• Structural Engineering and Mechanics
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• v.88 no.1
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• pp.95-107
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• 2023

In this study, circular thin-walled reinforced high strength concrete-filled steel tube (RHSCFST) stub columns with various tube thicknesses (i.e., 1.8, 2.5 and 3.0mm) and reinforcement ratios (i.e., 0, 1.6%, 2.4% and 3.2%) were fabricated to explore the influence of these factors on the axial compressive behavior of RHSCFST. The obtained test results show that the failure mode of RHSCFST transforms from outward buckling and tearing failure to drum failure with the increasing tube thickness. With the tube thickness and reinforcement ratio increased, the ultimate load-carrying capacity, compressive stiffness and ductility of columns increased, while the lateral strain in the stirrup decreased. Comparisons were also made between test results and the existing codes such as AIJ (2008), BS5400 (2005), ACI (2019) and EC4 (2010). It has been found that the existing codes provide conservative predictions for the ultimate load-carrying capacity of RHSCFST. Therefore, an accurate model for the prediction of the ultimate load-carrying capacity of circular thin-walled RHSCFST considering the steel reinforcement is developed, based on the obtained experimental results. It has been found that the model proposed in this study provides more accurate predictions of the ultimate load-carrying capacity than that from existing design codes.

• Structural Engineering and Mechanics
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• v.22 no.5
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• pp.541-562
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• 2006

This paper compares the performance of axially loaded concrete filled steel tube (CFST) columns cast using a conventionally vibrated normal concrete (NC) and a novel self-consolidating concrete (SCC) made with a new viscosity modifying admixture (VMA). A total of sixteen columns with a standard compressive strength of about 50 MPa for both SCC and NC were tested by applying concentric axial load through the concrete core. Columns were fabricated without and with longitudinal and hoop reinforcement (Series I and Series II, respectively) in addition to the tube confinement. The slenderness of the columns expressed as height to diameter ratio (H/D) ranged between 4.8 and 9.5 for Series CI and between 3.1 and 6.5 for Series CII. The strength and ductility of SCC columns were found comparable to those of their NC counterparts as the maximum strength enhancement in NC columns ranged between 1.1% and 7.5% only. No significant difference in strain development was found due to the presence of SCC or NC or due to the presence of longitudinal and hoop reinforcement. Biaxial stress development in the steel tube as per von Mises yield criterion showed similar characteristics for both SCC and NC columns. The confined strength ($f^{\prime}_{cc}$) of SCC was found to be lower than that of NC and $f^{\prime}_{cc}$ also decreased with the increase of slenderness of the columns. Analytical models for the prediction of confined concrete strength and axial strength of CFST columns were developed and their performance was validated through test results. The proposed models were found to predict the axial strength of CFST columns better than existing models and Code based design procedures.

• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.43-52
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• 2007

There is a growing range of applications for concrete-filled steel tube (CFT) member because of its superior performance. But a CFT member may be uneconomical or has weight problems because it is fully filled with concrete. In this study, a new type of member, called internally confined hollow (ICH) CFT member, was developed to solve the high cost and weight problems of the CFT member. To determine stress-strain model of the concrete in an ICH CFT column, possible failure modes of an ICH CFT column were suggested and confining pressure was derived from equilibriums for each failure mode. From the derived equations, a computer program was coded and parametric studies were performed for some examples. Analytical results showed that internally confined concrete has enhanced strength and ductility compared with those of unconfined or biaxially confined concrete.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.51-60
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• 1996

This study was performed to evaluate the effects of filler on engineering properties of permeable polymer concrete with unsaturated polyester resin. The following conclusions were drawn; 1. The unit weight was in the range of $1.804{\sim}1.919t/m^3$, the weights of those concrete were decreased 17~22% than that of the normal cement concrete. 2. The highest strength was achieved by stone dust filled permeable polymer concrete, it was increased 17% by compressive, 147% by tensile and 188% by bending strength than that of the normal cement concrete, respectively. 3. The ultrasonic pulse velocity was in the range of 2,722~3,060m/sec, which was showed about the same compared to that of the normal cement concrete. Stone dust filled permeable polymer concrete was showed higher pulse velocity. 4. The water permeability was in the range of $3.076{\sim}4.152{\ell}/cm^2/h$, and it was larglely dependent upon the mix design. These concrete can be used to the structures which need water permeability. 5. The compressive strength, tensile strength, bending strength and ultrasonic pulse velocity were largely showed with the increase of unit weight. But, it was decreased with the increase of water permeability, respectively.

• Magazine of the Korea Concrete Institute
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• v.8 no.2
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• pp.151-161
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• 1996

This paper presents a series of tests to produce the h~gh quality concrete to be filled Inside the steel tube columns. Thls concrete filled steel tube system requires not only the high strength, but a150 the flowable concrete. Laboratory test has been performed to clarlfy the material characteristics and to produce the optlmal mix design proportion. Full scale site mock up test has been then carried out to slnlulate the actual construct~on conditions including the product~on of concrete at the rermcon batch plant, transportation to the construction site, proper workabil~ ty and man power required , 4ddit1onal mock up test has finally been performec to irivesti gate any unfavorable construction s~tuatioils since the actual concrete placement has been sched uled in cold weather period, so that the high quality concrete construction is convinced to be successfully carried out.

• Steel and Composite Structures
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• v.31 no.6
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• pp.559-573
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• 2019

Spiral spacing effect on axial compressive behavior of reinforced concrete filled steel tube (RCFST) stub column is experimentally investigated in this paper. A total of twenty specimens including sixteen square RCFST columns and four benchmarked conventional square concrete filled steel tube (CFST) columns are fabricated and tested. Test variables include spiral spacing (spiral ratio) and concrete strength. The failure modes, load versus displacement curves, compressive rigidity, axial compressive strength, and ductility of the specimens are obtained and analyzed. Especially, the effect of spiral spacing on axial compressive strength and ductility is investigated and discussed in detail. Test results show that heavily arranged spirals considerably increase the ultimate compressive strength but lightly arranged spirals have no obvious effect on the ultimate strength. In practical design, the effect of spirals on RCFST column strength should be considered only when spirals are heavily arranged. Spiral spacing has a considerable effect on increasing the post-peak ductility of RCFST columns. Decreasing of the spiral spacing considerably increases the post-peak ductility of the RCFSTs. When the concrete strength increases, ultimate strength increases but the ductility decreases, due to the brittleness of the higher strength concrete. Arranging spirals, even with a rather small amount of spirals, is an economical and easy solution for improving the ductility of RCFST columns with high-strength concrete. Ultimate compressive strengths of the columns are calculated according to the codes EC4 (2004), GB 50936 (2014), AIJ (2008), and ACI 318 (2014). The ultimate strength of RCFST stub columns can be most precisely evaluated using standard GB 50936 (2014) considering the effect of spiral confinement on core concrete.

• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.641-655
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• 1998

It researched several jointing-methods of frame consisting of a concrete-filled steel tubular column and H-shaped beam. These beam-to-column connections is parameters to following: columns of square shape pipe infilled with or without concrete, joints assembled two types of diaphragm, outside-type and through-type. And it is testing that cyclically lateral loadings used hydraulic ram. In testing. we'll be on purposed to estimate the hysteretic behavior, strength and stiffness, energy absorption capacity, deformation capacity and failure configuration of each specimen. It is concluded that the frame specimens with outside-type are more stable and exhibit more energy absorption capacity compared with the through-type, in column of filled with concrete.

• Journal of Korean Association for Spatial Structures
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• v.2 no.4 s.6
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• pp.53-60
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• 2002

An analytic study on the bond stress between steel tube and concrete in concrete filled steel(CFT) rectangular column is presented in this paper. Recently buildings need members which are enhanced durability and ductility. Concrete filled rectangular column system is proposed as alternative plan. In this paper, ABAQUS/Standard Version 5.8 which is identified as usefulness for finite element analysis and has various element library is used. The variables in this study are the location and type of shear-connector. The modeling on contact problem practiced by Contact Pair and Contact Pressure method. In the step of physical bond, it is practiced by Change friction option After yielding of models, analytic results is less than that of experimental results.

• Steel and Composite Structures
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• v.47 no.5
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• pp.615-631
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• 2023

Steel corrosion induces structural deterioration of concrete-filled steel tubes (CFSTs), and any potential extreme action on a corroded CFST would pose a severe threat. This paper presents a comprehensive investigation on the lateral impact behaviour of CFSTs suffering from localised pitting corrosion damage. A refined finite element analysis model is developed for the simulation of locally corroded CFSTs subjected to lateral impact loads, which takes into account the strain rate effects on concrete and steel materials as well as the random nature of corrosion pits, i.e., the distribution patterns and the geometric characteristics. Full-range nonlinear analysis on the lateral impact behaviour in terms of loading and deforming time-history relations, nonlinear material stresses, composite actions, and energy dissipations are presented for CFSTs with no corrosion, uniform corrosion and pitting corrosion, respectively. Localised pitting corrosion is found to pose a more severe deterioration on the lateral impact behaviour of CFSTs due to the plastic deformation concentration, the weakened confinement and the reduction in energy absorption capacity of the steel tube. An extended parametric study is then carried out to identify the influence of the key parameters on the lateral impact behaviour of CFSTs with localised pitting corrosion. Finally, simplified design methods considering the features of pitting corrosion are proposed to predict the dynamic flexural capacity of locally pitted CFSTs subjected to lateral impact loads, and reasonable accuracy is obtained.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.508-513
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• 1996

The purpose of this paper, having chosen the connection method, filled by High-strength mortar, in conncetion of PC member, is to study the mechanical behaviour and practical usage of the method. The paper estimates the connection ability of Reinforced-bar, that is, Sleeve considering the effect of Reinforced-bar's dimeter. Sleeve's length and diameter in the structural behaviour of mortar-filled connection, therefore the behaviour of Splice-Sleeve exists in concrete practically. This paper discusses the effect of the concrete in Splice-Sleeve. Also, to estimate structural behaviour in a practical wall panel, the upper and bottom wall panels are produced and the behaviour of Splice-Sleeve is discussed. And then Vertical Tie Bar being designed by using Precast method, this paper presents the various application and the practicable method using Splice-Sleeve.