Concrete-filled Tube Research Articles

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.

Study on Combined Energy Absorption Support for Rockburst Disaster Control in Tunnelling

In order to better realize the rockburst disaster control mechanism and approach, the rockburst response of concrete blocks with different energy absorption levels under different energy storage conditions was observed and analyzed by loading tests. The occurrence and control mechanism of rockburst were explored from the perspective of energy aggregation and energy dissipation. On this basis, a combined energy absorption support system of concrete-filled steel tube frames and hollow steel pipes for rockburst disaster control was designed, and the effectiveness of the system was verified by numerical simulation and field tests. The results of loading tests show that the failure mode of the specimens changes from static failure to dynamic burst under energy storage loading. The occurrence of rockburst is inevitable when the energy supply is sufficient, but the disaster can be reduced or eliminated by strengthening constraints and improving energy-absorbing capacity to transform rockburst into large deformation. The combined structure consists of the hollow steel pipes being energy-absorbing part and the concrete-filled steel tube frames being strong confinement part was proposed to control rockburst disaster in tunnel support. The numerical analysis on the dynamic response of the support under strong rockburst impact shows that the hollow steel pipes effectively reduced the impact force on the concrete-filled tube frames, and accordingly, the deformation of the entire support system decreased. Given the condition that the hollow steel pipes be able to absorb all the impact energy during deformation, the smaller the strength of the hollow steel pipe is, the smaller the impact force and the displacement is. The combined energy absorption support provides an effective solution for rockburst disaster management in tunnels with strict clearance requirements.

Experimental study on a new V-cut RBS and CFT connections with bidirectional bolts under cyclic loadings

This paper presents experimental investigation on evaluation of performance of a new type of steel reduced beam section (RBS), designated as V-cut, and on its role in improving overall safety of RBS-CFT connections subjected to cyclic load. Detailed design steps adopted for design of the V-cut RBS with lower depth of cut, as compared to that in the conventional radius cut RBS, are reported in this paper. Behavior of two types of steel RBS and concrete filled tube (CFT) connections with bidirectional bolts were examined. An experimental study was performed to compare the performance of V-cut RBS with that of the conventional radius cut RBS under cyclic loading. It exhibited improved hysteretic behavior, and the new RBS-CFT connection is found to be semi-rigid in nature. Test results show that the energy dissipation in the composite steel connections with V-cut RBS is higher than that with radius cut RBS. The application of V-cut steel flange beam effectively enhanced ductility and reduced the residual torsional deformation. It reached a rotational capacity of 0.04 radians without any damage in the joint panel region, and thereby meets the seismic provisions of the AISC as a special composite moment-resisting frame. Further, a simplified numerical simulation of force-deformation hysteretic behavior of RBS-CFT connections was carried out using OpenSees software. Simulated force-deformation hysteresis loops are found to be in close agreement with those obtained from experimental investigation.

Hysteretic Behavior of Specimens of Circular Concrete-Filled CFRP-Steel Tubular Beam-Column

To study the difference in hysteretic behavior of specimens of circular concrete-filled CFRP-steel tube under different influencing factors, 12 specimens were designed, and their failure modes and P-Δ curves were studied. ABAQUS was used to simulate the specimens’ P-Δ curves and deformation mode. Based upon the simulation results, the stress distribution of all of the specimens’ component materials and the interaction between the steel tube and concrete was analyzed throughout the entire loading process, and the trilinear model, the restoring force model of circular concrete-filled CFRP-steel tube, was proposed. All of the specimens’ P-Δ curves were full and demonstrated excellent hysteretic behavior. The specimens’ P-Δ curves, the skeleton curves, and deformation mode were simulated by the ABAQUS, and the simulation results agreed well with the experimental results. Further, the results of the restoring force model built based upon the trilinear model agreed well with the finite element simulation results.

Full-scale tests on two-story SCBFs with Through–Gusset Plate in brace-to-CFT column connections

In Special Concentrically Braced Frames (SCBFs) with Concrete-Filled Tube (CFT) columns, brace force must be transferred through beam–brace–column joint and thereafter distributed between steel tube and concrete infill of column. In the common practice, gusset plates are directly welded to the steel tube of CFT columns where the majority of force is transferred to only a part of steel tube placed adjacent to the gusset plate resulting in distortion and fracture. Accordingly, Through–Gusset Plate (TGP) passing through CFT column is proposed for connecting brace to CFT column and distributing the brace force between steel tube and concrete infill. Moreover, the gusset plates in the braced frames may encounter pinching forces due to frame action. The current study resolves this problem through proposing a new method for connecting the beam to the gusset plate. In addition, beam–to–column connections in SCBFs tolerate large rotation demands due to frame action. Consequently, fracture and damage may occur at beam–to–column connections. This research considers moment connections between the beam and the column using a Through–Plate (TP) to evaluate their effects on the behavior of SCBFs. The cyclic performance of the proposed connections is experimentally assessed through full-scale tests conducted on two one-bay, two-story SCBFs with CFT columns and braces. The results showed desirable behavior of TGP connections that remained undamaged. The proposed method for beam-to-gusset plate connections eliminated the pinching force on the gusset plates. In addition, beam-to-column moment connections using TPs resulted in delaying brace fracture and strength degradation.

강섬유 보강 순환골재 콘크리트 충전 각형강관의 전단성능 실험

강섬유 보강 순환골재 콘크리트 충전 각형강관의 전단성능 실험

Theoretical and experimental study on axial compression concrete-filled tubes with different confinements

In order to investigate the mechanical properties of concrete-filled tube columns with a wider range of confinement factors under axial compression, 14 specimens, including plain concrete columns and concrete-filled PVC, plexiglass and steel tube columns are subjected to axial compression. The axial load-displacement curves and damage process of the columns are analyzed, and the results indicate that the ultimate axial compressive strength of the concrete-filled tubes increases as the confinement factor ascends. The stiffness and deformation capacity of columns with lower hoop restraint increase as the confinement factor ascends. The axial load-displacement curve of concrete-filled steel tube (CFST) columns with higher confinement factors can be divided into five stages, and the secondary strengthening effect of CFST columns is discovered and explained. The nominal Poisson's ratio of the steel tube under triaxial stress is derived by the elastic property and the geometric parameters of the concrete and tube. The local initial yield of the steel tube is discovered based on the plastic yield theory, which precedes the entire yield of the CFST columns. Theoretical formulas of the ultimate bearing capacity for the CFST columns based on the four yield criteria are presented and the present results are compared with the values calculated by the typical codes and the experimental results. The value calculated by Tresca yield criterion is more conservative and safer, so it is an appropriate reference for the lower limit design of axial compressive capacity of CFST columns.

Bending and Shear Behaviour of Waste Rubber Concrete-Filled FRP Tubes with External Flanges

An innovative beam concept made from hollow FRP tube with external flanges and filled with crumbed rubber concrete was investigated with respect to bending and shear. The performance of the rubberised-concrete-filled specimens was then compared with hollow and normal-concrete-filled tubes. A comparison between flanged and non-flanged hollow and concrete-filled tubes was also implemented. Moreover, finite element simulation was conducted to predict the fundamental behaviour of the beams. The results showed that concrete filling slightly improves bending performance but significantly enhances the shear properties of the beam. Adding 25% of crumb rubber in concrete marginally affects the bending and shear performance of the beam when compared with normal-concrete-filled tubes. Moreover, the stiffness-to-FRP weight ratio of a hollow externally flanged round tube is equivalent to that of a concrete-filled non-flanged round tube. The consideration of the pair-based contact surface between an FRP tube and infill concrete in linear finite element modelling predicted the failure loads within a 15% margin of difference.

Seismic Strengthening Effects of Full-Size Reinforced Concrete Frame Retrofitted with Novel Concrete-Filled Tube Modular Frame by Pseudo-Dynamic Testing

The present study proposes a new seismic retrofitting method using a concrete-filled tube modular frame (CFT-MF) system, a novel technique to overcome and improve the limitations of existing seismic strengthening methods. This CFT-MF seismic retrofitting method makes the most of the advantages of both concrete and steel pipes, thereby significantly improving constructability and increasing integration between the existing structure and the reinforcement joints. This method falls into the category of typical seismic retrofitting methods that focus on increasing strength, in which the required amount of seismic reinforcement can be easily estimated. Therefore, the method provides an easy solution to improving the strength of existing reinforced concrete (RC) structures with non-seismic details that are prone to shear failure. In the present study, a full-size two-story test frame modeled from existing domestic RC structures with non-seismic details was subjected to pseudo-dynamic testing. As a result, the effect of the CFT-MF system, when applied to existing RC structures, was examined and verified, especially as to its seismic retrofitting performance, i.e., restoring force characteristics, stiffness reinforcement, and seismic response control. In addition, based on the pseudo-dynamic testing results, a restoring force characteristics model was proposed to implement non-linear dynamic analysis of a structure retrofitted with the CFT-MF system (i.e., the test frame). Finally, based on the proposed restoring force characteristics, non-linear dynamic analysis was conducted, and the results were compared with those obtained by the pseudo-dynamic tests. The results showed that the RC frame (building) with no retrofitting measures applied underwent shear failure at a seismic intensity of 200 cm/s2, the threshold applied in seismic design in Korea. In contrast, in the frame (building) retrofitted with the CFT-MF system, only minor earthquake damage was observed, and even when the maximum seismic intensity (300 cm/s2) that may occur in Korean was applied, small-scale damage was observed. These results confirmed the validity of the seismic retrofitting method based on the CFT-MF system developed in the present study. The non-linear dynamic analysis and the pseudo-dynamic test showed similar results, with an average deviation of 10% or less in seismic response load and displacement.

Compressive Strength Testing of Hybrid Concrete-Filled Fiber-Reinforced Plastic Tubes Confined by Filament Winding

In this study, an experiment on compressive strength of the hybrid concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) confined by filament winding was conducted to improve the longitudinal strength while considering the thickness of filament winding as a variable. A maximum error of 17% was observed when the results of performing the finite element analysis (FEA) by applying the mechanical properties of the fiber-reinforced polymer (FRP) materials suggested in previous studies were compared to those of the compressive strength experiment on the hybrid-CFFT. Moreover, a maximum error of 15% was exhibited when the results derived from the strength equation proposed by analyzing the compressive strength experiment were compared. Furthermore, the compressive strength of the hybrid-CFFT increased by up to 14% when the longitudinal compressive strength of the pre-tensioned spun high strength concrete (PHC) pile and concrete-filled tube (CFT) were compared.

Flexural Behavior of Post-Tensioned Normal- and High- Strength Concrete-Filled Fiber-Reinforced Polymer Tubes

Flexural Behavior of Post-Tensioned Normal- and High- Strength Concrete-Filled Fiber-Reinforced Polymer Tubes

Parametric analysis and new design formulas of a prefabricated energy‐dissipating composite slotted shear wall

AbstractIn a conventional wall frame system, shear walls typically exhibit less deformation capacity under earthquakes than the frame. In this study, an innovative prefabricated slotted composite shear wall was proposed, abbreviated as CDSW. Featured with concrete‐filled‐tube (CFT) wall segments, I‐shaped steel connectors, vertical slots and bolted connections with the frame, the CDSW has significantly improved deformation capacity, energy dissipation capacity and construction efficiency compared with conventional shear walls. Its seismic behaviors were investigated through applying quasi‐static cyclic loads, where the specimen exhibited satisfactory cyclic response. Based on the test results, finite element analysis (FEA) models were established to validate the test results, and 12 parametric FEA cases were conducted to optimize the parameters of CDSWs. A new design method of a CDSW with highly accurate formulas was proposed based on a new parameter termed as equivalent stiffness ratio (ESR). With ESR, the stiffness and internal force of a CDSW can be obtained with satisfactory precision. Based on the analytical result and the new design formulas, it can be concluded that the ESR between 0.706 and 1.25 is recommended for practical engineering applications, which took into consideration the governing factors of yield and peak strength, stiffness, deformation capacity and energy dissipation. Additionally, the installation of the upper and lower sets of connectors at about 40% and 60% of the height of CDSW is suggested, respectively.

Experimental Study of Octagonal Steel Columns Filled with Plain and Fiber Concrete under the Influence of Compressive Axial Load with Eccentricity

In recent years, Concrete Filled Tube (CFT) columns have been very much taken into consideration due to the many advantages of the instrument. In experimental studies, the focus has been on compressive loading. Although in many cases the eccentric loading (the presence of a bending moment) has also been investigated, further research is needed in this regard. Therefore, in this study, the steel columns filled with concrete with a regular octagonal cross section were studied under the influence of pressure axial load with eccentricity. The parameters studied in this study include bearing capacity, coefficient of ductility and energy absorption. To test and compare the stated parameters, specimens of 150 cm height, which were filled with plain concrete and fiber reinforced concrete were tested. The compressive axial load has been applied to the specimens by the eccentricity of 50, 100 and 150 mm. The results show that at pure compressive loading, the increase in concrete core capacity increases the load bearing capacity of the specimens so that by increasing the concrete compressive strength by 50%, the bearing capacity of the cross section increases by about 15%. Also, based on the results, the average ductility coefficient for specimens was 7.4, and it seems that this value is independent of the type of loading. The use of concrete with intermediate grade resistance can increase the energy absorbed. However, according to the results, it seems that by increasing the bending moment the positive effects of the concrete core are greatly reduced.

Analysis of a more ductile connection between steel beams and concrete-filled tube columns

To resolve the problem of ductile fracturing of beam flanges in traditional connections with concrete-filled steel tube columns using site-welded side plates, an alternative connection design requiring minimal site welding was designed and studied. An explicit analysis method, considering the fracture strain criterion developed by the stress triaxiality path, was adopted to study the seismic performance and fracture resistance of the proposed connection. The results of a verified finite-element model indicated that the steel beam flange in the connection never fractured. The connection exhibited a notably higher maximum bending moment and ductility than the traditional connection. The side plates in the proposed connection were tension-bending or compression-bending elements, unlike in the traditional connection. The failure modes, maximum bending moment, ductility and stress distribution of the side plates were compared and analysed parametrically. Based on the stress distribution of the side plates according to the finite-element results, a fitting formula related to the width and thickness of the side plates was obtained. A formula to calculate the flexural capacity was also developed according to the force model of the proposed connection. The calculations and finite-element results were in good agreement.

Effects of two admixtures on the axial compression of concrete-filled fibreglass tubes

This paper reports on an investigation into the influence of an expansive admixture (EA) and fly ash (FA) on the axial compressive behaviour of concrete-filled glass-fibre-reinforced polymer (GFRP) tube columns. The effect of EA and FA on the compressive strength and restrained expansion ratio was studied for two concrete strength grades, and optimised mixtures of expansive FA concrete were selected. It was found that the desired concrete strength and maximum expansion was obtained with 12% substitution of EA and 10% substitution of FA. For this study, 12 concrete-filled GFRP tube columns of circular cross-section were designed and fabricated considering parameters including the GFRP tube thickness, EA content, FA dosage and concrete strength. Their axial compressive behaviour was investigated through their failure modes, load-carrying capacity, ultimate stress and stress–strain curves. The results showed that increases in the thickness of the GFRP tube and EA content can enhance the axial compressive strength of concrete-filled GFRP tube columns. The theoretical ultimate load results showed good agreement with the experimental data.

Investigation of BFRP bar reinforced geopolymer concrete filled BFRP tube columns

An experimental investigation was carried out on a novel type of concrete-filled tube column, which used geopolymer concrete and basalt-fibre-reinforced-polymer reinforcing bars and confinement tube. Geopolymer concrete was used in place of ordinary Portland cement concrete to counter the sustainability challenges of conventional cement manufacture. Longitudinal basalt-fibre-reinforced-polymer bars were used to replace steel reinforcement to avoid corrosion, while basalt-fibre-reinforced-polymer tube confinement was used to replace the conventionally used steel helix to enhance strength and ductility. Compressive load–deformation behaviour of 200 mm dia., 800 mm high specimens under concentric, 25 mm eccentric, 50 mm eccentric and four-point bending loads was experimentally investigated. Experimental axial load–bending moment diagrams were then produced. Although geopolymer concrete is normally considered to be more brittle than Portland cement concrete, the test results showed that the specimens with geopolymer concrete were more ductile compared to those with Portland cement concrete. It was also found that increased load eccentricity resulted in ductility enhancement in specimens with both types of concrete with basalt-fibre-reinforced-polymer bars and tubes, while steel-reinforced specimens suffered loss of ductility with increased load eccentricity.

Behaviour of high strength concrete-filled short steel tubes under sustained loading

Concrete filled steel tubes (CFSTs) are extensively used in a variety of structures due to their structural and economic advantages over other types of structures. Considerable research has been conducted with regards to their short-term behaviour, and very limited studies have focused on their long-term behaviour. In this study, a series of tests were carried out on high strength squat (short) CFSTs and concrete cylinders under controlled conditions of temperature and humidity to better understand their time dependent behaviour. A number of parameters were investigated including the influence of steel and concrete bond, confinement, level of sustained load and sizes of specimens. The results revealed that creep strains increased by more than 40% if there was no bonding between steel tube and concrete core. As expected, creep and shrinkage of concrete inside a steel tube were significantly less than those developed in exposed concrete. At the end of a creep period of six months, all the specimens were tested to failure to observe the influence of sustained loads on the ultimate strength. It was found that creep does not have a major effect on the strength of short CFSTs in the specific experimental study conducted here, which was less than 2.5%.

Cyclic Behavior of SCBFs with Through-Gusset Plate Connections and Concrete-Filled Tube Columns

ABSTRACT In Hollow Structural Section (HSS) column-beam-brace connections, offset between gusset plate and HSS column webs leads to large distortion and out-of-plane deformation in HSS column face. To alleviate such undesirable effect, this paper proposes a new connection which consists of concrete infill and gusset plate passing through HSS column, called Through-Gusset Plate (TGP).The results indicated that the proposed connection increases the lateral stiffness, lateral strength, and energy dissipation capacity of frame specimens by up to 74, 67, and 73%, respectively. Moreover, due to using this novel connection, the normal force component capacity of connection is enhanced by approximately 3.2 times.

Modified damaged plasticity and variable confinement modelling of rectangular CFT columns

Concrete damage plasticity (CDP) model is widely used to represent the constitutive behaviour of confined concrete in finite element analysis of concrete-filled tube (CFT) columns. This model requires a constant dilation angle and a stress-strain base curve of concrete as the main input parameters. However, in the case of rectangular CFT columns, the variation in the level of confinement across the cross-section makes both the dilation angle and stress-strain base curve to be solution-dependent. In this study, a novel algorithm has been developed to estimate the dilation angles and to generate the multiple stress-strain curves of concrete under various confining pressures. A numerical technique has been proposed for the modelling of confined concrete in the modified CDP model through the implementation of a solution dependent field variable (SDFV). The efficacy of the proposed modelling technique has been verified through finite element validation of twenty previously tested reinforced concrete (RC), CFT and reinforced-CFT (RCFT) columns under both concentric and eccentric axial loads. Tension stiffening effect of concrete has also been considered in the modelling of eccentrically loaded CFT columns. The proposed numerical models accurately predicted the load-deformation behaviour of CFT columns with and without confining reinforcement under concentric and eccentric axial monotonic loads.

Seismic behavior of braced frames with different connection details to concrete filled tube columns

Concentrically braced frames (CBFs) represent one of the most efficient lateral-load-resisting systems considering its numerous advantages. Using concrete filled tube (CFT) columns provides many economical and aesthetical benefits; however, it requires the use of complex connections. Many alternatives exist in shape and detailing of these connections. Unfortunately, designers are usually faced by lack of supporting procedures related to modelling, design, and detailing of such connections. An extensive study was performed to investigate behavior of different connection configurations to CFT columns. Summary of research results are outlined. Afterwards, influence of different details on the general performance of CBF with concrete filled tube columns under cyclic loading is investigated through an experimental study. Five concentrically braced frames are tested under displacement-based cyclic loading to evaluate their behavior, lateral drift, load capacity, hysteresis responses, ductility, and stiffness degradation. Connections details include gusset plates welded to the outside shell of steel columns with and without shear connectors. Results are investigated and discussed.