• Journal of the Korea Concrete Institute
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• v.12 no.2
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• pp.53-62
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• 2000

Under severe lateral loads, ductile moments-resisting reinforced concrete frames will be subjected to large loads and displacements. Thus, large deformation and shear stree are occurred at the beam-column joints which are the most critical region in ductile moments-resisting system. The purpose of this study was to investigate the shear strength of beam-column connection using high strength concrete. Four subassemblies were designed 2/3 scale of read structures and tested. The obtained results are as follows. 1) The transverse beams increase the shear resistance and ductility of joint, 2) The slab was contributed to increase of the flexural capacity of the beam, but was not contributed to increase the joint ductility under cyclic loads. 3) The shear stress factors. given by the ACI code would be modified in evaluating the shear strength of beam-column joints of frame which were constructed with high-strength concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.63-66
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• 2005

Six RC pier were tested under a constant axial load and a cyclically reversed horizontal load to investigate the performance of RC piers used in the high strength concrete and the high strength rebar. It is designed with a hollow section according to the Korean Bridge Design Standard. The variables of the test were concrete strength, rebar strength, a ratio of lap splice and a ratio of transvere rebar. The test results show that the performance of a RC Pier; failure mode, crack pattern, maximum load and ductility.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.419-422
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• 1999

This study was intended to investigate the cyclic behavior of high strength concrete beam-column connection. Four assemblies were designed 2/3 scale beam-column-slab joint and tested. The obtained results are follows. 1) The transverse beams increase the shear resistance and ductility of joint, 2) The slab was contributed to increase of the flexural capacity of the beam, but was not contributed to increase the joint ductility under lateral loads.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.23-28
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• 2001

Since the steel fiber used in concrete to improve shear and ductility capacity, a number of laboratory tests have been studied to define shear strengthening effect according steel fiber contents in concrete. This study investigates shear strengthening effect of steel fiber in RC columns according to compression strength of concrete. From the structural performance test, following conclusions can be made; the maximum enhancement of shear strengthening effect can be achieved at about 1.0 %~l.5 % of steel fiber contents in comparison with shear capacity ratio, and ductility capacity slightly improved as steel fiber contents increased.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.75-84
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• 1998

Korea is located in either low or moderate seismicity continental region. It is realized that design codes and underlying design concepts of high seismicity region may not be appropriate to low or moderate seismicity region. In this paper, test results on the seismic response of structures without seismic detailing are reexamined and compared with numerical analysis results. The seismic design concept based on limited ductility is proposed as an alternative seismic design approach in moderate seismicity regions.

• Korean Journal of Materials Research
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• v.26 no.7
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• pp.353-358
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• 2016

The hydrogen embrittlement of two austenitic high-manganese steels was investigated using tensile testing under high-pressure gaseous hydrogen. The test results were compared with those of different kinds of austenitic alloys containing Ni, Mn, and N in terms of stress and ductility. It was found that the ultimate tensile stress and ductility were more remarkably decreased under high-pressure gaseous hydrogen than under high-pressure gaseous argon, unlike the yield stress. In the specimens tested under high-pressure gaseous hydrogen, transgranular fractures were usually observed together with intergranular cracking near the fracture surface, whereas in those samples tested under high-pressure gaseous argon, ductile fractures mostly occurred. The austenitic high-manganese steels showed a relatively lower resistance to hydrogen embrittlement than did those with larger amounts of Ni because the formation of deformation twins or microbands in austenitic high-manganese steels probably promoted planar slip, which is associated with localized deformation due to gaseous hydrogen.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.197-208
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• 1999

The use of high-strength concrete which permits smaller cross sections, reduced dead loads, and longer spans has been getting more popular in tall buildings. However, there has been little research on behavior of high-strength concrete columns laterally reinforced with square ties and subjected to compressive loading. With the addition of transverse reinforcement which lead to triaxial compressive state, ductility behavior of high-strength column member shall be increased. In this study, rational quality and quantity evaluations were made to investigate the ultimate strength and strain ductility by confinement effect of tie reinforced high-strength concrete columns subject to uniaxial loads. Concrete failure theory at the triaxial compressive state and statistical results based on conventional experimental data were applied for this propose. Up to 185 columns, tested under monotonically increasing concentric loading, were evaluated in terms of strength and strain ductility. Analytical results show that confinement stress, maximum compressive strength, and increase of strain equations were developed with the consideration of concrete strength, yield strength, spacing, volumetric ratio, and configurations of tie reinforcement.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.798-806
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• 2010

The effects of alloying elements and the cooling condition on the microstructure, tensile properties, and Charpy impact properties of high-strength bainitic steel plates fabricated by a controlled rolling process were investigated in the present study. Eight kinds of steel plates were fabricated by varying C, Cr, and Nb additions under two different cooling rates, and their microstructures and tensile and Charpy impact properties were evaluated. The microstructures present in the steels increased in the order of granular bainite, acicular ferrite, bainitic ferrite, and martensite as the carbon equivalent or cooling rate increased, which resulted in a decrease in the ductility and Charpy absorbed energy. The steels containing a considerable amount of bainitic ferrite or martensite showed very high strengths, together with good ductility and Charpy absorbed energy. In order to achieve the best combination of strength, ductility, and Charpy absorbed energy, granular bainite and acicular ferrite were properly included in the high-strength bainitic steels by controlling the carbon equivalent and cooling rate, while about 50 vol.% of bainitic ferrite or martensite was maintained to maintain the high strength.

• Steel and Composite Structures
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• v.51 no.6
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• pp.661-678
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• 2024

The utilization of geopolymer recycled aggregate concrete (GRAC) as the infilled core of the concrete-filled steel tubular (CFST) columns provides superior economic and environmental benefits. However, limited research exists within the field of geopolymer recycled aggregate concrete considered a green and sustainable material, in addition to the limitation of the design guidelines to predict the behavior of such an innovative new material combination. Moreover, the behavior of high-strength concrete is different from the normal-strength one, especially when there is another material of high-strength properties, such as the steel tube. This paper aims to investigate the behavior of the axially loaded square high-strength GRACFST columns through the nonlinear finite element analysis (NLFEA). A total of thirty-two specimens were simulated using ABAQUS/Standard software with three main variables: recycled aggregate replacement ratio (0, 30, and 50) %, width-to-thickness ratios (52.0, 32.0, 23.4, and 18.7), and length-to-width ratio (3, 5, 9, and 12). During the analysis, the response in terms of the axial load versus the longitudinal strain was recorded and plotted. In addition, various mechanical properties were calculated and analyzed. In view of the results, it has been demonstrated that the mechanical properties of high-strength GRACFST columns such as ultimate load-bearing capacity, compressive stiffness, energy absorption capacity, and ductility increase with the increase of the steel tube thickness owing to the improvement of the confinement effect of the steel tube. In contrast, the incorporation of the recycled aggregate adversely affected the mentioned properties except the ductility, while the increase of the recycled aggregate replacement ratio improved the column's ductility. Moreover, it has been found that the increase in the length-to-width ratio significantly reduced both the failure strain and the energy absorption capacity. Finally, the obtained NLFEA results of the ultimate load-bearing capacity were compared with the corresponding predicted capacities by numerous codes. It has been concluded that AISC, ACI, and EC give conservative predictions for the ultimate load-bearing capacity since the confinement effect was not considered by these codes.

• Earthquakes and Structures
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• v.12 no.6
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• pp.643-652
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• 2017

One of the methods to strengthen the structures against the seismic lateral loading is the employment of the composite columns. A concrete-filled tube (CFT) has the cumulative advantages of steel and concrete. Concrete-filled steel tube columns have been widely used in the moment-resisting frame (MRF) structures, located in both non-seismic zones and high-risk seismic zones. In this paper, the results of studies on two important seismic parameters of ductility and the response modification factor (RMF) of the MRFs with CFT columns are submitted. While the studies are carried out, the effects of span length-story height ratio, the strength of materials and seismic behavior of MRFs are considered. In this regard, the ductility, RMF and the strength of 36 models of the steel MRFs with CFTs are analyzed. The fiber plastic hinges numerical simulation and pushover analysis method are used in the calculations. Based on the obtained results, the RMFs suitable for the 5-, 10- and 15- story frames are proposed.