• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.29 no.3
• /
• pp.269-275
• /
• 2016

In this paper, shear performance of concrete wide beams was evaluated through shear failure tests. The specimens were designed to have two continuous spans with a column at the center of the wide beam. Also the specimens were reinforced with plates with openings as shear reinforcements. For the test, total eight specimens, including five specimens were reinforced with steel plates and the other three specimens were reinforced with GFRP plates were manufactured. And the shear strengths obtained from the tests were compared with ones from the equation provided by ACI 318. Support width of wide beam, support section of wide beam and shear reinforcement material were considered as variables. The results showed that the support width was proportional to the increase of shear strength. Also, regardless of material type of shear reinforcement, the shear reinforcing effect was similar when the amount of shear reinforcement was the same.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.23 no.2
• /
• pp.191-198
• /
• 2010

This study investigated that the stress reduction of single edge cracked plates with patch repairs according to different type of patching such as material, size and thickness of patch and adhesive as well as single sided or double sided patches. As a numerical tool, the p-convergent partial layerwise model has been employed. The proposed model is formulated by assuming piecewise linear variation of in-plane displacement and a constant value of out-of-plane displacements across thickness. The integrals of Legendre polynomials are chosen to define displacement fields and Gauss-Lobatto numerical integration is implemented in order to directly obtain maximum values occurred at the nodal points of each layer without other extrapolation techniques. Also, total strain energy release rate method is adopted to obtain stress intensity factors. Numerical examples are presented not only to demonstrate the stress reduction effect in terms of non-dimensional stress intensity factor and deflection with respect to different type of patch repairs, but also the accuracy of proposed model.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.4A
• /
• pp.581-590
• /
• 2008

The panels are used as a composite part of the completed deck. They replace the main bottom transverse deck reinforcement and also serve as a form surface for the cast-in-place concrete upper layer that contains the top of deck reinforcement. In this paper, three types of the detail for joints was selected and their structural performance in terms of strength and crack contral was investigated through static tests on composite beams. Form the results, the validity of loop joints for continuity of half-depth precast deck was observed and especially an overlapping length of loop joint and transverse reinforcement were checked. The results suggest that increasing the loop overlapping length increases the flexural strength of half-depth precast deck with loop joints. In terms of crack contral, the loop joint with transverse reinforcement showed better performance.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.34 no.6
• /
• pp.1707-1721
• /
• 2014

Half-depth panels were developed with the merits of CIP (Cast In Place) decks and precast decks for constructability and fast construction. In this paper, details of half-depth panels with pre-tensioning were suggested. For evaluation of structural performance, five half-depth panel specimens were fabricated and static tests were conducted. The cross-sections of these specimens were composed of pre-tensioned half-depth panels and pre-tensioned two-span half-depth panels. Test parameters were the amount of the prestressing force and the longitudinal reinforcements. Static tests on simply-supported slabs showed that ultimate strength was 1.55 times greater than calculated nominal strength. The flexural strength was only 10 % increased and the influence on crack width control was negligible when the member of tendons was increased twice. For two-span continuous specimens, the ultimate strength increased 1.2 times and 1.38 times respectively as the reinforcement was additionally provided. The verified half-depth panels by this research can be effectively utilized for the fast replacement or construction of bridges.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.5A
• /
• pp.649-656
• /
• 2008

The enhancement of the service life of damaged or cracked structures is a major issue for researchers and engineers. The hierarchic void element based on the integrals of Legendre polynomials is used to characterize the fracture behaviour of unpatched crack as well as repaired crack with bonded composite patches by computing the stress intensity factors and stress contours at the crack tip. Since the equivalent single layer approach is adopted in this study, the proposed element is necessary to represent a discontinuous crack part as a continuum body with zero stiffness. Thus the aspect ratio of this element to represent the crack should be extremely slender. The sensitivity of numerical solution with respect to energy release rate, displacement and stress has been tested to show the robustness of zero stiffness element as the aspect ratio is increased up to 2000. The stiffness derivative method and displacement extrapolation method have been applied to calculate the stress intensity factors of Mode I problem. It is noted that the proposed hierarchical void element can be one of alternatives to analyze the patched crack problems.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.10 no.3
• /
• pp.211-218
• /
• 2006

From the development of residential flat plate system, continuously bended shear reinforcement is developed for the prevention of punching shear. To know the punching shear capacity of developed shear reinforcement in slab-column joint, structural test is performed. The testing parameters are shear reinforcement types, such as no reinforcement, bended shear reinforcement, and head stud reinforcement. To verify the lateral capacity, cyclic load is applied under the constant vertical load condition. The results of tests are compared to as global displacement, slab-column joint strength. From the test results, the resisting capacity of developed shear reinforcement system has a good performance in the story drift ratio.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.2 s.54
• /
• pp.215-222
• /
• 2009

In this study, steel and FRP jackets are used to confine concrete cylinders. The FRP jacket behaviors compositely with concrete since there is bonding between them. However, the used steel jacket in this study do not behavior compositely with concrete since there is not an adhesive between them. The steel jackets are attached by external forces and the welding. This study suggests the measuring method of the axial strain for the confined concrete cylinders showing noncomposite behavior with the jackets and the correcting method of the measured strain for the composite-behavior jackets. For the noncomposite-behavior steel jacket, the axial strain of the steel surface does not represent the axial strain of the concrete inside. Also, a compressormeter can not be used. Thus, the two rigid plates at the top and bottom of a cylinder are placed and the distance of the two plates are measured and used for estimating the axial strain of the concrete. For the composite-behavior FRP jacket, the vertical strain measured on the FRP surface can be used for estimating the axial strain of the concrete. However, the vertical strain on the FRP surface contains the tensile strain due to the bulge of the concrete and, thus, the tensile strain should be corrected from the vertical strain. The corrected verticals strains compared with the measured strain or a existing constitute model; the result is satisfactory. The uncorrected stress-strain curves have the potential to under estimate the ductile behavior and the energy-dissipation-capacity of the composite-behavior FRP jackets.

• Journal of Korean Society of Steel Construction
• /
• v.19 no.6
• /
• pp.695-702
• /
• 2007

The Thermal Prestressing Method for continuous composite girder bridges is a new design and construction method developed to induce initial composite stresses in the concrete slab at negative bending regions. Due to the induced initial stresses, prevention of tensile cracks at the concrete slab, reduction of steel girder section, and reduction of reinforcing bars are possible. Thus, the construction efficiency can be improved and the construction can be made more economical. The method for determining the optimum heating region of the thermal prestressing method has not been established although such method is essential for improving the efficiency of the design process. The trial-and-error method used in previous studies is far from efficient, and a more rational method for computing optimal heating region is required. In this study, an efficient method for determining the optimum heating region in using the thermal prestressing method was developed based on the neural network algorithm, which is widely adopted to pattern recognition, optimization, diagnosis, and estimation problems in various fields. Back-propagation algorithm, commonly used as a learning algorithm in neural network problems, was used for the training of the neural network. Through case studies of two-span and three-span continuous composite girder bridges using the developed procedure, the optimal heating regions were obtained.

• Proceedings of the KAIS Fall Conference
• /
• 2010.11b
• /
• pp.901-903
• /
• 2010

본 연구에서는 2007-2009년에 간호학과 및 스포츠과학부 해부학 강의에 있어 가상강의를 실시하였고 이에 따른 학생들의 가상강의 컨텐츠의 만족도와 가상강의실 활용빈도에 따른 학업성취도와의 상관관계를 분석하였다. 2007-2009학년도 1학기 해부학 강의를 가상강의 방식으로 수강한 2개 학과 231명을 대상으로 강의 종료 후 가상강의실 게시판 및 컨텐츠 활용 빈도, 개별 설문조사, 학기말 성적을 확보하여 상호간의 상관관계를 분석하였다. 각 학과별 일반 특성을 보기 위하여 연속 변수의 경우 평균과 표준오차를, 범주형 변수의 경우 그 분포 퍼센트를 이용하여 제시하였다. 학과별로 모든 학생들의 총점을 3분위수로 구분하여 낮음, 중간, 높음으로 분류하였으며, 조사된 모든 변수들의 일반 선형성을 GLM 모델을 이용하여 검증하였다. 사후 검증은 최소자승법을 이용하여 실시하였으며, 이를 이용하여 각각의 세부 집단별 점수 차이에 대한 유의성을 평가하였다. 관련 항목들 간 상관성 분석을 위하여 스피어만 상관계수를 이용하여 p 값 0.05를 기준으로 유의성 검증을 실시하였다. 모든 통계분석은 SAS 9.12 버전을 이용하여 분석하였다. 설문 대상자들은 학과와 해부학 성적에 상관없이 가상강의 전반에 대해 높은 만족도를 가졌다. 해부학 성적이 좋을수록 가상강의실 접속횟수가 유의하게 높았다. 아울러 해부학 성적이 좋을수록 난이도가 낮고 흥미도는 높게 나타났다. 또한 평가 요인들 간의 상관관계를 분석한 결과, 가상강의의 만족도는 흥미도와 전공과의 연계성과 밀접한 관련이 있었다. 가상강의 게시판을 통한 과제물 관리, 질의응답에 대한 적절성에 대해서는 성적에 따라 일부 유의한 차이가 나타났으나 높은 만족도를 나타내었다. 결론적으로 건강 및 의료 전공자들을 위한 해부학 강의에 있어 가상강의의 도입과 적용은 성공적이었으며, 이는 해부학 전공 교수진이 매우 부족한 현실에서 해부학 강의의 질적 저하를 막고 효율적인 교육을 위한 대안이 될 것으로 판단된다. 단, 해부학 가상강의 컨텐츠의 개선, 자료 보강 및 가상강의의 접근성 확보는 시급히 개선해야할 과제로 남아 있다.

• Journal of Chest Surgery
• /
• v.42 no.6
• /
• pp.777-780
• /
• 2009

We reported here on 2 cases of aortic regurgitation (AR) that were due to avulsion of the aortic valve commissure. Aortic valvuloplasty was attempted in both cases. In the 1st case, valvuloplasty was performed with reattaching the commissure using the 5-0 polypropylene continuous suture technique. However, aortic regurgitation recurred and this lead to reoperation on the postoperative $14^{th}$ day. The intraoperative finding revealed a completely re-detached commissure that required mechanical valve replacement. In the second case, we attempted to reattach the commissure using pledgetted multiple transverse mattress sutures with 5-0 polypropylene. Because the leaflet coaptation was incomplete, the aortic valve was replaced with a tissue valve.