Concrete-filled Steel Tube Columns Research Articles

Experimental and analytical investigation on precast concrete-encased concrete-filled steel tube column-to-column dry connections under axial tension

Precast technologies featuring rapid construction and reduced on-site manpower have been gaining widespread adoption in the construction industry, particularly in reinforced concrete (RC) structures and composite steel–concrete structures over the past few decades, due to rising labour cost. However, to date, no workable precast connections have been developed for concrete-encased concrete-filled steel tube (CECFST) columns, which are increasingly used in ultra high-rise buildings and large-span bridges owing to its superior structural performance and excellent fire resistance. In this regard, to promote applications of CECFST columns in countries with increasing labour cost, this study develops two innovative precast CECFST column-to-column dry connections (PCDCs), through which the construction of CECFST structures would minimise heavy on-site work, such as welding or grouting of joints, formwork, and propping systems. Ten laboratory tests including four component tests and six column-to-column connection tests, were conducted to investigate tensile performance of the developed PCDCs. Key test results of all the ten specimens, such as load versus deformation relationships and failure modes, showed that the PCDCs had excellent tensile resistance and ductility. Furthermore, this paper carried out a series of theoretical analyses to quantify the ductility and tensile strength of the PCDCs through proposed load transfer mechanisms and component-based models. The design method of the PCDCs was presented by a simple flowchart and a worked example. With excellent structural performance, the PCDCs developed in this paper demonstrated huge potential to replace conventional cast-in-place (CIP) connections of CECFST columns.

Seismic research on column base joint of L-shaped CFST columns under cyclic loading

The newly exposed column base (ECB) for L-shaped concrete-filled steel tube (CFST) columns investigated in this study consists of an outer base plate, a concrete cushion, and anchor bolts. Three ECB specimens of the L-shaped CFST column were tested under constant axial loading and cyclic horizontal loading to investigate their seismic behavior. The failure mode, moment versus rotation relationship, hysteretic behavior, and ultimate moment strength were analyzed. The test results indicated that the failure mode of ECB is the failure of the concrete cushion and yielding of the base plate and anchor bolts. Furthermore, a parametric analysis based on a verified finite element model was performed to investigate the influence of various parameters on the ultimate moment strength. Finally, a simplified strength model of ECB for L-shaped CFST based on the composite yielding method was proposed.

An experimental behavior of the bond-slip performance of hybrid fiber concrete-filled steel tube columns with shear studs

An experimental behavior of the bond-slip performance of hybrid fiber concrete-filled steel tube columns with shear studs

Mechanical behavior of steel-fiber-reinforced self-stressing concrete filled steel tube columns subjected to eccentric loading

Initial self-stress contributes to the pre-peak properties of concrete filled steel tube (CFST) columns, but brings salient brittleness at the post-peak stage. Adding steel fibers can alleviate the friability of concrete, helpful in the post-peak behavior of CFST columns. This study aims to investigate the coupling effect of initial self-stress and steel fibers on the mechanical behavior of CFST columns under eccentric loads. 42 eccentrically loaded specimens are conducted with various levels of self-stress, eccentricity ratio, steel fiber volume percentage, concrete strength grade and steel tube thickness. Moreover, a numerical analysis model is developed to capture the eccentrically loaded behavior of steel-fiber-reinforced self-stressing concrete filled steel tube (SSCFST) columns. The results show that the increases in the ultimate load (Nu) and the corresponding bending moment (Mu) are obtained by the self-stress. Adding steel fibers leads to a slight growth of Nu, but the bending moment shows an obvious growth after the ultimate state, indicating adequate safety margin. The axial-flexural interaction curves possess a more obvious convexity as steel fiber dosage is increased. Based on the numerical results, a new axial-flexural interaction model is proposed, which is capable of considering the influence of steel fiber dosage.

Modeling of Ultra-high Performance Fiber Reinforced Concrete Filled Steel Tube Columns under Eccentric Loading

Recently, ultra-high performance fiber reinforced concrete (UHPFRC) has been commonly used as a structural material. In this study, finite element (FE) model is constructed to investigate the behavior of ultra-high performance fiber reinforced concrete filled steel tube columns (UHPFRCFSTs) under axial or eccentric loading. The analysis included three-dimensional FE model using solid elements. The novelty of the suggested FE model is the consideration of the confinement of the UHPFRC in-filled material. Furthermore addition, the numerical model includes initial local and overall geometric imperfections, as well as the inelastic response of both UHPFRC and steel materials. The interaction between the steel tube and UHPFRC in-filled is modelled using surface to surface contact. Experimental results from the literature are used to validate the FE model. It is proved that the FE model can predict the ultimate capacities, failure modes, and post-cracking behavior accurately for both short and long UHPFRCFSTs. The FE interaction diagram agreed very well with the experimental results. Using the verified FE model, a parametric study on UHPFRCFSTs is carried out. Several parameters, including concrete strength material, steel yield strength, and aspect ratio of the columns (column diameter/tube thickness), are investigated. Eventually, comparisons are conducted between the results obtained from FE simulation and the existing design codes for predicting load-moment interaction diagram of UHPFRCFSTs. It has been found that the Eurocode 4 predictions in most analyzed cases are conservative for UHPFRCFSTs.

Assessment on seismic performance of circular concrete-filled thin-walled steel tube columns

Concrete-filled steel tubular (CFST) with circular section is a very efficient composite component bearing vertical loads, which takes advantage of the synergy of steel tube and concrete to fully develop the strengths of both materials. To promote the application of circular CFST columns in multi-story buildings or medium-span bridge piers with improved economic efficiency, circular CFSTs using thin-walled steel tubes were studied in this paper. 8 specimens were designed and tested to assess their seismic performance under constant axial compression and cyclic lateral loads. The key test parameters include axial compression ratio, diameter-to-thickness ratio of steel tube, as well as stiffening scheme. The effectiveness of two steel plate stiffeners (longitudinal stiffener, binding stiffener) at the potential plastic hinges of thin-walled circular CFST columns was verified and discussed. Although all specimens failed in a manner characterized by significant local buckling of steel tubes, they still performed a relatively ductile behavior with the ductility coefficients generally exceeding 4.0, and the ultimate drift ratios exceeding 1/40. The steel plate stiffeners did not achieve the expected enhancement in strength and ductility, due to the premature fracture in the steel tube which may be caused by the damage in the welding heat-affected zone. Based on the test results, a numerical model and a simplified hysteretic model were established to predict the seismic responses of the thin-walled circular CFST columns.

Compressive behaviour of UHPC-filled square high-strength steel tube stub columns under eccentric loading

This paper presents experimental and numerical studies on the compressive behaviour of ultra-high performance concrete (UHPC) filled rectangular high-strength steel tube (UFHST) stub columns under eccentric loading. A total of 16 compressive specimens with a maximum concrete strength of 150 MPa and a maximum steel strength of 846 MPa were designed and tested. The test results showed that the use of high-strength steel tube and UHPC without steel fibres largely enhanced the load-carrying capacity of concrete-filled steel tube columns. The use of fibre-free UHPC adversely influenced the ductility of the columns. The incorporation of steel fibres into UHPC when casting the columns, however, improved the ductility of the composite columns and at the same time gained additional load-carrying capacity. A finite element (FE) model was then developed using ABAQUS and verified with test results. The numerical parametric study using the verified FE model showed that the confinement effect from the high-strength steel tube onto the UHPC was obscure before peak stress of the column was achieved, but was gradually activated/increased in the post-peak stress stage. Therefore, subsequent to the peak value, the axial stress of the confined UHPC experienced a short decrease first and then a continued growth. The findings from the present study set an experimental and numerical basis for future investigations to expose optimistic design of the UFHST stub columns.

Behaviour of axially compressed CTHST stub columns with inner spiral stirrup

In this paper, a new type of concrete-filled thin-walled high-strength steel tube (CTHST) columns with inner spiral stirrup is proposed. This new type of columns provides dual constraints to the concrete core by both outer steel tube and inner spiral stirrup. To explore the structural performance of this new type of composite members, a pilot study into stub columns under axial compression was carried out. A total of 16 axially compressed specimens, 8 in circular section and 8 in square section, were tested with the various volumetric stirrup ratio (ρ, from 0 to 2.4 %) and yield strength of steel tube (fyt, 571.2 MPa and 648.9 MPa). The experimental results show that, the inner spiral stirrup has little impact on the overall failure pattern of each component of the specimens, but controls the horizontal angle of the failure plane, and the capacity, composite elastic modulus and ductility coefficient of the specimens increase as ρ and fyt increase. In addition, a nonlinear finite element (FE) model was established, and the representative mechanism of axially compressed CTHST stub columns with inner spiral stirrup under different ρ was further studied by the verified FE model. Finally, a calculation method to predict the capacity of the new composite members was developed, which considers the strength improvement of stirrup confined concrete. This method provided an accurate prediction of the capacity of axially compressed CTHST stub columns with inner spiral stirrup.

An Experimental Evaluation on the Fire Resistance and Post-fire Structural Performance of Concrete Filled Steel Tube Columns

An Experimental Evaluation on the Fire Resistance and Post-fire Structural Performance of Concrete Filled Steel Tube Columns

Experimental investigation into mild steel circular concrete-filled double skin steel tube columns

Constructing the concrete-filled double skin steel tube (CFDST) column involves placing concrete in between two steel tubes. Such tubes may have the same cross-section shape on the inside and outside, or they may have different cross-section shapes, as in the case of a square outer tube and a square inner tube, a circular outer tube, and a square inner tube, or a square outer tube and a circular inner tube, etc. In this article, the response of concrete-filled double-skinned steel tube columns (CFDST) to axial load is experimentally investigated. To create the CFDST column, two concentric mild steel circular tubes were filled with concrete. CFDST column behavior was illustrated using typical curves of axial load vs deformation and axial load versus longitudinal strain in the outer steel tube, inner steel tube, and concrete core. To further explore how changing the column's geometry and materials can affect its ultimate strength, parametric research was carried out. In the end, the experimental results were compared to the requirements specified in codes like Eurocode-4, AISC-360, ACI, and the equation given by Han et al. (2009).

Research on Performance of Vertical FRP Concrete Members

In this paper, the theoretical research on the mechanical properties of FRP concrete vertical stressed members is described. The research progress on the mechanical properties of FRP concrete columns is summarized from three aspects: types of fiber-reinforced composites, applications in civil engineering and development prospects. Finally, the advantages of mechanical properties of FRP concrete column are studied by comparing with concrete filled steel tube column, and the further research direction of FRP concrete column is supplemented.

Connection behaviour of through reinforced concrete beam to concrete-filled steel tube column after exposed to heating

The experimental study presented in this paper investigate the post-fire performance of through reinforced concrete (RC) beam to concrete-filled steel tube (CFST) column connection. A total of twelve connection specimens were tested under hogging moment. The connection specimens are grouped into two groups; group A-connections, without fire exposure and group F-connections that are exposed to fire. Two classical connection types were used in this study (type A and B) and one new connection type were proposed herein (type C) by associating additional steel plates to the connection zone. In addition, different beam reinforcement ratios were used. These parameters were considered to evaluate the strength, stiffness, joint classification, ductility, failure modes and strain response of the composite joints. Three failure modes of the connections were found. The connection specimens without fire exposure were found to be a rigid connection. The fire exposure significantly influenced the connection performance, and that influence is varied based on the connection type and beam reinforcement ratio. The proposed connection type is found to have the highest residual capacity among the other connection types. However, a comprehensive analysis of the post-fire behaviour of each connection type is illustrated.

Comparison of Seismic Analysis of Multi storey Buildings with RCC columns and CFST columns by Varying Heights

As there is an increase in population day by day, there is more requirement for land. But the availability of land on Earth’s surface is 29 % which should be used for various purposes and hence, there would be difficulty in providing accommodation to all the citizens. There comes the idea of vertical development of the structures i.e., multi-story structures. Usage of Reinforced Cement Concrete (RCC) for high rise structures with large spans would be very complex as it requires high grade concrete and steel and hence becomes risky. In that case, the composite structures give effective results due to the co-action of materials. Providing Concrete Filled Steel Tube (CFST) columns will reduce the requirement of formwork and will increase the functional area as the steel tube acts both as longitudinal as well as transverse reinforcement which gives mere resistance to tensile stresses. In this thesis, Multi Storied Structures of G+10, G + 20 and G + 30 were taken and variation was considered in the columns, the rest of the structural elements have been taken of RCC only. The seismic analysis of the structures has been carried out for both the type of structures for each height by using Response Spectrum analysis in Zone II following the guidelines of IS 1893:2016 code using ETABS software. The comparison of the structures has been shown in terms of earthquake response parameters such as story drift, story displacement, story shear etc. It has been concluded that structures with CFST columns have shown better seismic performance with increasing height compared to RCC structures.

Eccentric loading behavior of steel tube columns filled with steel‐fiber‐reinforced recycled concrete

AbstractA comprehensive study focuses on the eccentric compressive behavior of steel‐fiber‐reinforced recycled concrete filled steel tube (SRCFST) columns. A total 39 stub columns are tested, and the variables include eccentricity ratio (e/r), steel fiber volume, quality replacement rate of recycled aggregate, concrete strength grade, and diameter–thickness ratio of steel tube. Failure mode, the load–lateral deflection behavior and the moment–curvature response are analyzed. The load–moment interaction relationships, the load–strain responds and the neutral axis position are researched. The results show that the use of recycled aggregate causes the little‐to‐no influence on the eccentric loaded performance of SRCFST columns with a relative smaller e/r. However, the ultimate load and deformability of the columns with higher e/r both decreases rapidly. Adding steel fibers can offset this adverse effect. The addition of steel fibers sustains a higher relative compression region height in the cross section. The ultimate load descent of SRCFST columns due to the increase of e/r is slower than ordinary concrete filled steel tube and recycled aggregate concrete filled steel tube columns. Moreover, on the basis of the unified theory, a calculation model is proposed to predict the ultimate capacity of SRCFST columns under combined loadings. The model captures well the compressive response of SRCFST columns.

Detecting the interfacial bonding of concrete-filled steel tube columns after fire by two stress wave-based methods – A case study

For concrete-filled steel tubes (CFST), the steel tube can increase the stiffness of the member, while the filled concrete prevents column buckling and allows the steel tube to withstand high temperatures for longer periods of time. The bonding between the steel tube and the concrete is difficult to evaluate from the appearance. In this paper, the bonding conditions of the CFST columns of a high-rise building under construction after a fire was evaluated by two stress wave-based non-destructive test (NDT) methods in-situ. They are the Lamb wave-based method and the normalized impact-echo method. Among them, the Lamb wave dispersion curve, which is obtained by a single tapping of a steel ball and a receiver 0.4 m away, can quickly evaluate the interface bonding conditions under the measuring line. The normalized impact-echo can pin-point the precise location of interfacial debonding. The test results show that both NDT methods can accurately classify good bonding conditions in the region without fire damage. Combining the results of the two methods, we found that high temperature was likely to cause some damage, such as microcracks on the concrete surface or intermittent separation of steel from concrete, but there is no continuous gap at the steel–column interface.

Behavior and Strength of Composite Columns under the Impact of Uniaxial Compression Loading

The Concrete Filled Steel Tube Column (CFST) is classified as a composite structural element. This type of column was adopted as the main loaded member in many buildings due to its excellent mechanical properties. CFST columns have high strength and ductility behavior, and they can sustain heavy loads with high performance. These led to their adoption in many countries. In the current study, the behavior and strength of CFST columns under the effect of axial compression load with parameters such as the diameter to thickness ratio and the height to diameter ratio were investigated. Strength carrying capacity and axial and lateral deformations with axial and lateral strains were explored. The test results showed that smaller heights within the same material gave higher strength capacity. The stiffness of the CFST is more than concrete and hollow steel section specimens' due to its capability of high strength capacity with low displacement. Also, the composite action of CFST gave more stiffness.

Artificial Neural Network (ANN) Based Prediction of Ultimate Axial Load Capacity of Concrete-Filled Steel Tube Columns (CFSTCs)

Artificial Neural Network (ANN) Based Prediction of Ultimate Axial Load Capacity of Concrete-Filled Steel Tube Columns (CFSTCs)

Numerical Study of Hybrid Through Plate Connections to CFST Columns

The use of concrete-filled steel tube (CFST) columns is highly encouraged nowadays in modern multistory structures. The major reason is the extensive resistance offered by the hollow steel column to high compression. Nevertheless, further studies and data are desirable to exhaustively characterize these members and their connections to other members, such as beams. This paper investigated the behavior of concrete-filled columns connected to I-beams by through plates. Three simple types of plate connections (easy to assemble and construct) were proposed and evaluated. The behavior of these connections was examined under static loading by using advanced finite element based software (ABAQUS). The modeling techniques used in this study were validated by comparing the numerical results of a through plate connection model with the results of two relevant experimental studies. The proposed connections were classified as semi-rigid connections according to Eurocode-3. These connections were able to move the plastic hinge away from the column panel zone. The maximum plastic rotations of all connection types were greater than 40 mrad. The failure mode, and moment-rotation curves of the concrete-filled column to steel beam connections were discussed based on numerical results. The influence of through plate material and through plate thickness were evaluated via a parametrical study.

Experimental study on the behavior of circular ultra-high strength concrete-filled steel tube columns subjected to unequal end moments

Concrete-filled steel tube (CFT) columns in multi-storey frames may be subjected to unequal end moments, especially during earthquakes. The behavior of ultra-high strength concrete-filled steel tube columns (UHSCFT) with concrete strengths greater than 100 MPa subjected to unequal end moments has not been studied thus far. In this study, 22 UHSCFT columns were designed and tested to investigate the influence of the end moment ratio β, eccentricity ratio e/D, and slenderness ratio L/D on the behavior of UHSCFT columns under different end moments. The results suggested that varying β from 1.0 to 0 resulted in a higher axial load-bearing capacity for the UHSCFT columns with e/D = 0.4, L/D = 7.5, whereas for β ≤ 0, the effect of the end moment ratio was marginal. Moreover, the axial load-bearing capacity generally decreased with increasing L/D and/or e/D ratios. Smaller β, smaller e/D ratios, and/or larger L/D ratios generally led to more brittle behavior in UHSCFT columns. The second order effect of UHSCFT columns with equal end moments was significant, whereas those of specimens with unequal end moments (L/D ≤ 12, e/D ≤ 0.4) could generally be neglected. Current design codes, such as EC4, AISC 360 and GB 50936, are unable to well predict the resistance to compression and bending of UHSCFT columns under unequal end moments. It was observed that the accuracy of GB 50936 would be improved by assuming K'a ≥ 1.

Mechanical properties of CFDST column under eccentric compression after exposed to fire

This paper investigates the experimental behaviour of ten square concrete-filled double skin steel tube (SCFDST) columns subjected to eccentric compression after 60 min of fire time. The test parameters included slenderness ratio, eccentricity and hollow ratio. It was found that the slenderness ratio and eccentricity have significant influence on the residual deformation and bearing capacity. However, when the hollow ratio (χ) was 0.72, slenderness ratio has little effect on the bearing capacity. The accuracy of finite element analysis (FEA) models were verified by the presented test results, and they were in good agreement. A FEA model was established to conduct a parameter analysis of CFDST members, and the working mechanism was analyzed in depth. Based on the parametric analysis, it shows that nominal steel ratio, eccentricity and strength of external steel tube have significant influence on the member’s residual bearing capacity under eccentric compression after fire: The residual bearing capacity decreases with the increase of nominal steel ratio. When the eccentricity increased from 0 to 0.6, the bearing capacity can decrease about 42 % after fire. The hollow ratio and concrete strength have little effect on the bearing capacity after fire. With the increase of fire time from 0 min to 120 min, the proportion in bearing capacity of internal and external steel tube gradually increases 16.8 %. Finally, compared with the relevant codes, the results of the T/CCES 7–2020 code were in good agreement with the FEA results.