Concrete-filled Steel Tubular Members Research Articles

Strength Analysis of Concrete-Filled Steel Tubes on the Basis of Plasticity Conditions

The methods of calculating the strength of concrete-filled steel tubular members based on the theories of plasticity of Saint-Venan and Huber-Mises-Genka are developed in the article. The criterion for the destruction of the composite element is the ultimate limit state. The strength of the normal cross-section of a cylindrical concrete-filled steel member at axial compression is determined taking into account the meridional pressure of the concrete on the tube and axial stress in it. The equation of strength of the tubular member is obtained, in which the stress in the tube reaches the design yield strength of steel at the moment of destruction of the element, that is, the strength of the materials is used completely. An example of the calculation is performed and the results of the calculation is compared with the experimental data for 13 samples.

Flexural behaviour of stiffened and multi-cell L-shaped CFSTs considering different loading angles

Stiffened and multi-cell L-shaped concrete-filled steel tubular (CFST) members are often subjected to the loads from different loading angles as corner columns. Moreover, the flexural behaviour is the basis for the research of beam-columns and the determination of axial force-bending moment interaction curves. However, little work has been done on the flexural behaviour of these kinds of members at different loading angles. In this study, a total of 11 L-shaped CFST specimens with the variables of sectional type and loading angle were tested under pure bending. The failure mode, bending moment-deflection curves, moments-strain curves, deflection curves, flexural capacity and stiffness were investigated. It was found that the influence of loading angles is significant. The flexural capacity and stiffness of the specimens are highest at 135°, middle at 0° and 180°, and lowest at 45° and 225°. Setting longitudinal stiffeners or using multi-cell cross-section can improve the flexural capacity by about 20%. Then a finite element model was developed incorporating residual stress and cold-formed effect. Considering the effect of loading angles on the basis of the design model at 0°, the simplified formulas for flexural capacity of the stiffened and multi-cell L-shaped CFST members were proposed.

Out-of-plane stability of fixed concrete-filled steel tubular arches under uniformly distributed loads

In recent years, concrete-filled steel tubular (CFST) arches have been widely used and the out-of-plane buckling of CFST arches has become a major concern. So far, few studies have investigated the out-of-plane behaviours of CFST arches, and no codes have given the design formula of the out-of-plane stability bearing capacity. Therefore, in this paper fixed CFST parabolic arches with a circular cross-section under uniformly distributed loads are investigated. Considering the effect of material and geometric non-linearity, the distributions of the internal forces and deformations are observed, and on this basis an equivalent column model is established to derive the out-of-plane effective length coefficient. In addition, based on the stability theory, the nominalised slenderness ratio of CFST arches is modified considering the influence of rise-to-span ratios and can be substituted into any available stability coefficient equations in current design codes to calculate the out-of-plane bearing capacity of CFST parabolic arches. The proposed equation – which has a form of formula similar to the available stability equations in existing designing codes for CFST or steel members and which has an accuracy equal to or greater than the equations in the available literature – would be easier for the designers to accept and use.

Experimental and numerical studies on square steel-reinforced concrete-filled steel tubular (SRCFST) members subjected to lateral impact

Steel-reinforced concrete-filled steel tubular (SRCFST) structures were proposed in recent years and have been employed in engineering practices. To date, the existing studies mainly focused on the behaviours of SRCFST structural members under static or seismic load. Only very limited studies of the SRCFST structural members subjected to impact load, which might cause severe damage and even structural collapse, can be found in literature. In this study, experimental and numerical studies on square SRCFST specimens under lateral impact load are conducted. A total of eighteen square SRCFST specimens are fabricated and tested via a drop hammer impact device. Various parameters (i.e. impact velocity, boundary condition, impact direction, cross-section of steel profile and axial load level) are considered to evaluate their effects on impact responses of square SRCFST members. The damage modes, impact forces, mid-span displacement responses and energy absorption capacities of the tested specimens are extracted from testing data and analysed. Furthermore, by using the software ABAQUS, numerical model is established and validated with the testing results. With the validated numerical models, the damage evolution, sectional stress and energy distribution of the structure with different parameters and impacting scenarios are evaluated. The impact behaviours of square SRCFST and concrete-filled steel tubular (CFST) members are also compared and discussed.

Concrete filled double skin square tubular stub columns subjected to compression load

Concrete filled double skin tubular members (CFDST) consist of double concentric circular or square steel tubes with concrete filled between the two steel tubes. The CFDST members, having a hollow section inside the internal tube, are generally lighter than ordinary concrete filled steel tubular members (CFT) which have a solid cross-section. Therefore, when the CFDST members are applied to bridge piers, reduction of seismic action can be expected. The present study aims to investigate, experimentally, the behavior of CFDST stub columns with double concentric square steel tubes filled with concrete (SS-CFDST) when working under centric compression. Two test parameters, namely, inner-to-outer width ratio and outer square steel tube's width-to-thickness were selected and outer steel tube's width-to-thickness ratio ranging from 70 to 160 were considered. In the results, shear failure of the concrete fill and local buckling of the double skin tubes having largest inner-toouter width ratio were observed. A method to predict axial loading capacity of SS-CFDST is also proposed. In addition, the load capacity in the axial direction of stub column test on SS-CFDST is compared with that of double circular CFDST. Finally, the biaxial stress behavior of both steel tubes under plane stress is discussed.

Fully nonlinear inelastic analysis of rectangular CFST frames with semi-rigid connections

In this study, an effective numerical method is introduced for nonlinear inelastic analyses of rectangular concrete-filled steel tubular (CFST) frames for the first time. A steel-concrete composite fiber beam-column element model is developed that considers material, and geometric nonlinearities, and residual stresses. This is achieved by using stability functions combined with integration points along the element length to capture the spread of plasticity over the composite cross-section along the element length. Additionally, a multi-spring element with a zero-length is employed to model the nonlinear semi-rigid beam-to-column connections in CFST frame models. To solve the nonlinear equilibrium equations, the generalized displacement control algorithm is adopted. The accuracy of the proposed method is firstly verified by a large number of experiments of CFST members subjected to various loading conditions. Subsequently, the proposed method is applied to investigate the nonlinear inelastic behavior of rectangular CFST frames with fully rigid, semi-rigid, and hinged connections. The accuracy of the predicted results and the efficiency pertaining to the computation time of the proposed method are demonstrated in comparison with the ABAQUS software. The proposed numerical method may be efficiently utilized in practical designs for advanced analysis of the rectangular CFST structures.

Seismic Behavior of Elliptical Concrete‐Filled Steel Tubular Columns under Combined Axial Compression and Cyclic Lateral Loading

Elliptical concrete‐filled steel tubular (CFST) column is a new form of CFST columns, consisting of an outer elliptical tube filled with concrete. Although the study on mechanical performance of the elliptical CFST members is receiving more and more attention, they have been limited to static behavior. Against this background, an experimental study on elliptical CFST columns was carried out under combined axial compression and cyclic lateral loading. The failure modes, hysteretic curves, skeleton curves, load carrying capacity, deformability, stiffness degradation, and energy dissipation ability was obtained and discussed. The test results indicated that the elliptical CFST columns possess excellent seismic performance and ductility. Valuable experimental data were provided for the formulation of the theoretical hysteresis model of the elliptical CFST columns.

Transverse Impact on Hollow and Concrete Filled Steel Tubular Members

This paper clarifies a review of research progress in the transverse impact process on hollow and Concrete Filled Steel Tubular (CFST) members and their dynamic response under impact loading. This review emphases analytical, numerical and experimental studies recently performed by many researchers. It clarifies the influence of some fundamental parameters on the impact performance such as; axial load level, impact energy, steel ratio, constraining (confining factor), steel tube thickness, diameter-to-thickness ratio of the steel tube. In addition to exploring the effect of concrete and steel material properties and specimen boundary conditions. It also goes through the effect of using Carbon Fiber Reinforced Polymer (CFRP) jackets. The review explained with detailed discussions the stages of impact process, impact energy, dissipated energy, failure modes, life-cycle performance of Concrete Filled Steel Tubular (CFST) members subjected to impact load. The influence of strain rates on the performances of concrete and steel are discussed as well.

A Study on Effect of Steel Tube in Axial Behavior of CFST Stubs

Concrete filled steel tubular (CFST) columns are becoming popular due to its advantages from both steel and concrete in resisting loads. CFST members are made up of steel hollow section of rectangular or circular sections filled with plain or reinforced concrete. CFST columns can be used effectively in high raised structures and in bridges. The reduced cross sections of columns can be achieved by the composite action of steel and concrete. The steel tube provides confinement to the concrete and helps to improve load carrying capacity. The concrete core offers higher resistance to axial compression. The inward buckling of steel tube will be avoided due to concrete and the out buckling resistance may be improved due to higher stiffness of the column due to higher gross moment inertia with combined effect of steel and concrete. This experimental work made an attempt to understand the effect of thickness of steel tube in behavior of CFST stubs.In the present experimental study, a total of 24 cylindrical concrete filled steel tube specimens were prepared to evaluate the uniaxial compressive behavior and to understand the effect of thickness and aspect ratio (h/D) on the compressive strength. Two different thickness of steel tubes 3 mm and 5 mm and four aspect ratios (h/D) 1, 2, 3 and 4 are considered in the present study. M30 grade of concrete is used. From this study, as the aspect ratio increases the buckling loads decreases. The decrement is up to 37% in aspect ratio 4 when compared to aspect ratio1.

Thermal field of large-diameter concrete filled steel tubular members under solar radiation

Concrete-filled steel tubular (CFST) members have been widely used in engineering, and their tube diameters have become larger and larger. But there is no research on the thermal field of large-diameter CFST structure. These studies focused on the thermal field of the large-diameter CFST structure under solar radiation. The environmental factors and the actual placement position were considered, and the finite element model (FEM) of the thermal field of CFST members under solar radiation (SR) was established. Then the FEM was verified by practical experiments. The most unfavorable temperature gradient model in the cross-section was proposed. The testing results showed that the temperature field of the large-diameter CFST member section was non-linearly distributed due to the influence of SR. The temperature field results of CFST members with different pipe diameters indicated that the larger the core concrete diameter was, the slower the central temperature changed, and there was a significant temperature difference between the center and the boundary. Based on the numerical model, the most unfavorable temperature gradient model in the section was proposed. The model showed that the temperature difference around the center of the circle is small, and the boundary temperature difference is significant. The maximum temperature difference is 15.22oC, which appeared in the southern boundary area of the specimen. Therefore, it is necessary to consider the influence of SR on the thermal field of the member for large-diameter CFST members in actual engineering, which causes a large temperature gradient in the member.

Investigation on the lateral impact responses of circular concrete-filled double-tube (CFDT) members

To meet specific design requirements or achieve superior structural performances, a new type of concrete-filled steel tubular (CFST) composite structure called as concrete-filled double-tube (CFDT) was proposed in recent years. Despite intensive studies on structural performances of CFDT members under various loading conditions, very limited investigations on impact responses of CFDT members can be found in literature. During the service life structural members may be subjected to extreme loads such as impact load, therefore the investigation on impact responses of CFDT members is essential for impact resistant design and assessment. This paper presents experimental study and finite element analysis (FEA) results of lateral impact responses of circular CFDT members. A total of twelve circular CFDT specimens with various parameters are tested by utilizing a drop hammer impact system. The damage modes, impact forces, displacement responses and energy absorption capacities of CFDT members from the impact tests are evaluated and compared, followed by numerical simulations using explicit software ABAQUS. With the verified numerical models, the damage evolution of each component and its contribution to impact loading resistance are extracted and analysed. In addition, the performances of CFDT and common CFST members under impact loading are compared.

Behaviour and design of ultra-high-strength CFST members subjected to compression and bending

A comprehensive experimental and numerical study on the axial and flexural behaviour of square concrete-filled steel tubular (CFST) members incorporating S960 ultra-high-strength steels and high-strength concrete (C70 and C100) is reported in the present paper. An experimental programme that consisted of eighteen stub and slender CFST members under various loading conditions was conducted. The test results showed that the nominal compressive and flexural strength of ultra-high-strength CFST members were achieved. Steel coupon tests, concrete compressive strength tests and geometric imperfection measurements were also carried out. In addition, numerical models which accounted for geometric imperfections and residual stresses were developed. A confined concrete model was employed in the numerical analysis to simulate concrete confinement effects. Validation against the experimental results demonstrated the accuracy and reliability of the developed model. A series of parametric studies were performed to evaluate the effects on the ultimate strength by changing the steel yield strength, concrete compressive strength, steel tube width-to-thickness ratio and member slenderness ratios for different loading conditions. Comparisons of the results were made with the current codes of practice including AS/NZS 2327, Eurocode 4 and ANSI/AISC 360, which indicated that all the provisions were conservative in predicting the axial and flexural resistance of CFST members with recommended curves.

Experimental investigation and FE modelling of the flexural performance of square and rectangular SRCFST members

In this study, experimental investigation and finite element (FE) modelling of the flexural performance of square and rectangular steel-reinforced concrete-filled steel tubular (SRCFST) members are carried out. Six square SRCFST specimens and four rectangular ones are fabricated and tested to obtain their failure modes, the strain data, the deformation and the moment capacity under four-point bending. The effects of profiled steel configuration, loading planes, shear-span ratios (a/D) and depth-to-width ratios (D/B) on the flexural performance of SRCFST members are evaluated. Moreover, the experimental data reported in this study are employed to verify the numerical model comprehensively. Thereafter, the verified FEA model is utilized to evaluate the stress distribution, the interaction between steel and concrete, the moment resisted by each component and the role of embedded profiled steel. Finally, the measured bending moment capacities are adopted to calibrate the accuracy of existing design method on SRCFST members stipulated in Eurocode 4 (EC4) (2004), while the results demonstrate that high accuracy for the prediction of bending moment capacity can be obtained.

Performance of steel-reinforced circular concrete-filled steel tubular members under combined compression and torsion

Only limited investigations on mechanical behavior of circular steel-reinforced concrete-filled steel tube (SRCFST) under coupled compression and torsion have been reported in open literature. Therefore, eighteen circular SRCFST members were tested to study the torsional behavior. The effects of various parameters, i.e., sectional forms of steel reinforced, axial compression ratios, loading paths and slenderness ratios were considered, respectively. The failure modes, torsional moment-rotation angle curves and torsional moment-strain curves of SRCFST members derived from the loading tests were investigated and discussed, respectively. Test results show that the development of concrete crack is effectively restrained due to the embedded steel reinforced. When the ratio of steel reinforced is the same, the torsional bearing capacity of specimens with internal cross-shaped steel is very close to that of specimens with internal I-shaped steel. The axial compression ratios and the slenderness ratios showed significant impact on the torsional rigidity and ultimate torsional bearing capacity (Tue). In addition, a finite element model was developed and verified against the testing results, which can accurately predict the Tue, and finally the formulas for calculating the Tue of specimens with internal I-shaped steel and cross-shaped steel were proposed, respectively.

Prediction Formula for Temperature Gradient of Concrete-Filled Steel Tubular Member with an Arbitrary Inclination

Abstract Concrete-filled steel tubes (CFSTs) have been used extensively as main members with different inclinations in bridge structures; however, investigations on the influence of member inclinat...

Behavior of concrete-filled steel tubes subjected to axial impact loading

Investigations on concrete-filled steel tubular (CFST) members under static loads have been extensively reported. Still, limited researches have been conducted to investigate the behavior of CFST columns subjected to axial impact loading. This paper presents an experimental study on dynamic behaviors of twelve square and rectangular CFST stub columns subjected to axial impact loading using a drop-weight test apparatus. The instantaneous force and deformation states were recorded during the impact tests. Finite element (FE) models were established and verified using the experimental results and existing research data, in which the strain rate effects of steel and concrete were fully considered. Then the effects of cross-section shape, steel strength, concrete compressive strength, steel ratio and impact energy condition on the dynamic responses of the CFST stub columns were studied using the FE models. The experimental and analytical studies indicate that the circular CFST stub columns perform better than the square and rectangular ones. While, little difference can be found between the square and rectangular CFST stub columns. For all the three shaped CFST stub columns, the average platform impact force increases and the deformation decreases with the increase of steel strength, concrete compressive strength, steel ratio and section area. Based on the parameter studies, a simplified design method was proposed by establishing the relationship between the maximum axial displacement and the impact energy condition to predict the deformation response of CFST stub columns under axial impact.

Data for ultimate bearing capacity of concrete-filled steel tubular members and arches by the elastic modulus reduction method.

Homogeneous generalized yield function is adopted in this article to calculate the ultimate bearing capacity of 93 concrete-filled steel tubular components with detailed test data, and the ratios of the ultimate bearing capacity calculated to the tested are presented. Moreover, the incremental nonlinear finite element method and elastic modulus reduction method are adopted to evaluate the ultimate bearing capacity of 11 concrete-filled steel tubular arches, 7 among which with detailed test data. The component data cover those under different loading conditions, material strength and geometric parameters, and the arch data include those under different loading conditions and rise to span ratios. The data provided are useful to investigate the strength of CFST members and arches and to demonstrate the validation of other numerical methods. The current data are considered as a complementary for the main work “Linear elastic iteration technique for ultimate bearing capacity of circular CFST arches” [1].

Creep-Effected Dynamic Response of a Concrete-Filled Steel Tubular Member in Axial Compression and Impact Load

The finite element model of a tubular member under the combined action of axial compression, creep, and axial impact was constructed with the numerical analysis software, to evaluate the core concrete creep effect on the dynamic responses of a steel tubular member in axial compression. In the model, the creep effect of core concrete of different age is equivalent to the change of its elastic modulus. Then, the dynamic responses of a tubular member in axial compression and impact were simulated considering the creep effect, time-history curves of impact load, contact time, axial deformation, stress and strain were plotted, and the effect of creep on them was discussed. The impact load peak decreases with the development of the core concrete creep, and the most is about 51%; the contact time and axial deformation increase; the concrete stress decreases, but the concrete strain increases greatly. The minimum and maximum principal concrete strains after 30 years exceeded those after 28 days by 6.35 and 8.6 times, respectively. The core concrete creep has a less effects on the stress and strain of the steel tube. The fruits provide a scientific help for the impact resistance design of a concrete-filled steel tubular member in axial compression.

Concrete-filled steel tubes subjected to axial compression: Life-cycle based performance

This paper presents a life-cycle based finite element analysis modelling for concrete-filled steel tubular (CFST) stub columns. The effects of initial imperfections (e.g., residual stresses induced by cold forming or welding, and initial geometric imperfections), preloads during the construction process, long-term sustained loads and corrosion are considered in the modelling. To reveal the life-cycle time-dependent behaviour of CFST stub columns, influences of the above factors on the full-range load-displacement relations and the load-transfer mechanism are discussed in regard of five typical working conditions as: Case 0 - short-term loading; Case 1 - initial imperfection with short-term loading; Case 2 - initial imperfection, short-term loading followed by sustained load; Case 3 - initial imperfection, short-term loading followed by sustained load and corrosion; as well as Case 4 - initial imperfection, preload, short-term loading, sustained load and corrosion. Considering the effects of these factors, definition of the ultimate state of CFST stub columns under typical working conditions are discussed. Parametric studies are then carried out to calibrate the simplified design models for CFST stub columns at different loading cases. A database with information of 1096 CFST stub column specimens are established. Reliability analysis proves that the proposed simplified methods meet the reliability requirements in accordance with current design standards for CFST members under the five discussed cases. Partial factor for axial compressive strength of the composite section is suggested at the end of this paper.

Seismic performance of stiffened concrete-filled double skin steel tubes

The concrete-filled double skin steel tubular (CFDST) members have been used in many engineering projects. The stiffened outer steel tube could be used to further enhance the structural performance and reduce the steel consumption, while the seismic behaviour of the stiffened member needs investigation. In this study, tests of 6 stiffened CFDST beam-columns were conducted under both constant axial load and cyclic lateral load. Main test parameters were the axial load level and the hollow section ratio. The load, deformation and strain of all specimens were recorded and analysed. The influence of parameters was discussed in terms of the lateral resistance, the ultimate displacement, the ductility and the energy dissipation ability. It showed that the stiffened specimens exhibited good energy dissipation capacity under the cyclic loading. A finite element (FE) model was developed to carry out the mechanism and parametric analysis. The longitudinal stiffeners could effectively reduce the local buckling of the tube wall. The ductility and energy dissipation capacity of stiffened CFDST members are generally higher than that of unstiffened ones. Finally, equations for predictions of the flexural stiffness and strength, as well as the hysteretic model of the load-deformation relationship were proposed for stiffened CFDST members.