Composite Concrete-filled Steel Tube Research Articles

A study on low-frequency vibration mitigation by using the metamaterial-tailored composite concrete-filled steel tube column

The bandgap properties exhibited by local resonant metamaterials provide a potential approach for structural vibration reduction. In this work, we introduce the local resonance mechanism into the composite structure for the first time and propose a novel metamaterial column with 33.8–47.2 Hz low-frequency vibration mitigation based on practical engineering materials and utilizing material shear deformation. By vertically arranging metamaterials, the metamaterial concrete-filled steel tube column with low-frequency vibration reduction bandgap is designed. Its equivalent bandgap model is proposed by combining the Timoshenko beam and Bloch theorem. The bandgap formation mechanism and vibration mitigation effect of the metamaterial are clarified by finite element analysis. It is revealed that the bandgap generation depends on the contrary motion between the resonator and the substrate, thus the reaction force from the relative motion can cancel the external excitation. Then, the bandgap vibration mitigation effect of the metamaterial column is proved by shaking table tests at different amplitudes. This also supplies a feasible solution for vibration mitigation control and even earthquake protection for buildings, bridges, and major infrastructures. Finally, the theoretical, numerical, and experimental results are discussed to verify the validity of the theoretical approach and numerical model, and the rubber damping is found to widen the bandgap but weaken the vibration reduction capacity.

Seismic response mitigation of prefabricated industrial equipment structural frames through a hybrid isolation system

For reducing the excessive acceleration response of the critical equipment in a type of industrial equipment structural frames under strong earthquakes, a hybrid isolation system (HIS), incorporating linear natural rubber (LNR) and lead rubber (LR) bearings, is proposed. The efficiency and reliability of the HIS are verified through a series of full-scale shaking table tests on two prefabricated industrial moment resisting frames (MRFs), with respect to a corresponding fixed-base system (FBS). The structural dynamic characteristic and seismic performance of the two types of MRFs, i.e., reinforced concrete structure (RCS) and composite concrete-filled steel tube structure (CCFSTS), are examined both with the HIS and FBS subjected to a range of seismic intensities. The test results demonstrate the superior performance of the HIS in controlling transient acceleration response under near-fault, far-field and artificial ground motions. The average peak acceleration reduction coefficients (PARCs) of the HIS range between 75.60% and 79.51% in the two considered MRFs along two horizontal directions, with a strict satisfaction on the peak acceleration response for normal operation of the critical equipment. Also, the hysteretic behavior of the HIS is stable and controllable during the earthquake excitations. The peak transient displacement of the HIS is satisfactory, and the residual deformation is negligible even under the maximum considered earthquake (MCE) excitations. Besides, components of the two MRFs are undamaged during the whole test. Thus, with the capacity of protecting the acceleration-sensitive equipment and structural components, the proposed HIS possesses a great prospect in enhancing the structural resilience.

Study of impact factor of arch bridge made with continuous composite concrete filled steel tube beams

Impact factor is amplification factor of vertical dynamic effect produced by vehicles. It is a main parameter of bridge design and an important index of dynamic load effect evaluation. In order to study the influence of structure and excitation factors on the impact factor of highway bridges, and then obtain the real impact factor of the continuous beam arch composite bridge, taking a three-span arch bridge made with continuous composite concrete filled steel tube beams as an example, considering the vehicle-bridge coupling vibration effect, the spatial beam element model of the bridge and the half vehicle model with the three-axis are established by using ANSYS. The impact factor of different parts of the main beam and different responses affected by the deck surface roughness, the vehicle speed and the number of vehicles are analyzed. The binary regression formula of impact factor is obtained by taking the vehicle speed and the roughness of bridge deck as independent variables. Finally, the formula is verified by the measured data of two bridges with similar fundamental frequencies. The results show that the impact factor calculated by the current code is generally small for the bridge structure with complex structure and relatively low frequency, such as arch bridge made with continuous composite concrete filled steel tube beams. The impact factor is most affected by the roughness of bridge deck. When the roughness of bridge deck reaches grade B or above, the impact factor exceeds the specification value, and the maximum impact factor can reach 5.42 times of the specification value. For the main beam, the impact factors of different external excitation, different responses and different parts are not the same, and some impact factors exceed the specification value. The regression formula of impact factor given can be used to estimate the impact factor of main beams of similar structures.

Practical Machine Learning Application for Predicting Axial Capacity of Composite Concrete-Filled Steel Tube Columns Considering Effect of Cross-Sectional Shapes

Practical Machine Learning Application for Predicting Axial Capacity of Composite Concrete-Filled Steel Tube Columns Considering Effect of Cross-Sectional Shapes

Performance evaluation of composite concrete-filled steel tube columns by steel fibers and different cross-section shapes: Experimental and numerical investigations

Increasing the load-bearing capacity of columns without increasing their dimensions has become an essential issue for engineers. Concrete-filled steel tube (CFST) column is one of the common techniques used in different constructions. This study aims to assess the influence of steel fibers (SF) on the uniaxial performance of CFST columns to improve their behavior. 27 specimens are produced and tested under a uniaxial compressive load. Specimens are made with three cross-section shapes: circular, rectangular, and octagonal. Also, steel fibers are added at the three-volume percentages of 0%, 1%, and 2%. Low, normal, and high-strength concrete is used to manufacture concrete columns to consider the influence of compressive strength. The bearing capacity, load-axial shortening curves, and axial-hoop strain performance of columns are measured. Also, the obtained outcomes are compared with the requirements of current design codes and previous models. Based on the obtained results, new models are developed to predict the uniaxial bearing capacity of CFST columns with different concrete core compressive strengths, cross-section shapes, and SF contents. The results indicated that adding SF led to changing the softening behavior of the column to the hardening behavior due to raising the axial compressive strength of the concrete core. Nonetheless, this impact is more significant in CFST columns with octagonal and square cross-section shapes. Additionally, the proposed formulas in this study, with high accuracy, could be employed to predict the uniaxial bearing capacity of CFST columns with different concrete core compressive strengths, cross-section shapes, and SF contents.

Experimental Investigation on the Vertical Ductility of Rectangular CFST Columns Loaded Axially.

A total of 5 steel and 21 rectangular composite concrete-filled steel tube (CFST) columns of moderate slenderness were tested to investigate their ductility under axial compression. The importance of the vertical ductility of columns was discussed, and a novel ductility measure was proposed and utilized to examine the ductility of tested specimens. The analyses showed that the ductility of axially compressed CFST columns highly depends on their failure mode. The key feature influencing the ductility is their ability to dissipate the energy of imposed loads. The larger the volume of a material that may permanently deform and consequently dissipate the energy, the greater this ability. In consequence, the ductility of specimens exhibiting local failure mode was higher in comparison to the columns that underwent global or mixed global—local failure. It was found that both steel and composite columns were able to carry axial loads in the post-critical state; but due to the limitations of local buckling of the steel cross-section in the concrete core and concrete confinement, all tested composite columns showed greater ductility than their steel counterparts.

Flexural behavior of composite concrete-filled steel tube roof structure under symmetrical concentrated loads

This paper presents an experimental research on the composite concrete-filled steel tube roof (C-CFST-R) structure, which is proposed as a new type of tubular-roof structure. The longitudinal large-diameter steel tubes are connected by small-diameter steel tubes in transverse, forming the supporting structure after concrete casting. The mechanical performance and failure mode of the C-CFST-R members are analyzed and following parameters are tested: diameter of the connection tube, eccentricity of the connection tube, the presence of bottom steel plate, and the longitudinal tube spacing. A theoretical formulation for the transverse bending capacity of the cross-section of this structure is also presented. The results show that the failure mode of the test specimens exhibits ductile failure. The transverse stiffness and the bearing capacity increase with the increase of connection tube diameter, while the eccentricity of connection tube has unobvious impact on flexural behavior of the member. Welding the bottom steel plate significantly enhances the bending stiffness and capacity by more than 4 times. The increase of longitudinal tube spacing mainly causes reduction in transverse stiffness. The proposed theoretical calculation method shows a reasonable prediction of the bending capacity in compare with the test results.

The Horizontal Bearing Capacity of Composite Concrete-Filled Steel Tube Piles

Steel casings (SCs) are extensively and increasingly used to stabilize the borehole wall in the construction of bridge pile foundations. Steel casings (SCs), together with reinforced concrete piles (RCPs), form composite concrete-filled steel tube piles (CCFSTPs), which differ significantly from ordinary RCPs in horizontal bearing capacity. In this study, based on the characteristics of CCFSTPs, the horizontal bearing capacity of a CCFSTP was examined through a centrifugal model test with the length of the steel casing (LSC) and the modulus of the soil mass in the steel casing soil compaction zone (ESCSC_zone) as variables. Pile-side soil resistance, load-displacement curves, and pile moment curves were obtained for the CCFSTP. The results show that increasing LSC within a range of 12 cm significantly increases the ultimate horizontal bearing capacity of the CCFSTP, and further increasing LSC beyond 12 cm produces a continuous increase in the ultimate horizontal bearing capacity of the CCFSTP but only to an insignificant extent. In addition, increasing ESCSC_zone increases the ultimate horizontal bearing capacity of the CCFSTP, but to a relatively small extent. The results of this study provide a theoretical basis and technical support for the design and construction of CCFSTPs.

Experimental and Analytical Study of Seismic Behavior of Special-Shaped Multicell Composite Concrete-Filled Steel Tube Columns

AbstractSpecial-shaped multicell composite concrete-filled steel tube (CFT) columns have been used in several super-high-rise buildings. However, research on special-shaped multicell CFT columns un...

The Seismic Performance Study on Composite Concrete-Filled Steel Tube Column-Steel Beam Node

Based on the external stiffening ring node, a kind of node form of composite concrete-filled steel tube column-steel beam node with cover plate type external stiffening ring was proposed. Using the finite element software ABAQUS, 1 ordinary external stiffening ring node and 8 new cover plate type external stiffening ring column-steel beam nodes were established for low cycle repeated loading. The influence of axial compression ratio and column ring diameter-thickness ratio on the seismic performance of the nodes was studied through comparison and study of variation parameters. According to the results, the new composite concrete-filled column-steel beam node with cover plate type external stiffening ring has better seismic performance than the ordinary external stiffening ring nodes, and effectively avoids the stress concentration in the contact part between the external stiffening ring and the composite concrete-filled steel tube column. Besides, it has good seismic performance in the range of reasonable axial compression ratio and diameter-thickness ratio of column ring. Thus, it is more suitable for engineering design and application.

Analysis on composite action of concrete-filled steel tube columns reinforced by different confining materials

This study listed four types of composite concrete-filled steel tube columns, including hollow composite concrete-filled steel tube columns and concrete-filled steel tube columns reinforced steel tube or steel column or carbon fibre reinforced polymer cylinder. According to unified theory of concrete-filled steel tube, the axial bearing capacity was calculated by the equivalent confinement coefficient from different confining materials and the results are consistent with the actual experimental results. Then, some composite columns were designed according to the principle of same amount, and ultimate compressive strength and composite elastic modulus were calculated in order to analyse the composite action. The results showed that it had more theoretical significance and application value to apply concrete-filled steel tube reinforced by steel tube inside for both solid and hollow columns, and carbon fibre reinforced polymer cylinder had the most benefit for repair and retrofit of concrete-filled steel tube structure.

Study on equivalent confinement coefficient of composite CFST column based on unified theory

ABSTRACTThis article introduces the Unified Theory of Concrete Filled Steel Tube (CFST) into counting strength of composite CFST columns subjected to axial compression. There were four types of composite CFST columns listed, and one equivalent confinement coefficient was proposed with consideration of different sections of confining materials, so the whole cross section can be taken as one new composite material to research axial compressive behaviors of the composite CFST column. One unified design formula was derived from the Unified Theory, which was suitable for solid or hollow, circular or non-circular various cross sections of the composite CFST columns. The ultimate compressive bearing capacity was calculated in comparison with corresponding test results. The results show that the equivalent confinement coefficient can be used to calculate the compressive strength of the composite CFST column, and it has a linear relation with the enhanced coefficient of composite strength. Thus, the equivalent confinement coefficient was one important parameter to analyze the mechanical behavior and it can clearly reflect the confinement between concrete and confining material. This method is one more convenient and simpler approach for design work of composite CFST structures.

Modeling level selection for seismic analysis of concrete‐filled steel tube/moment‐resisting frames by using fragility curves

SummaryThe seismic behavior of plane moment‐resisting frames (MRFs) consisting of I steel beams and concrete‐filled steel tube (CFT) columns is investigated in this study. More specifically, the effect of modeling details of each individual component of CFT‐MRFs, such as the composite CFT columns, the beam‐column connections, the panel zones, and the steel I beams on their seismic behavior, is studied through comparisons against available experimental results. Then, fragility curves are constructed for three typical CFT‐MRFs, designed according to European codes, for various levels of modeling sophistication through nonlinear time‐history analyses. On the basis of these fragility curves, one can select the appropriate modeling level of sophistication that can lead to the desired seismic behavior for a given seismic intensity. Copyright © 2014 John Wiley & Sons, Ltd.

Fundamental behavior of CFT beam-columns under fire loading

This paper presents experimental investigations of the fundamental behavior of concrete filled steel tube (CFT) beam-columns under fire loading. A total of thirteen specimens were tested to determine the axial force-moment-curvature-temperature behavior of CFT beam-columns. The experimental approach involved the use of: (a) innovative heating and control equipment to apply thermal loading and (b) digital image correlation with close-range photogrammetry to measure the deformations (e.g., curvature) of the heated region. Each specimen was sequentially subjected to: (i) constant axial loading; (ii) thermal loading in the expected plastic hinge region following the ASTM E119 temperature-time T-t curve; and (iii) monotonically increasing flexural loading. The effects of various parameters on the strength and stiffness of CFT beam-columns were evaluated. The parameters considered were the steel tube width, width-tothickness ratio, concrete strength, maximum surface temperature of the steel tube, and the axial load level on the composite CFT section. The experimental results provide knowledge of the fundamental behavior of composite CFT beam-columns, and can be used to calibrate analytical models or macro finite element models developed for predicting behavior of CFT members and frames under fire loading.

BEHAVIOUR OF HOLLOW CONCRETE‐FILLED STEEL TUBULAR COMPOSITE ELEMENTS

Behaviour of composite steel‐concrete elements in various loading stages is quite well analysed by theoretical investigations and experiments. Concrete‐Filled Steel Tube (CFST) is one of many composite elements used at present in civil engineering. Different approaches and design philosophies were adopted in different design codes for it. But for hollow CFST elements, which are more effective than ordinary CFST, any code does not provide information about how to design these elements. Further investigations of hollow composite CFST elements are needed. In loading stage, when a particular level of stresses exists, an interaction between steel tube and concrete core appears and therefore a complex stress state of element takes place, which increases the load‐bearing capacity of the whole composite element. This interaction between components of CFST elements is reached because of different material properties, such as Poisson's ratio, elasticity modulus etc. In this article reasons of the above‐mentioned complex stress state appearance and behaviour of hollow CFST element components in different load stages of compressed stub structural member are analysed. The test results are presented in diagrams, tables. Previous researches of other investigators are summarised. Differences and similarities in behaviour of solid concrete and composite elements and hollow members with different number of concrete core layers are discussed.

Behaviour of hollow concrete‐filled steel tubular composite elements

Abstract Behaviour of composite steel‐concrete elements in various loading stages is quite well analysed by theoretical investigations and experiments. Concrete‐Filled Steel Tube (CFST) is one of many composite elements used at present in civil engineering. Different approaches and design philosophies were adopted in different design codes for it. But for hollow CFST elements, which are more effective than ordinary CFST, any code does not provide information about how to design these elements. Further investigations of hollow composite CFST elements are needed. In loading stage, when a particular level of stresses exists, an interaction between steel tube and concrete core appears and therefore a complex stress state of element takes place, which increases the load‐bearing capacity of the whole composite element. This interaction between components of CFST elements is reached because of different material properties, such as Poisson's ratio, elasticity modulus etc. In this article reasons of the above‐men...

Seismic behavior and modeling of high-strength composite concrete-filled steel tube (CFT) beam–columns

The behavior of square concrete-filled steel tube (CFT) beam–columns made from high-strength materials was investigated experimentally. The effects of the width-to-thickness ratio, yield stress of the steel tube and the axial load level on the stiffness, strength and ductility of high-strength CFT beam–columns were studied. Sixteen three-quarter scale CFT specimens, which included eight monotonic beam–column specimens and eight cyclic beam–column specimens, were tested. The experimental results indicate that cyclic loading does not have a significant influence on the stiffness or strength of CFT beam–columns. However, it causes a more rapid decrease of the post-peak moment resistance. The moment capacity of high-strength CFT beam–columns can be predicted with reasonable accuracy using the American Concrete Institute (ACI) code provisions for composite columns. Fiber-based models were developed for the CFT beam–column specimens. The uniaxial stress–strain curves for the fibers were derived from three-dimensional nonlinear finite element analyses of the CFTs. The results from the fiber analyses of the monotonic and cyclic beam–column specimens compare favorably with the experimental results.

A distributed plasticity model for concrete-filled steel tube beam-columns with interlayer slip

A fiber-based distributed plasticity finite element formulation is presented to perform three-dimensional monotonic analysis of square or rectangular concrete-filled steel tube (CFT) beam-columns. This stiffness-based beam-column element fomulation accounts comprehensively for all significant geometric nonlinearity exhibited by CFT beam-columns as part of composite frame structures, and the steel and concrete constitutive models account for the significant inelastic phenomena which are seen in CFT experiments. In addition, the finite element formulation accounts for slip between the steel and concrete components of the CFT by incorporation of a nonlinear slip interface. This formulation is able to capture behavior ranging from perfect bond to immediate slip. The calibration and verification of the slip formulation are presented, and the finite element model is verified against experiments of CFT beam-columns subjected to monotonic loading. Results from a preliminary study are presented on the effect of slip on CFT beam-column and composite frame behavior. A related paper extends this formulation to cyclic analysis of composite CFT frames, and provides details of the steel and concrete constitutive models.