Performance Of Concrete-filled Steel Tube Research Articles

Experimental investigation of the behavior of UHPCFST under repeated axial tension

A ultra-high performance concrete filled steel tube (UHPCFST) is a composite structural component that extends the performance of both steel and concrete. It is a promising component to be used in a diagrid structure to further reduce self-weight. Compared with the research on compressive performance of UHPCFST, there is a lack of knowledge on the mechanical behavior of UHPCFST under axial tension. This paper fills this knowledge gap by carrying out experiments on UHPCFST subjected to monotonic and repeated tension. The test parameters are steel tube thickness and volume fraction of ultra-high performance concrete (UHPC). The failure modes, load-strain curves, tensile strength and tensile stiffness are studied in detail. Stiffness degradation is also studied. The test results show that: (1) under axial tension load, a UHPCFST typically experiences fracture failure of the outer steel tube, followed by section fracture of the UHPC, and notable deformation before a final ductile failure; (2) tensile strength increases with the increase of the thickness of the steel tube, while it is less obvious in a UHPCFST with a higher steel ratio; (3) the force-strain curve of a UHPCFST under monotonical axial tension is close to that of the UHPCFST under repeated axial tension, suggesting that the accumulated damage during unloading and reloading is limited. An exponential decay formula is proposed to predict stiffness degradation observed in the repeated axial tensile tests. It is found that the design codes from Europe, USA, and China underestimate tensile strength and stiffness of UHPCFST. Finally, a three-phase empirical model is proposed for the load-strain curve of UHPCFST under tension.

Effect of dynamic constitutive differences in materials on the impact performance of CFST via secondary development of ABAQUS

To investigate the effect and adaptability of dynamic constitutive models on the impact performance of concrete-filled steel tubes (CFST), a numerical study on the dynamic properties of CFST under impact loading is conducted. By analyzing the impact response, including impact force, mid-span displacement, energy absorption, and mid-span bending moment, the effect of dynamic constitutive differences in materials on the impact performance of CFST is assessed quantitatively. Moreover, the HJC dynamic model was developed and validated by secondary development in ABAQUS. The findings show that the material model without considering strain rate effects would significantly underestimate the impact performance of CFST members. In contrast, the impact resistance of CFST is overestimated by using the J-C model and the C-S model with biased elastic conditions. The results obtained using the DIFavg model are most in agreement with the results of the actual model. The impact resistance of CFST is only slightly influenced by variations in the dynamic constitutive model of concrete. The impact performance of CFST is accurately predicted by using the VUMAT subroutine to program the HJC dynamic constitutive model.

Strain Characteristics of Large-Size Non-Studded Concrete-Filled Steel Tube Column under Construction

Interplay between the outer steel tubes and the core concrete provides an important guarantee for the superior performance of concrete-filled steel tube (CFST) columns compared to that of reinforced concrete columns. In order to optimize the construction of the large-size non-studded CFST columns in an on-going practical project, the strain distributions in the column under construction were measured and tracked, and the law of the strain distributions of the column under construction is revealed. The study finds that the plane section assumption was not applicable to the strain distributions of the column. Nonlinear variations in the strain levels were observed under bi-directional bending of the column. The absence of studs inside the steel tube significantly weakened the interplay of the outer steel tube and the core concrete by means of a significant slip between the concrete and the steel tube at the column corners. The concrete and the steel tube tended to be stressed and deformed independently. Practical suggestions are given for the design and construction of this type of column. The study results are expected to lay a basic and valuable foundation for in-depth investigations on the mechanical behavior of large-size non-studded concrete-filled steel tube columns under construction.

A Review of Research on the Bond-Slip Behavior of Concrete-Filled Steel Tubes with Varying Confinement Interface Damage

The structural safety of concrete-filled steel tubes primarily depends on the interfacial bonding between the steel tube and concrete, two heterogeneous materials. Simultaneously, varying confinement interfaces have diverse impacts on the bond-slip behavior of concrete-filled steel tubes, leading to a variety of damage and failure modes. This article reviews research on the performance of concrete-filled steel tubes, explores damage at different confinement interfaces, and collates findings on bond-slip behavior under various confinement interface conditions, aiming to provide a reference for subsequent studies.

Performance of circular concrete-filled steel tube beams under monotonic and cyclic loadings

This study explored the performance of concrete-filled steel tube (CFST) beams under monotonic and cyclic loadings. Experiments were performed on nine simply-supported 140-mm-diameter CFST beams, which were classified into three groups by the diameter-to-thickness (D/t) ratios of 56.0, 46.7, and 40.0, conforming to Eurocode 4. The experimental results indicated that CFST beams exhibited high ductility. The buckling of steel tubes governed the plastic behavior and the ultimate state of CFST beams. The deformation and curvature concentrated in the middle region of the beams, forming a plastic hinge. The yield load, ultimate load, and yield and plastic stiffness slightly increased when D/t decreased from 56.0 to 46.7. However, by further decreasing D/t to 40.0, the ultimate and yield loads were significantly increased by ∼100%, the elastic stiffness by up to 58.2%, and the plastic stiffness by at least 187.5%. With a decrease in D/t ratio, the yield deflections slightly increased, whereas the ultimate deflection significantly decreased by up to 56.3%. The strength degradation was more pronounced for CFST beams with a D/t ratio of 40.0. Decreasing D/t ratio increased the plastic-to-yield stiffness ratios. The absorbed energy increased linearly with the increase in deflection in the plastic range. The cyclic loading effect caused an average degradation of 1.7%/cycle for both loading and unloading stiffness, whereas it marginally impacted on strength degradation. A decoupling concept and simplifications were employed to propose a simple model for rapidly estimating the moment capacity of CFST beams, which can be useful in designing and evaluating CFST beams.

Axial compressive behaviour of ultra-high performance concrete filled steel tube stub columns at elevated temperatures

Ultra-high performance concrete (UHPC) has many advantages such as high strength, good plasticity and toughness, and excellent durability. However, it is more likely to experience explosive spalling at high temperatures than ordinary concrete due to its low porosity. The ultra-high performance concrete-filled steel tubes (UHPCFSTs), where steel tubes are placed outside of UHPC to reduce its high-temperature spalling, could be an effective structural type to make full use of the advantages of both steel and UHPC. Most of the existing fire protection design codes for concrete-filled steel tube structures are based on ordinary concrete, and the performance and failure mechanisms of UHPCFSTs under high temperatures are still unclear. On this basis, an experimental study on the axial compressive performance of UHPC filled circular steel tube stub columns at constant elevated temperatures was carried out. The effects of temperature, steel tube thickness and coarse aggregate content on the compressive properties and failure modes of UHPCFST members were analysed. The results have shown that the UHPCFST mainly suffered from the overall pier coarse type and drum type failure modes. The failure characteristics were highly influenced by temperature magnitude, and 400℃ was the critical temperature where the structural performance change significantly beyond this point. The constraint effect of the steel tube on UHPC increased with the increase of thickness of steel tube, but it would be weakened with the increase of temperature or the coarse aggregate content. Finally, based on the average temperature method, a formula for calculating the ultimate load bearing capacity and equivalent stress–strain relationship of an UHPCTST stub column under a constant high temperature was proposed.

Study on axial behaviour of concrete filled steel tubular columns

Concrete-filled steel tube (CFST) columns have gained wide acceptance in the construction of high-rise buildings due to their exceptional ability to withstand axial load. They are commonly employed as columns in large-span high-rise buildings, bridges, and piers. This research aims to investigate the performance of concrete-filled steel tube (CFST) columns when subjected to axial load. One key advantage is that the steel tube serves as a permanent confinement for the concrete. The concrete filling inside the tube prevents local buckling and enhances the lateral stability of the member. Moreover, the external steel tube acts as a formwork. Eight composite columns were constructed, comprising four CFST columns and four CFDST (Concrete-filled Double Skin Tubular) columns, and were subjected to axial loading for evaluation. The experimental study was conducted to determine the relationship between load, axial displacement, and lateral displacement, as well as the ultimate load-carrying capacity. Furthermore, finite element analysis using Abaqus was performed to investigate the composite columns analytically. A parametric study was also carried out, considering the diameter-to-thickness ratio and grade of concrete. Confinement significantly enhances the load-carrying capacity, and the presence of concrete infill reduces the lateral deflection of long columns.

A constitutive model of expansive concrete and steel fiber-reinforced expansive concrete under tri-axial compression

Expansive concrete (EC) or steel fiber-reinforced expansive concrete (SF-EC) have been adopted for enhancing the performance of concrete-filled steel tube (CFST) columns, while the investigations on confinement mechanism and theoretical model for EC and SF-EC are limited. This study aims to develop a constitutive model for EC and SF-EC under tri-axial compression. In the first part, the results of tri-axial compression tests on 52 concrete cubes, were summarized and collected to form a database. In the second part, the failure criterions of concrete cubes, and performances of four existing stress–strain models were assessed and discussed using the database. The results of tri-axial compression with equal lateral confining stresses generally complied well with the compressive meridians of Ottosen failure criterion, whereas the Lode angles were around 56°–58° for the true tri-axial compression results. However, the existing models substantially underestimated the axial strains at peak stresses by at least 40%, and thus the predicted stress–strain curves deviated considerably from the test results with much steeper initial ascending slopes. To this end, a modified constitutive model was proposed with Montoya et al.’s model as the base form and the key parameters updated as per the result database. The proposed model had good performances in predicting the peak axial stresses and the corresponding strains (average error at 8% and 19%, respectively), as well as the full axial stress–strain curves.

Experimental study and proposal of a design model of ultra-high performance concrete filled steel tube columns subjected to fire

To contribute a better understanding of the behaviors of ultra-high performance concrete filled steel tube (UHPCFST) under fire, fire resistance tests on twelve full-scale circular columns were performed in this study, with the emphasis on the evaluation of the effects of steel fiber content, coarse aggregate content, and load level. The failure mode, temperature distribution, axial deformation, and most importantly, the fire resistance of UHPCFST columns subject to the thermal-mechanical coupling action were analyzed. The test results showed that irrespective of the mix proportion of UHPC and the level of applied load, all the columns fail in the overall instability. Although the inclusion of steel fiber and coarse aggregate facilitates the heat transferring considerably, the temperature within the UHPC core is mostly below 400 °C during the whole heating process because of the low thermal conductivity. Moreover, as the content of steel fiber and coarse aggregate increases, better fire resistance of the UHPCFST column is generally observed, benefiting from the enhancement in global stability and the further hydration below the temperature of 400 °C. Finally, given the insufficient predictions of the fire resistance of UHPCFST columns upon the thermal parameters and the high-temperature reduction factors obtained from existing codes and research works, tailored modifications to the average temperature-based model proposed by the author previously were made. The satisfactory validation with the test results using material high-temperature reduction factors from independent research demonstrated the wide applicability of the proposed model.

Dynamic behavior of UHPC-FST under close-in explosions with large charge weight

Ultra-high performance concrete filled steel tube (UHPC-FST) pier columns have great potential to apply in the bridge engineering due to the excellent structural and constructional performance, which are under the risk of car bomb attacks with close-in distance. Based on the field explosion test and numerical simulation, this study aims to examine the dynamic behavior of UHPC-FST specimens under close-in explosion with large charge weight. Firstly, the field explosion test was performed on five 1/4 scaled UHPC-FST specimens with TNT charge weight of 25 kg at scaled distances of 0.10–0.17 m/kg1/3, where the influences of standoff distance and burst height were assessed. It shows that the UHPC-FST possesses excellent blast-resistance since the specimens could maintain integrity under intensive blast loadings. Moreover, the different dynamic behaviors of UHPC-FST specimens obtained from present and previous explosion tests under large and small charge weights were also compared. Secondly, to further conduct the corresponding numerical simulation, the parameters of the Karagozian & Case Concrete (KCC) model were comprehensively calibrated for UHPC, and the finite element (FE) models of the field explosion test on UHPC-FST specimens were established by using the commercial software LS-DYNA. Finally, by comparing the damage mode and global deflection of UHPC-FST specimens between the test and simulation results, the calibrated KCC model parameters and the established FE model were fully verified. The present work could provide helpful references for designing and evaluating the blast-resistance of UHPC-FST.

Experimental Studies on Seismic Performance of UHPSFRC-Filled Square Steel Tubular Columns

The excellent seismic performance of concrete-filled steel tube (CFST) structures has been widely recognized, but there is a paucity of research on composite columns using UHPC with added steel fibers. This paper presents the experimental studies and numerical analyses with OpenSees on seismic performance of ultra-high performance steel fiber-reinforced concrete (UHPSFRC)-filled square steel tubular columns. Five half-scaled specimens of UHPSFRC-filled square steel tubular columns were tested under a combination of constant axial compression and cyclic horizontal load, with parameters of width-to-thickness ratio (28.5, 19.9 and 14.7) and axial compression ratio (0.133, 0.266 and 0.399) of the steel tube. With the decrease in width-to-thickness ratio, the maximum bending moment capacity increased by 33.5% and 15.3%, and the energy dissipation capacity and ductility increased, while the strength degradation and stiffness degradation reduced. With the increased axial compression ratio, the loading capacity increased from 55.3 to 70.2 kNm (26.94%). The results indicate that UHPSFRC-filled square steel tubular columns improve seismic performance by decreasing the axial compression ratio and by increasing the width-to-thickness ratio. When the width-to-thickness ratio was reduced, the steel tubular was able to provide higher lateral restraint to the internal UHPC; thus, seismic performance was improved. With the increase in the axial compression ratio, the second-order damage effect of the members was greatly affected, and it accelerated the plastic damage. A modified UHPSFRC model considering steel tubular constraints was adopted, and the nonlinear dynamic modeling of the column response using OpenSees led to good agreement with the tested response of the column under cyclic motion. The theoretical calculation model can better predict the bending capacity of the UHPSFRC-filled square steel tubular columns. However, the calculation formulas of initial stiffness and yield bending moment need further research.

Combined compression-bending performance and design of CFST with localised pitting corrosion

This paper presents a comprehensive numerical study on the combined compression-bending performance of concrete-filled steel tubes (CFSTs) considering the commonly seen localised pitting corrosion damage in the marine environment. An advanced finite element modelling technique is utilised to simulate the localised corrosion pits on the outer surface of the steel tube considering its random nature. The differences between the load-moment interaction of CFSTs with uncorroded conditions, uniform corrosion simplification and pitting corrosion are discussed. The analytical results reveal the impact of localised pitting corrosion damage on the combined compression-bending performance of CFSTs can be grouped as the stress concentration around corrosion pits, premature local buckling of steel tubes and the reduction in effective confinement. An extended parametric study illustrates that the confinement factor and the mean pit depth have a considerable impact on the combined compression-bending behaviour of CFSTs with localised pitting corrosion. The feasibility of utilising existing design approaches calculates the load-moment interaction diagrams of locally pitted CFSTs following the DoV-based uniform corrosion simplification is evaluated. On this basis, simplified design methods accounting for the characteristic of pitting corrosion are proposed for estimating the post-corrosion load-bearing capacity of CFSTs under combined compression and bending, and reasonable accuracy is achieved.

Experimental study on random temperature field of ultra-high performance concrete filled steel tube columns under elevated temperature

Due to the change of microstructure and increased heterogeneity of ultra-high-performance concrete (UHPC) in comparison with normal concrete, the thermal properties of UHPC are much less uniform within the material. Consequently, the fire performance of UHPC filled steel tubes (UHPCFST) columns are affected by the random distribution of temperature within the concrete. In order to study the distribution of the random temperature field within UFPCFST columns under elevated temperature, high temperature tests on 16 circular UHPCFST columns subjected to the ISO-834 standard fire and a linear heating mode are carried out. The average temperature, temperature difference, temperature probability density distribution and the temporal and spatial correlation of the random temperature field are investigated. It is found that the columns with more steel fiber and coarse aggregate contents have higher temperature, small temperature gradient and higher temperature difference. It is also found that the correlation of the zero-centered temperature in the circumferential direction between different time is strong when the temperature continues to rise or fall. The aims of this paper is to provide the reference for the analysis of temperature field of UHPCFST considering the heterogeneity of UHPC core.

Behavior of hybrid PET FRP confined concrete-filled high-strength steel tube columns under eccentric compression

Fiber-reinforced polymer (FRP) wraps as external confining device have been employed to enhance the performance of concrete-filled steel tube (CFST) columns, and the axial compressive behavior of FRP-confined CFST columns have been intensively investigated. Although FRP confinement could enhance the mechanical performance of CFST columns with a high-strength steel (HSS) tube, they are prone to buckling failure, especially under eccentric compression. The purpose of this study is to experimentally investigate the mechanical performance of polyethylene terephthalate (PET) FRP-confined CFST columns (PFCCFSTs) under eccentric compression. A total of eight circular PFCCFSTs were tested for investigating the effects of a range critical parameters (i.e., column slenderness ratio, eccentricity-to-diameter ratio, and thickness of the PET FRP jacket) on the eccentric compressive behavior of PFCCFSTs. The test results show that the typical load-strain curve of PFCCFSTs generally consists of an initial linear ascending segment, followed by a transition segment and a descending segment. It is demonstrated that the load deterioration of PFCCFSTs is more sensitive to the increase of eccentricity-to-diameter ratio than the slenderness ratio, while the PET FRP thickness has little influence on the load bearing capacity of PFCCFSTs. The predictions from a theoretical model are compared with experimental results, and demonstrate that the model underestimates the ultimate lateral deflections due to the ignorance of the strain gradient effect in eccentrically loaded columns.

A comparative study on mechanical and environmental performance of concrete-filled steel tubes using molybdenum tailing aggregate

Aiming at utilizing molybdenum tailing (MoT) in structural concrete members, the mechanical and environmental performance of molybdenum tailing concrete filled steel tubes (MoTCFST) were experimentally studied and compared with those of reinforced molybdenum tailing concrete (RMoTC) counterparts. The results show that the strength reduction and dispersion for MoTCFST under various MoT replacement ratio are both less than those for RMoTC which reveals that concrete-filled tube is a promising structural concrete member in the utilization of molybdenum tailing. By considering MoT replacement ratio, the strength prediction methods for MoTCFST and RMoTC are proposed to conduct the full-range mechanical performance analysis. To achieve the same axial strength, using MoTCFST would show much less environmental impact than RMoTC. A ratio between the axial strength and environmental impact weighting value of molybdenum tailing concrete (MoTC) products is proposed to assess their mechanical-environmental performance efficiency. High-strength materials are beneficial to both the mechanical and environmental performance of MoTC products whilst increasing sectional steel ratio would remarkably reduce the mechanical-environmental performance efficiency of them.

Interfacial Bond Performance of Concrete-Filled Steel Tubes under Fire and Postfire Conditions: State-of-the-Art Review

The critical influencing factors of the interface bonding properties of concrete-filled steel tubes (CFSTs) under fire and postfire conditions are analyzed. This paper analyzes and summarizes the existing research related to the bonding performance of CFST interfaces under fire and postfire conditions at home and abroad, which includes the bonding mechanism of CFST structures, the bonding strength of CFSTs during and after fire exposure, and the main factors influencing bond strength. The analysis results indicate that the temperature has noticeable influences on the bond strength of a CFST during and after fire exposure. The bond strengths of the specimens are reduced more severely under high-temperature conditions than after high-temperature cooling. Shear connectors can significantly improve the bonding performance of CFSTs and effectively reduce the relative slip between steel tubes and concrete. The paper concludes with an analysis of the deficiencies in bond-slip research on the bonding properties of the CFST interface during and after fire exposure and future research directions. First, we can study the use of new technologies and materials to solve the problem of bonding and slipping of CFSTs during and after fire exposure. Second, we can perform extensive experimental research and theoretical simulation analysis to enrich the research in this field, which can provide a reference for engineering practice.

CIRCULAR DOUBLE SKIN STAINLESS STEEL TUBULAR COLUMN FILLED WITH UHPFRC SUBJECTED TO IMPACT LOAD

Concrete filled steel tube (CFST) column is an important type of structural member and its protective design is essential to enhance its structural performance under various dynamic loads. Previously carried out studies on CFST columns tried to determine how to improve their structural response under various loadings, such as axial compression, lateral impact, blast, seismic, etc. Apart from investigations on transverse impact loading, the majority of the other studies on CFST under various loads established solutions and protective measures. Therefore, this study aim is to improve the performance of CFST under transverse impact loads. The geometrical and mechanical properties, boundary conditions, impact loading and dynamic explicit analysis employed in that study. This paper proposes a novel design in terms of cross-sectional configuration and smart materials to be applied on the CFST in order to improve its performance under lateral impact loading. The proposed investigation is exclusively numerical and its results were verified with the experimental results from literature. The considered three main variables were including (1) concrete-filled double skin steel tubular – CFDST with both first sandwich layer and internal carbon steel tube filled with normal strength concrete – NSC, (2) CFDST with first sandwich layer filled with Ultra High-Performance Fiber-Reinforced Concrete – UHPFRC. a. The parameters including failure modes, maximum mid-span deflection, and residual displacements were presented.

Understandings on the Performance of Concrete-Filled Steel Tube with Different Kinds of Concrete Infill

In recent years, concrete-filled steel tube (CFST) has gained attention in the construction sectors due to its unique static and earthquake resistant properties. The steel-concrete composite member is formed by filling the concrete inside the hollow steel tube of various shapes. The experimental and numerical investigations were carried out for CFST members filled with different types of concrete of the same grade. The types of concrete used for this study are conventional concrete, steel fiber-reinforced concrete, geopolymer concrete, and expansive concrete, respectively. The concretes were cast in the form of cubes followed by curing underwater and self-curing conditions. The specimens cured for 7 and 28 days of age were subjected to axial compressive strength testing. The effect of curing conditions on the strength of concrete was evaluated by comparing the obtained results. Self-curing, the only possible way of curing infilled concrete in the case of CFST columns, was found to have no influence on the strength of concrete, and the same curing method was adopted for the CFST columns tested in this study. A total of 24 CFST specimens were cast by different types of concrete infill, and their load carrying capacity under axial compression and their bond strength were determined through experimental investigations. The characteristic strengths measured for the CFST columns with different types of concrete infill were compared, and the results are presented. The analytical investigations were carried out by using Eurocode-4 to predict the load-bearing capacity of CFST columns under axial compression. Finally, the load carrying capacities of CFST columns under axial compression obtained through experimental and simulation studies were compared and the results are presented.

Designing new hybrid artificial intelligence model for CFST beam flexural performance prediction

A substantial number of experimental studies have reported on the flexural performance of concrete-filled steel tube (CFST) beams. Due to the problem complexity, theoretically modeling of the flexural bending capacity (Mu) and the flexural stiffness at the initial and serviceability limits ( $$K_{{\text{i}}}$$ and $$K_{{\text{s}}}$$ ) of CFST beams remains challenging mission in the structural engineering field. Hence, this research proposes new numerical models for modeling the flexural capacities (Mu, $$K_{{\text{i}}}$$ , and $$K_{{\text{s}}}$$ ) of CFST beams under static bending load. For this purpose, numerous existing experimental and numerical results of CFST beams are collected for developing a new numerical model called as hybridized artificial neural network (ANN) model with particle swarm optimization (PSO) algorithm. The results of the proposed model validated against the existing results of CFST beams tested over the literature. In addition, PSO–ANN model verified with those obtained by the existing standards and approaches (EC4, BS5400, AISC, AIJ, and others) for the same corresponding beams. The proposed PSO–ANN model confirmed its capability to be used as an alternative theoretical approach to predict the flexural strength and stiffness capacities of CFST beams. The PSO–ANN model achieved mean values of about 0.933–0.989 with a coefficient of variation ranged from 4.98 to 9.53% compared to the existing results that obtained by others.

The prediction of fire performance of concrete-filled steel tubes (CFST) using artificial neural network

Search for enhancing the efficiency has led to composite structures such as concrete-filled steel tubes (CFST) with increasing applications across the world. The fire performance of CFST columns needs to be understood comprehensively. In this paper, the effectiveness of the most important parameters on fire resistance rating (FRR) and residual strength index (RSI) was evaluated using artificial neural network (ANN). Relationships were derived from the developed ANN model for predicting the FRR and RSI of CFST columns. Near 300 experimental data points were extracted from the literature and were used for training, validating, and testing the ANN models. The correlation coefficient (R) of the network for FRR and RSI is 0.967 and 0.97, respectively. The derived relationships from the ANN model have the R coefficient of 0.61 and 0.74 for FRR and RSI, respectively. Also, the limitations of existing empirical relationships were compared with the derived relationships. The comparative results indicated that the ANN model was more stable and accurate than the existing relationships. Moreover, a graphical user interface was developed to predict the FRR and RSI of CFST columns. The derived relationships can be used for the design of new CFST columns, retrofit the existing ones, and risk assessment in fires.