• 복합신소재구조학회 논문집
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• 제2권3호
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• pp.1-11
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• 2011

본 연구에서는 하위 요소로(sub-element) 구성된 3차원 대칭 단위 요소들로 조합된 트러스 격자 구조물의 연속적인 물성치를 제안하였다. 개별적인 트러스 격자 물성치는 균질화 작업을 통하여 유효한 응력과 변형률 관계로 이루어진 연속적인 물성치 모델로 나타낼 수 있다. 미시적인 규모(micro scale) 스트럿의 인장이나 압축 응답에 의한 축강성은 전체 격자재료의 대부분의 강도를 차지하고, 이러한 스트럿의 부피 분율(fraction)은 효과적인 강도뿐만 아니라 복제 가능한 단위 요소로 이루어진 격자판의 상대밀도에 큰 영향을 주었다. 그러므로 균질한 강성부재로 구성된 연속적인 구성모델은 미시적인 규모로 간주되는 스트럿의 강도, 내부응력 상태 및 부피 분율과 관련된 역학적인 특성들을 포함하고 있다는 것을 확인할 수 있었다. 미시적인 규모의 응력에서 소성흐름은 균질한 구성식에서 파생된 거시적인 규모에서의 (macro-scale)응력 표면에 있는 연속적인 응력함수의 영역을 확장한다. 따라서 본 연구를 통하여 3차원 대칭 단위요소 구조물의 기본 기하학을 조사하고 압력에 의존적인 마크로 규모에서의 (macro-scale) 응력함수를 예측하는 연속적인 소성모델을 공식화하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제18권6호
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• pp.60-71
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• 2014

대표적인 장대교량 형식인 사장교는 공용 중에 케이블 손상이 발생하는 경우 전체 구조계의 손상을 유발할 수 있으므로 신속한 유지관리가 필요하다. 손상발생 이후 대응시간을 가능한 단축하기 위해서 손상신호로부터 직접 이상거동을 판단할 수 있는 알고리즘에 대한 많은 연구가 진행되고 있다. 이상거동 감지 알고리즘의 정확도를 향상시키기 위해서는 구조물의 다양한 손상에 대한 충분한 양의 계측결과가 필요하다. 그러나 공용중인 교량에 손상을 주어 이상거동을 계측할 수 없으므로 수치적인 방법으로 이상거동을 모사하는 것이 효율적인 대안이 될 수 있다. 사장교 케이블의 손상을 모사하는 지금까지의 연구는 케이블의 강성변화를 단순한 장력변화로만 모사하여 해석하는 방법이 주를 이루었다. 이러한 해석방법은 설계목적의 정밀도는 확보할 수 있지만 케이블의 손상에 의한 구조물의 정확한 응답을 재현하지 못한다. 본 연구는 사장교의 손상을 모사하기 위해 강성 및 질량의 변화를 고려하는 직접적분법 Gradual Bilinear Method (GBM)을 제안하고 해석프로그램을 개발하였다. 개발된 해석방법을 단순모델을 이용하여 검증하고 실제 사장교모델을 이용하여 손상시각 및 손상지연시간에 따른 응답의 변화를 관찰하였다. 수행된 연구결과는 향후 건축/대형구조물의 안전관리를 위한 고정밀도 이상거동 감지알고리즘을 개발하고 검증하는데 활용될 수 있다.

• 대한토목학회논문집
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• 제37권1호
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• pp.1-7
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• 2017

일반적으로 구조물에 폭발, 충돌, 지진과 바람 등과 같이 짧은 시간에 큰 하중이 작용하게 되면 구조물은 국부적으로 재료의 대변형(large deformation), 대회전(large rotation), 대변형률(large strain)등이 발생하게 된다. 이와 같은 현상을 해석하려면 전산연속체 역학에 기초하여 유체-구조물 상호작용 등을 고려할 수 있는 하이드로코드(Hydrocode)의 도움이 필요하다. 또한, 폭발로 인해 발생되는 순간 동역학적인 폭발 메커니즘은 매우 복잡하기 때문에 폭발실험을 병행하여 거동을 예측하는 것이 합리적인 방법이지만 막대한 비용과 시설이 요구되므로 한계가 있는 것도 사실이다. 따라서 본 논문에서는 하이드로코드인 AUTODYN을 사용하여 폭발해석한 결과를 기수행된 철근콘크리트 슬래브의 폭발실험 결과와 비교하여 폭발해석 방법의 타당성을 검토하였고, 동일한 폭발해석 모형에 대하여 철근 배근간격, 피복두께의 변화 및 수직철근 유무에 따른 폭발 손상도를 비교검토하였다. 검토한 결과, 철근의 배근간격에 대한 철근콘크리트 슬래브 두께의 비가 커질수록, 지름이 큰 철근보다 지름이 작은 철근을 많이 사용할수록, 마지막으로 수직철근을 배근할수록 콘크리트 구조물의 내폭성능이 향상됨을 알 수 있었다.

• Steel and Composite Structures
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• 제34권1호
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• pp.1-15
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• 2020

This paper presents experimental and numerical studies on effects of local damages on the in-plane elastic-plastic buckling and strength of a fixed parabolic steel tubular arch under a vertical load distributed uniformly over its span, which have not been reported in the literature hitherto. The in-plane structural behaviour and strength of ten specimens with different local damages are investigated experimentally. A finite element (FE) model for damaged steel tubular arches is established and is validated by the test results. The FE model is then used to conduct parametric studies on effects of the damage location, depth and length on the strength of steel arches. The experimental results and FE parametric studies show that effects of damages at the arch end on the strength of the arch are more significant than those of damages at other locations of the arch, and that effects of the damage depth on the strength of arches are most significant among those of the damage length. It is also found that the failure modes of a damaged steel tubular arch are much related to its initial geometric imperfections. The experimental results and extensive FE results show that when the effective cross-section considering local damages is used in calculating the modified slenderness of arches, the column bucking curve b in GB50017 or Eurocode3 can be used for assessing the remaining in-plane strength of locally damaged parabolic steel tubular arches under uniform compression. Furthermore, a useful interaction equation for assessing the remaining in-plane strength of damaged steel tubular arches that are subjected to the combined bending and axial compression is also proposed based on the validated FE models. It is shown that the proposed interaction equation can provide lower bound assessments for the remaining strength of damaged arches under in-plane general loading.

• 대한인간공학회지
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• 제30권1호
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• pp.99-108
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• 2011

Almost all companies have paid much attention to the safety management ranging from maintenance to operation even at the stage of designing in order to prevent accidents, but fatal accidents continue to increase throughout the world. In particular, it is essential to systematically prevent such fatal accidents as fire, explosion or leakage of toxic gas at factories in order to not only protect the workers and neighbors but also prevent economic losses and environmental pollution. Though it is well known that accident probability is very low in NPP(Nuclear Power Plants), the reason why many researches are still being performed about the accidents is the results may be so severe. HRA is the main process to make preparation for possibility of human error in designing of the NPP. But those techniques have some problems and limitation as follows; the evaluation sensitivity of those techniques are out of date. And the evaluation of human error is not coupled with the design process. Additionally, the scope of the human error which has to be included in reliability assessment should be expanded. This work focuses on the coincidence of human error and mechanical failure for some important performance shaping factors to propose a method for improving safety effectively of the process industries. In order to apply in these purposes into the thesis, I found 63 critical Performance Shaping Factors of the eight dimensions throughout studies that I executed earlier. In this study, various analysis of opinion of specialists(Personal Factors, Training, Knowledge or Experience, Procedures and Documentation, Information, Communications, HMI, Workplace Design, Quality of Environment, Team Factors) and the guideline for construction of PSF were accomplished. The selected method was AHP which simplifies objective conclusions by maintaining consistency. This research focused on the implementation process of PSF to evaluate the process of PSF at each phase. As a result, we propose an evaluation model of PSF as a tool to find critical problem at each phase and improve on how to resolve the problems found at each phase. This evaluation model makes it possible to extraction of PSF succesfully by presenting the basis of assessment which will be used by enterprises to minimize the trial and error of construction process of PSF.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 3차
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• pp.72-77
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• 2010

The Incheon Bridge, which was opened to the traffic in October 2009, is an 18.4 km long sea-crossing bridge connecting the Incheon International Airport with the expressway networks around the Seoul metropolitan area by way of Songdo District of Incheon City. This bridge is an integration of several special featured bridges and the major part of the bridge consists of cable-stayed spans. This marine cable-stayed bridge has a main span of 800 m wide to cross the vessel navigation channel in and out of the Incheon Port. In waterways where ship collision is anticipated, bridges shall be designed to resist ship impact forces, and/or, adequately protected by ship impact protection (SIP) systems. For the Incheon Bridge, large diameter circular dolphins as SIP were made at 44 locations of the both side of the main span around the piers of the cable-stayed bridge span. This world's largest dolphin-type SIP system protects the bridge against the collision with 100,000 DWT tanker navigating the channel with speed of 10 knots. Diameter of the dolphin is up to 25 m. Vessel collision risk was assessed by probability based analysis with AASHTO Method-II. The annual frequency of bridge collapse through the risk analysis for 71,370 cases of the impact scenario was less than $0.5{\times}10^{-4}$ and satisfies design requirements. The dolphin is the circular sheet pile structure filled with crushed rock and closed at the top with a robust concrete cap. The structural design was performed with numerical analyses of which constitutional model was verified by the physical model experiment using the geo-centrifugal testing equipment. 3D non-linear finite element models were used to analyze the structural response and energy-dissipating capability of dolphins which were deeply embedded in the seabed. The dolphin structure secures external stability and internal stability for ordinary loads such as wave and current pressure. Considering failure mechanism, stability assessment was performed for the strength limit state and service limit state of the dolphins. The friction angle of the crushed stone as a filling material was reduced to $38^{\circ}$ considering the possibility of contracting behavior as the impact.

• 한국지능시스템학회논문지
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• 제25권2호
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• pp.119-125
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• 2015

정수장, 하수처리장, 폐수처리장의 배출수 처리공정에서 고 농도의 슬러지 선별, 이송 및 약품 투입량 조절을 위한 기준으로 슬러지 농도계가 사용되고 있다. 그러나 슬러지에 함유된 이물질이 혼입될 경우 감쇄량이 증가하거나 초음파가 수신부에 전달되지 않아 실제 농도값 보다 높은 값을 출력하거나 헌팅현상이 발생한다. 또한 단일 센서에 슬러지 포착 또는 고장 등의 문제로 배출수 공정 자동화에 어려움이 많았다. 이러한 문제점을 개선하기 위해 초음파 다중빔 농도계를 개발하여 사용하고 있으나 특정 초음파 빔의 농도 측정값에 오류가 발생할 경우 전체 농도시스템의 성능이 떨어지는 단점이 있다. 따라서 본 논문에서는 초음파 다중빔 농도계 간의 신뢰성을 판단하고, 신뢰성이 높은 다중빔 농도계만을 사용하여 슬러지 농도 예측값의 성능 향상방안을 제시하였다. 예측 알고리즘으로는 뉴로-퍼지모델을 적용하였으며 다양한 실험을 통하여 제안된 방법의 타당성을 검증하였다.

• 한국운동역학회지
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• 제15권3호
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• pp.143-152
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• 2005

The purpose of this study was to predict the failure or success of the Snatch-lifting trial as a consequence of the stand-up phase simulated in Kane's equation of motion that was effective for the dynamic analysis of multi-segment. This experiment was a case study in which one male athlete (age: 23yrs, height: 154.4cm, weight: 64.5kg) from K University was selected The system of a simulation included a multi-segment system that had one degree of freedom and one generalized coordinate for the shank segment angle. The reference frame was fixed by the Nonlinear Trans formation (NLT) method in order to set up a fixed Cartesian coordinate system in space. A weightlifter lifted a 90kg-barbell that was 75% of subject's maximum lifting capability (120kg). For this study, six cameras (Qualisys Proreflex MCU240s) and two force-plates (Kistler 9286AAs) were used for collecting data. The motion tracks of 11 land markers were attached on the major joints of the body and barbell. The sampling rates of cameras and force-plates were set up 100Hz and 1000Hz, respectively. Data were processed via the Qualisys Track manager (QTM) software. Landmark positions and force-plate amplitudes were simultaneously integrated by Qualisys system The coordinate data were filtered using a fourth-order Butterworth low pass filtering with an estimated optimum cut-off frequency of 9Hz calculated with Andrew & Yu's formula. The input data of the model were derived from experimental data processed in Matlab6.5 and the solution of a model made in Kane's method was solved in Matematica5.0. The conclusions were as follows; 1. The torque motor of the shank with 246Nm from this experiment could lift a maximum barbell weight (158.98kg) which was about 246 times as much as subject's body weight (64.5kg). 2. The torque motor with 166.5 Nm, simulated by angular displacement of the shank matched to the experimental result, could lift a maximum barbell weight (90kg) which was about 1.4 times as much as subject's body weight (64.5kg). 3. Comparing subject's maximum barbell weight (120kg) with a modeling maximum barbell weight (155.51kg) and with an experimental maximum barbell weight (90kg), the differences between these were about +35.7kg and -30kg. These results strongly suggest that if the maximum barbell weight is decided, coaches will be able to provide further knowledge and information to weightlifters for the performance improvement and then prevent injuries from training of weightlifters. It hopes to apply Kane's method to other sports skill as well as weightlifting to simulate its motion in the future study.

• Journal of the Korean Wood Science and Technology
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• 제33권1호통권129호
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• pp.7-16
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• 2005

본 연구에서는 국산 낙엽송 부재를 이용한 이중 볼트 전단 접합부의 성능을 평가하였다. 주부재로 두께 39 mm, 89 mm, 139 mm, 189 mm로 제재된 국산 낙엽송 제재목과 국산 낙엽송으로 제조된 두께 80 mm, 140 mm, 170 mm 집성재를 사용하였으며, 측면 부재로는 동일 두께의 제재목과 6 mm 철판을 사용하였으며, 접합 철물로는 M12, M16, M20 볼트를 사용하였다. 접합부에 대한 하중 방향은 주부재와 측면 부재의 목리 경사에 대해 수직, 수평한 경우에 대하여 실시하였다. 다우얼 지압 강도 실험을 통해 부재의 다우얼 지압 강도를 산출하고, 볼트 휨 실험을 통해 볼트의 휨 강도를 구한뒤, 최종 볼트 접합부 실험을 통해 접합부 성능을 평가하였으며, 최종 결과는 EYM (European Yield Model)을 사용한 계산값과 비교 평가하였다. 연구 결과 국산 낙엽송 부재의 이중 전단 볼트 접합부 성능은 EYM을 사용하여 얻어진 계산값과 비교하였을 때 그에 상응하거나 그 이상임을 알 수 있었으며, 특히 측면 부재가 제재목인 경우는 거의 일치함을 알 수 있었다. 파괴 모드는 옹이나 건조 결함 등의 영향을 많이 받으며 주부재의 두께가 작을 경우는 mode I, 주부재가 커짐에 따라 mode III으로 옮겨감을 알 수 있었다.

• 한국문헌정보학회지
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• 제8권
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• pp.183-207
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• 1981

Library standards have been the source of considerable controversy, whereas many problems are involved in developing stardard for university library collections. For evaluation purposes, standards should be precise, quantifiable and measurable. In the United States, however, standards for academic libraries are limited to qualitative statements and principles. Quantitative standards, when given, are ususally related to the number of population in the institution being served, or the prescribed quantitative objectives are often arbitrarily formulated by value judgements. The study in this paper attempts to explain the problems involved in developing quantitative standard for academic library collections. Two problems facing in the formulation of the optimal size of collection are identified. One is the theoretically faulty concept of adequacy of collection to meet the situations of diversity of university libraies, and the other is the difficulties in quantification and measurement, along with the lack of concept of adequacy of collection. However, quantification of adequate size of collection is proved to be useful on the pratical level, even though not valid theoretically. ACRL, Clapp/Jordan and Voigt developed formulas or models for setting the optimal size of a library collection for any particular university library. The main purpose of this study is the analysis of the above formulas. ACRL standard was drawn from obervation and analysis of statistcs in leading library collections. In academic field, this judgement appears to have been based on the assumption that a high-grade institution would be apt to have a good library collection. This study criticizes ACRL standard for its failure to include some determinants of measurements, and points out the limitations of the standard. In contrast. Clapp/Jordan developed a formula rather scientifically based upon bibliographical sources. This is similarly empirical but has the advantage of bringing into play the elements which make universities diverse in nature. Both ACRL and Clapp/Jordan formulas share two major defects. (1) the specific subject needs of the collection are not indiacted directly, and (2) percentage rate of growth is an indicator in measuring the potential utility of a collection. Thus both formulas failed to provide a basis for meaningful evaluation. Voigt further developed a model for determining acquisition rates for currently published materials based on bibliographic technique. Voigt model encourages experimentation with different programs and different allocations of input resources, designed to meet the needs of the library's particular population. Standard for university library collections can be formulated in terms of input(traditional indicator), or additionally, in terms of output(cost-effectiveness). Cost effectiveness is expressed as user satisfaction, ability to provide wanted materials within a reasonable time period. Thus simple quantitative method does not cover all the situations of diversity of university library collections, nor measures the effectiveness of collections. Valid standard could not be established without further research.