusion for researchers and engineering designers. In addition, given the similarity of their mechanical mechanisms, there may be a generic prediction model for these columns. Hence, the authors aim to provide a simple and effective unified ultimate compression prediction model for axially loaded circular composite short columns. A rich experimental database is firstly established. Then the force analysis of a typical concrete-filled double-skin steel tubes (CFDST) column is illustrated, and it can be easily extended to other types of composite columns. Based on the above force analysis, the stress state of each component of the column can be determined via different sections and loading concepts. Contributions of the inner steel tube to the load-bearing capacity are further clarified, and the passively confined compressive strength of the concrete core is also investigated on the basis of the proposed equivalent confining stress. Subsequently, the calculation flow of the ultimate compression strength is briefly demonstrated. Finally, the ultimate compression prediction model is evaluated by the established test database, and good consistency can be observed for circular composite short columns with a widely varied parameter.

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.

Circular concrete columns confined with GFRP tubes under repeated and sequential impact loads

The experimental work conducted in this study aims to develop more understanding of the dynamic response of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) columns under lateral impact load by testing 16 specimens. Three different types including reinforced concrete (RC), unreinforced CFFT and steel reinforced CFFT columns were tested. The specimens were tested under both repeated and sequential impact load testing protocols. Four parameters were investigated: the cross-section size, the thickness of the FRP tube, and the presence of longitudinal reinforcement. In addition, the effect of adding polypropylene fibers (PPF) to the concrete was also studied. Based on the experimental results, the damage mechanism, impact loads, deflections and strains were monitored and discussed. The results of this investigation confirmed that steel reinforced CFFT columns exhibited superior damage control characteristics when compared to RC columns. Increasing the thickness of the FRP tube decreased the displacement by up to 18 % and the residual displacement by up to 15 %. Adding PPF delayed the failure of the specimen and slightly enhanced its response. The experimental findings showed that longitudinal internal steel reinforcement played an important role in columns’ overall behavior and increased impact capacity.

Evaluation of Confining Pressure Models for Circular Concrete-Filled Steel Tube Short Columns under Concentric Loading

It is well known that the confinement effect provided by the steel tube significantly increases the strength and ductility of circular Concrete Filled Steel Tube (CFST) columns under concentric loading. The lateral pressure is an important factor to calculate the strength enhancement of CFST columns. To reliably predict the ultimate strength of circular CFST columns, many models have been developed for predicting the lateral pressure due to the confinement effect. This paper aims to evaluate some of these confining pressure models. The values of the compressive strength of confined concrete and lateral confining pressure of circular CFST short columns were calculated using these existing models and were compared with those obtained from previous test results. In addition, a comparison between the ultimate loads predicted by these models and by Eurocode 4 (EC4) was carried out. Based on the comparison results, some suitable models for circular CFST short columns with the use of normal-strength, high-strength, and ultra-high-strength concrete were indicated.

Development of design equations for ultra-high strength steel CHS columns under transient fire conditions considering thermal creep and axial restraint effects

Despite their potential for widespread structural applications, the use of ultra-high strength steel (UHSS) members in buildings is currently hindered by the lack of suitable design relationships for these components. In response to this technical gap, this paper presents design equations for Grade 1200 UHSS circular hollow section (CHS) columns under transient fire conditions. The design relationships are derived from an extensive parametric study on the in-fire behavior of UHSS tube columns using advanced finite element (FE) simulations in ABAQUS software. However, to verify the FE modeling framework, experiments are also conducted on axially-compressed UHSS tube specimens. The thermal creep of the UHSS tubes is explicitly included as a user-defined subroutine in the modeling by a robust creep model exclusively developed for the UHSS material under transient fire conditions. In addition to the utilization factor, the effects of non-dimensional slenderness, heating rate (or thermal creep), and axial restraint stiffness ratio are also studied and considered in the design equations obtained for the UHSS CHS columns. Finally, it is shown that the present design relationships can predict the columns' buckling and failure temperatures with a maximum absolute error (MAE) of 4%.

Experimental Investigation on Post-fire Response of Concrete-Filled Steel Tube Column Subjected to Elevated Temperature

Experimental Investigation on Post-fire Response of Concrete-Filled Steel Tube Column Subjected to Elevated Temperature

Behaviour and Design of Innovative Connections of Prefabricated CFST Columns under Tension

This paper investigates the tensile behaviour of prefabricated concrete-filled steel tube (PCFST) columns with bolted connections. Innovative bolted column-column (BCC) connections are developed using standard structural bolts to simplify the construction process for the connection of two PCFST columns, especially for the corner, edge, and interior columns. The behaviour of BCC connections in PCFST columns under tension has been investigated, adopting the finite element (FE) modelling approach. Parametric studies are carried out to understand the influence of bolt arrangements (TB = 4, 6, 7, 8), base plate thickness (tbp = 8, 10, 14, and 18 mm), bolt diameters (db = 16, 18, 20, 24 mm), vertical stiffeners (ths = 4, 6, 8, 10 mm), horizontal stiffeners (ths = 10, 12, 13, 15 mm), and yield strength of steel tube (fy,t = 380, 450, and 550 MPa) on the behaviour of PCFST columns with developed BCC connections. The results show that the PCFST columns with the developed BCC connections can attain sufficient tensile strength and satisfy the tensile strength requirements recommended in AS5100 and the robustness requirements in AS1170. The outcome of this paper will be useful to practising structural engineers to design prefabricated CFST columns with BCC connections under tension.

Study of the Axial Compressive Behaviour of Cross-Shaped CFST and ST Columns with Inner Changes

In this study, novel cross-shaped concrete-filled steel tube (CFST) and steel tube (ST) columns were developed. CFST columns have a high load-carrying capacity and excellent performance under seismic conditions, and the construction process is fast. In order to investigate the axial load bearings and failure mechanisms, six specimens of CFST and ST columns were tested under the axial load. Three different forms of CFST were employed in this study; one was an ordinary cross-shaped CFST (OC-CFST), while the other two were executed with significant inner changes; namely, stiffeners cross-shaped CFST (SC-CFST), and multi-cell cross-shaped CFST (MC-CFST) filled with concrete. The other group has the same OC-ST, SC-ST, and MC-ST, but these test subjects were without filled concrete. Through discussion of the failure mechanism, load displacement and load strain correlations are determined. The effects of parameters on ultimate resistance, failure pattern, and ductility index were studied. The axial load-carrying performance of the cross-shaped CFST columns was 75–80% better than that of ST columns; and each ST column displayed cooperative behavior. The finite element model (FEM) was simulated, and the outcomes of the experiments were used to validate it. The load–displacement relationships were established using parametric analysis. Existing design standards were used to calculate CFST column loading capacity. Finally, mathematical formulas were improvised to determine the ultimate load of the cross-shaped CFST column.

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 < 2.5% and correlation > 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.

A prospective observational study to evaluate effect of heat inactivation on ABO titers performed by column agglutination technology and conventional tube technique.

When determining ABO antibody titers, immunoglobulin G (IgG) antibodies can be masked by immunoglobulin M (IgM) antibodies. Hence, the measurement of actual concentration of IgG requires methods like heat inactivation (HI) of plasma. This study was aimed at determining the effects of HI on IgM and IgG titers performed by conventional tube technique (CTT) and column agglutination technique (CAT). This was a prospective, observational study conducted from October 2019 to March 2020. All consecutive A, B, and O group donors who gave consent for participation were included. All samples were consecutively tested by CTT and CAT, before and after HI (pCTT, pCAT). A total of 300 donors were included. IgG titers were found to be more than IgM titers. For group O, IgG titer results were higher for both anti-A and anti-B compared to group A and B. For group A, B, and O, pretreatment results were higher than posttreatment IgG titer results. Median anti-A titers were similar to median anti-B titers across all categories. Median IgM and IgG titers were higher for group O individuals than nongroup O individuals. There was reduction in IgG and IgM titers after HI of plasma. One log reduction in median titers was observed when ABO titers were performed by CAT and CTT. There is one log difference between median antibody titers estimated using heat inactivated and nonheat inactivated plasma. The use of HI for ABO isoagglutinin titer estimation can be considered in low resource settings.

Parametric study on lateral behaviour of composite shear walls with high-strength manufactured sand concrete

The traditional reinforced concrete (RC) shear wall showed limited seismic performance under extreme earthquakes when deployed at the bottom of high-rise buildings, due to the presence of high axial compression ratios. In this study, a novel composite shear wall was proposed to improve the seismic performance at high axial compression ratios, in accordance with recent demands for eco-friendly materials. The novel composite wall integrated the high-strength manufactured sand (MS) concrete, ring-stirrup and steel tube to fully maximize material efficiency and achieve inter-enhancement. A quasi-static test was at first carried out on the proposed composite shear wall, which validated the expected enhancement on its lateral mechanical behaviour preliminarily. On this basis, a refined finite element (FE) model was established for the test specimen by considering the nonlinearity and cyclic behaviour of materials, in order to provide further insights into its behaviour under lateral loads. The established FE model was verified against the test data, which showed a good agreement between the numerical prediction and the test result. Meanwhile, a list of key parameters was identified according to their influence on the lateral behaviour of the composite wall, including the axial compression ratio, yield strength of steel tubes, compressive strength of concretes, reinforcement ratio in concrete-filled steel tube (CFST) columns, and space between ring-stirrups. On this basis, a series of parametric investigations were carried out with the validated FE model, by varying the selected key parameters. In general, the research output offered a constructive guideline and data support for the expected engineering application of the proposed composite shear wall.

SLENDER COLUMN STRENGTH OF INNOVATIVE CONCRETE FILLED STEEL TUBE COLUMNS WITH HIGH‐PERFORMANCE BUILDING MATERIALS

AbstractThis paper presents a comprehensive experimental and numerical study on the load‐carrying behaviour of innovative high performance materials steel‐concrete composite columns: Namely concrete‐filled steel tube columns with solid steel core (CFSTCSC) and concrete‐filled double steel tube columns (CFDST). The experimental results exemplify the basic load‐carrying behaviour. In addition to that, the application range of high‐strength materials is evaluated in relation to the slenderness. Finally, the influence of geometric imperfections on the load‐carrying behavior is investigated based on the manufacturing tolerances of such multi‐component cross‐sections.