• Journal of Korean Society of Steel Construction
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• v.12 no.1 s.44
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• pp.55-63
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• 2000

This paper is a study on the behavior of Concrete-Filled Square Tubular(CFST) column to H-beam connections reinforced with external stiffeners and reinforcing bar. The cyclic loading tests of 5 test specimens were carried out. The main Parameters are as follows; 1)the length of the stiffener: 200mm, 250mm, 2)the diameter of reinforcing bar: HD16, 19. The results of the researches demonstrate that the increase of the stiffener length was more effective than the increase of the area of reinforcing bar in the point of both strength and stiffness. By reinforcing external stiffeners, stable hysteretic behavior was shown and plastic hinge was formed on the beam flange. Cold-formed tube sections should be used carefully to avoid the welding fracture at the round corners of section, and the proposed welding methods are suitable for this connections.

• Journal of Korean Society of Steel Construction
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• v.14 no.2
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• pp.311-318
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• 2002

This paper described the ultimate strength and deformation limit of welded T-joints in cold-formed square hollow sections. Previous studies showed that the strength of a T-joint still increases with increasing deformations at a ratio of branch width to chord width (${\beta}$) of below 0.8. Therefore, the strength at a certain deformation (chord flange indentation) limit can be regarded as the ultimate strength of a T-joint. The chord flange failure modes were investigated for the ratio of branch width to chord width (${\beta}$) and the ratio of chord width to chord web thickness (B/T). Experimental results including tests done by Kato proposed a deformation limit of 3%B for $16.7{\leq}B/T{\leq}41.6$ and $0.27{\leq}{\beta}{\leq}0.8$. The strength formula of CIDECT and other researchers were compared with the test results. Finally, the strength formula based on yield-line theory was proposed.

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.499-509
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• 2014

This study focuses on mixing steel fiber in the concrete to improve the ductility and toughness of the columns. The purpose of the study is to evaluate the load capacity and deformation capacity associated with the amount of steel fiber and loading condition and to analyze the interplay between the steel fiber reinforced concrete and the welding built-up square tube in terms of structure and fire resistance performance. Reinforcement of concrete with steel fiber(Vf=0.375%), when cross-section shape and boundary condition (load ratio) remained unchanged, improved fire resistance performance by 1.1~1.3 times. It is deemed that the area resisting thermal load increased and fire resistance performance was improved since the concrete reinforced with steel fiber restrained cracking. In addition, the fact that the cross-sections of the concrete were barely damaged indicates that load share capacity was greatly improved.

• Journal of Korean Society of Steel Construction
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• v.17 no.3 s.76
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• pp.325-335
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• 2005

This study tackles the development of an improved detail of partially restrained CFT square column-to-beam connection and the evaluation of its mechanical behavior under monotonic loading. The connection is designed to strengthen shearing capacity at the bottom of the connection due to the ultimate behavior of PR-CC by its detail of the bottom connection and simplify the fabrication process. The suggested connection is the welded bottom beam flange connection(M-2) and is compared with the existing PR-CC of bolted seat angle connection(M-1). Two specimens were fabricated in actual size and tested under monotonic loading. Based on the test results, the welded bottom beam flange connection exhibited about 85% of the stiffness of steel beam. It was similar to the bolted seat angle connection and behaved as PR-CC. The specimen of the supposed connection type failed at the shear connection of web but was similar to the bolted seat angle connection until the failure. It obtained sufficient stiffness and capacity through the reinforcingsteel and the capacity and deformational ability equivalent to the full-plastic moment through the anchor inside the steel tube at the web connection. So, it can be said that the suggested connection exhibits sufficient ductile behavior.

• Journal of Korean Society of Steel Construction
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• v.26 no.4
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• pp.311-322
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• 2014

Concrete filled tubular structure should be installed diaphragms for moment connection. However internal and through diaphragm should be special welded when connected to column tube. The other hand, that has become increase of stress concentration and extend of construction error. Therefore, In this study the seismic performance of beam to column connections with External Diaphragms and implement cycle loading experiment. we had evaluated seismic performance with mentioned experiment which is concrete filled or not, variable shapes, to be welded or not of diaphragm. Also, formula of strength of external diaphragm was analyzed and looked into adequacy with regard to formula of tension strength.

• Journal of Korean Society of Steel Construction
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• v.14 no.3
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• pp.403-411
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• 2002

This paper described the ultimate strength and deformation limit of welded T-joints in cold-formed square hollow sections. Previous studies showed that the T-joint has an obvious peak load. with the failure mode of chord-web buckling at a ratio of branch width to chord width ($\beta$) of above 0.8. Similar to a T-joint with chord-flange failure mode, the strength at a certain deformation limit can be regarded as the ultimate strength of a T-joint Based on the experimental results including tests done by Kato and Zhao, the deformation limit was proposed as 3%B for $10.7{\leq}2{\gamma}(B/T){\leq}42.3$ and $0.8{\leq}{\beta}{\leq}1.0$. The strength formula of CIDECT and those of other researchers were also compared with the test results. Finally, the strength formula based on the column buckling was proposed.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.453-461
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• 2014

In this study, the stub columns of built-up H-section and square hollow section subjected to eccentrical loads are tested to evaluate the applicability of the structural members with 800MPa high-strength steel (HSA800) on current design specification. Analytical studies of FE model are conducted to validate the test results and then the verified FE models are used for extensive parametric studies for checking up the applicability of current design code. The parameters are width-to-thickness ratios and axial load ratios. From P-M correlations on parameter models, all stub columns with non-compact sections exceed the current design requirements about axial force and flexural strength ratios are sufficiently secured as the axial load ratios are decreased. The built-up hollow sections with slender section model do not satisfy the current design specification about axial force.

• Journal of Korean Society of Steel Construction
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• v.14 no.5 s.60
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• pp.657-664
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• 2002

This paper described the ultimate strength and deformation limit of the new uniplanar T-joints in cold-formed square hollow sections. In the configuration of the new T-joint, only a branch member is orientated to a chord member at 45 degrees in the plane of the truss. This study focused on the branch-rotated T-joints that were governed by chord flange failure in previous studies. Test results of the T-joint in cold-formed square hollow sections revealed a deformation limit of 3%B for $16.7{\leq}2{\gamma}(=B/T){\leq}33.3$ and $0.27{\leq}{\beta}(=b1/B){\leq}0.6$. The existing strength formulae for traditional T-joint were determined and a new yield-line model for the branch-rotated T-joint proposed. Finally, the strength formula on the yield-line analysis was compared with test results and the application range of the proposed formula recommended.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.2
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• pp.32-39
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• 2015

So far, square concrete filled tubular(CFT) columns have been used in a limited width thickness ratio. The reason is that local buckling occurs in steel tube easily. Once the local buckling occurs, the confinement effect of steel tube on concrete disappears. In this study, we developed welded built-up square steel tube with reinforcement which are placed at the center of the tube width acts as an anchor. 3 specimens of slender welded built-up square CFT columns and 3 specimens of slender welded built-up square steel tube columns were manufactured with parameters of width(B) of steel tube, width thickness ratio(B/t). we conducted a experimental test on the 6 specimens under eccentric load, and evaluated the structural resistance and behavior of 6 specimens.

• Journal of Korean Society of Steel Construction
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• v.28 no.1
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• pp.23-34
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• 2016

Concrete filled steel tube system has two major advantages. First, the confinement effect of steel tube improves the compressive strength of concrete. Second, the load capacity and deformation capacity of members are improved because concrete restrains local buckling of steel tube. It does, however, involve workability problem of using stud bolts or anchor bolts to provide composite effect for larger cross-sections. While the ribs inside the columns are desirable in terms of compressive behavior, they cause the deterioration in load capacity upon in-plane deformation resulting from thermal deformation. Since the ribs are directly connected with the concrete, the deformation of the ribs accelerates concrete cracking. Thus, it is required to improve the toughness of the concrete to resist the deformation of the ribs. Welding built-up tubular square columns can secure safety in terms of fire resistance if the problem are solved. This study focuses on mixing steel fiber in the concrete to improve the ductility and toughness of the columns. In order to evaluate fire resistance performance, loaded heating test was conducted with 8 specimens. The behavior and thermal deformation capacity of the specimens were analyzed for major variables including load ratio. The reliability of heat transfer and thermal stress analysis model was verified through the comparison of the results between the test and previous study.