• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.571-579
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• 2014

The steel braces are used to control the lateral drift of high rise buildings. The braces are designed as tensile members since the braces consisted of slender member can not resist compressive loads by elastic buckling. To resolve this problem, a lot of research were performed to develop the non-buckling member. The force limiting device (FLD.) is one of them. The purpose of this study is the development of FLD. to prevent a elastic buckling for a slender member. The folded plate type is proposed to induce the yielding before occurring elastic buckling. In this study, member test and FEM analysis for proposed type were performed. Further, It is verified that the structure with FLD member is stable by high energy absorption. The proposed folded plate type FLD could be effective to preserve the compressive member from the elastic buckling.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.439-445
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• 2008

This paper suggests a modified bond reduction coefficient considering the average CFRP (Carbon Fiber Reinforced Polymer) strain concept for the unbonded prestressed CFRP plate strengthening system. The strengthened length and the pure bending length were seen to influence the variation of the strain of unbonded CFRP plate. Therefore, a new bond reduction coefficient considering such effect was suggested. Comparison with the experimental data revealed that the analytic results obtained by considering the proposed bond reduction coefficient were effective in estimating the strain of the unbonded CFRP plate in the CFRP plate prestressing system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.411-419
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• 2006

In this study, a new approach employing 3-dimensional strut-tie models for analysis and design of 3-dimensional structural concrete with disturbed regions that are not properly occupied by current design codes is proposed. In addition, a computer graphics program for the practical application of the approach is developed. The approach adopts a grid strut-tie model to exclude the subjectivity in the selection of strut-tie model and evaluates the effective strength of concrete strut by considering the 3-dimensional failure criteria of concrete and the deviation angles between the struts and compressive principal stress trajectories. To verify the appropriateness of the approach, nine pile caps tested to failure are analyzed and a bridge pier is designed. The analysis and design results are compared with those obtained by several different methods.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.147-158
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• 2004

Laboratory dynamic tests are carried out to assess the liquefaction potential of saturated sands in most countries. However, simple results such as the maximum cyclic shear stress and the number of cycles at initial liquefaction are used in the experimental assessment of liquefaction potential, even though various results can be obtained from the dynamic test. In addition, it seemed to be inefficient because more than three dynamic tests with different stress ratio have to be carried out to draw a liquefaction resistance experimental curve. To improve the present assessment method fur liquefaction potential, a new critical resistible characteristic far soil liquefaction is proposed and verified through conventional cyclic triaxial tests with Jumunjin sand. In the proposed method, various experimental data such as effective stress path, stress-strain relationship, and the change of excess pore water pressure can be used in the determination of cumulative plastic shear strains at every 1/4 cycle. Especially, the critical cumulative plastic shear strain to initiate liquefaction can be defined in a specific point called a phase change point in the effective stress path and it can be calculated from a hysteric curve of stress-strain relationship up to this point. Through this research, it is found that the proposed cumulative plastic shear strain can express the dissipated energy to resist dynamic loads and consider the realistic soil dynamic behavior of saturated sands reasonably. It is also found that the critical plastic shear strain can be used as a registible index of soils to represent the critical soil dynamic state, because it seems to include no effect of large deformation.

• Journal of the Korean Geotechnical Society
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• v.17 no.1
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• pp.131-139
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• 2001

화강토와 관련된 지반문제의 거동예측을 위한 수치해석의 적용이 양적인 면에서는 많이 확대되어왔지만 해석결과에 지대한 영향을 미치는 구성방정식 등 수치해석 모델링을 개선하고자 하는 노력은 부족하였다. 화강토 거동의 특징은 내재적 결합력으로 인한 구조화의 거동을 나타내는 것이며, 항복면이 평균유효응력 축에 대칭이고 Non-associated 소성거동을 보인다는 점이다. 본 연구에서는 이러한 화강토 거동을 표현하기 위하여 일반화된 한계상태모델을 도입하고, 이를 화강토의 경화거동 모델링이 가능하도록 확장하였다. 제안된 모델을 이용한 삼축시험의 유한요소 시뮬레이션 결과는 측정결과와 좋은 일치를 보였다. 화강토 지반내 터널에 대한 유한요소해석을 수행한 결과, 비선형 탄성모델과 조합된 확장된 한계상태모델이 현장계측결과와 잘 일치하는 결과를 주었다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.493-498
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• 2011

구름접촉피로는 차륜과 레일의 반복적인 접촉으로 인하여 발생하는 표면손상현상으로 점차 증가하는 레일손상 중 하나이다. 접촉마모 및 주기적 그라인딩보다 균열의 성장속도가 더 빨라 균열진전이 시작되는 최소균열크기(minimum crack size for growth)는 레일의 파괴방지 및 유효한 유지보수전략을 수립하는데 기초자료로 활용된다. 본 연구에서는 최소균열크기를 예측하기 위하여 차륜레일의 접촉에 영향을 미치는 주요 파라미터를 변화시키면서 최소균열크기의 변화를 살펴보았다. 이를 위하여 Fletcher와 Kapoor의 "2.5D"모델을 적용한 시뮬레이션 소프트웨어를 개발하였으며, 최대접촉하중(1174MPa), 표면마찰계수(0.1, 0.2, 0.3 and 0.4), 잔류응력, 접촉에 의한 표면마모(1.0nm/cycle), 그라인딩량(0.3mm/10MGT)을 파라미터로 하여 해석을 수행하였다. 해석결과 최소균열크기는 해석조건에 따라 1.41-1.95mm로 계산되었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.7
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• pp.601-611
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• 2007

Most of mechanically jointed aircraft structures are always encountered the fretting damages on the contact surfaces between two jointed structural members or at the edges of fastener holes. The partial slip and contact stresses associated with fretting contact can lead to severe reduction in service lifetime of aircraft structures. Thus a critical need exists for predicting fretting crack initiation in mechanically jointed aircraft structures, which requires characterizing both the near-surface mechanics and intimate relationship with fretting parameters. In this point of view, a series of fretting fatigue specimen tests for 2024-T351 Al-alloy, have been conducted to validate a mechanics-based model for predicting fretting fatigue life. And included in this investigaion were elasto-plastic contact stress analyses using commercial FEA code to quantify the stress and strain fields in subsurface to evaluate the fretting fatigue crack initiation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.3
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• pp.174-183
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• 2014

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were divided into two portions; (I) focusing on the dynamic response of structure, acceleration, deformation of seabed, and (II) focusing on the time variation in excess pore water pressure, liquefaction, effective stress path in the seabed. This paper corresponds to (II).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.3
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• pp.160-173
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• 2014

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were divided into two portions; (I) focusing on the dynamic response of structure, acceleration, deformation of seabed, and (II) focusing on the time variation in excess pore water pressure, liquefaction, effective stress path in the seabed. This paper corresponds to (I).

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.89-103
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• 1997

The flow forming process which is one of the technologies to manufacture the various missile propulsion combustion chambers, was analyzed using the rigid plasticity finite element modeling. The numerical analysis was performed using 3 rollers which forms the basic tools for the plastic deformation of the tubes. As a result of this study, the distribution of the plastic strain and the stress are obtained and compared. It was found that there exists a significant difference in the plastic deformation as well as the stress distribution due to the preform initial thickness as a result of these numerical experiments. Moreover, under ideal process condition, flow forming process results in a uniform plastic deformation in the radial direction.