• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.251-258
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• 2000

Based on the numerical investigations using steel bridge pier subjected to strong seismic excitations a new approach to seismic damage assessment for steel structures and their members has been proposed in conjunction with the suggested definition of failure state. The relevant failure form of the steel pier is evaluated. It is revealed that when a seismic load has a short period, the failure of global buckling beyond the allowable displacement is more dominant than that by that of the local buckling caused by the accumulation of plastic strain. When a seismic load is not beyond this certain part, but repeats within the range of where a plastic deformation occurs, the plastic strain is accumulated on the partial element of bottom edge of steel pier and the failure occurs by the local buckling from the accumulated plastic local strain.

• Journal of the Korean Geotechnical Society
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• v.18 no.3
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• pp.105-112
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• 2002

Increases in excess pore water pressure without change of surcharge load were reported in clay underneath embankment at Berthierville and Olga sites after the end of construction. These abnormal phenomena could not be explained by classical consolidation theory. This paper presents a nonlinear viscoplastic model to interpret an increase in pore water pressure on natural clay, The proposed model can consider the combined processes of pore water pressure dissipation according to Darcy's law and pore water pressure generation due to viscoplastic strain, as well as time-dependent viscoplastic behaviour and strain rate dependency of preconsolidation pressure. The calculated results using numerical analysis are compared with measured ones under embankments built on soft clay at Berthierville and Olga in Quebec, Canada. It may be possible to explain the phenomenon of excess pore water pressure increase after the end of construction using the proposed nonlinear viscoplastic model.

• Journal of Korean Association for Spatial Structures
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• v.9 no.4
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• pp.73-80
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• 2009

It is very important that predict the inelastic seismic behavior exactly for seismic performance evaluation of a building in the performance based seismic design. But, it is difficulty that predict the building behavior of actual and exact in simplified load-deformation relation of structural material and members. In this study, system ductility and story ductility capacity of building structure used to the Backbone hinge Model are estimated and compared considering the characteristics of load-deformation relation of structural material and members. Analyses results, bilinear hinge model has lower system ductility and story ductility demands than those of backbone hinge model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2165-2172
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• 1995

Optimization of mesh discretization has been proposed to improve the accuracy of limit analysis solution of collapse load by using the Rigid Body Spring Model(R. B. S. M) under the plane strain condition. Moreover, the fracture behaviour of materials was investigated by employing the fracture mechanism of a spring connecting the triangular rigid body element. It has been clarified that the collapse load and the geometry of slip boundary for optimized mesh discretization were close to those of the slip line solution. Further, the wedge-shaped fracture of a cylinder under a lateral load and the central fracture of a strip in the drawing process were well simulated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.431-438
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• 2012

The mechanical behavior of the polymeric material, HDPE depends on both time and temperature. The study of the tensile behavior at different strain rates is important in engineering design of the orthopedics device such as X-band plate. The mechanical properties and deformation mechanisms of HDPE are strongly dependent on the applied strain rate. Generally, the deformation behavior of HDPE based on the stress-strain curve is complex because of the highly inhomogeneous nature of plastic deformation, particularly that of necking. Therefore, we attempted to determine the mechanical behavior of HDPE in this study. Normally, tensile testing under various strain rates of the HDPE has been used to determine the mechanical behavior. We performed tensile tests at various strain rates (1 to 500 %/min) to analyze the viscoelastic behavior on increasing the strain rate. A tensile stress-strain curve was plotted from the data, and the point of transition was marked to calculate the transition stress, strain, and modulus.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.118-121
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• 2010

초대형 플로팅 구조물의 상부구조는 육상 구조물과는 달리 파랑하중의 영향을 받기 때문에 하부부체의 변형에 의해서 상부구조물에는 부가 모멘트가 크게 발생한다. 이와 같은 부가모멘트의 저감을 위하여 보-기둥 접합부에 반강접의 도입에 관한 연구와 반강접의 비선형 거동을 고려한 상부구조물의 연구는 초기단계이다. 본 연구에서는 초대형 플로팅 구조물의 상부구조물에 정적하중과 진폭의 크기가 다른 파랑하중이 동시에 작용할 경우 강접 골조와 부분적으로 반강접 접합부가 사용된 상부구조체에 대한 1, 2차 소성해석을 수행하였다. 접합부는 웨브에 더블 앵글을 가진 상하 앵글(TSD)접합을 적용하였으며 상부 구조물에 파랑하중이 작용할 경우 소성거동에 따른 응답특성에 대하여 분석하였다.

• Magazine of the Korea Concrete Institute
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• v.1 no.1
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• pp.105-114
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• 1989

휨을 받는 철근콘크리트 부재 단면의 연화현상은 구조물의 파괴하중 해석시 중요한 인자로 작용한다. 일반적인 탄-소성 이론에 근거한 소성한계해석법을 사용할 경우 철골 구조물에는 적합하지만 철근콘크리트 구조물에는 최대하중 이후의 연화현상으로 인하여 이 이론은 부적합하게 된다. 따라서 본 논문의 주목적은 변위제어방법을 사용하여 철근콘크리트 구조물이 파괴될 때까지의 완전한 거동을 이끌어 내는 것이다. 프로그램을 사용한 계산결과를 보다 빠르고 경제적으로 이끌어 내기 위하여 단면의 성질인 모멘트-곡률, 축력-축\ulcorner향 변형률, 그리고 전단력 변형률 곡선 등을 여러개의 직선적으로 단순화한 모델식을 사용하여 해석한다. 또한 연화현상을 고려한 유한요소의 해석결과는 사용된 요소의 크기에 따라 결과가 매우 다르게 나타나기 때문에 이를 방지하기 위하여 파괴에너지 개념을 도입하여 모멘트-곡률 곡선을 보정하여 구조계산에 적용시킨다. 이와 같이 단면을 층으로 나누어 해석하지 않고 직접 단면의 성질을 나타내는 곡선들을 적용한 본 프로그램으로 보와 골조를 해석한 결과는 실제적인 실험결과와 비교하였을 경우 거의 일치하게 나타난다.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.21-28
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• 2010

Creep behaviors of the solder balls in a flip chip package assembly during thermal cycling test is investigated.. A material models used in the finite element analysis are viscoplastic model introduced by Anand and creep model called partitioned model. Experiment of two temperature cycles using moir$\acute{e}$ interferometry is conducted to verify the reliability of material models for the analysis of thermo-mechanical behavior. Bending deformations of the assemblies and average strains of the solder balls due to temperature change and dwell time are investigated. The results show that time-dependent shear strain of solder by the partitioned model is in excellent agreement with those by moir$\acute{e}$ interferometry, while there is considerable difference between results by Anand model and experiment. In this paper, the partitioned model is employed for the time-dependent creep analysis of the FC-PBGA package. It is also shown that the thermo-mechanical stress becomes relaxed by creep behavior at high temperature during temperature cycles.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.655-664
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• 2007

The inherent characteristic of concrete tensile cracks, directional nonlocal crack damage, causes so-called rotating tensile crack damage and softening of compressive strength. In the present study, a plasticity model was developed to describe the behavior of reinforced concrete planar members In tension-compression. To describe the effect of directional nonlocal crack damage, the concept of microplane model was combined with the plasticity model. Unlike existing models, in the proposed model, softening of compressive strength as well as the tensile crack damage were defined by the directional nonlocal crack damage. Once a tensile cracking occurs, the microplanes of concrete are affected by the nonlocal crack damage. In the microplanes, microscopic tension and compression failure surfaces are calculated. By integrating the microscopic failure surfaces, the macroscopic failure surface is calculated. The proposed model was implemented to finite element analysis, and it was verified by comparisons with the results of existing shear panel tests.

• Composites Research
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• v.12 no.5
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• pp.1-11
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• 1999

Cyclic deformation and fatigue behavior of $Al/$Al_2O_3$ metal matrix composites and matrix alloy were studied. Hatigue strength Al/$Al_2O_3$ composites was about 210MPa, and that of Al matrix alloy was 170MPa. Most of the resultant displacement due to permanent plastic deformation occurred in less than the first 5% of fatigue life. In case of composites, decrease of cyclic displacement was smaller than that of matrix because the reinforcements acted as barriers to dislocation movement. Consequently, cyclic stress-displacement response curve can be considered to have these atages ; an initial few cycles of rapid hardening, followed by progressive hardening for most the fatigue life, and then just prior to failure, an instantaneous drop in stress carrying capability of the material due to multiple microcrack initiation, eventual coalescence of microcrack to form a macrocrack and then rapid macroscopic crack growth.