• Steel and Composite Structures
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• 제3권6호
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• pp.421-438
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• 2003

Aging and deterioration of existing steel structures necessitate the development of simple and efficient rehabilitation techniques. The current study investigates a methodology to enhance the flexural capacity of steel beams by bonding Glass Fibre Reinforced Plastic (GFRP) sheets to their flanges. A heavy duty adhesive, tested in a previous study is used to bond the steel and the GFRP sheet. In addition to its ease of application, the GFRP sheet provides a protective layer that prevents future corrosion of the steel section. The study reports the results of bending tests conducted on a W-shaped steel beam before and after rehabilitation using GFRP sheets. Enhancement in the moment capacity of the beam due to bonding GFRP sheet is determined from the test results. A closed form analytical model that can predict the yield moment as well as the stresses induced in the adhesive and the GFRP sheets of rehabilitated steel beam is developed. A detailed finite element analysis for the tested specimens is also conducted in this paper. The steel web and flanges as well as the GFRP sheets are simulated using three-dimensional brick elements. The shear and peel stiffness of the adhesive are modeled as equivalent linear spring systems. The analytical and experimental results indicate that a significant enhancement in the ultimate capacity of the steel beam is achieved using the proposed technique. The finite element analysis is employed to describe in detail the profile of stresses and strains that develop in the rehabilitated steel beam.

• 구강회복응용과학지
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• 제18권3호
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• pp.145-155
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• 2002

본 연구에서는 knitted glass fabric 강화 레진에 대한 치과보철소재로서의 적용가능성을 평가하기 위한 목적으로, 가장 높은 수준의 교합하중이 작용하게 되는 구치부 3본 고정성국소의치에 이 재료를 사용하는 경우에 대해 해석을 수행하였다. 우선 구치부3본 고정성국소의치에 대해 knitted glass fabric 강화 레진을 적용한 두 가지 설계 개념을 상정하였고, 각 설계형상에 대한 유한요소해석을 하였다. 강도 평가를 위해서75N의 생리적인 반복 수직 교합 하중 조건을 부여, 보철물에 유도되는 국소응력을 피로강도측면에서 고찰하였다. 각각의 설계에는 knitted glass fabric을 모재로 하고 보강재로 unidirectional 형의 glass 복합재가 사용되었다. 본 연구에서 개념설계 된 두 가지의 3본 고정성국소의치는 수직 교합 하중 75N 에 대해 충분한 강성과 강도를 가진 것으로 분석되었다. 가공치와 knitted caps사이의 연결 부위에서 국소적인 응력 집중이 관찰되었으나 그 크기는 재료의 피로강도 범위 이내였으며 국소적인 설계변경을 통하여 응력분포를 더욱 개선할 수 있을 것으로 추정하였다. 본 연구를 통해 knitted glass fabric 은 새로운 치과 보철 소재로서의 그 가능성이 기대된다.

• Steel and Composite Structures
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• 제32권3호
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• pp.361-372
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• 2019

Tubular joints are used in the construction of offshore structures and other land-based structures because of its ease of fabrication. These joints are subjected to different environmental loadings in their lifetime. At the time of fabrication or modification of an existing offshore platform, tubular joints are usually strengthened to withstand the environmental loads. Currently, various strengthening techniques such as ring stiffeners, gusset plates are employed to strengthen new and existing tubular joints. Due to some limitations with the present practices, some new techniques need to be addressed. Many researchers used Fibre Reinforced Polymer (FRP) to strengthen tubular joints. Some of the studies were focused on axial compression of Glass Fibre Reinforced Polymer (GFRP) strengthened tubular joints and found that it was an efficient technique. Earlier, the authors had performed studies on Carbon Fibre Reinforced Polymer (CFRP) strengthened tubular joint subjected to axial compression. The study steered to the conclusion that FRP composites is an alternative strengthening technique for tubular joints. In this work, the study was focused on axial compression of Y-joint and in plane and out of plane bending of T-joints. Experimental investigations were performed on these joints, fabricated from ASTM A106 Gr. B steel. Two sets of joints were fabricated for testing, one is a reference joint and the other is a joint strengthened with CFRP. After performing the set of experiments, test results were then compared with the numerical solution in ANSYS Parametric Design Language (APDL). It was observed that the joints strengthened with CFRP were having improved strength, lesser surface displacement and ovalization when compared to the reference joint.

• 항공우주시스템공학회지
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• 제16권6호
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• pp.64-73
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• 2022

페어링은 상용차가 주행 시 전면부에서 발생하는 유동박리의 저항을 제어하여 상용차 공기 저항력을 감소시키는 장치이다. 본 연구에서는 랭킨 반체 이론을 적용하여 3D페어링 형상을 설계하고 공력 해석을 통해 설계 결과를 검증하였다. 그리고 페어링의 구조적 안전성을 위해 상용차 과속조건과 돌풍 조건을 함께 고려하여 공력하중을 도출하였다. 이러한 공력 해석 결과를 기반으로 유리섬유/에폭시 복합재료를 적용하여 안전계수 3을 만족하는 페어링 구조 설계를 수행하였다. 최종 본 연구에서 가장 경량화된 페어링의 구조 해석을 수행하여 구조 안전성이 확인되었다.

• Composites Research
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• 제28권3호
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• pp.104-111
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• 2015

본 연구에서 자연 섬유를 적용한 500W급 수평축 풍력 터빈 블레이드의 구조 설계 연구를 수행하였다. 기존의 유리섬유 재질 적용 블레이드와 아마 섬유 재질 적용 블레이드의 구조 설계 결과를 비교하였다. 블레이드의 구조 설계는 단순 설계 및 혼합 설계 기법를 적용하여 설계를 수행하였다. 설계된 블레이드의 구조적 안전성은 상용 유한요소프로그램을 사용하여 다양한 하중에 따라 선형 정적해석, 변형 해석, 좌굴 해석을 수행하였다. 제작공법으로는 RIM를 채택 하였으며, 시제품 제작을 통해 자연섬유에 완전 침투까지 요구된 시간을 Poly-worx 프로그램 해석 결과와 제작 결과를 비교하였다. 제작된 시제품 블레이드는 변형률, 고유 진동수, 변위 시험을 수행하여 구조해석 결과와 비교하였다. 비교 결과에 따라 해석 결과와 시험 결과가 잘 일치함을 확인하였다.

• 대한토목학회논문집
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• 제13권4호
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• pp.15-25
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• 1993

복합재료를 효과적으로 사용하기 위하여 복합재료 구조물의 설계기준 개발을 위한 연구가 진행되고 있다. 금속 셀의 좌굴에 대한 설계시에는 초기 결함의 영향과 탄성임계좌굴응력을 근거로 한 녹다운계수(Knock-down factor)를 정의하는 것이 중요한 과정이나 복합재료 쉘의 좌굴에 대한 설계시에는 초기 결함에 대한 민감도가 거의 연구되어 있지 않은 실정이다. 복합재료 쉘의 좌굴거동에 영향을 주는 설계변수는 많기 때문에, 쉘의 설계시 이 변수들로 인한 초기 결함 민감도를 분석하기 위하여 많은 실험을 필요로 하고 있으며 실험 이외의 다른 방법으로서는 이미 검증된 수치모델을 사용하는 것이다. 본 논문에서는 복합재료 쉘요소를 개발하는데 사용된 이론을 요약, 정리 하였으며 수치예제를 통하여 본 연구에서 제안한 쉘요소의 정확성을 검증하였다. 그리고 축방향으로 압축을 받는 GFRP 곡선형 판넬의 설계시 고려해야 하는 각 변수들을 다양하게 변화시키면서 좌굴거동에 미치는 영향을 유한요소 모델링에 의해 고찰하였다. 방법으로서 초기 결합 및 두께의 진폭을 고려한 비선형 해석과 고유치 해석을 수행하였으며 이 결과를 이용하여 녹다운 계수를 산출하였다.

• Structural Engineering and Mechanics
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• 제50권3호
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• pp.275-286
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• 2014

This paper reports the influence of number of layers and length of GFRP sheets wrapped onto RCC beams for strengthening. Twelve beams of size $700mm{\times}150mm{\times}150mm$ were cast and tested. Two beams without GFRP and ten beams wrapped in different lay-up patterns with one and two layers of GFRP sheets was subjected to three point loading test and ultrasonic pulse velocity test. Initial crack load, ultimate failure load and types of failure have been observed and noted. Experimental results indicate a significant increase in initial and ultimate load carrying capacity of GFRP wrapped beams compared to unwrapped beams. The failed control specimen was retrofitted using U wrap scheme and tested under three point loading.

• Geomechanics and Engineering
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• 제28권6호
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• pp.599-611
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• 2022

Tendon reinforced cemented soil is applied extensively in foundation stabilisation and improvement, especially in areas with soft clay. To solve the deterioration problem led by steel corrosion, the glass fiber-reinforced polymer (GFRP) tendon is introduced to substitute the traditional steel tendon. The interface bond strength between the cemented soil matrix and GFRP tendon demonstrates the outstanding mechanical property of this composite. However, the lack of research between the influence factors and bond strength hinders the application. To evaluate these factors, back propagation neural network (BPNN) is applied to predict the relationship between them and bond strength. Since adjusting BPNN parameters is time-consuming and laborious, the particle swarm optimisation (PSO) algorithm is proposed. This study evaluated the influence of water content, cement content, curing time, and slip distance on the bond performance of GFRP tendon-reinforced cemented soils (GTRCS). The results showed that the ultimate and residual bond strengths were both in positive proportion to cement content and negative to water content. The sample cured for 28 days with 30% water content and 50% cement content had the largest ultimate strength (3879.40 kPa). The PSO-BPNN model was tuned with 3 neurons in the input layer, 10 in the hidden layer, and 1 in the output layer. It showed outstanding performance on a large database comprising 405 testing results. Its higher correlation coefficient (0.908) and lower root-mean-square error (239.11 kPa) were obtained compared to multiple linear regression (MLR) and logistic regression (LR). In addition, a sensitivity analysis was applied to acquire the ranking of the input variables. The results illustrated that the cement content performed the strongest influence on bond strength, followed by the water content and slip displacement.

• Journal of Nutrition and Health
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• 제8권4호
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• pp.9-14
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• 1975

Growth retardation and a variable degree of body disproportion are recognized features of malnutrition, and mild and moderate protein-calorie malnutrition(PCM). Among the various body measurements suggested to assess the prevalence of all grades of PCM as judged by growth retardation and by body disproportion, the 'mid-upper-arm circumference'-abbreviated to 'arm-circumference' has been suggested as a potential useful simple field index for the assessment of PCM showing that the measurement would give composite information simultaneously on three important effects on PCM-deficit in the muscle protein reservoirs, availability of calorie stores in the form of subcutaneous fat, and growth failure. And this is selected because of its easy accessibility, and less involvement with clinical edema. This study is conducted to make a comparison between the percentage of Korean weight for age standards and the percentage of mid-upper-arm circumference for age standards of 175 preschool children aged $3{\sim}72$ months who are selected among the low-income residents in Seoul. In this study, a comparison is made between the results obtained by expressing the observed weight of the child as a percentage of Korean standard, referred to as 'weight-for-age' and the observed arm-circumference expressed as a percentage of the age-specific arm standard of Jelliffe, referred to as 'arm-for-age'. All the measurements were taken following the techniques described by Jelliffe. The left mid upper arm was measured using a glass-fibre tape and the Fairbanks Morse beam balance was used for weighing. 80% level of weight for age Korean standard and 85% level of arm for are Jelliffe standard were used as an upper borderline limit for PCM. Comparing the 80% weight-for-age and the 85% arm-for-age standard as an upper limit for PCM, for children aged $3{\sim}72$ months, results in 84.6% agreement with the sensitivity of 86.4% and its specificity of 83.5%. If arm circumference alone had been measured and judgement made on this basis, then only 5.1% of the children would have been 'wrongly' classified. And there is a moderately close correlation between arm circumference and weight for age as the data in Table 4 shows. The problem therefore lies in the standard for arm circumference in normal children and in determining what is the lower limit of normal. Once this is clearly difined, one can rely more confidently on arm circumference measurements alone for the nutritional assessment of early childhood.