• 한국지반공학회논문집
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• 제21권6호
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• pp.5-18
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• 2005

본 연구에서는 배수면으로부터의 거리에 따라 점진적으로 진행되는 압밀이 차후의 압밀 거동에 미치는 영향에 대하여 고찰하였다. 이를 위해 압밀진행에 따른 위치 별 투수계수 및 부피압축계수의 변화를 고려할 수 있는 유한차분 압밀해석기법 및 프로그램을 개발하였다. 개발된 해석 프로그램을 이용하여 간극비 변화에 따른 투수계수와 부피압축 켸수의 변화 정도가 다른 다양한 특성의 지반에 대하여 연직배수재가 설치된 모형지반의 압밀거동을 분석하였다. 또한 실제 지반조건에서의 영향 정도를 살펴보기 위하여, 낙동강 하구의 정규압밀 점성토 및 재성형 카올리나이트의 지반 특성을 근간으로 입력치를 결정, 해석을 수행하여 위치 별 점진적 압밀에 의한 영향을 분석하였다. 해석 결과 점진적 압밀 진행에 따른 압밀 지체가 현장의 압밀 거동 이해에 매우 중요하며, 또한 압밀 초기에, 소성성이 크고, 재하하중이 클수록 현저하게 나타남을 알 수 있었다.

• 한국정밀공학회지
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• 제15권6호
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• pp.22-32
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• 1998

This paper describes a research work of developing a computer-aided design of irregularly shaped-sheet metal product with bending and piercing operation for progressive working. An approach to the CAD system is based on the knowledge-based rules. Knowledge for the CAD system is formulated from plasticity theories, experimental results and the empirical knowledge of field experts. The system has been written in AutoLISP on the AutoCAD with a personal computer and is composed of five main modules, which are input and shape treatment, flat pattern-layout, production feasibility check, blank-layout, and strip-layout module. Based on knowledge-based rules, the system is designed by considering several factors, such as radius and angle of bend, material and thickness of product, complexities of blank geometry and punch profile, and availability of press. This system is capable of unfolding a formed sheet metal part to give flat pattern and automatically account for the adjustment of bend allowances to match tooling requirements by checking dimensions and the best utilization ratio of blank-layout within bending production feasibility area which is beyond ${\pm}30^{\circ}$ degrees intersecting angle between grain flow and bending edge line and which is suitable to progressive bending operation. Also the strip-layout drawing generated by a bending and a piercing operation according to punch profiles divided into automatically for external area of irregularly shaped-sheet metal product is displayed in graphic forms.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.389-392
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• 1999

Fatigue is a process of progressive permanent internal structural change in a material subjected to repeitive stresses. These change may be damaging and result in progressive growth of cracks and complete fracture if the stress repetitins are sufficiently large. For structural members subjected to cyclic loads, the continuous and irrecoverable damage processes are taking place. These processes are referred as the cumulative damage processes due to fatigue loading. Moreover, increased use of high strength concrete makes the fatigue problem more important because the cross-section and dead weight are reduced by using high strength concrete. The purpose of this study is to investigate the shear fatigue behavior of reinforced concrete beams according to shear reinforcement ratio and concrete compressive strength under repeated loadings. For this purpose, comprehensive static and fatigue tests of reinforced concrete beams were conducted. The major test variables for the fatigue teats are the concrete strength and the amount of shear reinforcements. The increase of deflections and steel strains according to load repetition has been plotted and analyzed to explore the damage accumulation phenomena of reinforced concrete beams. An analytical model for shear fatigue behavior has been introduced to analyze the damage accumulation under fatigue loads. The failure mode and fatigue lives have been also studied in the present study. The comparisons between analytical results and experimental data show good correlation.

• 소성∙가공
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• 제22권8호
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• pp.442-449
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• 2013

The solenoid valve case of an 8-speed automatic transmission plays a role in maintaining the valve seal, which prevents an inflow of foreign substances into the transmission. The seal increases the reliability of the automatic transmission's performance. As a solution to pollution-related problems and to reduce fuel consumption, transmissions are being made with more gears to work more economically and have reduced fuel consumption. These newer transmission require greater dimensional tolerances and need to be manufactured with more precision. In the current study, the design of a multistage drawing considering both the product's height and limit draw ratio (LDR) of the material was performed using both a theoretical analysis and the expertise of industrial experts. The finite element modeling (FEM) simulation was performed using the commercial software, PAM-stamp, and tests of the dimensional measurements for a prototype were performed to verify the optimal progressive process.

• Steel and Composite Structures
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• 제28권2호
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• pp.209-221
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• 2018

An empirical and efficient method is presented for calculating the dynamic increase factor to amplify the applied loads on the affected bays of a steel frame structure with semi-rigid connections. The nonlinear static alternate path analysis is used to evaluate the dynamic responses. First, the polynomial models of the extended end plate and the top and seat connection are modified, and the proposed polynomial model of the flush end plate connection shows good agreement as compared with experimental results. Next, a beam model with nonlinear spring elements and plastic hinges is utilized to incorporate the combined effect of connection flexibility and material nonlinearity. A new step-by-step analysis procedure is established to obtain quickly the dynamic increase factor based on a combination of the pushdown analysis and nonlinear dynamic analysis. Finally, the modified dynamic increase factor equation, defined as a function of the maximum ratio value of energy demand to energy capacity of an affected beam, is derived by curve fitting data points generated by the different analysis cases with different column removal scenarios and five types of semi-rigid connections.

• Structural Engineering and Mechanics
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• 제74권1호
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• pp.69-82
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• 2020

A significant defect of space structures is the progressive collapse issue which may restrict their applicability. Force limiting devices (FLDs) have been designed to overcome this deficiency, though they don't operate efficiently in controlling the force displacement characteristics. To overcome this flaw, a new type of FLD is introduced in the present study. The "all steel accordion force limiting device" (AFLD) which consists of three main parts including cylindrical accordion solid core, tubular encasing and joint system is constructed and its behavior has been studied experimentally. To improve AFLD's behavior, Finite element analysis has been carried out by developing models in ABAQUS software. A comprehensive parametric study is done by considering the effective design parameters such as core material, accordion wave length and accordion inner diameter. From the results, it is found that AFLD can obtain a perfect control on the force-displacement characteristics as well as attaining the elastic-perfect plastic behavior. Obtaining higher levels of ultimate load carrying capacity, dissipated energy and ductility ratio can be encountered as the main privileges of this device. Ease of construction and erection are found to be further advantages of AFLD. Based on the obtained results, a procedure for predicting AFLD's behavior is offered.

• Steel and Composite Structures
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• 제12권3호
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• pp.231-248
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• 2012

This research aims to investigate the structural behavior of concentrically braced frames after element loss by performing nonlinear static and dynamic analyses such as Time History Analysis (THA), Pushdown Analysis (PDA), Vertical Incremental Dynamic Analyses (VIDA) and Performance-Based Analysis (PBA). Such analyses are to assess the potential and capacity of this structural system for occurrence of progressive collapse. Besides, by determining the Failure Overload Factors (FOFs) and associated failure modes, it is possible to relate the results of various types of analysis in order to save the analysis time and effort. Analysis results showed that while VIDA and PBA according to FEMA 356 are mostly similar in detecting failure mode and FOFs, the Pushdown Overload Factors (PDOFs) differ from others at most to the rate of 23%. Furthermore, by sensitivity analysis it was observed that among the investigated structures, the eight-story frame had the most FOF. Finally, in this research the trend of FOF and the FOF to critical member capacity ratio for the plane split-X braced frames were introduced as a function of the number of frame stories.

• 한국산학기술학회논문지
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• 제9권3호
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• pp.569-573
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• 2008

본 논문에서는 픽업프레임의 스트립 레이아웃 도를 작성하였다. 프레스 금형에 있어서 스트립 레이아웃 도는 제품 양산을 결정하는 중요 요인이다. 장착되는 다른 부품과의 간섭요인을 용이하게 수정하기 위하여 3D CAD/CAM 시스템을 적용하였다. 블랭크 레이아웃을 최적화하고 광폭배열로 스트립 레이아웃 하여 재료 이용률을 28.49%로 향상시켰다. 사용된 3D CAD/CAM 소프트웨어는 Unigraphics NX 4.0이며 12개 공정으로 스트립 레이아웃 도를 작성하였다.

• Steel and Composite Structures
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• 제50권1호
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• pp.107-122
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• 2024

Following an internal column failure, adjacent double-span beams above the failed column will play a critical role in the load transfer and internal force redistribution within the remaining structure, and the span-to-depth ratios of double-span beams significantly influence the structural resistance capacity against progressive collapse. Most existing studies have focused on the collapse-resistant performances of single-story symmetric structures, whereas limited published works are available on the collapse resistances of multi-story steel frames with unequal spans. To this end, in this study, numerical models based on shell elements were employed to investigate the structural behavior of multi-story steel frames with unequal spans. The simulation models were validated using the previous experimental results obtained for single- and two-story steel frames, and the load-displacement responses and internal force development of unequal-span three-story steel frames under three cases were comprehensively analyzed. In addition, the specific contributions of the different mechanism resistances of unequal-span, double-span beams of each story were separated quantitatively using the energy equilibrium theory, with an aim to gain a deeper level of understanding of the load-resistance mechanisms in the unequal-span steel frames. The results showed that the axial and flexural mechanism resistances were determined by the span ratio and linear stiffness ratio of double-span beams, respectively.

• 대한수의학회지
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• 제29권1호
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• pp.57-60
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• 1989

This study was carried out to evaluate the possibility of sex preselection by gradients methods using bovine serum albumin in rabbits. Artificial insemination was performed with sperm from the top and bottom layer of rabbit semen separated by bovine serum albumin gradients. Various characteristics of separated sperm, and the conception rate and secondary sex ratio at artificial insemination with separated sperm were compared. The results obtained were as follows. 1. The sperm from the bottom layer showed significanty high value in motility, percent of normal sperm and progressive motility as compared with control sperm and the sperm and the sperm from the top layer. 2. The conception rate of sperm from the bottom layer was higher than that of the top layer. But secondary sex ratio was not altered by this methods.