• Structural Engineering and Mechanics
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• 제66권4호
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• pp.543-555
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• 2018

Fiber Reinforced Polymer (FRP), which has a high strength to weight ratio, are now regularly used for strengthening of deficient reinforced concrete (RC) structures. While various researches have been conducted on FRP strengthening, an area that still requires attention is predicting the debonding failure load of prestressed FRP strengthened RC beams. Application of prestressing increases the capacity and reduces the premature failure of the beams largely, though not entirely. Few analytical methods are available to predict the failure loads under flexure failure. With this paucity, this research proposes a method for predicting debonding failure induced by intermediate crack (IC) for prestressed FRP-strengthened beams. The method consists of a numerical study on beams retrofitted with prestressed FRP in the tension side of the beam. The method applies modified Branson moment-curvature analysis together with the global energy balance approach in combination with fracture mechanics criteria to predict failure load for complicated IC-induced failure. The numerically simulated results were compared with published experimental data and the average of theoretical to experimental debonding failure load is found to be 0.93 with a standard deviation of 0.09.

• 대한금속재료학회지
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• 제49권9호
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• pp.708-714
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• 2011

The premature failure of a servovalve used for six months in a thermal power plant has been analyzed. The servovalve was made of stainless steel, containing 16Cr-0.44Mo, along with other elements. An overload of oil-supply pumping and an abnormal increase in the oil flux were observed during operation. A study revealed that erosion and corrosion could be the main causes of the failure. The visual examination of the servovalve did not show any appreciable damage. However, corrosion and erosion of the servovalve were observed using scanning electron microscopy (SEM). Upon examination of the servovalve, the corrosion was found to have occurred throughout the bushing and spool; however, erosion occurred at only the edge-side. In addition, the condition of the electrohydraulic control system (EHC) oil was investigated with respect to its satisfaction of the management standard.

• 한국공간구조학회논문집
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• 제22권4호
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• pp.99-107
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• 2022

Existing reinforced concrete building structures constructed before 1988 have seismically-deficient reinforcing details, which can lead to the premature failure of the columns and beam-column joints. The premature failure was resulted from the inadequate bonding performance between the reinforcing bars and surrounding concrete on the main structural elements. This paper aims to quantify the bond-slip effect on the dynamic responses of reinforced concrete frame models using finite element analyses. The bond-slip behavior was modeled using an one-dimensional slide line model in LS-DYNA. The bond-slip models were varied with the bonding conditions and failure modes, and implemented to the well-validated finite element models. The dynamic responses of the frame models with the several bonding conditions were compared to the validated models reproducing the actual behavior. It verifies that the bond-slip effects significantly affected the dynamic responses of the reinforced concrete building structures.

• Clinical and Experimental Pediatrics
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• 제55권8호
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• pp.272-279
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• 2012

Purpose: The aim of this study was to develop an appropriate nursing information guideline according to corrected age, after investigating parents' concerns about the growth, development, and diseases of their premature infants after discharge from the neonatal intensive care unit (NICU). Methods: The parents of premature infants (birth weight, <2,500 g; gestational age, <37 weeks) who went to a neonatal follow-up clinic after NICU discharge at Seoul St. Mary's Hospital from January 2005 to December 2009, were asked with regard to their concerns about their infants through a questionnaire survey. The results of physical examinations, including body measurements and neurodevelopmental status at 4, 8, 12, and 18 months of corrected age, were retrospectively reviewed in 390 infants. Results: The most common parental concerns were developmental delay, poor growth, and feeding and nutritional problems. Parental concerns about developmental delay, growth failure in improvement in body weight and length, and overweightness were high in specificity but very low in sensitivity. After NICU discharge, 30% of premature infants experienced infectious diseases before 18 months of corrected age, the most common of which was respiratory tract infection. Conclusion: For guiding of premature infants in outpatient day clinics after NICU discharge, it is necessary to identify the parents' highest concerns, to educate them about the possibilities of growth and neurodevelopmental disabilities in their infants and to provide them with handouts containing guidelines on the management of infectious diseases, especially respiratory infections.

• Journal of Chest Surgery
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• 제30권6호
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• pp.585-590
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• 1997

미숙아에 있어서 동반되는 동맥관개존증은 향후 환아의 경과에 지대한 영향을 미친다. 본 연구는 미숙아 에 있어서 동맥관 개존증으로 진단되어 치료를 받은 례를 관찰 분석하여 그 성적을 살피고 향후 동맥관개 존증의 치료 방향을 설정하고자 하였다. 1994년 12월 부터 1996년 10월까지 신생아 중환자실에 입원하여 동맥관개존증으로 진단을 받은 환자 57 명중을 대상으로 하여 임상기록지를 관찰하였다. 인도메타진 등의 내과적 치료를 받은 환자(I 군)는 48명 (남자 29명, 여자 19명) 이었으며, 수술적 교정을 받은 환아(II 군)는 9명(남자 5명, 여자 4명)이었다. 각군에서의 환아의 평균 재태기간은 각각 29.6$\pm$3.1주, 28.1$\pm$1.6주0>0.05), 평균 출생시 체중은 각각 1,413$\pm$ 580gm, 1,098$\pm$235gm(p.0.05)이였다. 모든 환아에서 일차적으로 인도메타진 치료를 하였으며, 그중 인도메타 진 치료에도 불구하고 동맥관이 막히지 않고 패출혈, BUN의 상승, 소변량 감소 등으로 수술 대상이 되었 (9/57, 16%). 수술은 환자를 이동시키지 않고 신생아중환자실에서 결찰을 시행하였다. 2명의 환아들이 술 후 15일, 47일째 술전 부터 발생한 지속적인 패혈증및 기관지패 鎌紈봐塚막\ulcorner사망하였다. 수술과 직접적으 로 관련된 합병증 및 사망 례는 없었다. 인도메타진으로 내과적 치료만 한 환자 47명중 9명이 합병증(패혈 증, 기관패이형성증, 패내출혈, 신부전 등)으로 인하여 사망하여(19%) 내과적 치료의 실패는 520lo(18fsf였 다. 출생체중을 기준으로 보았을때 체중이 1500gm미만인 경우가 1500gm이상인 경우보다 그 실패율이 높았다(41% 15/38, 16% 3/19, p<0,05). 상기 결과로 부터 크기가 큰 동맥관 개존증, 체중이 적은 미숙아, 선천성 심기형을 동반한 경우 등 일부 미숙아에 있어서는 수술적 결찰술이 일차적 치료법으로 고려 되어야 할 것으로 사료된다. 또한 환아를 수 술장으로 이동하지 않고도 중환자실에서 안전하게 수술할 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.84-87
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• 2004

Nominal flexural strength of RC members strengthened with FRP sheets is generally based on the tensile strength of composite materials obtained from coupon tests. This method is based on the assumption that bond failure does not occur until the FRP sheet reaches its rupture strength. According to the previous researches, however, bond failure often occurs before the FRP sheet reaches its rupture strength. Some attempts were made to control debonding failure by increasing the bonded length of sheet or wrapping the section around their side of the member(U-wrap). In this study, the flexural failure mechanism of RC beams strengthened with AFRP sheets with different bond lengths is investigated. Their strengthening details to prevent the premature debonding failure are also suggested and its effectiveness is verified.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.899-916
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• 2015

Upgrading or strengthening of existing reinforced concrete (RC) infrastructure is an emerging demand nowadays. Near Surface Mounted (NSM) technique is very promising approach for flexural strengthening of RC members. However, premature failure such as concrete cover separation failure have been a main concern in utilizing this technique. In this study, U-wrap end anchorage with carbon fiber reinforced polymer (CFRP) fabrics is proposed to eliminate the concrete cover separation failure. Experimental programs were conducted to the consequence of U-wrap end anchorage on the flexurally strengthened RC beams with NSM-steel. A total of eight RC rectangular beam specimens were tested. One specimen was kept unstrengthened as a reference; three specimens were strengthened with NSM-steel bars and the remaining four specimens were strengthened with NSM-steel bars and U-wrap end anchorage using CFRP fabrics. A 3D non-linear finite element model (FEM) was developed to simulate the flexural response of the tested specimens. It is revealed that NSM-steel (with and without end-anchors) significantly improved the flexural strength; moreover decreased deflection and strains compared with reference specimen. Furthermore, NSM-steel with end anchorage strengthened specimens revealed the greater flexural strength and improve failure modes (premature to flexure) compared with the NSM-steel without end anchorage specimens. The results also ensured that the U-wrap end anchorage completely eliminate the concrete cover separation failure.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.341-348
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• 2000

The existing solid circular RC pier without seismic detailing is found to have poor ductility due to the premature bond failure of lap spliced longitudinal bars. The steel-jacket was introduced to prevent this unexpected type of failure. The nonlinear behavior and he seismic performance of the retrofitted pier were examined through the scale model test and compared with those of existing one. It is confirmed from the test results that the steel-jacket retrofitting can be used as an measure to improve seismic performance considerably.

• Journal of Chest Surgery
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• 제24권7호
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• pp.656-662
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• 1991

endocarditis, 1.475% /pt-yr, overall valve failure, 3.319% /pt-yr; and primary tissue failure, 1.475% /pt-yr. The actuarial probability of survival was 94.3$\pm$3.6% and the probability of freedom from thromboembolism 90.6$\pm$4.6% at 11 years after surgery respectively. And, the probability of freedom from primary tissue failure was 60.4$\pm$16.9% also at 11 years The evidence of possible premature and accelerated failure of the pericardial valve in the aortic position among the young population was not clear on the age-related analysis of the structural failure, and no suggestion could be made to indicate age limit when the use of the pericardial valve would better be avoided.

• 국제초고층학회논문집
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• 제2권2호
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• pp.141-152
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• 2013

This paper presents a brief overview of the recently developed performance-control method of moment frame design subjected to monotonously increasing lateral loading. The final product of any elastic-plastic analysis is a nonlinear loaddisplacement diagram associated with a progressive failure mechanism, which may or may not be as desirable as expected. Analytically derived failure mechanisms may include such undesirable features as soft story failure, partial failure modes, overcollapse, etc. The problem is compounded if any kind of performance control, e.g., drift optimization, material savings or integrity assessment is also involved. However, there is no reason why the process can not be reversed by first selecting a desirable collapse mechanism, then working backwards to select members that would lead to the desired outcome. This article provides an overview of the newly developed Performance control methodology of design for lateral resisting frameworks with a view towards integrity control and prevention of premature failure due to propagation of plasticity and progressive P-delta effects.