Tube Columns Research Articles

Parametric Study on the Behavior of Steel Tube Columns with Infilled Concrete—An Analytical Study

Concrete-filled steel tube (CFST) columns are used in tall buildings and bridges, and they provide more rigidity and higher bearing capacity, but buckling affects their behavior. There is an exceptional need to study the behavior of these columns under various conditions. The numerical method is beneficial in supplementing the experimental works and is used to explore the effects of various parameters because of the limitations in cost, apparatus, and time of the experimental program. The various parameters, such as the different slenderness ratios, i.e., column-height-to-cross-section-dimension (H/D), different steel-tube-thickness-to-column-dimension (D/t), and different compressive strength of concrete to yield strength of steel tube ratio (fc/fy) under concentric axial loading are considered in this current study. Firstly, a finite element model used the “ANSYS” software program and was constructed to validate the results of the experimental works. The extensive numerical models were carried out to extensively widen the study in this field. The numerical work was conducted on sixty-four specimens. Moreover, the analytical calculations from the different international codes/standards were compared with the numerical results to test their reliability in predicting the ultimate carrying loads. The study provided results that show the improvement effect of CFST columns with the high compressive strength of infilled concrete, while no remarkable enhancement effect with the high yield strength of steel tube was observed. Increasing the columns’ diameter is more effective in enhancing the load capacity (about three times more) than increasing the tube thickness (about 1.3 times). Ring stiffeners for long CFST columns (H/D > 12) do not lead to any enhancement of the column behavior due to yielding occurring firstly at the location of the rings. ECP205-2007 is the most conservative design code in predicting the load capacity of CFST columns, while the AIJ design code is good at predicting the ultimate load failure compared to the other codes/standards. Eurocode 4 provides underestimation values of the load-carrying capacity of CFST columns.

Experimental study on seismic performance of hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete-filled circular steel tube columns

In this paper, 1 recycled aggregate concrete-filled circular steel tube column (RACFST) and 11 hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete-filled circular steel tube (HFRACFST) columns were designed given the variables of steel fiber (SF) volume content (Vsf = 0.6 %,1.2 %,1.8 %), polypropylene fiber (PPF) content fractions (Vpf = 0.05 %,0.10 %,0.15 %), concrete strengths (C40, C50, C60), thickness of steel tube (t = 2.70 mm, 3.65 mm, 4.50 mm), axial compression ratios (n = 0.25, 0.35, 0.45). Then the influence of variables on hysteretic curves, ductility, energy dissipation and stiffness degradation were studied experimentally using the pseudo-static tests. Subsequently, the restoring force models of HFRACFST were proposed based on the experimental results. The results indicated that: (1) The incorporation of HF (hybrid steel-polypropylene fiber) could enhance the hysteretic behaviour of HFRACFST columns. An increase in PPF content had little effect on the lateral bearing capacity and energy dissipation capability. Nevertheless, it could improve the ductility to some extent. As the SF content increased, the lateral bearing capacity, energy dissipation capability and ductility of the specimens increased. (2) An increase in concrete strength resulted in the increase of the bearing capacity and energy dissipation capability, but led to inferior ultimate deformation and ductility. (3) The comprehensive hysteretic behaviour was improved significantly as the thickness of steel tube increased, especially in the energy dissipation capability. (4) The specimens with higher axial compression ratio experienced inferior ultimate deformation and ductility. (5) The ductility indexes of all specimens were higher than 3.0. The yielding elastic and ultimate elastoplastic drift ratios were in the ranges 0.012–0.013 and 0.038–0.054, respectively. The hysteretic performance of HFRACFST columns could satisfy the requirement of seismic design. It is feasible to apply the HFRACFST columns to vertical load-bearing structures in the seismic zones.

Axial Compression Behavior of Steel Angle-Corrugated Steel Plate-Confined Concrete Columns

This paper proposes a novel type of steel angle-corrugated steel plate-confined concrete column (SA-CS column). The axial compression behavior of the SA-CS column was investigated by load experiments and finite element (FE) simulation. The study also compared the load–displacement curves, core concrete strength index, and specimens’ ductility indices between the SA-CS columns and concrete-filled steel tube (CFST) columns. The results indicated that the mechanical properties of the SA-CS column were better than those of the CFST column with a similar steel ratio. The rationality and reliability of the finite element model were confirmed by comparing the experimental results’ load–displacement curves and failure modes. Based on the FE model, a supplementary parametric analysis of the effects of the compressive strength of core concrete, thickness, yield strength, and wave height of the corrugated steel plate, thickness, and yield strength of the steel angles was conducted. Moreover, some existing design codes were assessed based on the numerical results available in this study. A new calculating model for the SA-CS column was proposed, which is capable of reasonably predicting the numerical results.

Axial compressive behaviors of engineered cementitious composites-encased concrete filled steel tube columns after fire exposure

Engineered cementitious composite (ECC)-encased concrete filled steel tube (CFST) column, which is composed of outer steel reinforced ECC and inner CFST components, has broad application prospects in high-rise buildings due to its higher strength and ductility than the concrete-encased CFST column counterpart. This paper investigates the fire performance of ECC-encased CFST columns under and after fire exposures. Totally thirteen ECC-encased CFST columns and two concrete-encased CFST columns were prepared and tested considering different parameters, i.e., heating-up time, stirrup spacing and fire sides. It was found that the outer ECC component provides better fire protection to the inner CFST than the conventional concrete. Besides, the axial compressive strength and ductility of the ECC-encased CFST column were 32.2 % and 10.3 % higher than those of concrete-encased CFST columns after fire exposure. A finite element (FE) model and design equations were also proposed and verified by the experimental results, which could be applied to simulate and predict the compressive behavior of ECC-encased CFST columns after fire exposure.

Analytical model for evaluating lateral force capacity of precast concrete-filled steel tube column

Precast segmental columns have been frequently applied in regions of low seismicity due to rapid construction, high quality, and low downtime. Their lateral force–displacement curves were always calculated using iterative models in former studies, which could be time-consuming and arduous. Whereas, a non-iterative model can greatly improve computational efficiency and is preferred by designers. In this study, a non-iterative simplified analytical model was firstly proposed considering different neutral axis depths of the rocking interface. The neutral axis depth approached a constant value during lateral loading according to the results of the former tests and numerical studies. Then, a quasi-static test and finite element model of a precast segmental concrete-filled steel tube (PS-CFST) column were conducted to verify the proposed analytical model. Based on the finite element model, a nonlinear regression equation was set up to predict the constant neutral axis depth of the PS-CFST column according to the simulation results of 48 cases. Finally, the influence of the initial prestressing force, area of the prestressed tendons and gravity load on the lateral force capacity of the PS-CFST column were investigated. It was concluded that the constant value of neutral axis depth was positively related to axial ratio and diameter-thickness ratio, and negatively related to yield strength of steel tube of PS-CFST columns. The analytical model without iteration proposed in this study was appropriate to predict lateral force capacity of post-tensioned precast segmental columns, and it had a favorable agreement with testing and numerical results. Furthermore, the precast column with the lower gravity load and the higher reinforcement ratio of prestressed tendons would result in the larger post-yield stiffness.

Seismic performance of T-shaped CFST column to U-shaped steel-concrete composite beam joint

Both novel composite structures, special-shaped concrete-filled steel tube (CFST) column and cold-formed U-shaped steel-concrete composite beam with stiffened rebar truss (CUCB), have advantages of good mechanical behavior, appealing architecture, and convenient construction. In this study, a series of five half-scaled specimens of CUCB to T-shaped CFST column frame joints with vertical ribs were tested under cyclic loading. Different connection detail types were designed considering both mechanical and constructional aspects. The bearing capacity, stress distribution, stiffness degradation, energy dissipation capacity, ductility, and joint stiffness were evaluated to understand the seismic performance of these new joints. Experimental results show that joints with vertical ribs have favorable seismic performance and could be considered as rigid joint in a braced frame according to Eurocode 3. Based on the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method, a multi-criteria analysis model for evaluating the joint performance was performed to determine the most effective connection detail considering the mechanical behavior and construction cost. As a result, the proposed novel joints are seismically feasible.

Compression tests on stocky and slender columns of high strength S690 cold-formed square tubes

An experimental investigation into the structural behaviour of both stocky and slender columns of high strength S690 cold-formed square tubes (CFST) under compression is presented in this paper. A total of 8 stocky columns with two section types of four different cross-sectional dimensions were tested. Moreover, a total of 24 slender columns with two section types of six different cross-sectional dimensions were tested. Typical residual stresses of these two section types were also obtained. As expected, all of these columns of S690 CFST failed under compression similar to those stocky and slender columns of S355 CFST, namely, i) local plate buckling in stocky columns, and ii) overall axial buckling in slender columns. Hence, these tests may be regarded to be confirmatory tests to provide experimental evidence and test data on cross-section resistances of the stocky columns, and member resistances of the slender columns of these S690 CFST. In addition, the measured resistances of these columns were directly compared with those design resistances determined according to Structural Eurocode EN 1993-1-1 based on measured geometrical dimensions and mechanical properties. It is demonstrated that the measured resistances of these columns are significantly larger than those design values, and hence, these test data provide a scientific basis to enhance structural efficiency of the design rules.

Study on seismic performance of honeycomb stiffened rib shaped concrete filled steel tube columns

This paper presents concrete columns with inclined honeycomb stiffened rib steel tubes and proposes three special shaped cross-section columns to improve the overall force capacity of steel tube concrete columns on the basis of saving steel. Variables (type of section, direction of load application, honeycomb opening, strength class of concrete and steel) are set in this paper to investigate the seismic performance of inclined honeycomb stiffened rib concrete columns. The effect of honeycomb ribs on the seismic performance of shaped columns with different cross-sectional forms varies, and the improvement in cross-sectional performance is more obvious for T-shaped sections; the effect of load application direction is more obvious for asymmetric sections; the installation of honeycomb openings in stiffened ribs has a weak effect on the overall mechanical performance of the specimen, but the seismic performance in both directions is improved; the results are consistent when modeled using ABAQUS software and compared in tests. The setting of honeycomb holes in the stiffening ribs improves the bonding capacity of the stiffening ribs to the concrete, and the welding of the honeycomb stiffening ribs to the outer steel pipe improves the joint working capacity of the outer steel pipe and the concrete; the diagonal placement of the stiffening ribs improves the two-way seismic capacity of the shaped column. The new structural form of oblique honeycomb stiffening rib steel pipe concrete column is conducive to promoting the development of steel pipe concrete column.

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.

Mechanical performance of marine concrete filled CFRP-aluminum alloy tube columns under axial compression: Experiment and finite element analysis

This study presents the mechanical performance of marine concrete filled carbon fiber reinforced polymer (CFRP)-Aluminum alloy tube columns (CFRP-CFAT) through axial compression experiment and finite element analysis. 18 specimens were tested including 3 marine concrete filled aluminum alloy tubes (CFAT) and 15 CFRP-CFATs. The effects of the CFRP pasting position (outer and inner CFRP) and the number of CFRP layers were investigated. The typical failure pattern of specimens without inner CFRP was waist drum failure of aluminum alloy tube and concrete crushed, aluminum tube and concrete of specimens with inner CFRP were shear failure, the CFRP of all specimens was fractured. CFRP and aluminum alloy tube have fine deformation coordination performance. With the confinement of CFRP, the ultimate bearing capacity and energy absorption capacity of CFRP-CFATs were increased by up to 60.0% and 37.3%, respectively, also effectively inhibited the damage development of specimens. Moreover, a finite element model was developed, a parametric study was carried and a model for calculating the ultimate bearing capacity of CFRP-CFAT was proposed. The simulated results and calculated results were consistent with experimental results.

Axial behavior of circular CFST encased seawater sea-sand concrete filled PVC/GFRP tube columns

In order to directly apply seawater and sea sand in construction without desalination, a new type of circular concrete-filled steel tube (CFST) encased prefabricated seawater sea-sand concrete filled Polyvinyl Chloride (PVC)/Glass Fiber Reinforced Polymer (GFRP) tube column was proposed. 24 short columns were tested under uniaxial loads and the test parameters included types of inner tubes, seawater sea-sand concrete replacement ratios, concrete strength, the wrapping area of Carbon Fiber Reinforced Polymer (CFRP) strips and the thickness of inner tube. Moreover, the effects of the parameters on bearing capacity, ductility, stiffness, and strain responses were discussed. The results indicate that the bearing capacity and the strength index of specimens with PVC tube wrapped with CFRP strips and GFRP tube as the inner tube was significantly improved, and the improvement level increased as the wrapping area of CFRP strips or the thickness of GFRP tube increased. The increase in the concrete strength can also improve the bearing capacity and stiffness. In addition, an analytical model was proposed for the composite column with PVC tube wrapped with CFRP strips or GFRP tube as the inner tube.

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.

Numerical analysis of circular tubed high-strength concrete columns with embedded steel tubes under axial compression

This paper presents an in-depth investigation into the compressive behavior of the circular tubed high-strength concrete with embedded steel tubes (THSC-ST) columns using a finite element (FE) approach. The composite action of the columns is comprehensively explored. It can be detected from the numerical results that the confinement provided by the external steel tube in the THSC-ST column is significantly enhanced since the external steel tube does not carry the axial load directly. Besides, increasing the diameter of the internal steel tube can effectively improve the axial stress of confined concrete. Moreover, more effective confining stress of the external tube is observed after wrapping FRP jackets, leading to stiffer the post-peak behaviors for the core and sandwich concrete simultaneously. An extensive parametric analysis is also performed based on the validated FE model to explore the effects of the internal steel tube location, the number of FRP layers, the thickness and yield strength of the steel tube, and concrete compressive strength on the structural behaviors of the THSC-ST columns. Finally, a new formula is proposed to estimate the axial load capacity of the THSC-ST columns and high predicted accuracy is found by the comparisons between the theoretical and experimental results.

Numerical Investigation on the Axial Load Behaviour of Polygonal Steel Tube Columns

Hollow steel tubes members with different properties are being increasingly used for structural applications, such as columns in frame structures, roof structures, truss columns, and other applications. These structural members are primarily subjected to compressive and flexural loading. Due to the insufficient studies regarding the influence of the cross-section’s shapes on the axial load behaviour of hollow steel columns, this study has presented eight different cross-sections shapes and has indicated their effect on the axial load behaviour of the polygonal hollow steel columns. Eighty different FE models have been designed and analysed to find the effect of the cross-section shape, thickness, length, and materials on the axial load behaviour of the polygonal hollow steel columns. The FE results have proved that the cross-sectional shapes affect the ultimate axial load behaviour of the hollow steel tubes by 14%. The highest ultimate axial load resistance recorded by Rec. model has been followed by Squ. unlike Cir. model, which has presented the lowest ultimate axial load resistance followed by Ova. model. This study also demonstrates that when the cross-sectional shape of the hollow steel tubes is near to a rectangular shape, the ultimate axial load resistance will be higher, while, if it is near to a circular shape then low ultimate axial load has been registered. Moreover, there is a small effect of the steel tube thickness, length and material on the axial load behaviour of the hollow steel tubes with different cross-sectional shapes, with almost -2% to -14%.

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

Cyclic loading tests and horizontal bearing capacity of recycled concrete filled circular steel tube and profile steel composite columns

To investigate the seismic performance of recycled aggregate concrete (RAC) filled circular steel tube and profile steel composite columns, the cyclic loading tests were conducted for eleven columns. The influences of design parameters on the seismic performance of composite columns were considered and investigated in detail, including the replacement percentage of recycled coarse aggregate (RCA), diameter to thickness ratio of circular steel tube, axial compression ratio, profile steel ratio and section form of profile steel. The failure characteristics, hysteresis loops, skeleton curves, stiffness degradation, ductility and storey drift ratio of columns were presented and discussed in detail. The results show that the column base forms an obvious plastic hinge under the combined action of horizontal cyclic loads and vertical loads, which belongs to the typical compression-bending failure. The hysteresis loops of composites columns are plump and spindle-shaped, indicating good energy dissipation capacity. With the increase of RCA replacement percentage, the ductility and energy dissipation capacity of columns decrease gradually, while the bearing capacity and stiffness of columns firstly reduce and then increase. The seismic performance of columns is significantly improved by the increasing wall thickness of circular steel tube and profile steel ratio. Increasing the axial compression ratio is unfavorable to the seismic performance of columns. The greater the axial compression ratio, the worse the ductility and energy dissipation capacity of column. Based on the test analysis and relevant specifications, the modified formulas on the horizontal bearing capacity of RAC filled circular steel tube and profile steel composite columns were proposed, and the validity of formula was verified by comparing with the test results.

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.

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.

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.

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.