• Title, Summary, Keyword: 한계하중

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Stochastic Reliability Analysis of Armor Units of Rubble-Mound Breakwaters Subject to Multiple Loads (다중하중에 따른 경사제 피복재의 추계학적 신뢰성 해석)

  • Lee, Cheol-Eung
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.24 no.2
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    • pp.138-148
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    • 2012
  • A stochastic reliability analysis model has been developed for evaluating the time-dependent stability performance of armor units of rubble-mound breakwaters subjected to the multiple loads of arbitrary magnitudes which could be occurred randomly. The initial structural capacities and the damage rates of armor units of rubble-mound breakwaters could be estimated as a function of the incident wave height with a given return period by using the modified Hudson's formula and Melby's formula. The structural stability performances of armor units of rubble-mound breakwaters could be analyzed in detail through the lifetime reliability investigations according to the limit states such as the serviceability or ultimate limit state and the conditions of multiple loads. Finally, repair intervals for the structural management of armor units of rubble-mound breakwaters could quantitatively be evaluated by a new approach suggested in this paper that has been based on the target probability for repair and the accumulated probabilities of failure obtained from the present stochastic reliability analysis model.

Fracture Mechanics Assessment for Different Notch Sizes Using Finite Element Analysis Based on Ductile Failure Simulation (유한요소 연성파손 모사기법을 이용한 노치 결함 반경 크기에 따른 파괴역학적 평가)

  • Bae, Keun Hyung;Jeon, Jun Young;Han, Jae Jun;Nam, Hyun Suk;Lee, Dae Young;Kim, Yun Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.8
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    • pp.693-701
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    • 2016
  • In this study, notch defects are evaluated using fracture mechanics. To understand the effects of notch defects, FE analysis is conducted to predict the limit load and J-integral for middle-cracked and single-edge cracked plates with various sizes of notch under tension and bending. As the radius of the notch increases, the energy release rate also increases, although the limit load remains constant. The values of fracture toughness($J_{IC}$) of SM490A are determined for various notch radii through FE simulation instead of conducting an experiment. As the radius of the notch increases, the energy release rate also increases, together with a more significant increase in fracture toughness. To conclude, as the notch radius increases, the resistance to crack propagation also increases.

Evaluation of Shape Parameter Effect on the J-R Curve of Curved CT Specimen Using Limit Load Method (한계하중법을 이용한 Curved CT 시험편의 파괴저항곡선에 미치는 형상변수 영향 평가)

  • Shin, In Hwan;Park, Chi Yong;Seok, Chang Sung;Koo, Jae Mean
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.7
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    • pp.757-764
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    • 2014
  • In this study, the effect of shape parameters on the J-R curves of curved CT specimens was evaluated using the limit load method. Fracture toughness tests considering the shape factors L/W and $R_m/t$ of the specimens were also performed. Thereafter, the J-R curves of the curved CT specimens were compared using the J-integral equation proposed in the ASTM (American Society for Testing and Materials) and limit load solution. The J-R curves of the curved CT specimens were also compared with those of the CWP (curved wide plate), which is regarded to be similar to real pipe and standard specimens. Finally, the effectiveness of the J-R curve of each curved CT specimen was evaluated. The results of this study can be used for assessing the applicability of curved CT specimens in the accurate evaluation of the fracture toughness of real pipes.

A Study on the Determination of Bearing Capacity of Soft Silty Ground and Polluted Silty Ground with Wastewater and Factory Waste Oil (연약한 실트지반과 생활오폐수와 공장폐유로 오염된 실트지반의 지지력 결정에 관한 연구)

  • Ahn, Jong-Pil;Park, Sang-Bum
    • Journal of the Korean Geotechnical Society
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    • v.24 no.4
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    • pp.5-13
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    • 2008
  • Laboratory model test with soft silty ground (ML) and polluted silty ground with wastewater and factory waste oil ($ML_p$) was conducted and the applicability of changes of bearing capacity from the increase of pollutants was compared and analyzed with existing findings. As silty ground polluted with wastewater and factory waste oil had increased contents of pollutants, plasticization of ground was fostered compared to soft silt ground due to the influence of pollutants, and characteristics of ground strength decreased. Critical surcharge value of soft silty ground $q_{cr}=4.14c_u$, ultimate bearing capacity value $q_{ult}=9.53c_u$, critical surcharge value of silty ground polluted with wastewater and factory waste oil $q_{cr}=1.78c_u$ and ultimate bearing capacity value $q_{ult}=4.39c_u$. Critical surcharge and ultimate bearing capacity of silty ground polluted with wastewater and factory waste oil were less than those of soft silty ground. It meant that shearing resistance due to the increase of pollutants decreased and rather a smaller value was obtained.

Assessment of Partial Safety Factors for Limit States Design of Foundations (한계상태설계법의 기초설계 적용을 위한 부분안전계수의 평가)

  • Kim Bum-Joo
    • Journal of the Korean Geotechnical Society
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    • v.20 no.9
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    • pp.77-89
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    • 2004
  • While limit states design (LSD) is currently the standard structural design practice, it is relatively new in the geotechnical design. Adoption of LSD far geotechnical design is an international trend. In the present study, various LSD codes from the United States, Canada, and Europe were reviewed. A simple first-order-second-moment (FOSM) reliability analysis was performed to determine theoretically the ranges of load and resistance factor values for representative loads and foundation bearing capacity, respectively. In order for foundation design to be consistent with current structural design practice, it would be desirable to use the same loads, load factors and load combinations. The values of load factor, obtained from the FOSM analysis, were found to be generally consistent with those given in the codes, whereas the values of resistance factor indicated overall lower ranges due to high values of coefficient of variation used in the analysis. Since the degree of uncertainties included in bearing capacity of foundations varies with the methods used to estimate the bearing capacity, different values of resistance factor should be used fur different methods. For the purpose, continuous efforts are needed to be made first to accurately identify and quantify the uncertainties in the methods.

Analysis and Test for Turn-buckle of Capacity for Measuring Tensile Force (용량별 인장력 측정용 턴버클의 해석 및 실험)

  • Shin, Kyung-Jae;Lee, Swoo-Heon;Lee, Hee-Du
    • Journal of Korean Society of Steel Construction
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    • v.23 no.6
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    • pp.715-724
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    • 2011
  • A turn buckle inserted between tension members that sustain the structural loads in a suspension structure system is a device that is capable of adjusting the tensile force. The tension member is an important element of a tension structure, but no simple and economical method of measuring a tensile force applied to members has been proposed yet. Thus, a turn buckle for measuring the tensile force in a tension member was developed in this study. The turn buckles of the measurement limit loads of 100kN, 200kN, and 300kN were tested through a theoretical analysis and a finite element analysis. There was no significant difference in the results of the theoretical analysis, FEA, and the test. In addition, the ultimate strength of the turn buckle using FEA showed that a new turn buckle is sufficiently safe to use even when there is a five-times overload in the measurement limit load.

Reliability Analysis Offshore Wind Turbine Support Structure Under Extreme Ocean Environmental Loads (극한 해양 환경하중을 고려한 해상풍력터빈 지지구조물의 신뢰성 해석)

  • Lee, Sang Geun;Kim, Dong Hyawn
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.26 no.1
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    • pp.33-40
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    • 2014
  • Reliability analysis of jacket type offshore wind turbine (OWT) support structure under extreme ocean environmental loads was performed. Limit state function (LSF) of OWF support structure is defined by using structural dynamic response at mud-line. Then, the dynamic response is expressed as the static response multiplied by dynamic response factor (DRF). Probabilistic distribution of DRF is found from response time history under design significant wave load. Band limited beta distribution is used for internal friction angle of ground soil. Wind load is obtained in the form of thrust force from commercial code called GH_Bladed and then, applied to tower hub as random load. In a numerical example, the response surface method (RSM) is used to express LSF of jacket type support structure for 5MW OWF. Reliability index is found using first order reliability method (FORM).

Plastic Limit Load Solutions for Circumferential Surface Cracked Cylinders Under Combined Loading (복합하중이 작용하는 원주방향 표면균열배관에 대한 소성한계하중식)

  • Shim, Do-Jun;Kim, Yun-Jae;Kim, Young-Jin;Hwang, Seong-Sik;Kim, Joung-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.9
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    • pp.1469-1476
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    • 2003
  • This paper provides plastic limit load solutions of cylinders with circumferential part-through surface cracks under combined axial tension, internal pressure and global bending. Such solutions are developed based on detailed three-dimensional (3-D) finite element (FE) limit analyses using elastic-perfectly-plastic material behaviour, together with analytical solutions based on equilibrium stress fields. For the crack location, both external and internal cracks are considered. Furthermore, in terms of the crack shape, both semi-elliptical and constant-depth surface cracks are considered. The resulting limit load solutions are given in a closed form, and thus can be easily used in practical situations. Being based on detailed 3-D FE limit analysis, the present solutions are believed to most reliable, and thus to be valuable information for integrity assessment of piping.

Plastic Limit Loads for Through-Wall Cracked Pipes Using 3-D Finite Element Limit Analyses (3차원 유한요소 한계해석을 이용한 관통균열 배관의 소성한계하중)

  • Huh Nam-Su;Kim Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.5
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    • pp.568-575
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    • 2006
  • The present paper provides plastic limit load solutions of axial and circumferential through-wall cracked pipes based on detailed three-dimensional (3-D) finite element (FE) limit analysis using elastic-perfectly-plastic behavior. As a loading condition, axial tension, global bending moment, internal pressure, combined tension and bending and combined internal pressure and bending are considered for circumferential through-wall cracked pipes, while only internal pressure is considered for axial through-wall cracked pipes. Especially, more emphasis is given for through-wall cracked pipes subject to combined loading. Comparisons with existing solutions show a large discrepancy in short through-wall crack (both axial and circumferential) for internal pressure. In the case of combined loading, the FE limit analyses results show thickness effect on limit load solutions. Furthermore, the plastic limit load solution for circumferential through-wall cracked pipes under bending is applied to derive plastic $\eta\;and\;{\gamma}$-factor of testing circumferential through-wall cracked pipes to estimate fracture toughness. Being based on detailed 3-D FE limit analysis, the present solutions are believed to be meaningful fur structural integrity assessment of through-wall cracked pipes.

Limit Load and Fully Plastic Stress Analysis for Circular Notched Plates and Bars Using Fully Plastic Analysis (완전소성해석을 이용한 원형노치 인장시편의 한계하중 및 완전소성응력장 해석)

  • Oh Chang-Kyun;Myung Man-Sik;Kim Yun-Jae;Park Jin-Moo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.12
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    • pp.1605-1614
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    • 2005
  • For the last four decades, tension test of notched bars has been performed to investigate the effect of stress triaxiality on ductile fracture. To quantify the effect of the notch radius on stress triaxiality, the Bridgman equation is typically used. However, recent works based on detailed finite element analysis have shown that the Bridgman equation is not correct, possibly due to his assumption that strain is constant in the necked ligament. Up to present, no systematic work has been performed on fully plastic stress fields for notched bars in tension. This paper presents fully plastic results for tension of notched bars and plates in plane strain, via finite element limit analysis. The notch radius is systematically varied, covering both un-cracked and cracked cases. Comparison of plastic limit loads with existing solutions shows that existing solutions are accurate for notched plates, but not for notched bars. Accordingly new limit load solutions are given for notched bars. Variations of stress triaxiality with the notch radius and depth are also given, which again indicates that the Bridgman solution for notched bars is not correct and inaccuracy depends on the notch radius and depth.