• 국제초고층학회논문집
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• 제10권4호
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• pp.265-283
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• 2021

To ensure that fire induced collapse of a building is prevented it is important to understand the sequence of events that can lead to this event. In this paper, the initiation of collapse mechanisms of generic a multi-storey steel frame subjected to vertical and horizontal travelling fires are analysed computationally by tracking the formation of plastic hinges in the frame and generation of fire induced loads. Both uniform and travelling fires are considered. In total 58 different cases are analysed using finite element software LS-DYNA. For the frame examined with a simple and generic structural arrangement and higher applied fire protection to the columns, the results indicate that collapse mechanisms for singe floor and multiple floor fires can be each split into two main groups. For single floor fires (taking place in the upper floors of the frame (Group S1)), collapse is initiated by the pull-in of external columns when heated beams in end bays go into catenary action. For single floor fires occurring on the lower floors(Group S2), failure is initiated (i.e. ultimate strain of the material is exceeded) after the local beam collapse. Failure in both groups for single floor fires is governed by the generation of high loads due to restrained thermal expansion and the loss of material strength. For multiple floor fires with a low number of fire floors (1 to 3) - Group M1, failure is dominated by the loss of material strength and collapse is mainly initiated by the pull-in of external columns. For the cases with a larger number of fire floors (5 to 10) - Group M2, failure is dominated by thermal expansion and collapse is mainly initiated by swaying of the frame to the side of fire origin. The results show that for the investigated frame initiation of collapse mechanisms are affected by the fire type, the number of fire floors, and the location of the fire floor. The findings of this study could be of use to designers of buildings when developing fire protection strategies for steel framed buildings where the potential for a multifloor fire exists.

• Advances in materials Research
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• 제13권4호
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• pp.299-319
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• 2024

Due to higher strength-to-weight ratio of composite laminates, they find uses in many weight-sensitive applications like aerospace, automobile and marine structures. From a reliability point of view, accurate prediction of failure of these structures is important. Due to the complexities in the manufacturing processes of composite laminates, there is a variation in the material properties and geometric parameters. Hence stochastic aspects are important while designing the composite laminates. Many existing works of composite laminate failure analysis are based on the deterministic approach but it is important to consider the randomness in the material properties, geometry and loading to predict accurate failure loads. In this paper the statistics of the ultimate failure load of the [0/θ]_s laminated composite plate (LCP) containing the edge crack and voids subjected to the tensile loading are presented in terms of the mean and coefficient of variance (COV). The objective is to better the efficacy of laminate failure by predicting the statistics of the ultimate failure load of LCP with random material, geometric and loading parameters. The stochastic analysis is done by using the extended finite element method (XFEM) combined with the second-order perturbation technique (SOPT). The ultimate failure load of the LCP is obtained by ply-by-ply failure analysis using the ply discount method combined with the Tsai-Wu failure criterion. The aim is to know the effect of the stacking sequence, crack length, crack angle, location of voids and number of voids on the mean and corresponding COV of the ultimate failure load of LCP is investigated. The results of the ultimate failure load obtained by the present method are in good agreement with the existing experimental and numerical results. It is observed that [0/θ]_s LCPs are very sensitive to the randomness in the crack length, applied load, transverse tensile strength of the laminate and modulus of elasticity of the material, so precise control of these parameters is important. The novelty of the present study is, the stochastic implementation in XFEM for the failure prediction of LCPs containing crack and voids.

• 품질경영학회지
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• 제46권2호
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• pp.327-338
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• 2018

Purpose: A risk evaluation procedure is proposed for common failure causes in FMEA(Failure Mode and Effects Analysis). The conventional FMEA does not provide a proper means to compare common failure causes with other failure causes. This research aims to develop a risk evaluation procedure in FMEA where common failure causes and other failure causes exist together. Methods: For each common failure cause, the effect of each combination of its resulting failures is recommended to be reevaluated considering their interactive worsening effect. And the probability that each combination of failures is incurred by the same common cause is also considered. Based on these two factors, the severity of each common cause is determined. Other procedures are similar to the conventional method. Results: The proposed procedure enables to compare and prioritize every failure cause. Thus, the common causes, each of which incurring two or more failures, and other causes, each of which is corresponding to one failure, can be fairly compared. Conclusion: A fair and proper way of comparing the common failure causes and other causes is provided. The procedure is somewhat complicated and requires more works to do. But it is worth to do.

• 대한전자공학회논문지SD
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• 제40권7호
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• pp.507-517
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• 2003

메쉬 기반의 파장분할다중화(WDM)망에서는 단 하나의 광섬유 케이블의 장애로도 심각한 데이터의 손실을 야기할 수 있다. 따라서, 이러한 장애에 대한 효율적인 복구 알고리즘이 필요하다 본 논문에서는 메쉬기반의 WDM 망에서의 복구 기법에 대한 새로운 알고리즘을 제안하였고 기존의 복구 기법과 비교하였다. 복구 방법으로는 경로 복구, 링크 복구의 대표적인 두 가지 기법이 있다. 이러한 기법들의 한 가지 공통점은 단일 링크장애에 대해서 논하고 있다는 것이다. 본 논문에서 제안한 복구 기법에서는 각각의 링크 장애에 대한 복구 경로를 확보하지 않는다. 메쉬 기반의 WDM망을 여러 개의 작은 폐루프로 분리하고 폐루프내에서 단일 링크 장애가 발생하면 그 폐루프를 우회하여 복구 경로가 결정되는 복구 기법과 복구 경로가 폐루프 내에서만 결정되는 복구 기법을 제안하였다. 경로 복구 기법과 링크 복구 기법과 더불어 제안된 기법의 성능을 비교하였다. 시뮬레이션 결과 제안된 두 기법은 비록 총 사용되는 파장 마일리지가 기존의 복구 기법보다 10%에서 50% 정도 증가하게 되지만 경로 설정에 소요되는 실행시간(CPU Time)은 경로 복구 기법과 링크 복구 기법에 비해 상당히 감소되는 결과를 얻게 되었다.

• Ocean Systems Engineering
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• 제8권4호
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• pp.409-426
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• 2018

This paper presents the strengthening of tubular joint by wrapping Carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). In this study, total number of layers, stacking sequence and length of wrapping are the different parameters involved when fiber reinforced polymers (FRP) composites are used for strengthening. For this, parameters where varied and results were compared with the reference joint. The best stacking sequence was identified which has the highest value in ultimate load with lesser deflections. For determining the best stacking sequence, numerical investigation was performed on CFRP composites; length of wrapping and number of layers were fixed. Later, the studies were focused on CFRP and GFRP strengthened joint by varying the total number of layers and length of wrapping. An attempt was done to propose a parametric equation from multiple regression analysis, which can be used for CFRP strengthened joints. Hashin failure criteria was used to check the failure of composites. Results revealed that FRP was having a greater influence in the load bearing capacity of joints, and in reducing the deflections and stresses of joint under axial compressive loads. It was also seen that, CFRP was far better than GFRP in reducing the stresses and deflection.

• Geomechanics and Engineering
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• 제13권6호
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• pp.977-995
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• 2017

It is well accepted that rock failure mechanism influence the cutting efficiency and determination of optimum cutting parameters. In this paper, an attempt was made to research the factors that affect the failure mechanism based on discrete element method (DEM). The influences of cutting depth, hydrostatic pressure, cutting velocity, back rake angle and joint set on failure mechanism in rock-cutting are researched by PFC2D. The results show that: the ductile failure occurs at shallow cutting depths, the brittle failure occurs as the depth of cut increases beyond a threshold value. The mean cutting forces have a linear related to the cutting depth if the cutting action is dominated by the ductile mode, however, the mean cutting forces are deviate from the linear relationship while the cutting action is dominated by the brittle mode. The failure mechanism changes from brittle mode with larger chips under atmospheric conditions, to ductile mode with crushed chips under hydrostatic conditions. As the cutting velocity increases, a grow number of micro-cracks are initiated around the cutter and the volume of the chipped fragmentation is decreasing correspondingly. The crack initiates and propagates parallel to the free surface with a smaller rake angle, but with the rake angle increases, the direction of crack initiation and propagation is changed to towards the intact rock. The existence of joint set have significant influence on crack initiation and propagation, it makes the crack prone to propagate along the joint.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 1996년도 춘계공동학술대회논문집; 공군사관학교, 청주; 26-27 Apr. 1996
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• pp.377-380
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• 1996

Most manufacturing systems are large and complex. It is natural to divide the control into a hierarchy consisting of a number fo different levels. Each levels is characterized by the length of the planning horizon and the kind of data required for the decision making process. This paper describes an approach for the incorporation of Maintenance times into a hierachical scheduling for a failure prone flexible manufacturing system. The Maintenance should not be performed too often because of the resulting reduction of capacity. The machine failure and preventive maintenance are considered simultaneously.

• Journal of Chest Surgery
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• 제21권2호
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• pp.347-350
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• 1988

Recent advances in the managements of chronic renal failure have increased the number of the candidates for cardiac operation in patients with chronic renal disease. There have been reports that the operative mortality of the open cardiac surgery in patients with end stage renal diseases was equal to that of the patients with normal renal function. Aortic valve replacement and mitral annuloplasty was successfully performed in a patient with chronic renal failure, and the pre-and postoperative managements are presented.

• 한국항공우주학회지
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• 제45권2호
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• pp.92-98
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• 2017

열분해 현상을 겪는 고분자 복합재료의 내부에서는 기공이 형성되며, 이는 열기계적 거동에 영향을 미칠 수 있다. 본 논문에서는 기공이 형성된 복합재료의 분층형 삼차원 유한요소 모델을 개발하고 이를 이용하여 기공 탄성 및 파손 해석을 수행하였다. 유한요소 모델의 삼차원 확장 효과와 기공이 복합재료 내부에 미치는 영향을 확인하기 위하여 분층수와 기공도에 따른 분층형 유한요소 모델을 사용하였다. 해석 결과로서 유효 탄성 계수 및 기공 탄성 계수는 기공도가 0.5까지 증가함에 따라 최대 74.0%, 442.1%, 분층 수가 5까지 증가함에 따라 최대 98.7%, 37.2% 차이를 보였다. 또한, 초기 및 최종 파손 강도는 기공도에 따라 최대 88.2%, 90.0%, 분층에 따라 최대 87.5%, 171.8%까지 감소함을 확인하였다.

• 품질경영학회지
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• 제23권2호
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• pp.43-52
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• 1995

A replacement policy under two types of failures, repairable or irrepairable, is considered, In the policy, the system is replaced at the n-th failure if all the previous (n-1) failures are repairable; Otherwise it is replaced at the first irrepairable failure. Assuming that the j-th failure is repairable with probability ${\alpha}_j$ and minimal repairs are performed for repairable failures between replacements, we derive the expected cost rate through the application of NHPP in order to determine the optimal number $n^*$. The policy includes some previous studies as special cases.