• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.649-658
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• 1997

When steel tube as a column is filled with concrete, it is common that the load-bearing capacities of CFST(Concrete Filled Steel Tube) column are increased substantially, And the CFST column can obtain a capacity of fire resistance without any additional detail on the surface of the steel tube for fire protection. In order to clarify the behavior of CFST column during fire occurrence, a theoretical study is performed, that is, a thermal analysis is used to find temperature gradient dependent on the time on the steel tube and the infilled concrete. N-M (axial force-moment) interaction curves are summarized under the consideration for time dependent variation. The material properties of concrete and steel in accordance with a temperature variation are referred to the existing general data. Thermal transient analyses are performed by finite element method through ANSYS and then these results are verified by comparing with the existing test results. On the basis of analytical results, load-carrying capacities (N-M interaction curves) are calculated by numerical analysis method.

• Smart Structures and Systems
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• v.19 no.4
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• pp.371-382
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• 2017

Concrete filled steel tubes are extensively applied in engineering structures due to their resistance to high tensile and compressive load and convenience in construction. But one major flaw, their vulnerability to environmental attack, can severely reduce the strength and life of these structures. Degradation due to corrosion of steel confining the concrete is one of the major durability problems faced by civil engineers to maintain these structures. The problem accelerates as inner surface of steel tube is in contact with concrete which serves as electrolyte. If it remains unnoticed, it further accelerates and can be catastrophic. This paper discusses a non-destructive degradation monitoring technique for early detection corrosion in steel tubes in CFST members. Due to corrosion, damage in the form of debonding and pitting occurs in steel sections. Guided ultrasonic waves have been used as a feasible and attractive solution for the detection and monitoring of corrosion damages in CFST sections. Guided waves have been utilized to monitor the effect of notch and debond defects in concrete filled steel tubes simulating pitting and delamination of steel tubes from surrounding concrete caused by corrosion. Pulse transmission has been used to monitor the healthy and simulated damaged specimens. A methodology is developed and successfully applied for the monitoring of concrete filled steel tubular sections undergoing accelerated chloride corrosion. The ultrasonic signals efficiently narrate the state of steel tube undergoing corrosion.

• Structural Engineering and Mechanics
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• v.56 no.1
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• pp.67-83
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• 2015

The load transfer mechanism and load-bearing capacity of cast steel joints for H-shaped beam to square tube column connection are studied based on the deformation compatibility theory. Then the monotonic tensile experiments are conducted for 12 specimens about the cast steel joints for H-shaped beam to square tube column connection. The findings are that the tensile bearing capacity of the cast steel joints for beam-column connection depends on the ring of cast steel stiffener. The tensile fracture happens at the ring of the cast steel stiffener when the joint fails. The thickness of square tube column has little influence on the bearing capacity of the joint. The square tube column buckles while the joint without concrete filled, but the strength failure happens for the joint with concrete filled column. And the length of welding connection between square tube column and cast steel stiffener has little influence on the load-bearing capacity of the cast steel joint. Finally it is shown that the load-bearing capacity of the joints for H-shaped beam to concrete filled square tube column connection is larger than that of the joints for H-shaped beam to square tube column connection by 10% to 15%.

• International journal of steel structures
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• v.18 no.4
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• pp.1153-1166
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• 2018

This paper was concerned with the nonlinear analysis on the overall stability of H-type honeycombed composite column with rectangular concrete-filled steel tube flanges (STHCC). The nonlinear analysis was performed using ABAQUS, a commercially available finite element (FE) program. Nonlinear buckling analysis was carried out by inducing the first buckling mode shape of the hinged column to the model as the initial imperfection with imperfection amplitude value of L/1000 and importing the simplified constitutive model of steel and nonlinear constitutive model of concrete considering hoop effect. Close agreement was shown between the experimental results of 17 concrete-filled steel tube (CFST) specimens and 4 I-beams with top flanges of rectangular concrete-filled steel tube (CFSFB) specimens conducted by former researchers and the predicted results, verifying the correctness of the method of FE analysis. Then, the FE models of 30 STHCC columns were established to investigate the influences of the concrete strength grade, the nominal slenderness ratio, the hoop coefficient and the flange width on the nonlinear stability capacity of SHTCC column. It was found that the hoop coefficient and the nominal slenderness ratio affected the nonlinear stability capacity more significantly. Based on the results of parameter analysis, a formula was proposed to predict the nonlinear stability capacity of STHCC column which laid the foundation of the application of STHCC column in practical engineering.

• Architectural research
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• v.23 no.1
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• pp.11-17
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• 2021

A concrete-filled circular steel tube beam was fabricated, and a bending test was performed to analyze its failure modes, displacement ductility, bending-shear strength, and load-central deflection relationship. For the bending test, the installation position of the shape memory alloy (SMA) inside and outside the double-skin steel tube was used, and the rebar installation position, the concrete strength, the mixing of fibers, and the inner-outer diameter ratio as the main parameters. The test results showed that the installation positions of the reinforcements inside and outside the double-skin steel tube and the inner-outer diameter ratio of the steel tube affected the ductility, maximum load, and failure mode. In general, the specimen made of general concrete with SMA installed outside and inside (OI) the double-skin steel tube showed the best results.

• Magazine of the Korea Concrete Institute
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• v.7 no.5
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• pp.133-144
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• 1995

This study investigated to the properties of structural behaviors through a series of experiment with the key parameter, such as diameter-to-thickness(D/t) ratio, selenderness ratio of steel t~ube and strength of concrete under loading condition simple confined concrete by steel tube as a fundmental study on adaptability with structural members in high-rise building. The obtained results are sumnarised as follow. (1) The fracture mode of confined concrete was presented digonal tension fracture in the direction of $45^{\circ}$ with compression failure at the end of specimen in stub column, but the fracture mode of long column was assumed an aspect of bending fracture transversely. (2) The deformation capacity and ductility effect was increased by confine steel tube for concrete. (3) 'The emprical formula to predict the ultimate capacity of confined concrete by steel tube and concrete filled steel tube column using restraint of concrete considered D / t ratio, selenderness ratio of steel tube anti strength of' concrete were proposed.

• Smart Structures and Systems
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• v.20 no.2
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• pp.175-180
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• 2017

The load-carrying capacity and structural behavior of concrete-filled steel tube (CFST) structures is highly influenced by the grouting compactness in the steel tube. Due to the invisibility of the grout in the steel tube, monitoring of the grouting progress in such a structure is still a challenge. This paper develops an active sensing approach with combined piezoceramic-based smart aggregates (SA) and piezoceramic patches to monitor the grouting compactness of CFST bridge structure. A small-scale steel specimen was designed and fabricated to simulate CFST bridge structure in this research. Before casting, four SAs and two piezoceramic patches were installed in the pre-determined locations of the specimen. In the active sensing approach, selected SAs were utilized as actuators to generate designed stress waves, which were detected by other SAs or piezoceramic patch sensors. Since concrete functions as a wave conduit, the stress wave response can be only detected when the wave path between the actuator and the sensor is filled with concrete. For the sake of monitoring the grouting progress, the steel tube specimen was grouted in four stages, and each stage held three days for cement drying. Experimental results show that the received sensor signals in time domain clearly indicate the change of the signal amplitude before and after the wave path is filled with concrete. Further, a wavelet packet-based energy index matrix (WPEIM) was developed to compute signal energy of the received signals. The computed signal energies of the sensors shown in the WPEIM demonstrate the feasibility of the proposed method in the monitoring of the grouting progress.

• Steel and Composite Structures
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• v.3 no.1
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• pp.47-64
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• 2003

In a nonlinear finite element study on the mechanical behavior of simple beam connections to continuous concrete-filled steel tube columns, two principally different connection types were analyzed: one with plates attached to the outside of the tube wall, relying on shear transfer, and one with an extended plate inserted through the steel section to ensure bearing on the concrete core. The load was applied partly at the connection within the column length and partly at the top, representing the load from upper stories of a multistory building. The primary focus was on the increased demand for load transfer to ensure composite action when concrete with higher compressive strength is used. The results obtained from the analyses showed that the design bond strength derived from push tests is very conservative, mainly due to the high frictional shear resistance offered by pinching and contraction effects caused by connection rotation. However, with higher concrete strength the demand for load transfer increases, and is hard to fulfill for higher loads when connections are attached only to the steel section. Instead, the connection should penetrate into the concrete core to distribute load to the concrete by direct bearing.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.05a
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• pp.213-214
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• 2012

This paper presents basic study to develop high performance concrete for concrete filled tube with addition content of steel fiber. In this study, all mixtures was added to nylon fiber (1.5 kg/㎥) and steel fiber was mixed by 0, 20 and 40 kg/㎥ respectively. To evaluate the property of high performance concrete was used to various test methods which were slump flow, air content, U-box test, O-lot test and L-flow(to 300 mm, 500 mm). Also, compressive strength test was measured by ages.

• Structural Engineering and Mechanics
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• v.37 no.3
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• pp.321-330
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• 2011

Long-term properties of concrete affect structures in many respects, not excepting dynamic behaviors. This paper investigates the influence of concrete creep on the dynamic behaviors of concrete filled steel tube (CFT) arch bridges, by means of combining the analytical method for the creep of axially compressed CFT members, which is based on Model B3 for concrete creep, with the finite element model of CFT arch bridges. By this approach, the changes of the stress and strain of each element in the bridge with time can be obtained and then transformed into damping and stiffness matrices in the dynamic equation involved in the finite element model at different times. A numerical example of a long-span half-through CFT arch bridge shows that creep influences the natural vibration characteristics and seismic responses of the bridge considerably, especially in the early age. In addition, parameter analysis demonstrates that concrete composition, compressive strength and steel ratio have an obvious effect on the seismic response of the CFT arch bridge.