Capacity Of Concrete-filled Steel Tubes Research Articles

A Simple Method to Evaluate the Bearing Capacity of Concrete-Filled Steel Tubes with Rectangular and Circular Sections: Beams, Columns, and Beam–Columns

This study investigates the behavior and capacity of concrete-filled steel tubes (CFTs) with rectangular and circular sections under various loading conditions: axial loads, pure-bending, and combined axial load-bending moments. A finite element-based numerical model is developed and validated against existing experimental data. Using an extensive databank generated from finite element analysis, this research proposes analytical empirical relations for determining the bearing capacity of rectangular and circular composite beams, columns, and beam–columns. These relations provide a direct, concise, and efficient method for calculating the ultimate strength of CFT members, making them valuable for engineering design. Comparisons between the proposed analytical results and previous experimental studies demonstrate the high accuracy of this method in analyzing rectangular and circular CFT member behavior. The findings contribute to a better understanding of CFT structural performance and offer practical tools for designers working with these composite elements.

Numerical simulation and load-bearing capacity of concrete-filled steel tubes strengthened with CFRP grid-reinforced ECC under axial compression

A numerical study on the compressive behavior and load-bearing capacity of the concrete-filled steel tube (CFST), strengthened with a carbon fiber-reinforced polymer (CFRP) grid-reinforced engineered cementitious composite (ECC), is presented. The numerical simulation, which was based on a previous test performed by the authors, indicated that an increase in the number of CFRP grid layers results in a significant increase in the bearing load on the concrete core. The confinement is provided to the concrete core by the strengthening layer only after the yielding of the steel tube, which occurs because of the contact pressure between the steel tube and ECC. Parameter studies that considered the effect of the number of CFRP grid layers and the strength of the CFRP, compressive strength of the ECC and concrete core, diameter-to-thickness ratio, and yield strength of the steel tube were conducted. The increase in fcu and decrease in Ds/t weakened the function of the confinement of the strengthening layer, and the influence of fcu was more significant. Furthermore, an analysis model that considered the nonlinear confining behavior and stress history for predicting the load-bearing capacity of the CFST columns strengthened with CFRP grid-reinforced ECC was established. The stress increment iteration method was employed to determine the varying confining pressure during loading. The proposed model showed high accuracy for predicting the load-bearing capacities of the strengthened columns.

An Improved Equation for the Bearing Capacity of Concrete-Filled Steel Tube Concrete Short Columns Based on GPR

The determination of the bearing capacity prediction model of concrete-filled steel tubular columns is a key issue in the structural design of prefabricated buildings, which directly relates to the stability and safety of prefabricated buildings. The purpose of this paper is to study the bearing capacity model of concrete-filled steel tubular columns, and propose an explicit formula based on the Gaussian process regression algorithm to calculate the bearing capacity. In order to solve the problem of low accuracy of the traditional empirical bearing capacity model, this paper first proposes a more accurate bearing capacity prediction model based on Gaussian process regression algorithm to automatically learn and capture the characteristics of 122 groups of test data; the paper then determines the function of high sensitivity parameters and section influence parameters through the established bearing capacity prediction model, and this process gives the display formula. Compared with the implicit formula given by a machine learning model, the explicit formula proposed in this paper is more suitable for practical engineering design. In order to verify the validity of the formula, we generated the bearing capacity data through the proposed formula based on the test data and used the descriptive statistical method to verify. The results show that the proposed formula is superior to other existing methods, the error between the data generated by the proposed formula and the test data is smaller, and its accuracy reaches 93.73%, which is more suitable for calculating the bearing capacity of concrete-filled steel tubes with different cross sections.

Experimental investigations of FRP-interlayer-steel confined concrete columns under axial compression

A fibre-reinforced polymer (FRP)-interlayer-steel confined concrete (FISC) column is proposed in this study to improve the corrosion resistance and bearing capacity of concrete-filled steel tube (CFST) structures. In FISC columns, grouting material is used to bond the FRP tube and steel tube to produce a dual-confined composite skin for the core concrete. To establish the performance levels of FISC columns, 35 specimens in two batches of four types of columns, including FISC columns, FRP-confined concrete-filled steel tubular columns, concrete-filled FRP tubular columns, and CFST structures were used. The specimens were tested under axial compression, and the FRP types (glass- and carbon-fibre-reinforced polymer), FRP thickness, and steel thickness were the main parameters examined in the tests. Failure patterns, load–axial shortening curves, and strain development were observed, and the dual confining effect of FRP tube and steel tube on core concrete was discussed. The test results showed that the FRP tube and grouting material suppressed the outward buckling of a steel tube, and the load-bearing capacity of the core CFST was substantially enhanced. In addition, owing to the existence of an interlayer, a strain lag was observed on the strain transfer from the steel tube to the FRP tube, effectively delaying the cracking of the resin on the FRP tube. Furthermore, the bearing capacity and ultimate axial deformation of FISC columns increased linearly with the addition of FRP thickness but had little changes when the thickness of the steel tube differed.

Application of Random Forest and Multi-layer Perceptron ANNS in Estimating the Axial Compression Capacity of Concrete-Filled Steel Tubes

Application of Random Forest and Multi-layer Perceptron ANNS in Estimating the Axial Compression Capacity of Concrete-Filled Steel Tubes

Axial compressive performance of CFRP confined rectangular CFST columns using high-strength materials with moderate slenderness

The bearing capacity of concrete-filled steel tube (CFST) columns can be significantly increased by using high-strength materials. However, the ductility of high-strength CFST columns is reduced due to the brittleness of high-strength concrete and the buckling of thin-walled high-strength steel tubes, especially for slender columns. By wrapping the carbon fiber reinforced polymer (CFRP) to increase the confinement on the steel tube, the ductility can be improved. This paper presents experimental and theoretical studies on the axial compressive performance of CFRP confined rectangular CFST columns using high-strength steel and concrete with moderate slenderness. The influence of the section aspect ratio, concrete strength, and CFRP confinement on the axial behavior was analyzed. The experimental results indicate that the local buckling of CFRP-confined specimens is delayed compared with the unconfined specimens. The horizontal CFRP confinement increases the yield load by 1.5–25.6%, and the peak load by 2.5–11.2%. The bearing capacity and ductility of specimens are improved under the confinement of CFRP. The calculation method for axial compression bearing capacity considering the stability of moderate slender specimens was proposed. The ratio of the experimental results to the calculated value is between 0.86 and 1.09, which verified the accuracy of the calculation method.

New Prediction Model for the Ultimate Axial Capacity of Concrete-Filled Steel Tubes: An Evolutionary Approach

The complication linked with the prediction of the ultimate capacity of concrete-filled steel tubes (CFST) short circular columns reveals a need for conducting an in-depth structural behavioral analyses of this member subjected to axial-load only. The distinguishing feature of gene expression programming (GEP) has been utilized for establishing a prediction model for the axial behavior of long CFST. The proposed equation correlates the ultimate axial capacity of long circular CFST with depth, thickness, yield strength of steel, the compressive strength of concrete and the length of the CFST, without need for conducting any expensive and laborious experiments. A comprehensive CFST short circular column under an axial load was obtained from extensive literature to build the proposed models, and subsequently implemented for verification purposes. This model consists of extensive database literature and is comprised of 227 data samples. External validations were carried out using several statistical criteria recommended by researchers. The developed GEP model demonstrated superior performance to the available design methods for AS5100.6, EC4, AISC, BS, DBJ and AIJ design codes. The proposed design equations can be reliably used for pre-design purposes—or may be used as a fast check for deterministic solutions.

Estimation of axial load-carrying capacity of concrete-filled steel tubes using surrogate models

The main objective of the present work is to estimate the load-carrying capacity of concrete-filled steel tubes (CFST) under axial compression using hybrid artificial intelligence (AI) algorithms. In particular, the adaptive neuro-fuzzy inference system (ANFIS) with various metaheuristic optimization methods, such as the biogeography-based optimization (ANFIS-BBO), the particle swarm optimization (ANFIS-PSO), and the genetic algorithm (ANFIS-GA), have been employed taking into account the variability of input parameters. Commonly used statistical criteria, such as the coefficient of determination (R2), the a20-index, and the root mean squared error (RMSE), were utilized to evaluate and compare the effectiveness of the proposed AI models. The Monte Carlo approach was used to propagate the variability in the input space to the predicted output. The results showed that the ANFIS system, optimized by PSO, was the most effective and robust model with respect to three considered criteria (a20-index = 0.881, R2 = 0.942 and RMSE = 185.631). Sensitivity analysis was performed, indicating that the minor axis length and thickness of the steel tube exhibited the highest contribution to the axial compression load-carrying capacity of the CFST.

Linear elastic iteration technique for ultimate bearing capacity of circular CFST arches

The current primary numerical methods for ultimate bearing capacity of concrete-filled steel tube (CFST) arches are of nonlinear iterative procedures, which are time consuming and inaccurate. In order to overcome this problem, a linear elastic iteration technique was introduced for plastic limit analysis of the CFST arches with small or medium nominal slenderness ratio in this paper. Firstly, generalized yield functions were derived from the interaction equation of circular CFST members. Then, homogeneous generalized yield functions (HGYF) with appropriate order powers were developed by means of regression analysis. Furthermore, a reference element bearing ratio was presented as a dynamic threshold to distinguish the highly-stressed elements in CFST arches on basis of the HGYFs, while an adaptive strategy of elastic modulus adjustment is presented for linear elastic iterative analysis of the ultimate bearing capacity of CFST arches with small or medium nominal slenderness ratio. Test data for ultimate strength of 100 CFST members and arches were adopted in examples to demonstrate the accuracy and efficiency of the proposed HGYF and the linear elastic iteration method. It was also verified that the proposed method can be successfully applied to common single-circular-tube CFST arches under consideration of buckling effect in engineering practice.

Research of The Calculation Method for round-end concrete-filled steel tube under the eccentric load

Round-end concrete-filled steel tube (RCFST) columns have been applied to bridge structures. There is not the formula of RCFST under the eccentric load in code. Based on the equation of axial force and moment, the basic correlation equations of the strength and stability capacity of concrete-filled steel tube under the eccentric load are obtained through theoretical derivation. Formula results compared with finite element simulation results show results are in good agreement.

Optimum model for bearing capacity of concrete-steel columns with AI technology via incorporating the algorithms of IWO and ABC

In a composite column, the performance of both the concrete and steel has a considerable effect on the structural behaviour under different loading conditions. This study applies several artificial intelligence (AI) techniques to optimise the bearing capacity of concrete-filled steel tube (CFST) columns. First, the bearing capacity values of the CFST columns are estimated by an artificial neural network (ANN) technique. Using 303 datasets, the outer diameter, concrete compressive strength, tensile yield stress of the steel column, thickness of the steel cover, and length of the applied samples are considered as the model inputs. Following a series of analyses, several ANN models are developed. The ANN model with 8 neurons and 250 iterations is determined as the best model to predict the bearing capacity of the CFST columns. Subsequently, the invasive weed optimisation (IWO) technique, which is considered the most current optimisation algorithm, is developed to maximise the results of the bearing capacity by considering the selected ANN model. To highlight the ability of IWO, the artificial bee colony (ABC) algorithm is also applied. Consequently, it is found that both optimisation algorithms can design input parameters such that the maximum value of the bearing capacity can be obtained. The bearing capacity of the CFST columns from the ABC and IWO techniques indicates that IWO has a better capability of maximising the bearing. Thus, IWO can optimise similar problems with a high rate of performance.

CFRP-reinforced concrete-filled steel tubes with timber core under axial loading

This paper experimentally investigates the effect of Carbon Fibre Reinforced Polymer (CFRP) on the axial capacity of concrete-filled steel tubes with different timber cores. The stub columns were designed having the size of the infill and the CFRP as the main two variables. The structural response including failure, ductility, stiffness and structural efficiency were evaluated and discussed. It was found that the effect of timber core is significant in lightening the weight of the composite, although the total capacity of the composite depends upon the material properties of the core versus the grade of concrete and steel employed in the composite columns. For the structural applications, where the weight reduction and ductility are crucial, the development of this innovative composite is highly recommended. To quantify this, the ratio of ductility index to weight is introduced including these two crucial parameters in the seismic design. An equation is also developed to estimate the axial capacity of timber-concrete-filled steel tubes. Furthermore, the environmental and sustainability assessment are touched on briefly to pave a path for the future work aiming at possibly reducing the contribution of the concrete in the construction.

Study of the Ultimate Bearing Capacity of Concrete-filled Steel Tube K-Joints

To study the ultimate bearing capacity of Concrete-Filled Steel Tube (CFST) K-joints, theoretical analysis and numerical simulation methods were adopted. A finite element model of a K-joint was established and verified with test data. Based on this model, the failure modes of the K-joint were studied. The results showed that the load-displacement curves of CFST K-joints can be divided into three stages: an elastic stage, an elastic-plastic stage and a failure stage. There were two types of failure modes for K-joints: local buckling failure at the connection between a branch pipe and the main pipe due to compression and tearing failure at the connection between a branch pipe and the main pipe due to tensile forces. The factors that influence the ultimate bearing capacity of CFST K-joints were studied, and the results were as follows. The ultimate bearing capacity increased as the radius-thickness ratio of the main pipe, radius-thickness ratio of the branch pipes and gap between branch pipes decreased. Additionally, the ultimate bearing capacity of the CFST K-joints increased with increasing core concrete grade, outer diameter ratio and thickness ratio between the branch pipe and main pipe. As the angle between the axis of the branch pipe and the axis of the main pipe increased, the ultimate bearing capacity initially decreased and then increased. As the axial pressure level in the main pipe increased, the ultimate bearing capacity of the K-joint initially increased and then decreased. A positive linear correlation was observed between the growth coefficient of the ultimate bearing capacity and the scaling factor. Moreover, the ultimate bearing capacity of CFST K-joints can be significantly improved by using core concrete. Finally, formulas for the ultimate bearing capacity of K-joints under different failure modes were proposed, and the results provide a reference for the design of CFST arch bridges.

Load-bearing capacity of concrete elements reinforced with steel and composite coatings

In the article, the compressive strength of steel-concrete structures defined as CFST (Concrete Filled Steel Tubular) has been checked. The steel elements used in CFST columns have high tensile strength and ductility while the concrete elements have high compressive strength and stiffness. Therefore, CFST elements have a large range of applications in construction. The analysis included 8 examples of elements consisting of a steel tube filled with a concrete core. The examples differed in the thickness of the steel coating and the compressive strength of the concrete core. Analytical calculations and experimental studies for them were carried out. The analytical calculations were based on the author’s method of assessing the load-bearing capacity of concrete-filled steel tubes. In experimental verification, CFST samples were subjected to a static compression test. The calculation method was also used to calculate the load capacity when composites reinforcement is the outer coating for the concrete core. Three types of composites were analysed. The obtained results show a large influence of the steel coating thickness on the compressive strength for the CFST elements. The load-bearing capacity of the elements depends on the appropriate ratio of the surface of the steel coating to the concrete coating.

Mechanical Behavior of Recycled Aggregate Concrete-Filled Steel Tubular Columns before and after Fire.

Recycled aggregate concrete (RAC) is an environmentally friendly building material. This paper investigates the mechanical behavior of recycled aggregate concrete filled steel tube (RACFST) columns exposed to fire. Two groups of 12 columns were designed and tested, under axial compression, before and after fire, to evaluate the degradation of bearing capacity due to fire exposure. Six specimens were subjected to axial compression tests at room temperature and the other six specimens were subjected to axial compression tests after a fire exposure. The main parameters of the specimens include the wall thickness of the steel tube (steel content) and the type of concrete materials. Several parameters as obtained from the experimental results were compared and analyzed, including the load-bearing capacity, deformation capacity, and failure characteristics of the specimens. Meanwhile, rate of loss of bearing capacity of specimens exposed to fire were calculated based on the standards EC4 and CECS28:90. The results show that concrete material has a large influence on the rate of loss of bearing capacity in the case of a relatively lower steel ratio. While steel content has little effect on the rate of loss of bearing capacity of concrete-filled steel tube (CFST) columns after fire, it has a relatively large influence on the loss rate of bearing capacity of the RACFST columns. The loss of bearing capacity of the specimens from the experiment is more serious than that from the calculation. As the calculated values are less conservative, particular attention should be given to the application of recycled aggregate concrete in actual structures.

Effect of Concrete Age and Creep on the Behavior of Concrete-Filled Steel Tube Columns

The influence of concrete age and creep on the ultimate axial loading capacity of concrete-filled steel tube (CFST) columns is experimentally and numerically investigated. After validation of numerical models, a parametric study is conducted and the results are used to formulate empirical formulas for predicting the ultimate axial load-bearing capacity of the columns. Formulas are also proposed for predicting both the composite creep and aging coefficients of the CFST columns, which consider the confinement action of steel tubes on concrete. Then, the proposed formulas are validated independently by comparing their predictions with existing test results performed by other researchers. The comparisons show that the empirical formulas have the potential to be used in the practical design of CFST columns.

A new calculation method for axial load capacity of separated concrete-filled steel tubes based on limit equilibrium theory

A new calculation method for axial load capacity of separated concrete-filled steel tubes based on limit equilibrium theory was proposed, which took into account the decrease of confinement effect by steel tube and the non-uniform distribution of ultimate stress in cored concrete. The accuracy of the analytical result is validated through running the numerical result by finite element method (FEM) and experimental data as well. The influences of the key parameters on the load capacity of the concrete-filled steel tube (CFST) was studied, including the separation ratio, concrete compressive strength, and steel strength. The results indicate that the load capacity of the tube increases with concrete strength and steel strength under the separation ratio less than 4%, while decreases with a higher separation ratio improved.

Study on External Prestressed Concrete-Filled Steel Tubular Flexural Member

According to good property of concrete-filled steel tubes(CFST) when they are subjected to compression load and their disadvantage to bending load. A new type of composite external prestressed concrete-filled steel tubular structure has been presented in this paper, which has the high tension strength of prestressed tendon and good anti-compression capacity of CFST. Based on the analysis of the mechanism, the flexural capacity of the structure can be greatly enhanced. And the criterion and method is given.

Experimental Study of Behavior of Ceramsite Concrete Filled Steel Tubes after Exposure to Fire

The post-fire behavior of a set of ceramsite concrete filled steel tubes (note as CCST) after exposure to fire are experimentally studied. Effect of the maximum value of fire response temperatures of the tubes and their geometric parameters on the strength and ductility of the specimens were especially discussed. The test results show that the specimens of CCST have higher post-fire bearing capacity and better ductility, there was no obvious descent segment in post-fire load-displacement curves of the most specimens subjected to fire load. It was concluded that the maximum response temperature of specimens has great effect on the post-fire bearing capacity of concrete-filled steel tubes subjected to fire load.

One-Dimensional Dynamic Performance of Concrete-Filled Steel Tube

The paper puts forward the one-dimensional strain rate related dynamic constitutive model of concrete-filled steel tube. The calculation results are in good agreement with the experimental results. Uniaxial compression performance finite element analysis at the strain rate among 10/s-5—10/s-2 is completed based on the conclusions. The results showed that considering concrete strain rate effect, the bearing performance of CFST is obviously changed. It showed that with the strength of concrete and strain rate increasing, ultimate bearing capacity of concrete-filled steel tube is improved and ductility is reduced. With the confining ratio and strain rate increasing, the ultimate bearing capacity and ductility of CFST are improved. With the slenderness ratios and strain rate increasing, the ultimate bearing capacity and ductility are reduced.