Ultimate strength of horizontally curved I-girders subjected to equal end moments

이기세 Graduate School, Korea University 2015 국내박사

The curved girder system is expected to be subjected to not only bending moment but also additional torsional moment simultaneously due to its initial curvature, although the primary load is usually supposed to be gravitational load. The torsional moment makes the curved girder behave in a complex manner than the straight beam. When a straight I-girder is subjected to bending moments, sometimes the section shows lateral and rotational displacement without any torsional moment as external loads, so-called lateral torsional buckling. On the other hand, the lateral and rotational displacement is inevitable behavior for curved member because there are always torsional moment acting on. Therefore, in the case of horizontally curved girder, the lateral torsional behavior cannot be regarded as a kind of buckling any more. Moreover, the ultimate strength is reduced because of torsional moment which is caused by curvature effect. In spite of these matters, there has been very few of studies for ultimate strength of curved girder. Even AAHSTO LRFD Bridge Design Specifications 2014, which is regarded as the most progressive specifications, does not suggest any provisions for horizontally curved girders. In this study, a number of numerical analyses to verify main reasons that affect ultimate strength of curved girder, and finally a strength equation is suggested. With this equation, the strength of horizontally curved girder can be calculated with considering all the geometrical properties.

Ultimate Limit State Design of Ship Structures : 선박구조의 최종한계상태 설계

김봉주 부산대학교 대학원 2003 국내박사

최근까지 선박과 같은 강판 구조물의 설계 및 강도평가는 경험적으로 구해진 허용응력과 좌굴강도에 기준하고 있다. 이와 같은 방법에서는 대상구조물에 작용하는 응력과 과거의 구조설계 경험을 바탕으로 적절히 설정된 허용응력을 상호 비교하여 구조 안전성 수준을 평가하게 된다. 이러한 방법은 구조설계 실적이 많은 기존의 구조물에 대한 강도 설계에는 나름대로의 실용성이 인정되지만 구조설계 실적이 없거나 부족한 신구조방식의 구조물에는 적용하기 어렵다. 이에 반해 최종한계상태를 기준으로 한 설계 및 강도평가법에서는 한계상태, 즉 설계시부터 계획된 구조물의 기능을 상실하는 상태를 기준으로 강도를 평가하기 때문에 구조물의 안전성과 신뢰성이 훨씬 더 높고, 신구조방식의 구조물에도 용이하게 적용 가능한 특징이 있다. 이와 같은 이유로 국제표준화기구(ISO : International Organization for Standardization)의 표준규격 ISO 2394에서는 각종 강구조물의 안정성 신뢰성은 한계상태를 기준으로 평가하도록 권고하고 있으며, 현재 국제선급연합회(IACS : International Association of Classification Societies) 산하 각국 선급에서도 최종강도 기준의 강도 평가/설계법에 대한 연구가 한창 진행 중인 실정이다. 선박과 같은 강판구조물을 구성하는 구성부재인 비보강판, 보강판 및 지지부재에 대해서 기하학적/재료적 특성 및 하중특성 등을 고찰하고, 그 고찰을 바탕으로 최종한계상태 기준의 강도평가/설계식을 이론해석적으로 도출하고, 도출된 강도평가/설계식은 선행 연구자들의 모형실험결과 및 탄소성 유한요소해석 결과와 비교 검증하여 그 적용성을 검증하고 있다. 도출된 강도평가/설계식은 작용 가능한 모든 하중특성과 구성부재의 가능한 모든 붕괴형태를 고려하고 있으며, 강판 구조물 제작상 필연적으로 발생하는 용접결함의 영향을 고려하고 있다. 이는 현재 제한적인 조건하에서만 적용 가능한 강도평가/설계식보다 진보되어 있으며, 적용하기 용이한 형태의 명확한 설계식을 제시하고 있다. 특히 40여척의 실제 선박에 대하여 개발된 강도평가/설계식을 적용하여 그 적용성을 검증하였다. 본 연구의 결과는 선박뿐만 아니라 교량과 같은 육상 강구조물의 강도평가/설계에도 보다 안전하고 신뢰성 있는 평가와 설계를 가능하게 할 것으로 기대된다.

The Relationships between Ultimate Reality, Human Being and Nature in Korea

김석호 University of Edinburgh 2005 해외박사

During the Korean War (1950-1953), most of the Korean peninsula was devastated by indiscriminate bombing, and those who survived the war suffered poverty and famine in the 1950s. In the 1960s and 70s, industry and the economy became the top priority in the setting of national policies. As a result, water and air was intolerably polluted by industrial and domestic waste and by the smoke emissions of vehicles and factories, and environmental concern consequently became an urgent priority in the 1980s-90s. Although there were some voices of protest from environmental organizations against this indiscriminate industrialisation, their campaigns could not prevent the onslaught. The old Korean proverb "body and land are not two but one (身土不二)", reflects the belief of most Korean people that they cannot live apart from the land of Korea. The contemporary ecological crisis reminds us of a serious question: Can people and nature continue to co-exist in the future? The environmental movement, apart from aiming at protecting the natural world from human beings' exploitation, should seriously find a way to change a world view or one's sense of values which continuously influence people's lifestyle. 'Ecological worldview' in this thesis denotes a religious or philosophical reflection on the way that humanity and all other organisms can co-exist, critically reviewing the failings of the existing world views, which led to the present ecological crisis, and suggesting a relationship model between humanity and other organisms. Shamanism, Taoism, Confucianism, Donghak, Christianity, etc were introduced, accumulated, and shaped the Korean mentality during the course of history and contributed to a unique Korean culture in which various religions co-exist. Presently, Buddhism and Christianity are statistically the major religions of Korea. Shamanism, Taoism, Confucianism, etc have widely influenced the customs of Korean society. In this understanding of the multi-religious context, this thesis examines Korean ecological theology through three thinkers who have their backgrounds in Donghak, Buddhism and Christianity, respectively. Chiha Kim, a poet, writer, and civil activist, Pomnyun, a Buddhist monk and campaigner for South and North Korea unification, and Hyunju Lee, a Methodist minister and writer of children's stories, are all well-known representatives of ecological theology at present. They all argue that understanding the relationship between ultimate reality, humanity, and the natural world can overcome ecological crisis, although they are not satisfied with this artificial classification of ultimate relality, humanity, and nature. The basis for the relationship has been described according to their religious backgrounds as 'life', 'dependent origination', and 'incarnation', but they commonly describe it in terms of 'indivisibility', 'interconnectedness', or 'oneness'. 'Life' is described as 'an endless dynamic generation' within all existences (Chiha Kim). 'Dependent origination' is the principle that states that all realities have been endlessly interconnected (Pomnyun). Hyunju Lee argues that all existences are an expression of divine incarnation, and all beings having spirituality cannot exist independent from each other but are one. Korean ecological theology in the multi-religious context point to 'Cheon-ji-in Habil Sasang (天地人合一思想, the Idea of the Unity of Heaven, Earth, and Humanity)'. That is, although all realities have their own independent natures and unique forms, they all have 'a triune nature' as their fundamental common nature which can be understood through the concepts of 'holistic dynamism', 'organic interconnectedness', and 'spirituality or sociality'. In this understanding, Korean ecological theology rejects any centrism, which may lead to hierarchy because ultimate reality, humanity, and the natural world exist in 'one inseparable community'.

사회인 야구 타자들의 손맛 체험에 관한 현상학적 연구

이환호 연세대학교 대학원 2017 국내석사

The “Ultimate feeling” which is experienced during the batting process of social baseball league is the experience from the aspect of performance and it is considered as meaningful phenomena for baseball practitioners. In these aspects, purpose of following research is to establish the essential nature, structure and meaning of the experience of ultimate feeling that social baseball team batters experiences from a phenomenological perspective. The major research problems have been set as follows: 1) What is fundamental characteristic and structure of ultimate feeling experience coming from social baseball team player’s batting process? 2) How is the meaning of ultimate feeling experience coming from social baseball team player’s batting process categorized? Currently, the baseball batting is one of the performance that is receiving attention from people in our country. Including the increased number of population playing social baseball league and screen baseball fever, the number of people who are enthusiastic with simple performance of batting baseball are gradually increasing. The “Ultimate feeling” experience that maybe tasted during the baseball batting is subjective and intrinsic dimensions that can be explored through expression about inner feelings of performers. The experimental factors that expressed in these form became the main resources to revealing the nature of batting experience and structure. The approach to understand how the phenomenon call ultimate feeling emerges during the experience of batting as sport performer and what that means is a phenomenological study method. The phenomenological study method has been mostly used to reveal the experimental meaning of diverse sport games, and through the literature discovered that it may become useful methodological tool to reveal the nature of baseball batting experience. The seven social baseball team players that has been selected for study participants were members of social baseball team who regularly participate in baseball games. The context and structure of ultimate feeling experienced in the baseball batting process were organized through their expressions and it has been collected by performing in-depth interviews composed with questions based on phenomenological studies. The descriptive methodology presented by Giorgi(1997) is composed with 4 phases of analysis and it has been used as analysis framework to reveal nature, structure and meaning of the ultimate feeling experienced by the social baseball team batters. According to the analysis, the following meanings has been shown as main concept of study. First, the ultimate feeling experiences that study participants shown through the analysis of data is extraordinary experience of batting that they regularly performed which gave different expression by participants, but it was forming structure by classifying similar factors. Second, The structure of experience has shown systematically by “Discover of ultimate feeling”, “Feeling of ultimate feeling” and “components of the batting”. Participants experienced ultimate feeling by coincidence opportunity discovers components by conscientizing the experience. The feeling of the ultimate feeling has been expressed as esthetics experience structure “Absence of negativity” Third, the 7 factors related to the batting experience has been discovered into “My swing”, “psychological preparation and thirst of ultimate feeling”, “immersion in the play”, “Bat selection”, “pitched ball”, “Pitcher as partner of ultimate feeling”, “role recognition and confliction”, and if their purposefulness become reality, they experienced the ultimate feeling. Fourth, with ultimate feeling, the essence of sport has been always pursued. In addition, participants interpreted about these experiences as meanings of “fulfilling”, “leisure participate attraction”, “self-realization” Fifth, the experienced ultimate feeling of the social baseball team batters as batting performer may explained by esthetics experience, and through these approach, this can be used as guideline study that can clarify the meaning of the experience that sport participants experience from performance. 사회인 야구 타격 과정에서 겪게 되는 ‘손맛’은 수행의 차원에서 발생하는 경험으로 야구 수행자들에게 매우 의미 있는 현상 중 하나라고 할 수 있다. 이러한 차원에서 본 연구의 목적은 사회인 야구 타자들이 경험하는 손맛 체험의 본질과 구조, 의미를 현상학적 관점에서 규명하는 데에 있다. 주요 연구문제들은 다음과 같이 설정되었다: 1) 사회인 야구 타격 과정에서 겪는 손맛 체험의 본질적 특성과 구조는 무엇인가? 2) 사회인 야구 타격 과정에서 겪는 손맛 체험의 의미는 어떻게 범주화 되는가? 야구의 타격은 현재 우리나라 국민들에게 주목받고 있는 수행 중 하나이다. 사회인 야구 참여 인구의 증가와 더불어 스크린야구 열풍까지 더해져 야구 배트로 공을 치는 단순한 행위에 열광하는 사람들이 점점 늘어나고 있다. 야구 타격에서 맛볼 수 있는 ‘손맛’ 체험은 주관적이고 내재적인 차원으로서 수행자들의 내면적 느낌에 대한 표현을 통해 탐구 될 수 있다. 이런 형태로 표현되는 체험적 요소는 타격 경험의 본질과 구조를 밝히는 데에 주요 근거로 활용되었다. 스포츠 수행자로서 경험하는 타격에서 손맛이라는 현상이 어떻게 생겨났으며, 그것이 무엇을 의미하는지에 대해 이해할 수 있는 접근은 현상학적 연구방법이다. 현상학적 연구방법은 다양한 스포츠 종목의 체험적 의미를 밝히는 데 주로 이용되었으며, 야구 타격 체험의 본질을 밝히는 데에도 유용한 방법론적 도구가 될 수 있음을 문헌들을 통해 확인하였다. 연구 참여자로 선정된 7명의 사회인 야구 참여자들은 정기적으로 야구 시합에 참여하는 동호인들이었다. 야구의 타격 과정에서 경험한 손맛의 맥락과 구조가 이들의 표현을 통해 구성되었으며, 이는 현상학적 연구에 기초한 질문을 구성하여 심층면담을 통해 수집되었다. Giorgi(1997)에 의하여 제시된 기술적(descriptive) 방법론은 총 네 단계의 분석을 통해 이루어지며, 사회인 야구 타자들이 경험한 손맛 체험의 본질과 구조, 의미를 밝히는 분석 틀로서 사용되었다. 분석 결과 다음과 같은 의미들이 연구의 주요 개념으로 나타났다. 첫째, 자료의 분석을 통해 나타난 연구 참여자들의 손맛 체험은 그들이 반복적으로 해오던 타격에서의 특별한 경험으로 참여자별로 표현 내용은 달랐으나, 유사한 요소들로 구분되어 구조를 형성하고 있었다. 둘째, 경험의 구조는 ‘손맛의 발견’, ‘감각적 경험’, ‘상황 인식’으로 체계화 되어 나타났다. 우연한 기회를 통해 손맛을 경험한 참여자들은 경험에 대해 의식화함으로써 구성 요소를 발견한다. 손맛의 느낌은 ‘부정의 부재’라는 미적 체험 구조로 표현되었다. 셋째, ‘나의 스윙’, ‘심리적 준비와 손맛의 갈증’, ‘승부에의 몰입’, ‘배트 선택’, ‘주어진 공’, ‘손맛 동반자로서의 상대 투수’, ‘역할 인식과 갈등’으로 타격 경험에 관련한 7개의 요소들이 발견되었으며, 이들의 합목적성이 실현되었을 때 손맛을 체험하게 되었다. 넷째, 손맛 체험에서 스포츠의 본질은 항상 추구되었다. 더불어 이러한 체험에 관해 참여자들은 ‘성취감’, ‘여가 참여 유인’, ‘신체적 살아있음’의 의미로 해석하였다. 다섯째, 사회인 야구 타자들이 타격 수행으로부터 경험한 손맛은 미적 체험으로 설명될 수 있으며, 이러한 접근을 통해 스포츠 참여자들이 수행으로부터 경험하는 체험의 의미를 보다 명료하게 펼쳐낼 수 있는 길잡이 연구로 활용될 수 있을 것이다.

Evaluation of ultimate compressive strength of flanges stiffened with u-ribs in wide steel box-girder

김종서 서울대학교 대학원 2015 국내박사

This study proposes a method to evaluate the in-plane ultimate compressive strength of stiffened flanges with U-ribs in a wide steel box-girder. When a primary bending moment and/or an axial force are applied to the steel box-girder, the main load component of top or bottom flanges is longitudinal in-plane axial compression. For the reason above, the stiffened flanges with U-ribs are separated from the box-girder and modeled by finite elements with idealized boundary conditions. Generally, the stiffened flanges between diaphragms are designed to behave as if simple support conditions were applied. If the diaphragms are stiff (thick) enough in the out of plane direction, loaded edges of the stiffened flanges will have the same displacement in longitudinal direction. This condition can be analyzed by displacement control. However, if the diaphragms are flexible (thin) enough in the out of plane direction, all parts of the loaded edges of the stiffened flanges will have different displacements in the longitudinal direction. This condition has to be analyzed by force control. Thus, the ultimate compressive strengths of the stiffened flanges are evaluated considering effects of the bending stiffness of the diaphragms on in-plane behaviors of the stiffened flange. This study shows that the effect of the diaphragm is negligible under the practical thickness. Thus, the force control is considered to be more appropriate than the displacement control for evaluation of the ultimate compressive strength of flanges stiffened with U-ribs. Based on the ultimate compressive strengths in the force control, a strength formula is proposed. The FHWA (Federal Highway Administration) provisions are reviewed and evaluated in terms of the finite element solution in this study. The FHWA provisions accurately estimate the ultimate compressive strengths of the stiffened flanges in the force control. The ultimate compressive strengths from the FHWA provisions are nearly the same as those from the proposed strength formula. Thus, this study recommends the proposed strength formula or the FHWA provisions for evaluation of the ultimate compressive strength of stiffened flanges with U-ribs. Either way, the ultimate compressive strengths are almost same. 본 연구에서는 U리브로 보강된 광폭 강박스거더 플랜지의 극한 압축강도를 평가하는 방법을 제안한다. 박스거더가 휨 또는 압축력을 받을 때, 박스거더의 상부플랜지나 하부플랜지는 면내 압축상태에 놓이게 된다. 만약 웹과 같은 다른 부재들이 충분한 강성을 가지고 있다면, 박스거더의 극한휨강도는 상부플랜지 또는 하부플랜지의 극한압축강도에 의해서 지배된다. 이러한 이유로 본 연구에서는 보강판의 극한압축강도 평가를 수행하였다. 이를 위해, U리브로 보강된 판을 박스거더에서 분리한 후, 적절한 경계조건을 적용하여 모델링하였다. 일반적으로, 보강판은 다이아프램 사이에서 단순경계조건으로 거동하도록 설계된다. 만약 다이아프램의 두께가 상당해서 면외 휨강성이 충분하다면, 보강판에서 하중이 재하되는 부분의 면내 변위는 모두 동일하게 발생할 것이다. 이 경우는, 변위제어법으로 해석할 수 있다. 그러나 다이아프램의 두께가 얇아서 면외 휨강성이 충분하지 않다면, 보강판에서 하중이 재하되는 부분의 면내 변위는 모두 다르게 발생할 것이다. 이 경우는, 하중제어법으로 해석해야 한다. 본 연구에서는 다이아프램의 면외 휨강성이 보강판의 면내 거동에 미치는 영향을 분석하여 U리브로 보강된 플랜지의 극한압축강도를 평가하였다. 본 연구에는 실제 설계에서 사용되는 다이아프램의 두께를 고려할 경우, 다이아프램의 효과가 무시할 만한 수준임을 확인하였으며, 변위제어법보다 하중제어법으로 보강판의 극한압축강도를 평가해야 함을 보인다. 또한, 하중제어법에 의해 산출된 극한압축강도를 바탕으로 강도평가식을 제안한다. 현재 널리 사용되고 있는 미연방도로관리청(FHWA)에서 제안한 강박스거더 강도평가식을 분석하였으며, 미연방도로관리청(FHWA)의 강도평가식이 본 연구의 하중제어에 의한 유한요소해석결과와 거의 일치함을 확인하였다. 미연방도로관리청(FHWA) 강도평가식과 본 연구의 제안식은 동일한 결과를 제공한다. 따라서, 본 연구에서는 U리브로 보강된 광폭 강박스거더 플랜지의 극한압축강도평가시, 미연방도로관리청(FHWA)의 설계규정 또는 본 연구의 제안식을 사용할 것을 추천한다.

생명과학의 과제 유형과 학습 구조가 초등학생의 과학 창의성에 미치는 효과

강민성 서울교육대학교 교육전문대학원 2020 국내석사

The purpose of this study is to find out how the task type and learning structure of biology affect the science creativity of elementary school students, and how the effects of cooperative learning on science creativity of elementary school students according to the biological task types. To this end, classes were conducted for two classes (36 students) of 5th graders attending M Elementary School located in Dongjak-gu, Seoul. Quantitative analysis was performed using the independent sample t-test using the activity sheets of the phenomena and ultimate tasks used in the class as test sheets. In addition, a qualitative analysis was conducted by conducting in-depth interviews with students. The main results of this study are as follows. First, as a result of classifying and analyzing the science creativity scores of elementary school students when they solved the task of phenomenological knowledge in individual learning situations into quadrants of science creativity, a majority of students appeared as routine type (52.8%). In other words, when solving the task of phenomenological knowledge alone, it can be said that students do not produce original and useful products. At this time, students had difficulty producing various ideas, which resulted in low creativity scores. On the other hand, the science creativity scores that emerged when solving the task of ultimate knowledge in individual learning were 41.7% and 38.9%, unlike the task of phenomenological knowledge, students produced ideas that were lower in terms of usefulness. Second, in the case of cooperative learning, the type of science creativity of elementary school students showed the most when they solved the task of phenomenological knowledge. Through interviews, students responded that they participated in cooperative learning with phenomenological task with more positive emotions than individual learning, and had enough time to discuss. On the other hand, in the cooperative learning situation, the creative type showed the most in the types of science creativity of elementary school students when solving the ultimate task of knowledge, 69.4%. In other words, students' originality and usefulness are all improved in cooperative learning that includes the ultimate task. In this regard, students responded that they had the opportunity to filter out ideas that were not useful through cooperative learning, and that the ideas produced with the group in the ultimate task of knowledge were wider than those of phenomenological knowledge. Third, cooperative learning showed a greater effect on science creativity when solving the ultimate task than when solving the phenomenological task. It was found that there was a significant difference as a result of comparing the science creativity scores of individual learning and cooperative learning in both the task of phenomenological knowledge and the task of ultimate knowledge. However, in the task of phenomenological knowledge, the individual learning creativity score was 43.22, and the cooperative learning creativity score was 51.62. In cooperative learning of phenomenological task, students' science creativity score improved by about 8.4 points on average. In the ultimate task, the individual learning creativity score was 42.86, and the cooperative learning creativity score was 58.33. In the cooperative learning of the ultimate task, the students' science creativity score improved on average by about 15.5 points. Fourth, as a result of investigating students' self-awareness about science creativity according to the task type and learning structure of biology, it was recognized that science creativity increases when solving the ultimate task in cooperative learning. In cooperative learning, on average, when solving phenomenological task, the average score was improved by about 14 points, and when solving the ultimate task, the students recognized that the creativity score was improved by about 31 points. In conclusion, for effective creativity education, practical school science education must include activities that include the ultimate knowledge, and the efficiency can be maximized through learning the ultimate knowledge with cooperative learning. 본 연구는 초등학생들의 과학 창의성에 생명과학의 과제 유형과 학습 구조가 어떤 영향을 미치는지, 협동학습이 생명과학의 과제 유형에 따라 초등학생의 과학 창의성에 미치는 효과는 어떠한지를 알아보는 데 그 목적이 있다. 이를 위해 서울시 동작구에 소재한 M초등학교에 재학 중인 5학년 2개 반(36명)을 대상으로 수업을 진행하였고, 수업에서 사용한 현상적 과제와 궁극인 과제의 활동지를 검사지로 활용하여 독립표본 t-검증을 이용, 정량적 분석을 시행하였다. 또한, 학생들을 대상으로 심층적인 면담을 하여 정성적인 분석도 시행하였다. 본 연구의 주요한 결과는 다음과 같다. 첫째, 개별학습에서 현상적 지식의 과제를 해결할 때 나타난 초등학생들의 과학 창의성 점수를 과학 창의 4분면으로 유형화하여 분석한 결과 과반수의 학생이 진부형(52.8%)으로 나타났다. 즉, 현상적 지식의 과제를 혼자서 해결할 때 학생들은 독창적이고 유용한 산출물을 생산하지 못하였다. 학생들은 이때, 다양한 아이디어를 생산하는 데 어려움을 겪었고, 이러한 어려움은 낮은 창의성 점수라는 결과를 낳았다. 한편, 개별학습에서 궁극인 지식의 과제를 해결할 때 나타난 과학 창의성 점수는 독창형과 진부형이 각각 41.7%, 38.9%로, 현상적 지식의 과제와 달리 학생들이 유용성 측면에서 하위에 해당하는 아이디어를 생산하였다. 둘째, 협동학습에서 현상적 지식의 과제를 해결할 때 나타난 초등학생들의 과학 창의성 유형은 창의형이 50.0%로 가장 많았다. 면담을 통해 학생들은 현상적 과제가 포함된 협동학습에서 개별학습보다 긍정적인 감정을 가지고 참여하였고, 충분히 토의하는 시간을 가질 수 있었다고 응답하였다. 한편, 협동학습에서 궁극인 지식의 과제를 해결할 때 나타난 초등학생들의 과학 창의성 유형 역시 창의형이 69.4%로 가장 많았다. 이때, 진부형은 0명으로 나타났다. 즉, 궁극인 과제가 포함된 협동학습에서는 학생들의 독창성과 유용성이 모두 향상된 것이다. 학생들은 이와 관련하여 협동학습을 통해 유용하지 않은 아이디어를 거를 기회를 갖게 되었고, 현상적 지식의 과제 보다 궁극인 지식의 과제에서 모둠원들과 함께 생산해 낸 아이디어의 폭이 넓었다고 응답하였다. 셋째, 협동학습은 현상적 과제를 해결할 때보다 궁극인 과제를 해결할 때 과학 창의성에 미치는 효과가 큰 것으로 나타났다. 현상적 지식의 과제와 궁극인 지식의 과제 모두에서 개별학습・협동학습의 과학 창의성 점수를 비교한 결과 유의한 차이가 있는 것으로 나타났다. 그러나 현상적 지식의 과제에서 개별학습 창의성 점수는 43.22, 협동학습 창의성 점수는 51.62로 현상적 과제의 협동학습에서는 학생들의 과학 창의성 점수가 평균적으로 약 8.4점이 향상된 반면, 궁극인 과제에서 개별학습 창의성 점수는 42.86, 협동학습 창의성 점수는 58.33로 궁극인 과제의 협동학습에서는 학생들의 과학 창의성 점수가 평균적으로 약 15.5점 향상되었다. 넷째, 생명과학의 과제 유형과 학습 구조에 따른 과학 창의성에 대해 학생들의 자기 인식을 조사한 결과, 협동학습에서 궁극인 과제를 해결할 때 과학 창의성이 높아진다고 인식하고 있었다. 학생들은 협동학습에서 현상적 과제를 해결할 때는 평균적으로 약 14점의 창의성 점수가 향상되는 것으로, 궁극인 과제를 해결할 때는 약 31점의 창의성 점수가 향상되는 것으로 인식하고 있었다. 결론적으로 효과적인 과학 창의성 교육을 위해서는 실질적인 학교 과학 교육에서 궁극인 지식이 포함된 활동을 반드시 개발・포함해야 하며, 협동학습을 통한 궁극인 지식의 학습을 통해 그 효율성을 극대화할 수 있을 것이다.

Unified Code Calibration for Short- to Medium-span and Long-span Bridges with New Vehicular Live Load Model

김세상 서울대학교 대학원 2018 국내석사

There are two bridge design codes in Korea adopting reliability-based load-and-resistance factor design for short- to medium-span and long-span bridges, respectively. Unified code calibration is required for the bridge design codes since their load-resistance factors were developed separately. Moreover, there is lack of consistency of theoretical backgrounds for a design vehicular live load and the statistical model of a vehicular live load effect. Therefore, the new statistical model of a vehicular live load effect and the corresponding design lane load are proposed based on the same data and the unified code calibration is conducted for the Ultimate Limit State I and V applying the current and new statistical models of the vehicular live load effect. The calibration is performed by adopting the optimization scheme for uniformly satisfying a target level of reliability. Load factors of the Ultimate Limit State I are defined depending on load compositions so the suggested load-resistance factors are applicable to design not only short- to medium-span but also long-span bridges. Furthermore, calibrations of the Ultimate Limit State V are conducted for short- to medium-span and long-span bridges, respectively. Reliability indices evaluated by proposed load-resistance factors more uniformly satisfy the target reliability index than those calculated by load-resistance factors in the current bridge design codes.

Ultimate analysis of steel cable-stayed bridges

김승준 Graduate School, Korea University 2010 국내박사

Recently, a cable-stayed bridge becomes the most popular bridge system due to its structural efficiency and aesthetics. The increasing popularity of contemporary cable-stayed bridges among bride engineers can be attributed to: the appealing aesthetics, efficient utilization of structural materials, the increased stiffness over suspension bridges, the efficient and fast mode of construction, the relatively small size of the bridge elements. Therefore cable- stayed bridge is considered as the optimum bridge system for long-span bridges because of these strong points. The cable-stayed bridge shows very complex nonlinear behavior because of its structural characteristics. The girder of cable-stayed bridge is supported by inclined cables. So these inclined cables become intermediate supports of girder. However, vertical and horizontal forces of cable tensile forces are subjected to mast and girder directly. So, compressive forces are subjected to girder and mast due to cable tensile forces. Consequently the interaction among girder, mast and cable of cable-stayed bridges occurs very complexly. The main purpose of this research is to investigate the ultimate behavior of steel cable-stayed bridges. To do this work, the ultimate analysis program was developed first based on the theory of nonlinear finite element analysis. Using 3-dimensional nonlinear frame element and nonlinear truss element with equivalent elastic modulus, geometric nonlinearities are considered in this program. And the refined plastic hinge method is used for considering the material nonlinearity of the main members. This developed program has three analysis modules such as initial shape analysis module, construction stage analysis module, and live load analysis modules. Therefore the ultimate analysis for the steel cable-stayed bridges under construction stage as well as the structure after construction can be performed using this developed program. Using this program, analytical studies of investigation on the ultimate behavior of steel-cable stayed bridges were performed in this research. And experimental studies were performed to investigate the ultimate behavior of steel cable-stayed bridges. Based on the results of analytical and experimental studies, governing ultimate behavior of steel cable-stayed bridges were classified refer to the various parameters.

(A) parametric study on load-bearing performance of pressure-dispersed horizontal anchors in soil

Jing, Shuju Sungkyunkwan university 2021 국내석사

The so-called "pressure dispersion type anchor plate" is to string together two or more anchor plates with a tie rod. Compared with the traditional anchor plate, it has the following advantages: (1) It has high bearing capacity and strong adjustability, which can effectively control and adjust the displacement of supporting structures or structures. Prestress can be applied to control and adjust the displacement of the structure and optimize the internal force distribution of the structure. (2)Can effectively reduce the "group anchor effect". it can effectively reduce the number of anchor plates, increase the vertical spacing of anchor plates, avoid mutual interference between anchor plates, and reduce the "group anchor effect". (3) Simple construction and good economy. Multiple anchor plates are arranged on the same height and the same tie rod, which is convenient for construction and good economic performance. (4) The anchoring force of the pressure-dispersed anchor rod is borne by the anchor rods of each unit. The stress is distributed evenly over the anchoring length, which improves the stress state of the anchoring section and avoids stress concentration. Based on the above-mentioned problems in the current research, this paper uses the finite element and limit analysis software Optum G2 to establish the numerical simulation model of single anchor plate and pressure-dispersed anchor plate through the reliability verification of bearing capacity and fracture surface. According to the research on the ultimate pull-up mechanism of the pressuredispersed anchor plate, the Optum G2 software is used to analyze the deformation characteristics of the soil shear strain cloud and displacement cloud when the pressure-dispersed anchor plate is pulled, so as to reveal the deformation mechanism and Forecasts provide the possibility. According to the research on the ultimate uplift bearing capacity of the pressure-dispersed anchor plate, the relationship between the equivalent single anchor plate and the bearing capacity of the pressure-dispersed anchor plate under different densities, different buried depths and different plate diameters is analyzed, and the pressure is determined under different conditions. The applicable parameters of decentralized anchor plates provide guidance for engineering practice.Based on the study of the ultimate bearing capacity of single anchor plate and pressure-dispersed anchor plate, the pressure-dispersed bearing capacity formula is established.

Prediction of ultimate strength reduction caused by corrosion for offshore wind turbines

Rahmdel, Sajad 부산대학교 대학원 2015 국내석사

The harsh environmental conditions of oceans cause significant pit corrosion on floating offshore wind turbines (FOWTs). Corrosion is a factor that decreases the ultimate strength of a structure, which can lead to structural failure in an aged structure. To overcome this issue, comprehensive ultimate strength assessment of these structures are required. The purpose of this work is to evaluate the ultimate strength performance of steel plates used on the body of FOWTs by considering the effects of pit corrosions. This study proposes a reliable method to predict the ultimate strength reduction (USR) caused by pit corrosion of a structure at various ages. This method can assist structural designers to consider the impacts of pit corrosion on the ultimate strength of the structures; thereby helping them to design more reliable and safer structures. The presented method has 6 steps and was assessed by applying it to the simplified example of a thin-plate panel structure. The ultimate strengths of the panel with different pit depths were calculated using Finite Element (FE) analysis. The effects of material and geometric nonlinearities, as well as the initial imperfections and buckling were also considered. A linear regression model, representing the relationship between the USR and pit depth, was then developed. Furthermore, using the experimental data and probabilistic approach, statistical analysis was carried out to acquire the weighted mean value of USR for different ages of the panel. Employing the results of this statistical analysis, a plot to elucidate the connection between the USR and age of the structure was then produced. The ultimate strength of a structure may be decreased up to 33% due to pit corrosion after 27 years of service. The introduced stepwise approach contemplates the nonlinearity of pit corrosion with time by considering the experimental data. As corroborated by the successful application of the presented methodology, this method is more accurate, compared to accepted practices available in the literature.