Concrete-filled Thin-walled Steel Research Articles

Vertical Diaphragms for Moment Connection of Thin-Walled CFT Column to Steel Beam

A vertical diaphragm scheme is proposed to connect the concrete-filled thin-walled steel tube (thin-walled CFT) column and steel beam, as an alternative to horizontal diaphragm connections: dual vertical diaphragms are installed inside the steel tube, considering poor out-of-plane resistance of the thin tube wall. For verification of the moment connection, two experimental programs were carried out. In the first experiment, an ultimate tension test was conducted for flange-to-column connections, to identify the fundamental behavior of the proposed connection (i.e., strength, failure mode, and out-of-plane deformation). The design parameters, such as the thickness, number, and continuity of the vertical diaphragms, were considered. All the test specimens exceeded the design strengths based on a yield line model (i.e., the tensile capacity-to-demand ratios ranged Tu/TYL = 1.11 ∼ 1.31), without early fracture of welded joints. In particular, at the design strengths, the tube out-of-plane deformations were more limited with the heavier diaphragms. In the second experiment, beam-to-column connections using prototype I-section steel were tested under cyclic flexure, to verify the joint flexural strength and rigidity as well as the seismic performance. The beam-to-column connections failed by the beam flexural mechanism, whereas damage was marginal at the joint wall (i.e., the flexural capacity-to-demand ratios ranged Mu/Mj = 0.87 ∼ 1.09). Overall, the dual diaphragms were effective in achieving rigid (full-strength) connections with satisfactory plastic rotation of the beam. On the basis of the test results, design considerations were recommended for the vertical diaphragm connections.

Analysis of the Bearing Capacity of Concrete-Filled Thin-Walled Square Steel Tubes with Helical Stiffening Based on Local Buckling

Analysis of the Bearing Capacity of Concrete-Filled Thin-Walled Square Steel Tubes with Helical Stiffening Based on Local Buckling

Axial compressive performance of thin-walled square steel tube concrete short column with built-in steel slag block

In the process of iron and steel production, steel slag is produced as waste. The steel slag processing method generally produces steel slag cement as a substitute for gravel and fine aggregates. Steel slag aggregates replace natural aggregate concrete used in concrete components. In addition, steel slag expansion can compensate for the shrinkage characteristics of concrete and steel pipes inside closed wet environments, and the outer steel tube hoop constraint can avoid late hydration expansion structure cracking. Through orthogonal testing, the wall thickness of the steel pipe (3 mm, 3.75 mm, 4.5 mm), content of the steel slag blocks (10 %, 15 %, 20 %) and particle size of the steel slag blocks (40–60 mm, 60–80 mm) were used as experimental variables to conduct axial compression tests on 9 groups of short columns made of slag aggregate concrete-filled thin-walled square steel tubes. Based on the analysis of the test process and displacement, strain, ductility and ultimate bearing capacity results, the failure pattern and mechanism of the short column specimens under axial compression were obtained, and a bearing capacity calculation formula was obtained according to the existing theoretical methods. The results indicate three failure patterns: local convexity, shearing and circumferential bulging. The factors influencing the bearing capacity, from most influential to least influential, are the particle size of the steel slag, the wall thickness of the steel pipe and the amount of steel slag. The Poisson's ratio of core concrete has an important effect on its passive binding force, which affects the longitudinal displacement and load-bearing capacity of the component. The deduced formula can be used to accurately calculate the ultimate bearing capacity of the square steel tube and steel slag concrete. This article transforms the drawbacks of steel slag concrete into advantages and, by combining the characteristics of steel tube concrete, proposes a new type of composite component that has a certain degree of innovation and application value.

Shear behavior of thin-walled concrete-filled steel tubular columns

Shear failure is a brittle type of failures, which should be avoided in any structure as it could cause property loss and human casualties. The shear behavior of thin-walled concrete-filled steel tubular (CFST) columns was hence investigated in this study, involving the tests of 24 thin-walled CFST columns and considering the following parameters: shear span-to-depth ratios = 0.15, 0.3, 0.5, 1, 1.5, and 2; confinement factor = 0.63, 1.27, 1.44, and 1.70; and axial load ratios = 0, 0.2, 0.4, and 0.6. The test results revealed the insights of the initial shear stiffness, failure modes, ultimate bearing capacity, load-deflection curves, load-strain curves, and ductility of the specimens. Based on the failure modes, a method is proposed to evaluate the load resistance, and explain the relationship between the shear span-to-depth ratio and the peak bearing capacity. A compression strut mechanism considering the confinement provided by the steel tube flange is also proposed. The effect of axial load on the shear strength of the concrete core is negligible when the axial load ratio doesn’t exceed 0.4. The predicted results from using the proposed simple model agree generally well with the experimental results.

Experimental investigation on residual capacity of steel-reinforced concrete-filled thin-walled steel tubular columns subjected to combined loading and temperature

Steel-reinforced concrete-filled thin-walled steel tube (SRCFST) is gaining popularity in construction, primarily due to its superior structural performance. However, there is still a scarcity of studies investigating the residual capacity of SRCFST columns subjected to a full-range fire. A comprehensive research was conducted in this, involving both experimental testing and numerical simulation, to investigate the residual capacity of SRCFST columns. Six SRCFST columns were tested under combined loading and temperature to achieve the temperature distribution, failure modes, residual strength, and structural response within the cross-section. The developed finite element (FE) model was used to validate the test results. Three different paths, including after exposure to fire and without initial load, the full-range fire, and the actual path in the current test, were considered toevaluate the influence of different time-load-temperature paths on the mechanical properties of SRCFST columns. Results reveal that the region comprised of profiled steel and surrounded concrete forms a composite constrained region, with little loss of strength and stiffness occurring in the core region. The initial load level and heating time ratio were found to have a significant negative influence on the residual load-carrying capacity and ductility of SRCFST columns. In contrast, circular SRCFST columns are more resistant to the effects of fire than square SRCFST columns. Finally, the existing design methods were used and extended to evaluate the residual load-carrying capacity of SRCFST columns subjected to a complete temperature-load-time process.

Strength Behavior and Ultimate Capacity Prediction of Self-Compacting Concrete-Filled Thin-Walled Medium-Length Steel Tubular Columns under Eccentric Compression

The development of self-compacting concrete-filled thin-walled steel tubular columns is a potential strategy to ease the challenge of conserving resources in society, which are largely consumed by the quickly developing civil industry. However, the application of these columns in the civil industry is rare due to insufficient research, especially research concerning the strength behaviors of the columns under eccentric compression. Therefore, the eccentric compressive behaviors of medium-length tubular columns made up of self-compacting concrete and thin-walled steel with circular sections were experimentally studied in the present paper. The feasibility of predicting the columns’ ultimate capacities using existing design codes was explored, and then comparisons between the predictions and experimental values were carried out. The results showed that the eccentric compression columns had a failure morphology, buckling together with a lateral deflection while they were moved from the bottom to middle positions as the wall thickness increased. Moreover, the ratios of the predicted ultimate capacity of the eccentric compressive columns to the experimental values were within the range of 0.35 to 0.94. This indicates that the predicted ultimate capacity is conservative and safe. The codes AISC-LRFD and JCJ 01-89 achieved the most conservative and the most precise predictive results, respectively. Additionally, the decrease ratio of the predicted ultimate capacity of the eccentric compressive columns to the experimental values was more evident than that of axial compressive columns. This paper can serve as guidance for the design and application of these columns, as well as foster a sustainable and resilient civil industry.

Eccentric Compression Behaviors of Self-Compacting Concrete-Filled Thin-Walled Steel Tube Columns.

For the sake of solving sustainability issues and analyzing the complicated service force states, eccentric compression experiments on self-compacting concrete-filled thin-walled medium-length steel tube columns with a circular cross-section were carried out in the present study. Thereafter, the influence of the eccentric ratios and the wall thickness factors on the mechanical behavior and failure characteristics of both the eccentrically loaded and axially loaded columns was comprehensively analyzed. Finally, prediction formulas for the ultimate load of the columns under eccentric compression were proposed, and a comprehensive comparison of the ultimate loads between the predicted values and experimental values was also conducted. The results indicated that the typical failure characteristics of the eccentrically loaded columns presented lateral deflection together with buckling, while the axially compressed columns displayed expansion and rupture at local positions. Moreover, the ultimate loads of the eccentrically loaded columns decreased by 43.0% and 34.5% in comparison to the columns under axial compression, with the wall thickness factor decreasing from 116.7 to 46.7, respectively. Meanwhile, the ratios of the ultimate loads calculated using design codes to the tested values were in the range of 0.70~0.90, which demonstrated that the design codes could predict the ultimate loads conservatively. Additionally, the ratios of the ultimate loads calculated using the proposed formulas to the tested values were within the range of 0.99~1.08, implying that the proposed formulas were more accurate than the design codes. At the same time, the initial stiffness of the columns under eccentric compression was correspondingly lower than that of the columns undergoing axial compression. The lateral deflections along the height of the columns were almost symmetrical at different loading levels. This study could provide a meaningful approach for designing columns and facilitate their application in civil industry.

Investigations on the seismic behaviour of concrete-filled thin-walled elliptical steel tubular column: Testing and novel FE modelling

This paper designs and tests a total of eight concrete-filled thin-walled elliptical steel tubular (CFEST) columns imposed with lateral cyclic load and axial force to acknowledge their seismic behaviour. The crucial seismic performance analyses on the failure modes, the seismic strength, the ductility index, the energy dissipation, the strength degeneration, and rigidity degeneration of the thin-walled CFEST columns are successively performed. Then a novel numerical analytical approach based on OpenSees software is developed initially by using a code programming process for the elliptical cross section. Particularly, the featured seismic properties of the CFEST column on the strength, rigidity and energy dissipation with respect to those of circular and square CFST columns are revealed. Development rules of CFEST columns’ seismic behaviour under the influence of various material and geometric parameters are investigated as well. Finally, calculation formulae for assessing the initial rigidity, peak force, peak displacement and descending rigidity of the CFEST column subjected to cyclic load are proposed. The findings indicate that the thin-walled CFEST column offers good seismic performance. Unlike the circular and square CFST columns, the outward local buckling failure of the steel tube is usually developed from the small to the large curvature regions. Under the same sectional area and steel ratio, the seismic resistance, initial rigidity, and energy dissipation of the CFEST column loaded along the major axis are much higher than those of the circular and square CFST columns, which should be fully used in engineering practice.

Experimental study on torsional behavior of tapered high strength thin-walled concrete-filled double-skin steel tubular columns

Comparing with traditional straight concrete-filled double-skin steel tubular (CFDST) members, tapered CFDST members have been increasingly used in the domain of power industry due to esthetics and special spatial experience. In addition, the utilization of high strength materials can reduce cross-sectional area and further lower construction cost. In this paper, the torsional behavior of tapered high-strength thin-walled CFDST (THSTW-CFDST) columns with or without longitudinal stiffeners was investigated and a total of twenty tapered THSTW-CFDST specimens were tested. The failure modes, torque-torsional angle curves and torsional capacity of the THSTW-CFDST columns were investigated. The results demonstrate that the installation of stiffeners can significantly improve the local stability of thin-walled steel tubes, but reduce the torsional capacity of the members. Compared with THSTW-CFDST specimens without stiffeners, the torsional capacities of those with stiffeners have been apparently reduced. Based on the experimental results, the finite element (FE) model was developed and verified, and then utilized to ascertain the force-transfer mechanism and the stress development process of each component of THSTW-CFDST columns. In addition, the effects of the various parameters including hollow ratio, diameter-to-thickness ratio, inner steel tube strength to outer steel tube strength ratio, concrete strength the torsional behavior of THSTW-CFDST members were quantitatively assessed. Finally, the accuracy of the existing methods for predicting the torsional capacity of THSTW-CFDST members was evaluated.

Analysis of ultimate seismic performance of thin-walled concrete-filled steel tube bridge piers under dynamic load

This study entailed the use of a cyclic loading test on a thin-walled concrete-filled steel tube (CFST) bridge pier to investigate its ultimate seismic performance. Additionally, a three-dimensional solid-shell finite element (FE) model of thin-walled CFST piers was established using ABAQUS. Cracks were introduced into in-filled concrete, and ductile damage was imposed on the steel tubes, in order to accurately reproduce the seismic performance degradation and post-earthquake residual displacement variation in thin-walled CFST bridge piers. The FE model was validated using pseudo-static and pseudo-dynamic loading tests performed on thin-walled CFST bridge piers. The analysis indicates that the FE model with concrete cracks can reflect the pinching effect of the hysteresis curve; the ductile damage can reflect the degradation of the bearing capacity during large plastic deformation under cyclic loading and the residual displacement under unidirectional and bidirectional dynamic loading. The seismic response of the full in-filled thin-walled CFST bridge pier was the least under the same intensity seismic wave, the in-filled concrete could improve ultimate seismic capacity. Finally, this study established a formula for the relationship between the residual and maximum displacements at the top of thin-walled CFST bridge piers under bidirectional seismic waves.

Uniaxial Monotonic and Cyclic Compressive Stress–Strain Model for Concrete-Filled Thin-Walled Helical Corrugated Steel Tubes

Uniaxial Monotonic and Cyclic Compressive Stress–Strain Model for Concrete-Filled Thin-Walled Helical Corrugated Steel Tubes

Modeling of cyclically loaded square thin-walled CSFT columns stiffened by diagonal ribs using OpenSees

Among various proposed stiffening forms, the diagonal binding ribs, made of thin-walled steel plates with circular holes and welded to the steel tube, were found to particularly effective in improve the cyclic-bending and cyclic-shear behavior of square thin-walled concrete-filled steel tubular (CFST) columns. Although the mechanical behavior can be obtained from the experiments, numerical models are still needed to expand the range of investigation beyond what was tested physically and to facilitate the practical design. A 3D model using shell and solid elements is able to explicitly show the influence of different parameters, and simulate the details including the holes in diagonal ribs and the contact interaction between different parts. However, such analyses are relatively complicated, time-consuming, and are susceptible to numerical issues that cause lack of convergence. By contrast, a 2D model using fiber-based beam–column elements is far more efficient thus allowing for a wider range of investigation. In this work, the fiber models of flexure-dominated diagonal ribs stiffened square thin-walled concrete-filled steel tubular (DSCFST) columns were firstly developed in OpenSees and validated based on the effective stress–strain relationships of steel tubes and moment–rotation curves of RC bases. The fiber models of shear-dominated DSCFST columns were further developed by defining the nonlinear shear force–deformation relationships at the section level. These models were verified by the test results, and then the effect of the deformable RC base, tube local buckling, shear effect, and types of beam–column elements was analyzed in detail. Based on extensive parametric analyses, the effective stress–strain relationships applicable to various square thin-walled steel tubes stiffened by diagonal ribs and infilled concrete were derived, and the simplified shear force–deformation relationships were proposed. These results facilitate understanding of the behavior of DSCFST columns and lay a foundation for further system-level analysis.

Experimental Study on Self-Compacting Concrete-Filled Thin-Walled Steel Tube Columns

Concrete-filled steel tubes present excellent structural and constructional performances because they ideally combine the advantage of concrete and steel tube. Thus, they are widely used in civil infrastructures. However, they inevitably suffer from either hard compacting or high costs. Thus, convenient and rapid construction for compacting concrete and cost saving are the urgent challenges for concrete-filled steel tubes. Therefore, this study investigates filling a thin-walled steel tube with self-compacting concrete to solve the challenges presented by traditional concrete-filled steel tube columns, such as poor compacting performance and high costs. This experimental study tests self-compacting concrete-filled thin-walled steel tube (SCCFTST) columns under concentric compression from loading to failure. Effects of wall thickness of the thin-walled steel tube on the failure modes, load-deformation behaviors, and the ultimate loads of the SCCFTST columns are comprehensively investigated. The ultimate loads between experiments and their calculated values in terms of design codes are also compared. The results suggest that buckling on thin-walled steel tube surface is the typical failure mode. The amount of local buckling increases with decreasing wall thickness, and the decreasing rate of the load-deformation curves in the descending branch decreases by increasing the wall thickness, as well as the ultimate load increasing with increases wall thickness. The ACI and CECS are the most conservative and accurate design codes, respectively, for predicting the ultimate load. Therefore, the SCCFTST columns can be used as structural components in civil infrastructures and their peak loads can be calculated using design codes for conventional concrete-filled steel tube columns. However, modification measures must be taken while predicting the ultimate loads of the SCCFTST columns by design codes. The experimental results of this paper can contribute towards the application of SCCFTST columns in practice.

Study on the Nonlinear Behavior and Factors Influencing the Axial Compression of High-Durability Fibrous Concrete Wrapped Steel Tube Composite Members.

Thin-walled steel pipe concrete has better economic performance, but the problem of local buckling is more prominent with a thin-walled steel pipe; meanwhile, thin-walled steel pipe is more sensitive to the environment and the influence of rusting is more prominent. To solve the above problems, this paper proposes new spiral stiffened rib thin-walled steel pipe concrete laminated members to obtain better force and economic performance. Based on axial compression tests on five forms of composite members, this paper studies the nonlinear behavior of the axial compression of this new type of laminated member and the factors influencing it. The following conclusions are obtained. Under the constraint of the spiral ribs, the new composite member has good integrity and each part can ensure cooperative stress; the buckling of the steel pipe is well limited and the mechanical performance is significantly improved. Compared with ordinary thin-walled concrete-filled steel tubular members, the bearing capacity is increased by about 20% and the deformation ability is increased by more than 30%. The nonlinear behavior of the member in compression can be better achieved through finite element analysis. The parametric analysis shows that the pitch and the steel tube width-to-thickness ratio greatly influence the force behavior of the member. In contrast, the spiral rib width-to-thickness ratio and the external reinforcement only need to meet the structural requirements. Finally, based on the superposition theory, the proposed method of calculating the member's axial compressive load-bearing capacity is given and design suggestions are made. The results of this paper can provide some basis for the engineering application of this new combination member.

The axial compression mechanical properties and factors influencing spiral-ribbed thin-walled square concrete-filled steel tube composite members

Thin-walled concrete-filled steel tubular members have significant economic advantages, but are prone to local buckling, which has a great impact on structural safety. Therefore, this paper proposes a new spiral stiffened thin-walled CFST composite column to solve the above problems. The axial compression test found that spiral stiffeners can significantly improve the buckling resistance of thin-walled steel tubes, with the ultimate bearing capacity increased by 18 % and the ductility coefficient reaching about 2.0. Through the study of the mechanical mechanism, it is found that the spiral rib has little contribution to the vertical stiffness of the component, mainly by restricting the transverse deformation of the steel pipe to improve the mechanical performance of the component. At the same time, it is also found that the spiral rib can also play a strong constraint on the external concrete, and with a small amount of reinforcement, it can ensure the synergistic force of each part of the component. Based on the test, a parametric analysis was conducted on the pitch, the width-thickness ratio of the spiral rib and the influence law were quantified, and the design suggestions were provided. Finally, based on the fitting method, a formula for calculating the bearing capacity of this superimposed member was proposed. The new composite member has the advantages of less steel consumption, good mechanical properties, strong fire resistance, corrosion resistance, and good engineering application prospects.

Assessment on seismic performance of circular concrete-filled thin-walled steel tube columns

Concrete-filled steel tubular (CFST) with circular section is a very efficient composite component bearing vertical loads, which takes advantage of the synergy of steel tube and concrete to fully develop the strengths of both materials. To promote the application of circular CFST columns in multi-story buildings or medium-span bridge piers with improved economic efficiency, circular CFSTs using thin-walled steel tubes were studied in this paper. 8 specimens were designed and tested to assess their seismic performance under constant axial compression and cyclic lateral loads. The key test parameters include axial compression ratio, diameter-to-thickness ratio of steel tube, as well as stiffening scheme. The effectiveness of two steel plate stiffeners (longitudinal stiffener, binding stiffener) at the potential plastic hinges of thin-walled circular CFST columns was verified and discussed. Although all specimens failed in a manner characterized by significant local buckling of steel tubes, they still performed a relatively ductile behavior with the ductility coefficients generally exceeding 4.0, and the ultimate drift ratios exceeding 1/40. The steel plate stiffeners did not achieve the expected enhancement in strength and ductility, due to the premature fracture in the steel tube which may be caused by the damage in the welding heat-affected zone. Based on the test results, a numerical model and a simplified hysteretic model were established to predict the seismic responses of the thin-walled circular CFST columns.

Behaviour of axially compressed CTHST stub columns with inner spiral stirrup

In this paper, a new type of concrete-filled thin-walled high-strength steel tube (CTHST) columns with inner spiral stirrup is proposed. This new type of columns provides dual constraints to the concrete core by both outer steel tube and inner spiral stirrup. To explore the structural performance of this new type of composite members, a pilot study into stub columns under axial compression was carried out. A total of 16 axially compressed specimens, 8 in circular section and 8 in square section, were tested with the various volumetric stirrup ratio (ρ, from 0 to 2.4 %) and yield strength of steel tube (fyt, 571.2 MPa and 648.9 MPa). The experimental results show that, the inner spiral stirrup has little impact on the overall failure pattern of each component of the specimens, but controls the horizontal angle of the failure plane, and the capacity, composite elastic modulus and ductility coefficient of the specimens increase as ρ and fyt increase. In addition, a nonlinear finite element (FE) model was established, and the representative mechanism of axially compressed CTHST stub columns with inner spiral stirrup under different ρ was further studied by the verified FE model. Finally, a calculation method to predict the capacity of the new composite members was developed, which considers the strength improvement of stirrup confined concrete. This method provided an accurate prediction of the capacity of axially compressed CTHST stub columns with inner spiral stirrup.

Behavior of Corroded Thin-Walled Concrete-Filled Steel Tubular Stub Columns

The behavior of two series of corroded thin-walled concrete-filled steel tubes (CFSTs) was investigated in this paper. One series, called the CT series, consists of fourteen CFST specimens corroded by NaCl solution, while the other, called the AT series, consists of six test pieces corroded in the atmosphere. Outer surfaces of corroded steel tubes were scanned using a 3D scanner machine, and a complete surface profile of each specimen was obtained for corrosion evaluation using different methods in this study. Entire test pieces were compressed to failure, and their behaviors under loading were recorded. It is shown that corrosion has a fractal feature, and it has a significant effect on the ductility of specimens. In addition, FEA models of corroded CFST specimens were established based on the 3D scanning profile results using the ABAQUS program and verified against column test results.

Cyclic-shear behavior of square thin-walled concrete-filled steel tubular columns with diagonal ribs

There is no doubt that stiffeners for square concrete-filled steel tubular (CFST) columns can improve the composite action in terms of delaying local buckling of steel tubes and enhancing the confinement on infilled concrete. Among various proposed stiffening forms, diagonal binding ribs, made of perforated thin-walled steel plates and welded at all the four pairs of adjacent sides of a square tube, are found particularly effective. Recent research has experimentally evaluated the axial compressive and cyclic-bending behavior of square thin-walled CFST columns stiffened by diagonal ribs. However, further investigation is necessary to better understand their cyclic-shear behavior. In this work, four diagonal ribs stiffened square thin-walled CFST columns and one unstiffened counterpart were designed and tested under combined cyclic-shear load and constant axial compression. Main parameters included the shear span to depth ratio, axial load ratio, width-to-thickness ratio of the steel tube, and thickness of diagonal ribs. Test results showed that the diagonal ribs improved the confinement from the steel tube to the infilled concrete. The stiffened specimens exhibited satisfactory cyclic-shear behavior with much higher load capacity, better ductility and larger energy dissipation than the unstiffened counterpart. Numerical modeling of the shear specimens was then conducted, indicating that the concrete and steel part contributed to the shear strength by 41.3%-57.4% and 42.6%-58.7%, respectively. Finally, the test results were compared with current design provisions, the average ratio of the predicted to tested shear strength were 0.60 and 0.66 for the calculation methods in the AISC specification and Eurocode, respectively.

Axial Compressive Behavior of Thin-Walled Concrete-Filled Double-Skin Steel Tubular Stub Columns with Connecting Strips

Axial Compressive Behavior of Thin-Walled Concrete-Filled Double-Skin Steel Tubular Stub Columns with Connecting Strips