• Computers and Concrete
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• v.26 no.4
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• pp.343-350
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• 2020

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 15.22℃, 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.

• Steel and Composite Structures
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• v.11 no.4
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• pp.307-324
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• 2011

With the increasing use of concrete-filled steel tubes (CFST) as structural members, there is a growing need to provide suitable measures for possible strengthening or repair of these kinds of structural elements. Fibre reinforced polymer (FRP) jacketing is a recent method and is particularly attractive in which it does not significantly increase the section size, and is relatively easy to install. Thus, it can be used to enhance strength and/or ductility of CFST members. Very little information is available on the performance of FRP-strengthened CFST members under fire conditions. This paper is an attempt to study the fire performance of CFST columns strengthened by FRP. The results of fire endurance tests on FRP-strengthened circular CFST columns are presented. Failure modes of the specimens after exposure to fire, temperatures in the cross section, axial deformation and fire resistance of the composite columns are analysed. It is demonstrated that the required fire endurance can be achieved if the strengthened composite columns are appropriately designed.

• Steel and Composite Structures
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• v.30 no.2
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• pp.171-183
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• 2019

As China's infrastructure continues to grow, concrete filled steel tubular (CFST) structures are attracting increasing interest for use in engineering applications in earthquake prone regions owing to their high section modulus, high strength, and good seismic performance. However, in a corrosive environment, the seismic resistance of the CFST columns may be affected to a certain extent. This study attempts to investigate the mechanical behaviours of square CFST members under both a cyclic load and an acid rain attack. First, the tensile mechanical properties of steel plates with various corrosion rates were tested. Second, a total of 12 columns with different corrosion rates were subjected to a reversed cyclic load and tested. Third, comparisons between the test results and the predicted ultimate strength by using four existing codes were carried out. It was found that the corrosion leads to an evident decrease in yield strength, elastic modulus, and tensile strain capacity of steel plates, and also to a noticeable deterioration in the ultimate strength, ductility, and energy dissipation of the CFST members. A larger axial force ratio leads to a more significant resulting deterioration of the seismic behaviour of the columns. In addition, the losses of both thickness and yield strength of an outer steel tube caused by corrosion should be taken into account when predicting the ultimate strength of corroded CFST columns.

• Steel and Composite Structures
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• v.15 no.6
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• pp.623-643
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• 2013

Concrete filled steel tubular members (CFST) become a popular choice for modern building construction due to their numerous structural benefits and at the same time aging of those structures and member deterioration are often reported. Therefore, actions like implement of new materials and strengthening techniques become essential to combat this problem. The application of carbon fibre reinforced polymer (CFRP) with concrete structures has been widely reported whereas researches related to strengthening of steel structures using fibre reinforced polymer (FRP) have been limited. The main objective of this study is to experimentally investigate the suitability of CFRP to strengthening of CFST members under flexure. There were three wrapping schemes such as Full wrapping at the bottom (fibre bonded throughout entire length of beam), U-wrapping (fibre bonded at the bottom throughout entire length and extended upto neutral axis) and Partial wrapping (fibre bonded in between loading points at the bottom) introduced. Beams strengthened by U-wrapping exhibited more enhancements in moment carrying capacity and stiffness compared to the beams strengthened by other wrapping schemes. The beams of partial wrapping exhibited delamination of fibre and were failed even before attaining the ultimate load of control beam. The test results showed that the presence of CFRP in the outer limits was significantly enhanced the moment carrying capacity and stiffness of the beam. Also, a non linear finite element model was developed using the software ANSYS 12.0 to validate the analytical results such as load-deformation and the corresponding failure modes.

• Steel and Composite Structures
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• v.25 no.4
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• pp.443-456
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• 2017

Many authors have established the usefulness of concrete filled steel tubular (CFST) sections as compression members while few have proved their utility as flexural members. To explore their prospective as part of CFST frame structures, two types of connections using extended end plate and seat angle are proposed for exterior joints of CFST beams and CFST columns. To investigate the performance and failure modes of the proposed bolted connections subjected to static loads, an experimental program has been executed involving ten specimens of exterior beam-to-column joints subjected to monotonically increasing load applied at the tip of beam, the performance is appraised in terms of load deformation behaviour of joints. The test parameters varied are the beam section type, type and diameter of bolts. To validate the experimental behaviour of the proposed connections in CFST beam-column joints, finite element analysis for the applied load has been performed using software ATENA-3D and the results of the proposed models are compared with experimental results. The experimental results obtained agree that the proposed CFST beam-column connections perform in a semi-rigid and partial strength mode as per specification of EC3.

• Steel and Composite Structures
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• v.13 no.3
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• pp.259-275
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• 2012

Concrete filled steel tubular (CFST) member has been widely used in the construction of high-rise buildings for its high axial bearing capacity. It can also be applied on long-span structures such as spatial structures or bridges not only for its high bearing capacity but also for its construction convenience. Concrete casting effect of CFST member is considered in the study of its bearing capacity in this paper. Firstly, in order to authenticate the applicability of constitutive relationship and yield criterion of steel and concrete based on FEM, two ANSYS models are built to simulate and compared with other's test. Secondly, in order to find the huge difference in bearing capacity due to different construction processes, two full-size CFST models are studied when they are horizontally cast and axially compressed. Finally, the effects of slenderness ratio (L/D) and confining parameter (D/t) of CFST members are studied to reveal the intrinsic links between bearing capacity and slenderness ratio or confining parameter.

• Steel and Composite Structures
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• v.47 no.5
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• pp.645-661
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• 2023

Concrete-filled steel tubular columns with double inner steel tubes (CFST-DIST) are a novel type of composite members developed from conventional concrete-filled steel tubular (CFST) columns. This paper investigates the structural performance of circular CFST-DIST stub columns using nonlinear finite element (FE) analysis. A numerical model was developed and verified against existing experimental test results. The validated model was then used to compare circular CFST-DIST stub columns' behavior with their concrete-filled double skin steel tubular (CFDST) and CFST counterparts. A parametric study was performed to ascertain the effects of geometric and material properties on the axial performance of CFST-DISTs. The FE results and the available test data were used to assess the accuracy of the European and American design regulations in predicting the axial compressive capacity of circular CFST-DIST stub columns. Finally, a new design model was recommended for estimating the compressive capacity of CFST-DISTs. Results clarified that circular CFST-DIST columns had the advantages of their CFST counterparts but with better ductility and strength-to-weight ratio. Besides, the investigated design codes led to conservative predictions of the compressive capacity of circular CFST-DIST columns.

• Steel and Composite Structures
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• v.35 no.1
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• pp.93-109
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• 2020

Developed from conventional concrete filled steel tubular (CFST) members, concrete-encased CFST has attracted growing attention in building and bridge practices. In actual construction, the inner CFST is erected prior to the casting of the outer reinforced concrete part to support the construction preload, after which the whole composite member is under sustained service load. The complex loading sequence leads to highly nonlinear material interaction and consequently complicated structural performance. This paper studies the full-range behaviour of concrete-encased CFST columns with initial preload on inner CFST followed by sustained service load over the whole composite section. Validated against the reported data obtained from specifically designed tests, a finite element analysis model is developed to investigate the detailed structural behaviour in terms of ultimate strength, load distribution, material interaction and strain development. Parametric analysis is then carried out to evaluate the impact of significant factors on the structural behaviour of the composite columns. Finally, a simplified design method for estimating the sectional capacity of concrete-encased CFST is proposed, with the combined influences of construction preload and sustained service load being taken into account. The feasibility of the developed method is validated against both the test data and the simulation results.

• Smart Structures and Systems
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• v.19 no.2
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• pp.181-194
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• 2017

In order to investigate the interface debonding defects detection mechanism between steel tube and concrete core of concrete-filled steel tubes (CFSTs), multi-physical fields coupling finite element models constituted of a surface mounted Piezoceramic Lead Zirconate Titanate (PZT) actuator, an embedded PZT sensor and a circular cross section of CFST column are established. The stress wave initiation and propagation induced by the PZT actuator under sinusoidal and sweep frequency excitations are simulated with a two dimensional (2D) plain strain analysis and the difference of stress wave fields close to the interface debonding defect and within the cross section of the CFST members without and with debonding defects are compared in time domain. The linearity and stability of the embedded PZT response under sinusoidal signals with different frequencies and amplitudes are validated. The relationship between the amplitudes of stress wave and the measurement distances in a healthy CFST cross section is also studied. Meanwhile, the responses of PZT sensor under both sinusoidal and sweep frequency excitations are compared and the influence of debonding defect depth and length on the output voltage is also illustrated. The results show the output voltage signal amplitude and head wave arriving time are affected significantly by debonding defects. Moreover, the measurement of PZT sensor is sensitive to the initiation of interface debonding defects. Furthermore, wavelet packet analysis on the voltage signal under sweep frequency excitations is carried out and a normalized wavelet packet energy index (NWPEI) is defined to identify the interfacial debonding. The value of NWPEI attenuates with the increase in the dimension of debonding defects. The results help understand the debonding defects detection mechanism for circular CFST members with PZT technique.

• Steel and Composite Structures
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• v.47 no.3
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• pp.405-421
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• 2023

An experimental study on six axially-loaded composite short columns with different thicknesses of steel tube and that of the concrete plate was carried out. Compared to the mechanical behavior of component specimens under axially compressed, the failure modes, compression deformation, and strain process were obtained. The two main parameters that have a significant enhancement to cross-sectional strength were also analyzed. The failure of an axially loaded UHPC-CFST short column is due to the crushing of the UHPC plate, while the CFST member does reach its maximum resistance. A reduction coefficient K'c, related to the confinement coefficient, is introduced to account for the contribution of CFST members to the ultimate load-carrying capacity of the UHPC-CFST composite short columns. Based on the regression analysis of the relationship between the confinement index ξ and the value of fcc/fc, a unified formula for estimating the axial compressive strength of CFST short columns was proposed, combined with the experimental results in this research, and an equation for reliably predicting the strength of UHPC-CFST composite short columns under axial compression were also proposed.