Concrete-filled Steel Tubular Structure Research Articles

Three-dimensional creep calculation model for reliability analysis of concrete-filled steel tubular (CFST) structure

For long-span concrete-filled steel tube (CFST) structure, it is essential to implement efficient and realistic prediction models for the long-term processes of core concrete creep. In order to systematically study the main influential factors in CFST structure creep effects, a probabilistic analysis can be performed. The objective of this paper is to analyse the long-term response of CFST structure by using time-dependent reliability method. To address the problem of creep calculation, a novel and comprehensive presentation was developed. By converting the integral-type creep law to a differential-type form with internal variables, based on the Kelvin chain model, an elastic structural analysis with generally orthotropic elastic moduli and eigenstrains was established. We have compiled a three-dimensional (3-D) finite-element analysis programme that considers the creep Poisson effect of core concrete to analyse the long-term performance of the CFST structure. This is achieved by developing a commercial finite element code, such as Usermat in ANSYS. As calculation examples, several time-dependent analyses of a CFST stub column and long-span CFST arch bridge were performed. The calculated results of long-term behaviour agree well with experimental and measured data. Considering the randomness of various input parameters, such as physical dimensions and materials of the CFST structure, we have analysed the uncertainty using the Latin-hypercube-sampling (LHS) stochastic finite-element method. The results of creep sensitivity analysis revealed that coefficient of creep model uncertainty, steel and concrete elastic modulus were the three most influential parameters for CFST stub columns’ creep, and load, coefficient of creep model uncertainty, relative humidity, steel and concrete elastic modulus were the five for CFST arch bridges’ long-term deflection. In addition, the use of Monte Carlo (MC) and response surface (RS) methods for structural stochastic reliability analysis demonstrates the ability of these approaches to assess the reliability index of long-span CFST arch bridges. This provides a valuable reference for the design and performance evaluation of CFST structures.

Trussed concrete-filled steel tubular hybrid structures subjected to axial compression: Performance and design calculation

This paper presents a study on the axial compression performance of trussed concrete-filled steel tubular (CFST) hybrid structures. A total of 26 specimens were tested, including 15 circular and 11 square cross-sectional specimens. The effects of cross-sectional types, yield strength of steel of CFST chord, web types, number of chords, and equivalent slenderness ratio were investigated to clarify the mechanical behavior of trussed structure. The analyses of the full-range response, the typical failure mode, and the distribution of the transverse deflection and strain of the structures were carried out. A finite element analysis (FEA) modelling of trussed CFST structure was established and validated against the experimental results. Through the numerical simulation, the analysis of the internal force and stress was conducted, and the hybrid effect between the web and CFST chord was revealed. Based on parameter analysis, the design calculation was proposed, and the trussed CFST hybrid structure was equivalent to a single CFST to calculate its load-bearing capacity by introducing equivalent slenderness ratio proposed.

Toward the balance between computational cost and model performance for the void detection of concrete-filled steel tubular structure using one-dimensional Mel-frequency cepstral coefficients and ensemble machine learning

Deep learning (DL) based percussion-acoustic methods have gained attention, but their multi-layer architectures and iterative processes increase computational time and power. This paper proposes a lightweight concrete-filled steel tubular (CFST) void detection method using Mel-frequency cepstral coefficient (MFCC) algorithm and ensemble machine learning. A global averaging pooling (GAP) layer was applied to downscale the two-dimensional MFCC matrix to one-dimensional (1D) time-frequency parameters. Combined with ensemble machine learning, lightweight models that require fewer model parameters, less computation, and smaller memory usage are constructed. Validation experiments were carried out on a CFST specimen with different depths of voids (0, 30, 50, and 80 mm). Robustness tests, considering tap intervals, sampling frequencies, and background noise, were performed by using data augmentation strategies. Two studies investigate feature extraction methods: the selection of the time-frequency analysis algorithm (MFCC or short-time Fourier transform) and the comparison of dimensionality reduction operation (average, maximum, and minimum pooling layers). Comparative analyses with a 1D dilated convolutional neural network (1D dilated CNN) reveal that the MFCC-based ensemble machine learning achieves excellent test accuracy on the raw signal dataset and better generalization capability on the reconstructed signal dataset. Moreover, the ensemble machine learning model exhibits significantly higher computational efficiency compared to DL models. Specifically, the training time of random forest is 17,510 times faster than the 1D dilated CNN. Therefore, the proposed lightweight CFST void detection method, incorporating 1D MFCC parameters and ensemble machine learning, achieves high model accuracy with low computational cost and holds promising potential for practical CFST applications.

Trussed square concrete-filled steel tubular hybrid structures subjected to axial compression

This paper introduced the mechanical performance of trussed square concrete-filled steel tubular (CFST) hybrid structure subjected to axial compression. A refined finite element analysis (FEA) modelling was established and verified against the experimental results. Based on the FEA modelling, the hybrid effect and the working mechanism of the structure were revealed through the comprehensive analysis of the internal force distribution, the axial compression force (N) versus average longitudinal strain (ε) relation, the typical failure modes, and the stress distribution. The N-ε relation was classified into five types according to the failure modes and critical factors elucidated. The criterion for determining the ultimate limit state of the trussed square CFST hybrid structure was established by investigating its load-bearing capacity and peak strain. An interface contact stress model was proposed to describe the hybrid effect of the structure. Based on parametric analysis, critical parameters used to characterize the hybrid effect were identified, thereby the equivalent slenderness ratio for straight trussed CFST hybrid structure and that for a curved one considering the influence of the initial curvature ratio were proposed. The quantitative relationships between the stability factor and equivalent slenderness ratio were established and validated so as to facilitate the calculation of the load-bearing capacity for both straight and curved trussed square CFST hybrid structures.

Modal analysis of concrete filled steel tubular structure under lateral impact loading

In this paper, deformation mode and the large deflection of the concrete filled steel tubular (CFST) structural member with fixed ends under lateral impact loading was studied by rigid-plastic modal approximation method and finite element analysis by ABAQUS. Using the yield criterion and beam-on-foundation model, the modal analytical solution for plastic behavior of CFST member under lateral impact is obtained considering the interaction of bending and axial stretching. The rigid-plastic modal solution captures the FE results and the deformation mode is accordance with the available experimental results. It shows that lateral deformation of CFST member can be effective predicted by the modal solution consisting of geometric and physical parameters variations. The influence of steel tube thickness, cross-section diameter, effective length, strength and density of concrete and steel, and initial impulsive are discussed in detail. The results show that deflection of the CFST member increase with the increase of the length to diameter ratio, initial impulse and smaller thickness to diameter ratio. Finally, the relationship between lateral deformation and geometric variations are established by optimal sets of modal solution.

Numerical investigation of concrete-filled double skin steel tubular (CFDST) structure subjected to underwater explosion loading

With the increasing applications in the offshore industry such as oil and gas jackets, submarine pipelines and wind turbine foundations, concrete-filled double skin steel tubular (CFDST) structures are encountering the ever-increasing risk of threats to underwater explosions (UNDEX). This study presents a systematical investigation on the structural behaviors and design recommendations of the CFDST structures subjected to UNDEX loadings through finite element analysis (FEA) approaches. Finite element models have been developed, where the non-linear material properties of the constitutive steel and concrete parts and the composite actions in-between have been considered. The FEA models are verified against the experimentally determined shock wave pressure history, the deformation shapes, and the residual strength. The full-range analyses were firstly carried out on the structural responses of CFDST structures, including the typical damage patterns and residual strength of the specimen after UNDEX. Then, the parametric studies show that the cross-section hollow ratio, charge weight, and explosion distance play great roles in determining the residual strengths. Thereafter, damage indexes considering the parameter of the hollow ratio and the scaled explosion distance has been formulated, and design recommendations have been suggested accordingly.

Shrinkage Compensation Technology of Concrete Filled Steel Tubular Structure of Large Cross-Sea Bridge

In view of the poor accuracy and unsatisfactory effect of shrinkage compensation for concrete-filled steel tubular structures of large cross-sea bridge (CSTS-LCSB), a new shrinkage compensation technology for CSTS-LCSB is proposed. The shrinkage mechanism of CSTS-LCSB is analyzed, including plastic shrinkage, dry shrinkage, autogenous shrinkage, and carbonation shrinkage. The proportion of dry shrinkage and autogenous shrinkage in ordinary concrete and high-strength concrete is determined. The CSTS-LCSB has different shrinkage forms in different environments, and the shrinkage strain state of CSTS-LCSB in different environments is calculated according to the difference. The shrinkage area of the concrete structure is determined, and the expansion agent is used to compensate for the shrinkage area of CSTS-LCSB. The experimental results show that the proposed compensation technology has a good effect on shrinkage compensation and has certain feasibility.

Seismic Performance of Concrete-Filled Square Steel Tubular Column-Steel Beam Sleeve Joint

The concrete-filled square steel tubular (S-CFST) structure has been widely used as a resistance system against earthquakes due to its good seismic performance. However, the application of the S-CFST structure is limited by its complex joint formulation. To overcome this shortcoming, a sleeve semirigid joint has been proposed, while its seismic performance has not been well examined. This study aims to discuss the behavior of sleeve joints with different parameters under low cyclic loading. The analysis results show that the simulation results of the finite element model established by ABAQUS were in good agreement with the experimental results, which further verified the good energy dissipation performance of the sleeve joint, and gave the design suggestions of the joint under different parameters to promote the engineering application of this type of joint.

Research on Thermal Response Behavior of the Intumescent Coating at High Temperature: An Experimental and Numerical Study

Intumescent coating is able to provide effective fire protection with both practicality and aesthetics. In this study, expansion performance and thermal physical property experiments are firstly carried out to obtain the basic parameters at different temperatures. Then, the thermal response model of the concrete-filled steel tubular (CFST) structure under the protection of intumescent coating in a fire is established. Finally, based on the experimental data and thermal response model, the effects of initial thickness, expansion rate, intra-pore emissivity and reaction heat on the structure temperature are discussed in detail. The results of this study can provide guidance on intumescent coating formulation design, as well as fire protection design.

Research on Influence Factors of Bearing Capacity of Concrete-Filled Steel Tubular Arch for Traffic Tunnel

When a traffic tunnel passes through special strata such as soft rock with high geo-stress, expansive rock, and fault fracture zones, the traditional supporting structure is often destroyed due to complicated loads, which threatens the construction and operation safety of tunnel engineering. Concrete-filled steel tubular (CFST) structure gives full play to the respective advantages of steel and concrete and has better bearing capacity and economic benefits than traditional support structure, which has achieved good results in some underground engineering applications. In order to promote the application of CFST in the construction of traffic tunnels with complex geological conditions and improve the bearing capacity of the initial supporting structure of tunnels, the influencing factors of the bearing capacity of CFST arch were studied by numerical simulation. The main achievements are as follows: (1) The load-displacement curves of CFST members under different material parameters are basically consistent. CFST members have significant restrictions on displacement in the elastic stage and have high ultimate bearing capacity. Although the bearing capacity decreases obviously after reaching the peak, it shows good extension performance. (2) The height of the steel tube section, the thickness of the steel tube wall and the grade of the core concrete have an approximately linear positive correlation with the bearing capacity of CFST arch, but the influence of these three factors on the bearing capacity of CFST arch decreases in turn, and when the grade of core concrete increases above C50, it has no significant effect on the bearing capacity of members.

Assessment of lateral performance of monopiles: monopile foundation equipped with concrete-filled double skin steel tubular structure and with steel wheel

Assessment of lateral performance of monopiles: monopile foundation equipped with concrete-filled double skin steel tubular structure and with steel wheel

A Comparative Study of Piers with DSCT and Steel Piles

Because of climate changes, the demand for securing marine space is increasing owing to problems such as sea level rise, design wave height increase, and lack of land and space, and research on the development of a new high-performance pier has been conducted. In the existing pier supported by steel piles, buckling failure and corrosion problems may lead to a risk of structural safety, and maintenance is difficult owing to a narrow span. The new type of double-skinned composite tubular (DSCT) structure, which has been extensively studied recently, is filled with concrete between the inner and outer tubes, increasing the strength of concrete because of the three-axis confined effect. In addition, it is advantageous in terms of ductility. Furthermore, owing to the hollow cross-section, it is economical because it weighs less than the concrete-filled steel tubular (CFT) structure, effectively saving materials. In this study, the performance of a pier with 30 steel piles and that of a pier supported with 20 DSCT piles was compared under the same external force through finite element analysis. Consequently, it was confirmed that the pier with DSCT piles showed higher performance in displacement and stress than the existing pier with steel piles.

Collapse Behaviour of a Concrete-Filled Steel Tubular Column Steel Beam Frame under Impact Loading

The progressive collapse of a concrete-filled steel tubular (CFST) frame structure is studied subjected to impact loading of vehicle by the finite-element software ABAQUS, in the direct simulation method (DS) and alternate path method (AP), respectively. Firstly, a total of 14 reference specimens including 8 hollow steel tubes and 6 CFST specimens were numerically simulated under transverse impact loading for verification of finite-element models, which were compared with the existing test results, confirming the overall similarity between them. Secondly, a finite-element analysis (FEA) model is established to predict the impact behaviour of a five-storey and three-span composite frame which was composed of CFST columns and steel beams under impact vehicle loading. The failure mode, internal force-time curve, displacement-time curve, and mechanical performance of the CFST frame were obtained through analyzing. Finally, it is concluded that the result by the DS method is closer to the actual condition and the collapse process of the structure under impact load can be relatively accurately described; however, the AP method is not.

Finite Element Analysis of Deformation Effect of Concrete Filled Steel Tubular Composite Frame under High Temperature

The research on the mechanical characteristics of concrete-filled steel tubular composite frame under high temperature is one of the hot topics. In this paper, through the finite element simulation software, the failure characteristics of the deformation of concrete-filled steel tubular composite frame and the simulation results of the deformation effect of concrete-filled steel tubular composite frame structure are analyzed, including the effect of each component in different temperature fields, different structural fields and various coupling fields, the redistribution and change of the local plastic region of the component under high temperature, and the change of the local plastic region of the component under high temperature. The comparative analysis of the flexural effect of two-story two span concrete-filled steel tubular composite frame under different fire positions shows that: with the rising of fire time, the vertical displacement is also increasing, the scope of local plastic area is expanding, the deflection redistribution is obvious, and finally the mechanism is formed, and the failure occurs. The deformation effect of condition 1 changes more than that of condition 2, which indicates that the two-story two span steel tubular composite frame has a large deformation effect. The fire resistance of concrete-filled tubular composite frame is better under the condition of full section fire. The research results can provide reference value for strengthening and repairing of concrete-filled steel tubular composite frame under high temperature.

Establishment of “AIJ Recommendation for Mix Design and Construction Practice of Concrete Filled Steel Tubular Structure”

日本建築学会建築工事標準仕様書JASS 5鉄筋コンクリート工事に示される鋼管充填コンクリートの節を補う指針として，鋼管充填コンクリート調合設計・施工指針（案）・同解説を制定した。本指針では，鋼管充填コンクリートに関する最新の知見などを収集し，現時点での合理的な調合設計方法や施工方法について取りまとめている。また，コンクリートの品質確認におけるブリーディング試験の実施に苦慮しているといった意見に配慮し，試験の合理化なども提案している。本報では，これらの要点について概説する。

Research on the Mechanical Characteristics of H-section Steel Frame under the Action of Thermo Mechanical Coupling

The research on the mechanical characteristics of concrete-filled steel tubular composite frame under high temperature fire environment is one of the research hotspots. In this paper, the finite element simulation software is used to analyze the concrete-filled steel tubular composite frame structure. The failure mode of the flexural deformation of the composite frame structure under high temperature fire environment is introduced. The simulation results of the deformation and displacement of the single-layer single span and two-layer two-span composite frame structure are deeply studied, including the different temperature field, structural field, structural field of each beam and column The results show that: with the temperature rising, the horizontal plastic strain, vertical displacement and local plastic region of beam and column are redistributed and changed in high temperature fire environment, and the flexural effect of two-story two-span concrete-filled steel tubular composite frame under different fire positions is analyzed. The results show that: with the temperature rising, the horizontal plastic strain at the concentrated load is not the results show that the deflection and deformation redistribution are obvious, and the deflection and deformation redistribution are obvious at the joint points of beams and columns. Finally, a mechanism is formed and destroyed. The flexure effect of mode 1 is larger than that of condition 2, which indicates that the flexural effect of two-story two span CFST composite frame under full cross-section fire is larger than that of condition 2 It should be better. The research results can provide reference value for the reinforcement and repair of CFST composite frame under high temperature fire.

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.

Seismic experiment on blind-bolted joint in concrete-filled double steel tubular structure

In this study, blind-bolted joints were designed for use between steel beams and concrete-filled double steel tubular (CFDST) columns to utilize the structural advantages offered by double steel tubes. Six joint specimens were tested under a constant axial load and lateral cyclic load for a CFDST column. The seismic behaviors of these blind-bolted joints were estimated in terms of the hysteretic curves, ductility, and energy dissipation. The effects of a T-plate section type and steel beam-type on the semi-rigid joints were studied. The test results showed that the failure of the joints began with the yielding of the T-plates, and that the final failure mode was plastic deformation at the steel beam ends. The obtained hysteretic curves were complete, and the energy dissipation ability of the bolted joint was strong. The bearing capacity and energy dissipation of ribbed joints were higher than those of unribbed joints. Based on a steel volume comparison, the installation of stiffening ribs proved to be considerably more effective than the thickening of the T-plate flanges. The strain response of the inner tube in each CFDST column was also estimated. It was concluded that the blind-bolted joints exhibit excellent deformation capacities and structural internal force redistributions. The results of this experimental research could be helpful for the application of blind-bolted joints in fabricated CFDST structures.

Detection of subsurface voids in concrete-filled steel tubular (CFST) structure using percussion approach

Concrete-filled steel tubular (CFST) structures are essential load-bearing components in many civil engineering structures. Subsurface voids between the contacting surface of the concrete and steel in a CFST structure reduce the load-bearing capacity of the CFST structure. This paper presents a novel, non-destructive, percussion-based approach to detect subsurface voids in CFST structures. In our approach, we exploit the contrasting sound produced by the percussion of surfaces with and without subsurface voids. Percussive acoustic signals in non-void and void zones are recorded. By analyzing the power spectrum density (PSD) of the percussion sound, nine features can be extracted. Two specimens (A and B) were fabricated in our experiment. The features of the sound signal extracted from the specimen A are used as the database for training and testing the support vector machine (SVM) model. Then, the trained SVM is applied to specimen B to determine whether or not a void between the concrete core and the outer steel tube exists. The experimental results show that the prediction precision is 94.17%. Therefore, the percussion-based approach is a simple, efficient, and accurate method to detect the void defects.