• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.362-365
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• 2005

The hub hole is usually formed with a flanging process followed by a blanking process of a ]tole. Since the hole is made by blanking, the blanked surface is so rough that the formability in the region is rather poor. The emerging task is to identify the formability of the blanked region in the forming simulation and to relate the criterion to the real forming process by experiments. In this paper, hole expansion tests are carried out with respect to various hole conditions to verify the hole condition effect on the hole expansion ratio. The hole of specimens is made by machining or punching. In the case of punching, two different punching clearances are used for making the hole. From the results of test, fracture mechanism of the hole expansion is explained.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.396-402
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• 2021

A cross section in RC flexural members must be designed to satisfy flexural strength and ductility requirements simultaneously. In design provisions, ductile behavior is ensured by a sufficient reinforcement ratio or depth of the neutral axis. If the reinforcement ratio is less than the balanced reinforcement ratio, ductile behavior is secured, and this value is theoretically the maximum reinforcement ratio. But for a cross section with less steel, brittle failure can occur regardless of ductile behavior because of unqualifying a cracking moment. Recently, designs with a minimum steel ratio have been increasing along with the use of high-strength material, so in design provisions, a minimum amount of reinforcement is suggested. In the KCI(2012) standard, a minimum amount of reinforcement was suggested in terms of strength of steel and concrete. But in the revised KCI(2017) standard, a minimum amount of reinforcement was suggested by a relationship between the design flexural strength and cracking moment indirectly. This code can reflect the effect of cover thickness, but a material model must be defined. Therefore, the minimum amount of reinforcement in KCI(2012) and KCI(2017) was examined, and a rational review method was studied by parametric analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.4
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• pp.747-757
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• 2015

The main purpose of this study is to investigate the static behavior of a horizontally curved prestressed concrete (PSC) girder. A 30m long full-scale curved PSC girder with 80.0m radius is fabricated by a portable curved form system. Deflections and concrete strains at the middle of span were measured. The obtained experimental results have been compared to those from F.E.A. analysis. When a initial crack developed, the applied load was 1.3 times the service design load and the vertical deflection at the middle of span satisfied the requirement for a live load state according to the Korea Bridge Design Specifications (2010). Also, the ductility of the full scale specimen satisfied the limit in the Specifications (2010). To verify the experimental results, a numerical F.E. analysis was carried and confirmed that the data were similar with results from the test above. The horizontally curved PSC girder fabricated on site was found to have enough strength for safety under and after construction.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1741-1751
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• 2013

The main purpose of this study is to investigate the static behavior of a prestressed concrete (PSC) girder using pre-tension method. A 30m long full-scale pretension PSC girder is fabricated by the portable fabrication system and tested. All results have been compared to those obtained from F.E.A results. Deflections at the middle of girders have been measured for evaluation. Also, strains of concrete at the middle of span have been measured. From the results of experimental, the load when initial crack was developed was obtained to be 1.75 time the unfactered design load in the full-scale girder specimen. Also, the data of specimen are satisfied the desgin requirements of ductility on the Korea Bridge Design Specification(2010). In service state, the vertical deflection at center of test specimen when a initial crack was developed is satisfied the vertical deflection requirement under live load of the Korea Bridge Design Specification(2010). To verify the experimental results, we numerical analyze the test and confirmed that the data were similar with results from the test above. The pretension girder fabricated in site were found to have enough strength for safety under and after construction.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.441-448
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• 2007

The beam-column assembly in a ductile reinforced concrete (RC) frames subjected to seismic loading are generally controlled by shear and bond mechanisms, both of which exhibit poor hysteretic properties. Hence the response of joints is restricted essentially to the elastic domain. The usual earthquake resistant design philosophy of ductile frame buildings allows the beams to form plastic hinges adjacent to beam-column assembly. Increased strain in these plastic hinge regions affect on joint strain to be increased. Thus bond and shear joint strength are decreased. The research reported in this paper presents the test results of five RC beam-column assembly after developing plastic hinges in beams. Main parameter of the test Joints was the amount of the longitudinal tensile reinforcement of the beams. Test results indicted that the ductile capacity of joints increased as the longitudinal tensile reinforcement of the beams decreased. In addition, both the tensile strain of the longitudinal reinforcement bars in the joint and the ductile ratio of the beam-column assemblages increased due to the yielding of steel bars in the plastic hinge regions.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05b
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• pp.709-714
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• 1995

영광 3, 4호기에 사용되고 있는 원전 압력용기용 SA-508 IH 강의 미세구조 및 상온 피로균 열성장 특성을 고찰하였다. 본 강재의 미세구조, 석출물 분포 및 형상을 투과전자현미경을 통하여 관찰하였으며 임계영역에서의 거동 및 균열닫힘에 주목하여 피로균열성장 특성을 연구하였다. 다양한 형태의 (Fe, MR)$_3$C 세멘타이트 및 Mo$_2$C 석출물이 입계, 래스경계면 및 입내에 분포되고 있음을 확인하였다. Paris 영역에서의 피로균열성장 속도는 ASME 기준선과 유사하였으며, 임계 영역에서는 일반적인 저합금강의 경우보다 다소 낮게 나타났다. 파면조사 결과 입내 연성파괴현상이 전 $\Delta$K 영역에서 나타나고 있으며, $\Delta$K$_{th}$ 부터 $\Delta$K가 12 Mpa√m 영역에서는 입계파괴 및 입내 평활면이 관찰되었다.

• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.179-187
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• 2017

The design provisions for the maximum steel ratio in reinforced concrete flexural members is normally provided to ensure sufficient ductility and economy by steel yielding at member failure. In the Concrete Structural Design Code (2012), the maximum steel ratio is expressed in terms of a net strain in tensile steel, and leading to very high steel ratio in the case of using high strength materials. Thereby, this may result in difficulty to satisfy a required workability at concrete placing. On the contrary, in the Korean Highway Bridge Design Code (Limit State Design) the maximum steel ratio is given in terms of the maximum neutral axis depth ratio that is 0.4. From these results, a rational model for the maximum steel ratio is suggested so as to satisfy a ductility as well as a workability.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.695-705
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• 2014

Precast concrete (PC) beam-column connections using ductile rods are proposed for earthquake zone. An existing beam-column connection, two PC specimens designed by considering failure modes and a conventional RC specimen were tested under cyclic loading to evaluate the seismic performance. The specimens were designed to satisfy the requirements of current design code. The variables are the yield strength of longitudinal reinforcing bars of PC beams. The test results showed that the proposed system applying smaller yield strength of the longitudinal reinforcing bars at the PC beams than the ductile rods was satisfied with seismic criteria. The deformation capacity and energy dissipation capacity of the proposed PC beam-column connections were greater than those of the existing DDC system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.143-149
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• 2019

In this study, a U-shape composite beam was developed to be effectively used for a steel parking lot which is 8m or lower in height. When the U-shape composite beam was applied to a steel parking lot, essential considerations were story-height and long-span. In addition, due to the mixed structural system with reinforced concrete and steel material, the U-shape composite beam needed to have a structural integrity and reliable performance over demand capacity. The main objective of this study was to investigate the performance of the structure consisting of the reinforced concrete (RC) slab and U-shape beam. A U-shape composite beam generally used at a parking lot served as a control specimen. Four specimens were tested under four-point bending. To calculate theoretical values, strain gauges were attached to rebar, steel plate, and concrete surface in the middle of the specimens. As the results, initial yielding strength of the control specimen occurred at the bottom of the U-shaped steel. After yielding, the specimen reached the maximum strength and the RC slab concrete was finally failed by concrete crush due to compressive stress. The structural performance such as flexural strength and ductility of the specimen with the increased beam depth was significantly improved in comparison with the control specimen. Furthermore, the design of the U-shape composite beam with the consideration of flexural strength and ductility was effective since the structural performance by a negative loading was relatively decreased but the ductile behavior was evidently improved.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.10-17
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• 2004

Shear tests were performed on four ends of full scale U-type beams which were designed by optimum process for the depth with a live load of 4903Pa. The ratio of width to depth of full scale 10.5 m-span, composite U-type beams with topping concrete was greater than 2. Following conclusions were obtained from the evaluation on the shear performance of these precast prestressed beams. 1) Those composite U-type beams performed homogeneously up to the failure load, and conformed to ACI Strength design methods in shear and flexural behaviors. 2) The anchorage requirements on development length of strand In the ACI Provisions preyed to be a standard to determine a failure pattern within the limited test results of the shallow U-type beams. 3) Those all shear crackings developed from the end of the beams did not lead to anchorage failure. However, initiated strand slip may leads the bond failure by increasing the size of diagonal shear crackings. 4) The flexural mild reinforcement around the vertical center of beam section was effective for developments of a ductile failure.