Concrete Filled Steel Tube Reinforced Concrete Research Articles

Cyclic behavior of self-centering RCFST column to beam joints with prefabricated connectors

This paper presents the cyclic behavior of reinforced concrete-filled steel tube (RCFST) column to beam joint with prefabricated connectors. The cyclic performance of four specimens was investigated to focus on the hysteretic behavior, reinforcement tension, residual deformation, and strain distribution of joints. The equivalent viscous damping coefficients (ξeq) corresponding to the four specimens range from 0.049 to 0.087 at the yield point. And the final residual drift ratio of the specimens ranged from 3.6% to 12.9%. The tested column-beam joint specimens had good hysteretic behavior, energy dissipation, and self-centering ability. The PT steel bars without hollow channel or weakened treatment enhanced the self-centering ability and workability of joints. The finite element models were developed to verify the main mechanical properties of the self-centering RCFST column to beam joint. The average of KE/ KFEA, Mc,y/ My,FEA and Mc,p/ Mp,FEA were 0.89, 0.98, and 1.03, respectively. The FEA models could predict mechanical properties of the joints with high accuracy.

Nonlinear finite element and analytical modelling of reinforced concrete filled steel tube columns under axial compression loading

Local buckling of steel and excessive spalling of concrete have necessitated the need for the evaluation of reinforced concrete columns subjected to axial compression loading. Thus, this study investigates the behaviour of concrete filled steel tube (CFST) columns and reinforced concrete filled steel tube (RCFST) columns under the axial compression using the finite element modelling and machine learning (ML) techniques. To achieve this aim, a total of 85 columns from existing studies were analysed utilising the finite element modelling. The ultimate load of the generated datasets was predicted employing various ML techniques. The findings showed that the columns' compressive strength, ductility, and toughness were improved by reducing transverse reinforcement spacing, increasing the number of reinforcing bars, and increasing the thickness and yield strength of outer steel tube. Under the axial compression loading, the finite element modelling analysis provided an accurate assessment of the structural performance of the RCFST columns. Compared to other ML approaches, gradient boosting exhibited the best performance metrics with R2 and root mean square error values of 99.925% and 0.00708 and 99.863% and 0.00717 respectively in training and testing stages, to predict the columns' ultimate load. Overall, gradient boosting can be applied in the ultimate load prediction of CFST and RCFST columns under the axial compression, conserving resources, time, and cost in the investigation of the ultimate load of columns through laboratory testing.

Experimental Study on Supporting Capacity of Hollow Reinforced Concrete Filled Steel Tube

Hollow reinforced concrete supported specimens with different slenderness ratio and steel content were designed and the load-displacement test was carried out. The load-displacement curve of hollow reinforced concrete filled steel tube supported showed no obvious decreasing section, and the curve remained almost unchanged or slightly decreased after reaching the ultimate load, with good ductility. The bearing capacity of the support increases with the decrease of hollow ratio. The heart rate decreases from 0.33 to 0.19, and the bearing capacity increases 2.037~2.28 times. The bearing capacity calculation formula of hollow reinforced concrete filled steel tube is derived, and the improved compressive strength calculation formula of hollow reinforced concrete filled steel tube is obtained by considering the stirrup action of the member and combining with the relevant test data. At the same time, using the stability coefficient formula obtained from the regression analysis, the stability bearing capacity calculation formula of hollow concrete filled steel tube axial compression medium long column is obtained.

Axial compression behavior of reinforced concrete beam to square thin‐walled concrete‐filled steel tube column joints stiffened by internal diaphragms

AbstractA joint system was proposed to connect square thin‐walled concrete‐filled steel tube (CFST) columns and reinforced concrete (RC) beams. In the system, longitudinal beam reinforcing bars are continuous through the joint zone by passing the rectangular holes in the steel tube, aiming to achieve direct load‐transfer of the beam and joint integrity; and the square thin‐walled steel tube with holes is strengthened by internal diaphragms. Previous cyclic tests showed that the proposed joint system satisfied the requirements of strong‐joint weak‐component, namely the shear capacity of the joint zone was larger than that provided by CFST columns and RC beams. However, further research was necessary to evaluate the behavior under axial compression, as the discontinuous diagonal ribs and holes in the joint steel tube weakened the load capacity. In this investigation, the effect of internal diaphragms was first evaluated based on the axial compression tests on six square CFST stub columns. The test results showed that the internal diaphragms effectively improved the strength and ductility. The finite element analyses (FEA) on square CFST columns and RC beam to CFST column joints stiffened by internal diaphragms were then carried out based on the verified FEA models. The analysis results showed that thicker internal diaphragms increased the strength, and changed the failure mode from the column‐center failure to column‐end failure for columns and from the joint failure to column failure for joints, respectively. Finally, the mechanics‐based models and axial strength equations of square CFST columns and RC beam to CFST column joints stiffened by internal diaphragms were proposed, and the predictions agreed well with the test and analysis results.

Numerical analysis of CFST-RC composite shear wall under axial compression and cyclic loads

The concrete-filled steel tube reinforced concrete (CFST-RC) composite shear wall is a new structure utilising the advantages of a reinforced concrete shear wall and CFST column. The finite element (FE) model for CFST-RC shear walls was validated by experimentation. Under the axial compression and cyclic loads, the mechanical properties were studied by changing the structure and material. Numerical simulation results indicate that compared with the concrete inside the tube, the concrete outside the tube can better limit the deformation of the steel tube, so it significantly affects the axial compression performance. Compared with the concrete, the steel tubes can effectively improve the seismic performance. However, when the steel content and steel tube strength increase to a certain value, the seismic performance decreases due to the synergistic effect of the concrete and the steel tube. Finally, a simple method for calculating the elastic modulus of shear walls is proposed based on the theory of composite materials. From the FE simulation results, the influencing factors of axial compression and seismic performance of CFST-RC shear walls with different parameters were also analysed, which can provide technical support for the design of shear walls and their safe application in practical engineering.

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.

Design method of fire-resistance capacity of reinforced-concrete-filled steel tube column under axial compression

Concrete-filled steel tube (CFST) columns are widely used in high-rise and superhigh-rise buildings because of their good mechanical properties, and the fire protection design of building structures must be considered. Under the same conditions, reinforced-concrete-filled steel tube (RCFST) columns show better fire-resistance performance than CFST columns. The theoretical calculation formula of its axial compressive fire-resistance capacity was derived in this study. The current structural design method adopted in China is a partial factor method based on reliability, in which the partial factors at room temperature are generally used for structural design at high temperatures. The strength of materials has greater dispersion at high temperatures, and it is necessary to develop reliability design methods for CFST columns at such temperatures. To consider this change fully, reliability theory was used to obtain the material partial factor at high temperatures. Then, based on the calculation theory of the axial bearing capacity of the RCFST column at high temperatures, a fire-resistant design method for the RCFST column was developed.

Creep behavior of reinforced concrete-filled steel tubular columns under axial compression

The reinforced concrete-filled steel tube (RCFST) column solves several of the problems of the concrete-filled steel tube (CFST) column in practical engineering applications. Moreover, RCFST has a simple joint structure, high bearing capacity, good ductility, and superior fire resistance. From a structural safety perspective, designers prioritize the creep performance of CFST members in structural design. Therefore, the creep behavior of RCFST columns should be thoroughly investigated in practical engineering design. To study the influence of the creep behavior of RCFST columns under axial compression, this work analyzed the mechanical behavior of composite columns based on their mechanical characteristics under axial compression and established a creep formula suitable for RCFST columns under axial compression. A creep analysis program was also developed to obtain the creep strain–time curve, and its correctness was verified by existing tests. On this basis, the effects of the main design parameters, such as the stress level, steel ratio, and reinforcement ratio, on the creep behavior were determined and analyzed. The creep of the tested composite columns increased rapidly in the early stages (28 days) of load action; the growth rate was relatively low after 28 days and tended to stabilize after approximately six months. The stress level had the greatest influence on the creep of RCFST columns under axial compression, followed by the steel ratio. The influence of the reinforcement ratio on the creep behavior was less. The results of this study can provide a reference for engineering practice.

Seismic behavior of a novel beam to reinforced concrete-filled steel tube column joint

This paper presents an experimental investigation of a novel beam to reinforced concrete-filled steel tube (RCFST) column joint. Four beam-to-RCFST-column specimens, varying with a cross-section of middle steel tube (250 × 250 × 6, 300 × 300 × 9, 350 × 350 × 12) and transfer sleeves (with or without), were tested under the cyclic loading to clarify the main seismic indicators, such as failure modes, hysteretic performances, stiffness degradation, strength degradation, energy dissipation capacity and the strain responses of the novel beam-to-RCFST-column joint. The hysteretic curves of the tested beam-to-RCFST-column joint show obvious pinch phenomena because of the slip around the transfer sleeve. Transfer sleeve is the key factor to affect the strength of the tested beam-to-RCFST-column joint. The finite element analysis (FEA) shows a reliable prediction of mechanical properties and failure modes.

Seismic Behavior of Concrete-Filled Steel Tube (CFST) Column and Reinforced Concrete (RC) Beam Connections under Reversed Cyclic Loading

Previous studies on the connection between concrete-filled steel tube (CFST) columns and reinforced concrete (RC) beams have shown a loss of joint confinement because the steel tube was completely or partially cut in the joint area. This research presents a new connection system that provides joint confinement through a continuous steel tube. Potential sliding shear at the smooth interface between the columns and beams in the joint face is mitigated using two mechanisms: (i) shear connectors and (ii) longitudinal web beam reinforcement. This study tested two CFST column and RC beam joints to 4.5% drift ratio under combined compression axial load and lateral cyclic load. The experimental results revealed no cracks at the joint zone and the specimens satisfied the ACI 374.1-05 criteria, despite minor sliding at the beam-column interface. The finite element (FE) model showed good agreement with the experimental results.

Analysis of Concrete-Filled Steel Tube Reinforced Concrete Column-Steel Reinforced Concrete Beam Plane Frame Structure Subjected to Fire

The ABAQUS finite-element analysis platform was used to understand the mechanical behavior of concrete-filled steel tube reinforced concrete (CFSTRC) columns and steel reinforced concrete (SRC) beam plane frames under fire conditions. Thermal parameters and mechanical constitutive model of steel and concrete materials were reasonably selected, the correct boundary conditions were chosen, and a numerical model for the thermal mechanical coupling of CFSTRC columns and SRC beam plane frame structure was established. The finite-element model was verified from related experimental test results. The failure modes, deformation, and internal force distribution of the CFSTRC column and SRC beam plane frames were analyzed under ISO-834 standard fire conditions and with an external load. The influence of beam and column fire-load ratio on the fire resistance of the frame structure was established, and the fire-resistance differences between the plane frame structures and columns were compared. The CFSTRC column-steel reinforced concrete beam plane frame may undergo beam failure or the column and beam may fail simultaneously. The frame structure fire-resistance decreased with an increase of column and beam fire-load ratio. The column and beam fire-load ratio influence the fire resistance of the frames significantly. In this numerical example, the fire resistance of the frames is less than the single columns. It is suggested that the fire resistance of the frame structure should be considered when a fire-resistant structural engineering design is carried out.

Experimental study on the fire resistance of concrete filled steel tube reinforced concrete (CFSTRC) column-RC beam frames

To reveal the temperature characteristics and mechanical properties of frame structures with concrete filled steel tube reinforced concrete (CFSTRC) columns under fire, the fire resistance of four planar frames consisting of CFSTRC columns and reinforced concrete (RC) beams subjected to ISO-834 standard fire was tested in this study. The test parameters included the column fire load ratio, beam fire load ratio, and beam-to-column linear stiffness ratio. In the test, the temperatures of the column, beam, and slab cross-sections in the joint and nonjoint zones were measured, and the fire resistance, beam and column deformation curves, and failure modes of the frame were investigated. The experimental results showed that the concrete volume was the main factor affecting the temperature distribution on each typical cross-section of the frame: the temperatures at the measuring points of the beam and column in the joint zone were significantly lower than the temperatures at the corresponding points in the nonjoint zone, and the concrete outside the steel tube significantly slowed the propagation of temperature to the steel tube and its concrete core. Hence, there was only a small loss of the bearing capacity of steel tube and the core concrete inside the steel tube. The column fire load ratio, beam fire load ratio, and beam-to-column linear stiffness ratio have obvious influences on the fire resistance: the larger the column fire load ratio or beam fire load ratio, the smaller the fire resistance; and the larger the beam-to-column linear stiffness ratio, the larger the fire resistance.

Discussion of “Shear Strength of Composite Circular Reinforced Concrete–Filled Steel Tubes” by Hadi Kenarangi and Michel Bruneau

Discussion of “Shear Strength of Composite Circular Reinforced Concrete–Filled Steel Tubes” by Hadi Kenarangi and Michel Bruneau

Closure to “Shear Strength of Composite Circular Reinforced Concrete–Filled Steel Tubes” by Hadi Kenarangi and Michel Bruneau

Closure to “Shear Strength of Composite Circular Reinforced Concrete–Filled Steel Tubes” by Hadi Kenarangi and Michel Bruneau

Axial Compressive Behaviour of Square through-Beam Joints between CFST Columns and RC Beams with Multi-Layers of Steel Meshes.

The axial compressive behaviour of an innovative type of square concrete filled steel tube (CFST) column to reinforced concrete (RC) beam joint was experimentally investigated in this paper. The innovative joint was designed such that (i) the steel tubes of the CFST columns were completely interrupted in the joint region, (ii) the longitudinal reinforcements from the RC beams could easily pass through the joint area and (iii) a reinforcement cage, including a series of reinforcement meshes and radial stirrups, was arranged in the joint area to strengthen the mechanical performance of the joint. A two-stage experimental study was conducted to investigate the behaviour of the innovative joint under axial compression loads, where the first stage of the tests included three full-scale innovative joint specimens subjected to axial compression to assess the feasibility of the joint detailing and propose measures to further improve its axial compressive behaviour, and the second stage of the tests involved 14 innovative joint specimens with the improved detailing to study the effect of the geometric size of the joint, concrete strength and volume ratio of the steel meshes on the bearing strengths of the joints. It was generally found from the experiments that (i) the innovative joint is capable of achieving the design criterion of the ‘strong joint-weak member’ with appropriate designs, and (ii) by decreasing the height factor and increasing the volume ratio of the steel meshes, the axial compressive strengths of the joints significantly increased, while the increase of the length factor is advantageous but limited to the resistances of the joint specimens. Because of the lack of existing design methods for the innovative joints, new design expressions were proposed to calculate the axial compression resistances of the innovative joints subjected to bearing loads, with the local compression effect, the confinement effect provided by the multi-layers of steel meshes and the height effect of concrete considered. It was found that the proposed design methods were capable of providing accurate and safe resistance predictions for the innovative joints.

Investigation of Cyclic-Shear Behavior of Circular-Reinforced Concrete-Filled Steel Tubes

The cyclic-shear behavior of composite circular concrete-filled steel tubes (CFSTs) and reinforced concrete-filled steel tubes (RCFSTs) was experimentally and numerically investigated. Specimens with 32.39 and 40.64 cm diameters were considered, with diameter-to-thickness ratios of 51 and 64, respectively. The effects of longitudinal and transverse reinforcement were experimentally studied. The experimentally obtained strength values were compared to those from existing shear strength equations. Experimental results showed that the presence of an internal reinforcement doesn’t significantly impact the shear strength of RCFSTs. All specimens exhibited some amount of ductility under cyclic shear but not necessarily to the extent that would make it a preferred ductile mechanism. The mechanics governing the shear behavior of the CFSTs were studied using validated finite-element models. It was observed that a compression strut develops in the concrete under shear deformations. This strut also contributed to the shear strength of the composite CFSTs.

An Experimental Research on Connection of Boundary Concrete Filled Steel Tube Columns and Reinforced Concrete Slab

A combination of outstanding advantages of concrete filled steel tube (CFST) column with reinforced concrete (RC) flat slab creates the effective and potential structure to replace traditional reinforced concrete frame structures in high-rise buildings. The CFST column – RC slab connection is the key factor for this structure type to work properly and effectively. Currently, the studies mainly focus on inner CFST column and RC slab connection, there are very few experimental studies on connection of edge or corner CFST columns and RC flat slab. This paper proposes edge and corner CFST columns to RC flat slab connection structures using H-shaped shear head and then conducts two large size tests to investigate behaviors of the connection.

Concrete Filled Steel Tube Column And Wide Beam Connection: Proposed Structures and Experiment

Structural solutions utilizing concrete filled steel tube (CFST) column and reinforced concrete (RC) wide beams are used effectively in high-rise buildings, especially for large span. Currently, there have not been many theoretical and experimental researches on CFST column - RC wide beam connection to ensure the effectiveness of this structure type. Moreover, there have not been any experimental researches on the connection of CFST column – Prestressed concrete (PC) wide beam, as well as on assessing the effect of prestressed cables and shear head shape on the shear strength of the connection. This paper proposes connection structures; conducts experimental program, analyzes and compares different types of connections between CFST column and RC, PC wide beam using large size specimens to evaluate the actual behavior of proposed connections. Experimental results give a better view of the effect of shear-head shape as well as the prestressed force on the shear strength of the wide beam at the connections.

Shear Strength of Composite Circular Reinforced Concrete–Filled Steel Tubes

AbstractThe shear strength of composite circular concrete-filled steel tube (CFST) and reinforced concrete–filled steel tube (RCFST) structural members was investigated using finite-element analysi...

RESEARCH ON THE DAMAGE CONDITION OF REINFORCED CONCRETE FILLED STEEL TUBES UNDER AXIAL LOAD USING ULTRASONIC TESTING

The ultrasonic technique was used to evaluate the damage conditions of plain concrete, reinforced concrete, concrete filled steel tubes (CFST) and reinforced concrete filled steel tubes (RCFST) subjected to axial load. The ultrasonic waveforms passing through the middle section of a column were obtained under different loads. The root mean square (RMS) amplitude and RMS amplitude ratio of waveforms are defined for analyzing the development of concrete cracks. The waveforms were transformed into the frequency domain by fast Fourier transform (FFT). According to the principle that the solid medium cracking absorbs high frequency sound wave energy that makes the ultrasonic main frequency shift from high to low frequency, the first main frequency and its amplitude variation were selected to investigate the damage condition of concrete and reinforced concrete in steel tubes. The experimental results show that the crack variation of concrete and reinforced concrete in steel tubes can be effectively reflected by the RMS amplitude, RMS amplitude ratio and the first main frequency and its amplitude. The damage condition of reinforced concrete under axial load can be divided into five stages, that is, the concrete crack generation and extension, concrete compaction resulted from steel tubular constraint, concrete crack rapid expansion, strengthening due to the steel tubular hoop effect and loss of component strength after the buckling of steel tubes. It is found that the constraint stage of steel tube to core concrete obtained from the strain analysis of steel tube is consistent with the damage evolution obtained from ultrasonic testing. Therefore, the ultrasonic testing method is an accurate tool to evaluate the damage of reinforced concrete inside steel tubes under axial load and to determine the hoop effect of steel tubes.