• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.04a
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• pp.335-342
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• 2001

In this paper, an improved Element-Free Galerkin (EFG) method is proposed by adding enrichment function to the standard EFG approximation and a discontinuity function is implemented in constructing the shape function across the crack surface. In this method, the singularity and the discontinuity of the crack are efficiently modeled by using initial node distribution to evaluate reliable stress intensity factor, though the standard EFG method requires placing additional nodes near the crack tip. The proposed method enables the initial node distribution to be kept without any additional nodal d.o.f. and expresses the asymptotic stress field near the crack tip successfully. Numerical example verifies the improvement and the effectiveness of the method.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1990.10a
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• pp.3-8
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• 1990

A new finite element technology based on p-version of F.E.M. is discussed with reference to its potential for application to stress intensity factor computations. In linear elastic fracture mechanics, especially cracked cylindrical shells. It is shown that the p-version nutlet is far better suited for computing the stress intensity factors than the conventional h-version models with the help of three test problems. The main advantage of this technology is that the accuracy of approximation can be established without mesh refinement or the use of special procedures.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.100-107
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• 2018

The material and geometrical nonlinear finite elment analysis of UHPFRC 50M composite box girder was carried out. Constitute law in tension and compressive region of UHPFRC and HPC were modeled based on specimen test. The accuracy of nonlinear FEM analysis was verified by the experimental result of UHPFRC 50M composite girder. The UHPFRC 50M segmental composite box girder which has 1.5% steel fiber of volume fraction, 135MPa compressive strength and 18MPa tensile strength was tested. The post-tensioned UHPFRC composite girder consisted of three segment UHPFRC U-girder and High Strength Concrete reinforced slab. The parts of UHPFRC girder were modeled by 8nodes hexahedron elements and reinforcement bars and tendons were built by 2nodes linear elements by Midas FEA software. The constitutive laws of concrete materials were selected Multi-linear model both of tension and compression function under total strain crack model, which was included in classifying of smeared crack model. The nonlinearity of reinforcement elements and tendon was simulated by Von Mises criteria. The nonlinear static analysis was applied by incremental-iteration method with convergence criteria of Newton-Raphson. The validation of numerical analysis was verified by comparison with experimental result and numerical analysis result of load-deflection response, neutral axis coordinate change, and cracking pattern of girder. The load-deflection response was fitted very well with comparison to the experimental result. The finite element analysis is seen to satisfactorily predict flexural behavioral responses of post-tensioned, reinforced UHPFRC composite box girder.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.357-361
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• 2011

본 논문에서는 확률적 불확실성을 포함한 손상 장에서 강성저감 효과를 추정하는 방법을 제안하였다. 실제 교량 구조물에 분포된 손상 장은 매우 불확실하며 손상의 위치와 형상 또한 정확히 알 수 없는 경우가 많다. 그러나 대부분의 손상 추정 문제는 균열이나 손상의 위치와 형상을 기지의 주어진 정보로 가정하고 손상을 추정한다. 제안 기법에서는 이러한 손상의 위치와 형태가 본질적으로 불확실하다는 가정 하에 이 불확실성을 수정 가우스 강성 저감 분포 함수를 도입하여 기술한다. 교량에 국부적으로 발생된 손상은 교량의 요소강성의 저감 분포로 변환되어 손상이 발생한 전체 시스템의 강성을 표현하고 이를 통해 손상이 발생한 시스템의 전체 응답을 해석할 수 있게 된다. 수정 가우스 강성 저감 분포 함수는 손상 분포의 개략적 중심을 표현하는 평균 변수와 강성 저감의 비국소적 분포 특성을 묘사하는 표준편차 변수, 손상 중심의 손상 정도를 표현하는 강성저감 변수로 구성된다. 본 논문에서는 손상 장에서 손상의 위치나 형태에 대한 확률적 불확실성을 기술하는 수정 가우스 강성 저감 분포 함수를 포함한 유한요소모델을 정식화하여 제시한다. 또한 단일 또는 복합 균열로 인해 교량 구조물에 국부적인 손상이 야기된 경우에 대한 수치 예제를 통하여 균열 등에 대한 정보가 불확실하더라도 수정 가우스 강성 저감 분포 함수를 통해 강성 저감 효과가 분석될 수 있음을 확인하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.1
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• pp.35-42
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• 2008

In the nuclear power plant, early detection of fatigue crack by non-destructive test (NDT) equipment due to the thermal cyclic load is very important in terms of strict safety regulation. To this end, many efforts are exerted to the fabrication of artificial cracked specimen for practicing engineers in the NDT company. The crack of this kind, however, cannot be made by conventional machining, but should be made under thermal cyclic load that is close to the in-situ condition, which takes tremendous time due to the repetition. In this study, thermal loading condition is investigated to minimize the time for fabricating the cracked specimen using simulation technique which predicts the crack initiation and propagation behavior. Simulation and experiment are conducted under an initial assumed condition for validation purpose. A number of simulations are conducted next under a variety of heating and cooling conditions, from which the best solution to achieve minimum time for crack with wanted size is found. In the simulation, general purpose software ANSYS is used for the stress analysis, MATLAB is used to compute crack initiation life, and ZENCRACK, which is special purpose software for crack growth prediction, is used to compute crack propagation life. As a result of the study, the time for the crack to reach the size of 1mm is predicted from the 418 hours at the initial condition to the 319 hours at the optimum condition, which is about 24% reduction.

• Magazine of the Korea Concrete Institute
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• v.8 no.4
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• pp.191-199
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• 1996

Cracks occur in mass concrete structures during construction if temperature of the concrete due to heat of hydration is suddenly changed. The temperature is also changed after placement of mass concrete by construction environments on structures. However, methods which can analyze the temperature history of mass concrete considering the construction environments have not been developed yet. In this research, an algorithm and finite element analysis program is developed for the analysis of temperature rise history of mass concrete considering quantitatively heat transfer coefficient and construction environmental conditions such as climate conditions, curing conditions, forms and form removal, and additive curing. By comparing analysis results of the program with experimental data, other research data, and analysis results by a finite element program ADINAT, validity and accuracy of the program is verified.

• Journal of the KSME
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• v.32 no.8
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• pp.685-690
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• 1992

가전제품의 제조와 관련된 열공학문제를 몇가지 예를 들어 검토하여 보았다. 제품은 강도가 커야 하고 설계공차 내에 들어야 하는 등의 조건을 만족함과 아울러, 그의 생산공정은 가급적으로 쉬워야 하고 재료를 절감할 수 있어야 한다. 제조공정 중의 열공학적인 과정이 제품 구조내의 열응력분포를 결정지우므로 열전달과정의 세심한 제어가 필요하다. 근래에 들어 컴퓨터의 발달로 열전달과정의 수치해석이 제조장비의 설계와 제조과정의 최적제어의 보조수단으로 등장하고 있다. 실제의 문제에서는 대부분 삼차원형상을 가지고 있고, 시스템을 고려하여야 하므로 여러 가지 현상이 연계되어 있다. 그러므로 수치계산에는 여전히 종래의 실험기법에 의한 실험식들과 여러 가지 축적된 경험의 도움을 필요로 한다. 이러한 측면에서 볼 때, 종래의 실험식, 경험식, 물성치, 기존의 수치해석의 결과 등을 컴퓨터에 데이터베이스(data base)화하여 소위 전문가 시 스템(expert system)을 구축하는 편이 단순히 공정의 극히 일부분 현상들을 수치해석하는 작업 보다 선행되어야 함이 바람직할 수 있다. 또한, 가전제품의 제조에는 열공학 또는 열전달현상에만 따로 주의를 기울이지 말고, 재질의 선택, 그의 유변학(rheology), 구조내의 균열문제 등을 연계 하여 고려하여야 한다.

• Computational Structural Engineering
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• v.10 no.3
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• pp.39-45
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• 1997

최근 우리 주변에는 기계, 구조물의 고속화 및 대형화에 따른 충격하중의 발생빈도가 급격하게 증가하고 있다. 따라서 이와 같은 충격하중을 받는 기계 및 구조물의 안전성 및 신뢰성 확보를 위하여는 먼저 충격하중 특성을 고려한 내충격 설계기법의 확립이 필요하다. 특히 충격하중의 경우 종래의 파괴역학적 관점에서 주로 다루어 왔던 정적하중 및 피로하중 하에서의 재료거동 특성과 달리 응력파의 전파특성이 재료의 충격강도 및 균열발생, 전파특성에 큰 영향을 미치기 때문에 이를 고려한 역학적 검토가 필요하다. 한편 이와 같은 충격하중이 반복적으로 작용하는 충격피로의 경우 지금까지 많은 연구로 내피로 설계기법이 확립된 일반 피로 특성과 달리 아직 그 주요 메카니즘이 규명되지 않은 부분이 많아 이 부분에 대한 체계적인 연구가 국내에서도 요구된다.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.283-292
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• 2007

A research projects is currently being conducted to develop a nonlinear finite element analysis methods for predicting the structural behavior of reinforced concrete frame structures, exposed to fire. As part of this, reinforced concrete frames subjected to fire loads were analyzed using the nonlinear finite-element program DIANA. Two numerical steps are incorporated in this program. The first step carries out the nonlinear transient heat flow analysis associated with fire and the second step predicts the structural behavior of reinforced concrete frames subjected to the thermal histories predicted by first step. The complex features of structural behavior in fire conditions, such as thermal expansion, plasticity, cracking or crushing, and material properties changing with temperature are considered. A concrete material model based on nonlinear fracture mechanics to take cracking into account and plasticity models for concrete in compression and reinforcement steel were used. The material and analytical models developed in this paper are verified against the experimental data on simple reinforced concrete beams. The changes in thermal parameters are discussed from the point of view of changes of structure and chemical composition due to the high temperature exposure. Although, this study considers codes standard fire for reinforced concrete frame, any other time-temperature relationship can be easily incorporated.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.137-144
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• 2009

This paper provides the results from evaluating the stiffness of Hi-Form joint by an experiment and the system identification method using the dynamic modal data, and the reasonable modeling method of Hi-Form joint which is proposed for improved stair construction recently. Based on the crack pattern and load-displacement relationship and the damage distribution, it can be judged that Hi-Form joint can't fully transfer the forces between the elements linked, and we propose that the joint is modeled as a element which have a stiffness with 50% decrease.