• Journal of the Korean Institute of Gas
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• v.7 no.2 s.19
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• pp.48-53
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• 2003

This study is to look at the effect for deformation of carbon steel for high-presure pipe, on the AE signals produced by tensile test. Acoustic emission(AE) has been widely used in various fields because of its extreme sensitivity, dynamic detection ability and location of growing defects. We investigated a relationship failure mode and AE signals by tensile test, From the tensile test, we could divide into four ranges of the failure modes of elastic range, yield range, plastic range before $\sigma$u, plastic range after $\sigma$u. And failure behaviors of elastic range, yield range, plastic range before $\sigma$u, plastic range after $\sigma$u could be evaluated in tensile test by AE counts, accumulation counts and time frequency analysis. It is expected to be basic data that can protect a risk according to tensile test and bending of pipe material for pressure vessel, as a real time test of AE.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.43-46
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• 2009

열탄성 부영역, 열탄점소성/손상 부영역, 공유면, 접촉 공유면에 기반을 둔 영역/경계 분할법을 적용하여 재료 비선형성을 갖는 열탄점소성 손상 문제와 경계 비선형성을 갖는 접촉 문제의 효율적인 해석을 제안하였다. 영역 및 경계 분할에 관련된 공유면 및 접촉 공유면에서의 연속 구속 조건을 처리하기 위하여 간단한 벌칙 함수 기법을 적용하였다. 결과적으로 재료 및 경계 비선형성은 소수의 부영역과 접촉 경계면에서 계산되는 유한요소 행렬들에 국한된다. 따라서 적절한 해석 알고리듬을 구성하면 대폭적인 효율성 향상이 가능하게 된다. 대변형과 같은 기하학적 비선형성은 고려하지 않았으며, 간단한 수치 실험을 통해서 열탄점소성 손상 및 접촉 해석의 효율성에 관련된 기본적인 특성을 분석하였다.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.75-87
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• 2006

A series of calibration chamber tests are performed to investigate the spatial distribution of the excess porewater pressure due to piezocone penetration into overconsolidated clays. It was observed that the excess porewater pressure increases monotonically from the piezocone surface to the outer boundary of the shear zone and then decreases logarithmically, approaching zero at the outer boundary of the plastic zone. It was also found that the size of the shear zone decreases from approximately 2.2 to 1.5 times the cone radius with increasing OCR, while the plastic radius is about 11 times the piezocone radius, regardless of the OCR. Based on the modified Cam clay model and the cylindrical cavity expansion theory, the expressions to predict the Initial porewater pressure at the piezocone were developed, considering the effects of the strain rate and stress anisotropy. The method of predicting the spatial distribution of excess porewater pressure proposed in this study was verified by comparing it with the porewater pressure measured in overconsolidated specimens in the calibration chamber.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.3
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• pp.227-235
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• 2004

Tunneling in rock mass produces two types of damages in the vicinity of a tunnel: structural and constructional damages. Structural damage represents the damage induced by the unbalance of geostatic stress caused by the tunneling, and constructional damage is the damage produced during the construction. In this study, formulations of tangential and radial stresses in the elastic and plastic zones near a tunnel, and the calculation of radius of plastic zone surrounding a tunnel are introduced by modifying the Hoek-Brown criterion of 2002 edition, which has capability of considering in situ rock mass characteristics and construction damage. From the parametric study, influences of rock mass quality, uniaxial compressive strength of intact rock, and the dimension of the tunnel on the plastic zone are investigated. The accuracy of the proposed approach is evaluated by comparing with results from the previous study.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.72-75
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• 2010

본 논문에서는 열탄점소성 손상과 접촉 문제의 효율적인 해석을 위하여 적응성 영역/경계 분할법을 제안하였다. 적응성 영역/경계 분할법은 시간 증분 또는 반복 기법 단계에서 열탄점소성 손상과 같은 재료 비선형성을 감안하여 부영역을 재설정하며, 접촉에 따른 경계 비선형성은 경계면을 통하여 부영역으로부터 독립적으로 분할한다. 분할된 각각의 부영역과 경계면을 기준으로 유한요소 정식화를 수행하며, 공유면 및 접촉 공유면의 연속 구속 조건을 처리하기 위하여 벌칙 함수 기법을 적용하였다. 결과적으로 재료 및 경계 비선형성은 일부 부영역과 접촉 경계면에서 계산되는 유한요소 행렬에 국한된다. 수치 실험을 통하여 적응성 해석 알고리듬의 기본적인 특성과 효율성 향상에 대하여 분석하였다.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.3 s.22
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• pp.37-45
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• 2006

In this study, displacement ductility capacity and plastic hinge regions of reinforced concrete multi-column bent with different transverse reinforcement ratio are investigated. The ductility increases remarkably as transverse reinforcement ratio increase and the multi-column bent loaded along transverse direction is more ductile. The plastic hinge length for special detailing requirements of transverse reinforcement is estimated. For high target ductility, plastic hinge length for confinement should be extended with increased transverse reinforcement ratio. The plastic hinge length of multi-column bent loaded along transverse direction is shorter than that along longitudinal direction, because of the different moment distribution.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.753-764
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• 2020

In this study, the plastic zone and internal earth pressure of the tunnel were calculated using the following three methods: metal plasticity to analyze the deformation of metal during plastic processing, Terzaghi's earth pressure theory from the geotechnical perspective and modified Terzaghi's earth pressure theory, and slip line theory using Mohr-Coulomb yield conditions. All three methods are two-dimensional mathematical analysis models for analyzing the plane strain conditions of isotropic materials. Using the theory of metallurgical plastics, the plastic zone and the internal earth pressure of the ground were obtained by assuming that the internal pressure acts on the tunnel, so different results were derived that did not match the actual tunnel site, where only gravity was applied. An analysis of the plasticity zone and earth pressure via the slip-line method showed that a failure line is formed in a log-spiral, which was found to be similar to the real failure line by comparing the results of previous studies. The earth pressure was calculated using a theoretical method. Terzaghi's earth pressure was calculated to be larger than the earth pressure considering the dilatancy effect.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.299-311
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• 2003

This paper presents a finite element procedure to estimate the ultimate strength of space frames considering spread of plasticity. The improved displacement field is introduced based on the inclusion of second-order terms of finite rotations. All the non-linear terms due to bending moment, torsional moment, and axial force are precisely considered. The concept of plastic hinges is introduced and the incremental load/displacement method is applied for elasto-plastic analyses. The initial yield surface is defined based on the residual stress, and the full plastification surface is considered under the combined action of axial forces, bending and torsional moments. The elasto-plastic stiffness matrices are derived using the flow rule and the normality condition of the limit function. Finite element solutions for the ultimate strength of space frames are compared with available solutions and experimental results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.2
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• pp.153-161
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• 2009

A domain/boundary decomposition method is applied for efficient analyses of thermo-elasto-viscoplastic damage and contact problems under the assumption of infinitesimal deformation. For the decomposition of a whole domain and contact boundaries, all the equality constraints on the interface and contact interfaces are restated with simple penalty functional. Therefore, the non-linearity of the problem is localized within finite element matrices in a few subdomains and on contact interfaces. By setting up suitable solution algorithms, the computational efficiency can be improved considerably. The general tendency of the computational efficiency is illustrated with some numerical experiments.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.92-101
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• 1994

A new analytical model is proposed to better understand the transfer bond performance in a prestressed pretensioned concrete beam. The transfer length is divided into an elastic and a plas tic zones in this model. The bond stress is assumed t.o increase proportionally with the slip t.o the lirnit of maximum bond stress within the elastic zone and remains at a constant maximum value wthin the plastic zone. Four main stress patterns: bond stress, slip, steel stress, and concrete stress distributions within the transfer length are obtained precisely. The total transfer length al\ulcornerd free-end slip obtained here give a close comparison to the test results by Cousins et al.