Concrete-filled Tubular Columns Research Articles

Experimental and analytical investigation of the behavior of diaphragm-through joints of concrete-filled tubular columns

Experimental and analytical investigation of the behavior of diaphragm-through joints of concrete-filled tubular columns

The Ultimate Strength of the Concrete-Filled Tubular (CFT) Section Columns

This paper describes design strength of concrete-filled tubular (CFT) section columns accounting for local buckling of steel skin. The local buckling has a negative effect on the ultimate compression strength based on the yield stress of steel skin and nominal compressive strength of in-filled concrete. A squash load formula for CFT stub columns is proposed to account for the post-local-buckling strength of steel skin. A compressive strength formula for filled-in concrete accounting for the confining effect of steel skin and strength ratio between filled-in concrete and steel skin is also proposed. The squash loads predicted by the proposed strength formula for the direct strength method were compared with the AISC (2010) and Eurocode4 (2004). The comparison showed that the squash load formula proposed can predict conservatively the squash load of circular and rectangular CFT columns with local buckling

Behaviour of restrained structural subassemblies of steel beam to CFT column in fire during cooling stage

During the well publicised Cardington structural fire research programme, parts of some connections suffered fracture during cooling. This led some to believe that fire spread and structural collapse may occur during the cooling stage of a fire and therefore this issue should be considered in structural fire engineering design. This paper focuses on steel framed structures using concrete filled tubular (CFT) columns and the objective of this paper is to find means of reducing the risk of structural failure during cooling. It reports the results of a study using the general finite element software ABAQUS to numerically model the behaviour of restrained structural subassemblies of steel beam to CFT columns and their joints both in fire, emphasising on the cooling stage. Validation of the finite element model was achieved by comparing the simulation and test results for the two fire tests investigating cooling behaviour, recently conducted at the University of Manchester on similar structures. In these two tests, the test assembly was heated to temperatures close to the limiting temperature of the steel beam and then cooled down while still maintaining the applied loads on the beam. One of the tests used reverse channel connection and the other test used fin plate connection. The finite element models give very good agreement with the experimental results and observations. Remarkable differences in tensile forces in the connected beams were observed during the tests depending on the beam temperature at which cooling started. This leads to the suggestion that in order to avoid connection fracture during cooling, it may be possible to reduce the limiting temperature of the connected beam by a small value (<50°C) from the limiting temperature calculated without considering any axial restraints in the beam.

Strength and ductility of concrete-filled tubular piers of integral bridges

In this paper, an analysis of the structural response of concrete-filled tubular columns (CFT) when subjected to combined bending and compression is presented. The reference frame of the study is the usage of such members as piers of integral bridges. The main objective of the study is to assess both the resistance and the ductility of these structural elements when subjected to lateral displacements. These displacements, together with the corresponding axial forces, represent actions to which the integral bridges piers might be subjected to. For the sake of studying this response, a numerical model is used as a simulation tool over a hypothetical matrix of CFT with realistic proportions. A parametric study is undertaken to monitor the influence of the steel contribution- and the length-to-diameter ratios on the strength and ductility of the CFT. These numerical studies together with a wide experimental database found in the literature have been useful for drawing conclusions concerning these topics. A design proposal concerning the cross-sectional capacity of the CFT, based on the studies performed by other researchers which accounts for confinement, is provided. This proposal has been compared with the present EN1994 formulation. In addition, design formulae which might characterize the ductility of the CFT in terms of the maximum allowable lateral displacements are provided for non-slender CFT piers of integral bridges.

Effect of transient strain on strength of concrete and CFT columns in fire – Part 1: Elevated-temperature analysis on a Shanley-like column model

This paper presents elevated-temperature analysis on a Shanley-like column model, as part of a study on the effect of transient strain on the strength of concrete and concrete-filled tubular columns in fire. Three high-temperature concrete material models are applied and the structural behaviours of the Shanley-like model using these three material models are compared. The effects of transient strain of concrete have been investigated by comparing the results of the analyses with and without considering this property, under the assumption that the temperature distribution within the model is uniform. The model has been evaluated against the tangent-modulus and reduced-modulus critical buckling loads at elevated temperatures. Numerical analyses have been carried out under both steady-state and transient heating scenarios, in order to investigate the influence of each on high-temperature structural analysis of the type described in this paper. It is seen that considering transient strain causes a considerable reduction of the buckling resistance, irrespective of the concrete material models and loading–heating schemes used.

Effect of transient strain on strength of concrete and CFT columns in fire – Part 2: Simplified and numerical modelling

This paper presents finite element analysis on columns of concrete and concrete-filled tubular section. This study has been conducted with Vulcan, a specialist structural fire engineering FE program, which has been further developed to incorporate the transient strain of concrete. The implementation of transient strain in Vulcan has been validated against a Shanley-like simplified model. A further extension of the simplified model has been carried out in order to provide direct comparability with the FE modelling. The effects of transient strain, considering thermal gradients through the column cross-section, have been evaluated with both the simplified and FE models. Finally, parametric studies on concrete-filled tubular columns, considering the effects of slenderness ratio, reinforcement, the steel casing and thermal gradient within the cross-section, have been conducted using Vulcan.

Simple calculation model for evaluating the fire resistance of unreinforced concrete filled tubular columns

This paper presents a method for calculating the fire resistance of unreinforced axially loaded concrete filled circular hollow section columns, based on the guidelines of Eurocode 4 Part 1.2 for the fire design of composite columns. The different design approaches which are currently available worldwide are reviewed in this paper, focusing in particular on the European code, which is discussed and analysed in depth. Several of the aspects which are nowadays missing or thought to be arguable by researchers in the Eurocode 4 method are studied and on the basis of parametric studies a new proposal is developed, so that designers can easily apply the code in the future. The parametric studies investigate the main factors affecting the fire resistance of unreinforced concrete filled tubular (CFT) columns, such as the outer diameter, the thickness of the steel tube wall, the relative slenderness of the column at room temperature and the fire exposure time, widely covering the range of values which can be found in practice. From the results of these parametric studies, equations for obtaining the equivalent temperatures of steel and concrete are developed, and appropriate flexural stiffness reduction coefficients are integrated in the simple calculation model of Eurocode 4. The method presented here is valid for centrally loaded circular CFT columns filled with unreinforced normal strength concrete, and makes possible the calculation of slender columns, extending the current limitations in buckling length of the European code.

Mechanical Behavior of Concrete-Filled Double Steel Tubular Columns under Axial Compression Load

This article analyzes five concrete-filled double steel tubular column models based on the large finite element analysis software ABAQUS. An axial compression test was carried out on specimens with different diameter-thickness ratio of internal steel tube in order to get the whole longitudinal load-displacement curves and the whole load- strain curves for internal and external steel tube and concrete. We get the ultimate bearing capacity for five specimens, the result of simulation agree well with the theoretical calculation data, that provide reliable data for concrete-filled double steel tubular column in respect of finite element (FE) simulation.

The 3D-numerical simulation on failure process of concrete-filled tubular (CFT) stub columns under uniaxial compression

Based on the heterogeneous characterization of concrete at mesoscopic level, Realistic Failure Process Analysis (<TEX>$RFPA^{3D}$</TEX>) code is used to simulate the failure process of concrete-filled tubular (CFT) stub columns. The results obtained from the numerical simulations are firstly verified against the existing experimental results. An extensive parametric study is conducted to investigate the effects of different concrete strength on the behaviour and load-bearing capacity of the CFT stub columns. The strength of concrete considered in this study ranges from 30 to 110 MPa. Both the load-bearing capacity and load-displacement curves of CFT columns are evaluated. In particular, the crack propagation during the deformation and failure processes of the columns is predicted and the associated mechanisms related to the increased load-bearing capacity of the columns are clarified. The numerical results indicate that there are two mechanisms controlling the failure of the CFT columns. For the CFT columns with the lower concrete strength, they damage when the steel tube yields at first. By contrast, for the columns with high concrete strength it is the damage of concrete that controls the overall loading capacity of the CFT columns. The simulation results also demonstrate that <TEX>$RFPA^{3D}$</TEX> is not only a useful and effective tool to simulate the concrete-filled steel tubular columns, but also a valuable reference for the practice of engineering design.

Experimental investigation of eccentrically loaded fibre reinforced concrete-filled stainless steel tubular columns

This paper presents an experimental investigation of axially and eccentrically loaded plain and fibre reinforced (FR) concrete-filled stainless steel circular tubular columns. The composite columns were pin-ended subjected to axial and eccentric loads. The stainless steel tubes were relatively slender having a diameter-to-plate thickness ratio of 50. The composite columns had different lengths varied from 3D to 12D. The column ultimate loads, load–axial shortening relationships, load–strain relationships, load–mid-height lateral deflection relationships and failure modes of the concrete-filled stainless steel circular tubular columns were measured from the tests. The study has shown that FR concrete-filled stainless steel tubular columns offer a considerable increase in column ductility compared with plain concrete-filled tubular columns. The test ultimate loads were compared with the design ultimate loads calculated using the Eurocode 4 for composite columns. Generally, it has been shown that the EC4 accurately predicted the ultimate loads of axially loaded concrete-filled stainless steel circular tubular columns, but were quite conservative for predicting the ultimate loads of the eccentrically loaded columns. It has also been shown that the conservatism of the EC4 predictions is increased as the eccentricity is increased. The test results provide useful information regarding the behaviour of FR concrete-filled stainless steel columns.

비재하 가열실험을 통한 이중강관 CFT기둥의 잔존강도 평가연구

콘크리트 충전강관 기둥은 내부의 콘크리트에 의해 축열효과로 인해 철골기둥에 비해 내화성능이 우수하며, 기둥 단면 내 철근 및 강관을 보강하여 구조적내력 및 내화성능 향상연구가 이루어져 오고 있다. 실제로 보강된 CFT기둥은 고축력을 요구하는 기둥부재로 사용 빈도 수가 증가되고 있는 추세이다. 이러한 상황에서 CFT기둥을 사용한 건축물에 화재가 발생하여 손상을 입게 되었을 경우 성능 저하정도를 정밀하게 측정할 수 있는 기법이 필요하다. 본 연구에서는 화재 발생시 CFT기둥에 대한 내부 온도 분포를 평가 하고, 단면내부의 온도분포에 따라 내부 충전콘크리트와 보강재의 내력 저하 정도를 파악하여 CFT기둥의 전체적인 잔존강도를 평가하고자 한다. The concrete-filled tubular square column is superior to steel frame column in terms of fire resistance because of the thermal storage provided by the concrete. Studies have been conducted on CFT column reinforcement with steel bars or with the use of an internal tube to improve its structural load capacity and fire resistance. In fact, reinforced CFT columns have been increasingly used to deal with high axial force. The functional deterioration of columns due to fire damage needs to be measured precisely. In this study, the temperature distribution inside the columns in case of a fire was evaluated and the degree of deterioration in the load capacity of the concrete and reinforcing members associated with temperature distribution was identified in order to evaluate the overall residual strength of the columns.

Influence of Slenderness on High-Strength Rectangular Concrete-Filled Tubular Columns with Axial Load and Nonconstant Bending Moment

AbstractForty-nine experimental tests were conducted on rectangular and square tubular columns filled with high-strength concrete (f′c=90 MPa) subjected to axial load and a nonconstant bending moment distribution. The test parameters were the length (2, 3, and 4 m), the cross-section aspect ratio (square or rectangular), the wall thickness (4 or 5 mm), and the ratio of the top and bottom first-order eccentricities r=etop/ebottom (1, 0.5, 0, and −0.5). The effect of slenderness combined with the influence of variable curvature is compared with the design loads from AISC 360-10 and Eurocode 4. The results show that, for the slender elements of this experimental campaign, both codes present a similar error close to 4%. The small error margin indicates that both standards are applicable to high-strength concrete, although the concrete tested is outside the upper bond of Eurocode 4 and AISC’s specifications. However, there are particular cases that present excessive unsafe errors. These errors correspond to th...

Earthquake Damage Model of Concrete-Filled Rectangular Tubular Column

Abstract. In order to establish damage model of concrete-filled rectangular tubular (CFRT) column, the paper utilized the cumulative dissipated hysteretic energy through 7 CFRT columns’pseudo static test. Moreover, the earthquake damage model based on CFRT columns has been set up by regression analysis. The damage model offers references for reinforcing the damaged structures caused by earthquakes and evaluating the ability of aseismatic of structures.

Methods of improving the survival temperature in fire of steel beam connected to CFT column using reverse channel connection

This paper presents the results of a numerical study, using ABAQUS, of the behaviour and methods of improving the survival temperatures in fire of steel beams to concrete filled tubular (CFT) columns using reverse channel connection. The beams are axially restrained by the connected columns and develop catenary action so their survival temperatures are primarily controlled by the joint tensile resistance and deformation capacity. Therefore, improving the beam survival temperature mainly relies on improving the joint performance. This study investigates five different joint types of reverse channel connection: extended endplate, flush endplate, flexible endplate, hybrid flush/flexible endplate and hybrid extended/flexible endplate. The connection details investigated include reverse channel web thickness, bolt diameter and grade, using fire-resistant (FR) steel for different joint components (reverse channel, end plate and bolts) and joint temperature control. The effects of changing the applied beam and column loads are also considered. It is concluded that by adopting some of the joint details to improve the joint tensile strength and deformation capacity, it is possible for the beams to develop substantial catenary action to survive very high temperatures. However, it is important that the additional catenary force in the beam is resisted by the connected columns.

Analysis of Suspended Structure System with Huge Concrete-Filled Tubular Steel Lattice Column

In order to meeting high-rise building anti-wind，anti-seismic and land for construction more angespannter situation of urban construction need, introduced a type of new structure which has advantages of seismic dissipation, a great use of materials with high strength and fewer floor spacing：the suspended structure system with huge concrete-filled tubular steel lattice column. Introduced its main structure form, member type and decorate situation by referenced to high-rise building and involved suspended structure theory，ant same time，we state fundamental way and connecting format to this structure system. So we can realize its design features，meditation and innovation case，lay a foundation for spread this new type of structure popularization and application.

Effects of Hollowness on Strength of Double Skinned Concrete Filled Steel Tubular Columns of Different Geometries under Axial Loading

Concrete filled tubular columns (CFT) have been used in buildings and bridges since long in history, and research reported in china is since 1970s. It has become popular as structural members due to their excellent structural performance characteristics, which include high strength, stiffness and high ductility. In modern building construction, steel rectangular hollow sections (RHS), square hollow sections (SHS) and circular hollow sections (CHS) are often filled with concrete to form a composite column. Such composite columns are well recognized in view of their high load carrying capacity, fast construction, small cross section, and high fire resistance. Compared to concrete-filled steel tubular (CFT) columns, the DSCFT can reduce its own weight while have a high flexural stiffness. Compared to traditional RC bridge columns and CFT columns it has high bending stiffness, avoids instability under external pressure, is light weight, possesses good damping characteristics due to increase in section modulus. In present study it is found that there is a definite increase in strength. Circular columns had all the properties better than other geometric shapes; strength increase was almost 20 % as compared to square columns. It is expected that if same ratios are maintained at projected scale, there would be a definite increase in strength and behavior of the columns. New concept of hollowness introduced is valid for all geometric shapes in DSCFTs and gives fairly good idea about its limits and effects on strength of columns. The equations given in different design codes give conservative values and hence need to be revised for DSCFTs both for seismic and normal designs.

Performance investigation of square concrete-filled steel tube columns

The behaviour of square concrete-filled steel tube columns under concentrical loading was studied. More than one hundred specimens were tested to investigate the effects of thickness of steel tube on the load carrying capacity of the concrete-filled tubular columns (CFTs). The effect of the grade of concrete and content of expansive agent were also investigated. The effect of these parameters on the confinement of the concrete core was studied as well. From the experimental study it was found that for both CFTs with different strength grade concrete core, the ultimate load carrying capacity increases with the increase in percentage of expansive agent up to 20% but it again decreases at 25% of expansive agent content. It was also shown that the failure mode of CFTs depends on the strength grade of concrete core.

Fire behavior of axially loaded slender high strength concrete-filled tubular columns

This paper describes sixteen fire tests conducted on slender circular hollow section columns filled with normal and high strength concrete, subjected to concentric axial loads. The test parameters were the nominal strength of concrete (30 and 80 MPa), the infilling type (plain concrete, reinforced concrete and steel fiber reinforced concrete) and the axial load level (20% and 40%). The columns were tested under fixed-pinned boundary conditions and the relative slenderness at room temperature was higher than 0.5 in all of the cases. A numerical model was validated against the tests, in order to extend the results and understand the failure mode of such columns. It is the aim of this paper to study the influence in a fire situation of the use of high strength concrete, as opposed to normal strength concrete. The results have shown that for slender columns subjected to high temperatures, the behavior of high strength concrete was different than for stub columns, spalling not being observed in the experiments. Furthermore, the addition of steel fibers was not found very advantageous in slender columns, since no increment in terms of fire resistance was obtained for the columns which used this type of reinforcement. However, the addition of reinforcing bars seems to be the solution in some cases, where the use of external fire protection wants to be avoided in the design of HSS structures, since the reinforcing bars allow the tube to resist a higher axial load.

Preliminary Research on Behavior of CFST Columns after Exposure to Overall Stage of Fire

A finite element analysis (FEA) model was proposed to predict the behavior of concrete-filled steel tubular (CFST) columns at overall stage of fire combined load based on ABAQUS. The whole stage includes initial loading, heating, cooling and post-fire phases. Accurate thermal and material model, element type, and solution method were chosen reasonably in the model considering the temperature and combined load. Due to lacking of test data about multi-phase of fires, the FEA model was verified with tests at different stages respectively. Some experimental specimens under different thermal and mechanical conditions were modeled using the FEA model, and the results obtained have good agreement with the experimental results. The mechanism of the CFST columns after exposure to overall stage of fire was also investigated based on the model.

Research on Seismic Behavior of Concrete Filled Square Tubular Joints with Reduced Beam Section under Cyclic Loading

The 3D nonlinear FEM models of concrete-filled square tubular column with internal diaphragms and steel beams with reduced beam section bolt-weld joints, involving geometric, materials and contact nonlinear were founded. The results of FEM are agreed to that of tests, so we can conclude that FEM in this paper is correct. Then the bearing capacity behavior of joints under cyclic loading are analyzed, including P-Δskeleton curves, P-Δ hysteretic curves, the dissipating energy ability and destruction form. The analysis results show that the plastic hinge in the joint with reduced beam section is removed to the reduced beam region. The joints that studied in this paper present excellent ductility and dissipating energy ability, therefore, all of them have a good seismic behavior.