Steel-concrete Composite Columns Research Articles

Experimental Investigation on the Axial Compressive Behaviour of Cold-Formed Steel-Concrete Composite Columns Infilled with Various Types of Fibre-Reinforced Concrete

The exceptional structural strength and low cost of steel-concrete composite columns make them a popular choice for civil engineering structures. Numerous forms of composite columns, including steel tubes filled with concrete, have been produced recently in response to various construction situations. Cold-formed steel tubular columns with concrete filling have higher strength and ductility due to their capacity to withstand inner buckling and postpone outward buckling. The objective of this research is to determine the ductile and strength performance of composite columns containing various forms of fibre-reinforced concrete when subjected to axial compression. Several different kinds of fibre-reinforced concrete (FRC) are employed as additives in hollow steel columns, including steel FRC, carbon FRC, glass FRC, coir FRC, jute FRC, and sisal FRC. Axial compression tests were performed on 24 columns, including three hollow steel columns and 21 composite columns. Three distinct slenderness ratios were developed and used. Axial bearing capacity, compressive stress-strain curves, ductility, peak strain, axial shortening, and toughness were among the topics covered by the axial compression test. Experimental findings demonstrated that all conventional composite columns experienced failure through overall buckling, Local buckling and crushing of concrete infill, which was transformed into more ductile failure using fibre-reinforced concrete infills. The test results revealed that fibre-reinforced concrete-infilled steel columns outperformed conventional composite columns in terms of strength, ductility, and energy absorption capacity. The percentage increase in load-carrying capacity was observed as 203.88%, 193.48% and 190.03% when compared to hollow cold-formed steel tubular columns in medium, short and stub columns, respectively. Under assessment of stub, short, and medium columns, the load-strain plots demonstrated that the steel fibre-reinforced concrete in-filled columns performed well in terms of ductility. Localized buckling and crushing of the concrete infill caused the composite columns with low slenderness ratios to fail. In contrast, concrete-filled steel tube columns with higher slenderness ratios showed column failure through the overall buckling of the composite column.

Strength of Partially Encased Steel-Concrete Composite Column for Modular Building Structures.

Modular structural systems have been used increasingly for low- and mid-rise structures such as schools and apartment buildings, and applications are extending to high-rise buildings. To provide sufficient resistance and economical construction of the high-rise modular structural system, the steel-concrete composite unit modular structure was proposed. The proposed composite unit modular system consists of the composite beam and the partially encased nonsymmetrical composite column. The outside steel member of the composite column has an open section, and is manufactured using a pressed forming procedure so that easy joining connecting work and manufacturing cost reductions are possible. However, the design methods are complicated due to the inherent nonsymmetrical properties of the section. Therefore, in this study, the focus was made on the strength evaluation and development of design methods for the partially encased nonsymmetrical steel-concrete composite column. Four full-scale specimens were constructed and tested. The experimental study focused on the effect of the slenderness ratio of the column, eccentricity, and the through bars on the strength of such columns. Additionally, the P–M interaction curve to estimate the strength of the proposed composite column under general combined loading was developed based on the plastic stress distribution method. The results indicate that the through bars are needed to delay the local buckling and distribute the loading uniformly throughout the composite column. Finally, the proposed design methods provide a conservative strength prediction of the proposed composite column.

Behaviour of cold-formed steel-concrete composite columns under axial compression: Experimental and numerical study

Concrete filled cold-formed steel-concrete composite columns exhibit improved strength and ductility characteristics due to its ability to resist inward buckling as well as delay the outward buckling. Though concrete infill prevents inward buckling, outward buckling still limits the steel section from reaching its yield strength. From the past studies, it is observed that the introducing of web stiffeners in cross-section of steel section may improve its buckling resistance. The present study focuses on assessing the effect of longitudinal stiffeners on the behaviour of square cold-formed steel–concrete composite columns for the various slenderness range (0.01 to 0.4) through experimental and numerical studies. Conventionally, the integrity of hollow tube cross sections is ensured by welding or by rolling process during the manufacturing. Welding process cannot be adopted in thin-walled cold formed sections since it may lead to higher degree of imperfection. In this study, the desired square cross sections were formed from flat steel sheet and overlapped using self-tapping screws. An intensive numerical analysis was carried out by varying stiffener angle as 90°, 120°, and 141° and the buckling curves for plain and profiled sections were presented. It is concluded that the axial compressive strength of plain and stiffened composite sections is almost equal, attributed to the inability of concrete to reach its maximum stress due to stress concentration at the stiffeners’ edges. The buckling reduction factor of stiffened composite columns showed higher values in the higher slenderness range, indicating the positive effect of the stiffeners.

Mechanical behavior of steel-concrete interface and composite column for circular CFST in fire

A refined numerical model was proposed to simulate the mechanical behavior of circular concrete-filled steel tubular (CFST) columns under fire conditions. The model was calibrated against the thermal and mechanical results from physical testing and showed good reliability. Based on the numerical analyses, the mechanical properties of steel-concrete interface and composite column for circular CFST with different confinement coefficients during the entire fire process were investigated in depth. Moreover, a series of parametric analyses were undertaken to investigate the influence of main factors, such as the load ratio, the steel tube ratio, the steel strength, the cross-sectional diameter and the concrete strength, on the mechanical behavior of the circular CFST column. Finally, a theoretical formulation and a simplified formulation for evaluating the ultimate bearing capacity of circular CFST columns with different length-diameter ratios under fire conditions were proposed, which showed an acceptable accuracy.

Finite element model for tapered three layers composite columns (Stobie poles)

A Stobie pole is a specific configuration of composite steel-concrete column which is being used widely as power poles in South Australia. It consists of two steel H sections, with the space between them filled with plain concrete. The two steel sections, and the concrete part in between, are connected by transverse bolts, which generate the composite action between them. These poles are tapered, from ground level to the top, and from the ground section to the toe. A 3D Finite element model (FEM) has been developed to analyse the structural behaviour of this type of composite column. This model considers the slippage between the different components e.g., the steel profile and concrete, bolt washers and steel profile, bolt shanks and the concrete, and the effect of the material nonlinearity of the steel profiles, steel bolts, and the concrete, including the damage of the concrete (in tension and compression). Also, the axial tensile forces initiated in the bolts because of the tightening is simulated to get the real behaviour of these poles. After defining the boundary and load conditions, the 3D FEM's results agreed well with the experimental results. Load-deformation curves, failure progression, shear distribution between different components as well as the stress distribution have all been presented.

Structural fire design of square tubed-reinforced-concrete columns with connection to RC beams in composite frames

The tubed-reinforced-concrete (TRC) column is an innovative type of steel-concrete composite column that is gaining increasing engineering usage, and structural fire performance should be an important consideration of its design. As affected by the adjacent members and beam-to-column joints, the fire behaviour of TRC columns integrated into a frame may largely differ from that of isolated columns with idealised end conditions. However, the fire performance of TRC columns in composite frames has not been studied, except for some work done on the fire performance of isolated TRC columns with certain end restraints. This paper presents finite element analysis on single-storey and single-span non-sway frames with square TRC columns, employing the software package ABAQUS. The thermal and deformation behaviour, development of axial stress, axial force and bending moment during heating, working mechanism and failure mode of the frame exposed to fire are numerically investigated. The difference between the fire performance of TRC columns in a frame and those of equivalent isolated columns is quantified. The fire resistance of the framed column is found to lie between those of the columns with rotational end restraints and columns with idealised pinned ends. The complex effects of the connected RC beam on the fire behaviour of TRC columns, e.g. the beneficial restraining effect and the negative effect due to restrained differential thermal expansion, are clarified. Finally, a practical fire resistance design approach is proposed for TRC columns considering the continuity and interactions between structural elements within a composite frame.

Experimental analysis of beam-to-column connection with partially encased concrete column with varying inertia axis

This study investigates the behaviour of beam-to-column connections of partially encased steel–concrete composite columns and steel beams connected using endplates and bolts. Four cruciform connections were tested in the experimental program, with varying column positions to study the flexural behaviour about the weak axis of inertia. The objective of the study was investigating the effect of uninterrupted fibre-reinforced concrete in a connection region on the ultimate capacity and stiffness of the connection. The experimental results demonstrated the effectiveness of uninterrupted fibre-reinforced concrete at the connection, regardless of the axis of inertia of the column; the obtained strengths, rotations, displacements, and deformations were analysed.

State of the Art Report on Steel-Concrete Composite Columns Infilled with Self Compacting Concrete

This paper aims at presenting an extensive critical review of the steel-concrete composite column section infilled with Self Compacting Concrete (SCC). Modern construction widely uses Concrete filled Steel Tubes (CFST) a composite section that enhances the structural capacity of the section and improved stiffness. This paper outlines the research work carried out on the structural behaviour of composite columns with SCC infills of different grades subjected to various loadings and analyzed experimentally and numerically and summarized in the tabular form. In addition, design code formulae for predicting the ultimate load carrying behaviour of the CFST section also highlighted in this paper. Keywords: Composite columns, CFST, Self-compacting concrete, CCR, Slenderness ratio, Bond strength.

Seismic behavior of single plate shear connection between steel-concrete composite beam and RC column

This paper aims to investigate the seismic behavior of single plate shear (SPS) connection between steel–concrete composite (SCC) beam and reinforced-concrete (RC) column. A total of four SCC beam to RC column composite joints were fabricated: one specimen was tested under monotonic loading, and three specimens were tested under cyclic loading. The failure modes, hysteretic and skeleton curves, strain distribution of anchor bars, RC slab and longitudinal reinforcement, ductility, energy dissipation and stiffness degradation were discussed, and the influence of longitudinal reinforcement ratio ρsl and the type of embedded parts on the seismic performance of joint were studied. The results indicated that the joint exhibited good seismic behavior. With the increase of ρsl, the initial stiffness, hogging moment and rotation capacities increased, while the ductility and energy dissipation capacity decreased slightly. The type of embedded parts had influence on the failure modes and initial stiffness, but had little effect on the moment and rotation capacities, ductility and energy dissipation capacity of joint. Finally, based on the Zhang’s model, considering the composite action of the floor slab and the contribution of additional bending moment, a calculation method was proposed to predict the ultimate sagging moment capacity of the joint, and the strength of the embedded parts of all specimens in this study and open literature were checked. The results showed that the Zhang’s model and the proposed model have a good prediction accuracy, and it is suggested that when designing the embedded parts of the joint under sagging moment, the cross-sectional area of anchor bars should be checked to avoid early failure.

CONNECTIONS BETWEEN STEEL-CONCRETE COMPOSITE COLUMN AND STEEL BEAM

Composite steel-concrete columns of circular cross-section have high strength and stiffness, which theoretically could help to reduce the cost of construction, but their advantages are still widely unexploited. In comparison with other constructions, composite columns account for a diminutive market share. One of the many reasons for this, is the complexity of connections that may require on-site welding, which not only slows down the construction, but also makes it more expensive. With the recent extensive development of blind bolts, new design options for the tube columns emerged. Such bolted joints would eliminate onsite welding and speed up installation. In this review a particular attention is paid to the circular columns, because these columns have the least studied connections. This article reviews the most recent stage in the development of the connections between steel-concrete composite columns and steel beams, as well as provides provisions for using such connections and outlines the directions for further research.

Numerical Parametric Study of Fully Encased Composite Columns Subjected to Cyclic Loading

This paper investigates the cyclic behaviour of steel-concrete encased composite columns. By investigating the cover concrete and the steel-concrete coefficient of friction on the behaviour (strength, ductility, stiffness, and energy dissipation) of composite columns subjected to combined axial load and cyclically increasing lateral load to improve the strength and performance of the composite column. Eight of the columns were designed to study the cover concrete effect, and eleven other columns were designed to study the coefficient of friction effect in the dynamic behaviour to the cyclic load. Additionally, in this study, the finite element models created in ANSYS software were verified and calibrated against previously published experimental results (load-displacement curve, load capacity and failure mode). The numerical results obtained from the finite element model indicate that the ductility and the energy dissipated increased by +11.71 and +18.93% receptively by the increase of the cover concrete until reaching the limit of the cover concrete. Beyond this limit, the ductility and the energy decrease by 27.33 and 24.97% receptively. The results also indicate that the ductility and the energy dissipated increased by 12.62 and 7.82% receptively by the increased coefficient of friction until reach 0.6, after that the energy decreases by 4.47%. Doi: 10.28991/CEJ-2022-08-01-04 Full Text: PDF

Interaction Strength of Steel-Concrete Composite Beam-Columns Including the Balance Point

The maximum bending moment capacity of steel-concrete composite column cross sections occurs with concurrently applied axial compression. This is seen in the shape of the interaction diagram, where the bending moment capacity increases with increasing axial compression before reaching the balance point. The size of this bulged region of the interaction diagram can be significant, especially for concrete-dominant sections. However, it is often neglected in design because of two stability-related concerns. First, the simple transformations that are recommended to convert cross-section strength to member strength produce illogical results near the balance point, with member strength exceeding cross-section strength. Second, research has shown that the stiffness reductions used in elastic analyses are not sufficient for highly slender concrete-dominant composite members subjected to high bending moments. This work seeks to address these issues through the development of more advanced transformations and stiffness reductions. These new recommendations will more accurately capture the strength of composite members and allow for more efficient designs.

Behavior comparison of seven-types of steel–concrete composite stub columns under axial compression

Steel-concrete composite columns are widely used in civil engineering structures for superior structural performance and economical cost. In response to the varying construction conditions, extensive types of composite columns have been developed nowadays, including concrete-filled steel tubes (CFST), CFST with steel bar (CFST-B) or steel section embedded (CFST-S), steel tubed concrete (T-C), steel tubed reinforced concrete (T-RC), steel tubed steel-reinforced concrete (T-SRC), and the newly proposed steel-tube-confined CFST (T-CFST), etc. A systematic and comparative experimental study was conducted for the seven types of steel–concrete composite stub columns with the same steel ratio, aiming to clarify their differences and facilitate an appropriate selection. Experimental results showed that all the conventional composite columns suffered from brittle failure, which was changed to ductile failure for T-CFST. Moreover, the employment of internal rebar or structural steel led to a variation of 13.3% in the ultimate load of CFST members; setting steel gap at the column ends for T-C columns increased the ultimate load by about 10% further; the addition of outer steel tube and sandwich material in T-CFST achieved up to 42.4% higher ultimate load. The enhanced mechanical properties of T-C and T-CFST were resulted from the increasing concrete confinement by the outer steel tube. The current design codes for different types of composite columns were examined by the experimental results, and a more suitable design method is needed for T-CFST.

Buckling resistance of concrete-filled cold-formed steel (CF-CFS) built-up short columns under compression

The steel–concrete composite columns (SCCC) are widely used in the construction sector. The buckling phenomenon of the steel part (especially thin-walled steel) of the SCCC due to compressive loading is the governing characteristic of these columns. The present paper reports an experimental and numerical study on the compressive behavior of innovative concrete-filled (CF) closed built-up cold-formed steel (CFS) columns to investigate the applicability of EN 1994-1-1 for the prediction of the buckling resistance. Twelve CF-CFS short columns were tested. The finite element (FE) design, test setup, procedure, and results, including the load-carrying capacities, load–deformation, and buckling modes, were fully reported. Additionally, the numerical results and EN 1994-1-1 predictions were compared assessing the validity of the EN 1994-1-1 formulations for the estimation of the contributions of each component. Since the closed built-up cross-sections are composed of Class 4 individual cross-sections, both gross and effective sectional areas were considered to estimate the steel contribution to the overall resistance of the composite columns. Based on the FE results it was observed that using the gross area the EN 1994-1-1 formulation overestimates the steel contribution and underestimates it when the effective area is used. Therefore, a modification was proposed for determining the effective cross-sectional areas of Class 4 closed built-up CFS cross-sections, by considering the overlapping plates, fastener positioning, and the concrete encasement of the individual plate elements resulting in a close agreement between the proposed methodology and experimental results.

ANALYTICAL MODEL FOR THE PREDICTION OF THE ELASTIC RESPONSE OF CURVED T-STUBS

Composite steel-concrete columns utilise the advantages of both materials, by combining high strength and ductility of steel with the compressive strength of the concrete. But the wide adaptation of composite structures is limited, mainly because of the lack of cheap and easy to construct connections, as many of which require costly and timeconsuming on-site welding, when circular concrete filled steel tubes (CFST) are adopted. New connections, like those incorporating the use of blind bolts and curved end-plates, may represent a valuable alternative. Such joints can be adapted to circular CFST to eliminate on-site welding, but they require the creation of new curved T-stub components. This paper proposes an analytical model for the evaluation of bolt forces in the curved T-stubs within the elastic range. The model is then validated against experimental results of joints between circular CFST columns and steel beams, with both preloaded and snug tightened bolts. Analytical model shows good agreement with experimental data, but needs further development to take into account the prying forces.

Behavior and Design of Steel-Concrete Composite Columns Subjected to Combined Axial Compression and Biaxial Moment

AbstractSteel-concrete composite columns are strong and efficient structural members. However, their strength is not consistently recognized within design standards. In particular, current provisio...

L-shaped steel-concrete composite columns under axial load: Experiment, simulations and design method

The research has analyzed the axial behavior of an innovative L-shaped composite column. The L-shaped composite columns could work as series rectangular composite columns, which could take advantage of the steel tubes and the inner concrete. Seven specimens have been tested to analyze the failure progress, load-carrying capacity and failure mode. Main parameters were the length-to-width ratio and length-to-depth ratio. The shear failure mode accompanied by local buckling appeared for the tested specimens. The results showed that such columns possessed high strength and good ductility. A finite element model was established and verified by the experimental results. Results showed that the finite element model could simulate the axial behavior of the L-shaped composite columns well. Parametric analysis was conducted to analyze the influence on the axial behavior of composite columns. Furthermore, a theoretical model was proposed to calculate the axial strength of such component and was in good agreement with the experimental results. A simplified formula has been proposed for determining the axial strength according to the results of parametric analysis of FEA and the theoretical model. In addition, the calculated results based on design methods specified in EC4, CECS and AISC have been compared with the experimental results, the results of theoretical model and the results of simplified formula. Among them, the results of EC4 were the closest to the experimental results.

Numerical Modelling of the Behavior of Steel-Concrete Composite Columns of Different Types of Circular Cross Section Subject to Lateral Impact

Numerical Modelling of the Behavior of Steel-Concrete Composite Columns of Different Types of Circular Cross Section Subject to Lateral Impact

Numerical studies on steel-concrete composite structures

The paper focuses on the seismic performances of steel-concrete composite structures made with fully encased steel-concrete composite columns and steel beams. An important objective is to study the influence of the structural steel ratio on the behaviour of composite columns. To meet the proposed objectives, a numerical study was developed on composite structures. Some comments, design recommendations and an economical study conclude the paper.

Performance of Impulse Response Testing on Prismatic Members with Intermediate Joints

Nondestructive Testing (NDT) methods have extensively been used to assess the conditions of civil infrastructure in the recent decades. Among various NDT techniques, Impulse Response (IR) has a vast application due to its simplicity and low cost. However, factors such as reflections from changes in impedance along the investigated members can adversely influence the success of the method. Numerous numerical and experimental studies have already been performed to evaluate the effect of change in mechanical impedances such as bulging, necking and similar anomalies. In this study, the effect of the presence of joints connecting the investigated members to other members, as another source of impedance change, is demonstrated. A three-story steel-concrete composite column of a building was selected for testing and IR tests were conducted. The obtained mobility graphs were clear, and the height of the column was easily measured with an acceptable error. The results of this study show that although the joints located between the top and bottom of the tested member are sources of change in mechanical impedance, they do not result in concealing the resonant frequencies from the wave reflected from the bottom of the member. Thus, IR method seems to be applicable in determining the length of prismatic members with intermediate joints such as piles of unknown bridge foundations with bracing and columns of buried buildings.