• Title, Summary, Keyword: 한계하중

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An evaluation of influence factors based on the limit state design-AASHTO LRFD for structural analysis of shield tunnel segment lining (한계상태설계법-AASHTO LRFD를 적용한 쉴드터널 세그먼트 라이닝의 구조해석 영향인자 평가)

  • Kim, Yang-Woon;Kim, Hong-Moon;Kim, Hyun-Su;Lee, Seong-Won
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.1
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    • pp.99-118
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    • 2018
  • Recently, the limit state design method in the design of the structure is in global trend, but it is limited to a few structures in Korea. Since the introduction of the limit state design method has recently been attempted for tunnels, which are the main underground structures, it is surely necessary to understand the latest limit state design method. Therefore, based on the recently published AASHTO LRFD Road Tunnel Design and Construction Guide Specification (2017), structural load factors and load combinations were reviewed, and various factors which should be applied for the review of structures have been analyzed. In this study, utility tunnel section and subway tunnel sections used in Korea were analyzed by the limit state design method, and we have analyzed the direction of application of limit state design method through studying the tendency of member force by various influential factors such as ground conditions, load modifier and joint stiffness.

Analysis of Prestress Effect and Reliability of PSSC Composite Girder Bridge (PSSC 합성거더 교량의 프리스트레스 효과 및 신뢰도 해석)

  • Hwang, Chul-Sung;Paik, In-Yeol
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.6
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    • pp.214-224
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    • 2008
  • Member force, strain and stress distribution of a section are obtained for optimized standard 25m~45m PSSC composite bridge subjected to dead and live load in order to interpret the effect of prestressing and deformation of tendon. The stress and strain distribution and moment capacity are obtained for both noncomposite and composite section and for allowable stress limit state, yield limit state and strength limit state. Reliability analysis is conducted after assuming limit states for stress and flexural strength. The reliability index for standard PSSC composite bridge which is designed to satisfy the allowable stress for flexural strength are higher than 3.5 which is required reliability indexes on American code for LRFD. Reliability of PSSC girder which is designed based on allowable stress of bridge design code is high for flexural strength.

Mis-Match Limit Load Analyses and Approximate J-Integral Estimates for Similar Metal Weld with Weld-Center Crack Under Tension Load (용접부 중앙에 표면균열이 존재하는 인장 평판에 대한 강도 불일치 한계하중 해석 및 간략 J-적분 예측)

  • Song, Tae-Kwang;Kim, Yun-Jae;Kim, Jong-Sung;Jin, Tae-Eun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.32 no.5
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    • pp.411-418
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    • 2008
  • In this work, the effect of strength mismatch on plastic limit loads is quantified for similar metal weld plates with cracks under tension load, via three-dimensional, small strain elastic-perfectly plastic finite element analyses. Relevant variables related to plate geometry and crack length are systematically varied, in addition to the weld width. An important finding is that mis-match limit loads can be uniquely quantified through strength mis-match ratio and one geometry-related parameter. Based on the proposed limit load solutions, reference stress based J-integral estimates is also investigated. When the reference stress is defined by the mis-match limit load, predicted J-integral values agree overall well with FE results.

Dynamic Frictional Behavior of Artificial Rough Rock Joints under Dynamic Loading (진동하중 하에서 거친 암석 절리면의 동력 마찰거동)

  • Jeon Seok-Won;Park Byung-Ki
    • Tunnel and Underground Space
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    • v.16 no.2
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    • pp.166-178
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    • 2006
  • Recently, the frequency of occurring dynamic events such as earthquakes, explosives blasting and other types of vibration has been increasing. Besides, the chances of exposure for rock discontinuities to free faces get higher as the scale of rock mass structures become larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, artificially fractured rock joint specimens were prepared in order to examine the dynamic frictional behavior of rough rock joint. Roughness of each specimen was characterized by measuring surface topography using a laser profilometer and a series of shaking table tests was carried out. For mated joints, the static friction angle back-calculated ken the yield acceleration was $2.7^{\circ}$ lower than the tilt angle on average. The averaged dynamic friction angle for unmated joints was $1.8^{\circ}$ lower than the tilt angle. Displacement patterns of sliding block were classified into 4 types and proved to be related to the first order asperity of rock joint. The tilt angle and the static friction angle for mated joints seem to be correlated to micro average inclination angle which represents the second order asperity. The tilt angle and the dynamic friction angle for unmated Joints, however, have no correlation with roughness parameters. Friction angles obtained by shaking table test were lower than those by direct shear test.

Mechanical strength of Zirconia Abutment in Implant Restoration (지르코니아 임플란트 지대주의 기계적 강도에 관한 연구)

  • Shin, Sung-ae;Kim, Chang-Seop;Cho, Wook;Jeong, Chang-Mo;Jeon, Young-Chan;Yun, Ji-Hoon
    • Journal of Dental Rehabilitation and Applied Science
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    • v.25 no.4
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    • pp.349-360
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    • 2009
  • Purpose: As the esthetic demands of dental implant patients are increased, the demands of zirconia as implant abutment material are also increased. It has non-metalic color, good biocompatibility, high strength and high toughness. Even thought the advatage of zirconia abutment, there are a few studies about mechanical properties of zirconia abutment. This study evaluated the mecanical strength with compressive bending strength and endurance limit of implant-zirconia abutment assembly. Materials and Methods: Static and cyclic loading of implant-Zirconia abutment assembly were simulated under worst case condition according to ISO. Test groups were implants of external butt joint with straight regular diameter and angled regular diameter zirconia abutment, implant of external butt joint with narrow straight diameter zirconia abutment and implant of internal conical joint with straight narrow diameter zirconia abutment. All test group were evaluated the mecanical strength with compressive bending strength and endurance limit. After fatique testing, fracture surface were examined by SEM. Results: The compressive bending strengths exceed 927N. Regular diameter zirconia abutment were stronger than narrow diameter zirconia abutment(P<.05). The endurance limits ranged from 503N to 868N. Conclusion: Within the limitation of this study, zirconia implant abutment exceeded the estabilished values for maximum incisal biting forces reported in the literature.

The Critical Repeated Stress and Behavior of the Isotropic Normally Consolidated Clays Subjected to Repeated Loads. (반복하중을 받는 등방정친압밀점토의 거동 및 한계반복응력)

  • 김팔규;송전섭
    • Geotechnical Engineering
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    • v.4 no.3
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    • pp.43-52
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    • 1988
  • The behavior of clays subjected to Repeated loading has been shown to be very different from the behavior under a single load application. Especially the behavior of pore water pressure is Qf considerable importance. The objective of this work is to experimentally study the stress-strain characteristics of clays, and this study includes the pore water pressure which is built up during the load repetition. For this study, the samples were consolidated isotropically in the triaxial cell during 24 hours, .and monotonic strain controlled triaxial test is carried out by uslng the tests of Compression failure, Cycled at failure, and Nonfailure equilibrium on remoulded samples under undrained .condition . Consequently there exists a critical level of repeated loading which seperates the behavior of a particular sample into two distinctly different patterns.

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Redistribution of Negative Moments in Beams Subjected to Lateral Load (횡하중에 대한 휨재의 부모멘트 재분배)

  • Eom, Tae-Sung
    • Journal of the Korea Concrete Institute
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    • v.23 no.6
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    • pp.731-740
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    • 2011
  • Provisions for the redistribution of negative moments in KCI 2007 and ACI 318-08 use a method for continuous flexural members subjected to uniformly-distributed gravity load. Moment redistributions and plastic rotations in beams of reinforced concrete moment frames subjected to lateral load differ from those in continuous flexural members due to gravity load. In the present study, a quantitative relationship between the moment redistribution and plastic rotation is established for beams subjected to both lateral and gravity loads. Based on the relationship, a design method for the redistribution of negative moments is proposed based on a plastic rotation capacity. The percentage change in negative moments in the beam was defined as a function of the tensile strain of re-bars at the section of maximum negative moment, which is determined by a section analysis at an ultimate state using KCI 2007 and ACI 318-08. Span, reinforcement ratio, cracked section stiffness, and strain-hardening behavior substantially affected the moment redistribution. Design guidelines and examples for the redistribution of the factored negative moments determined by elastic theory for beams under lateral load are presented.

Behavior of Elastic and Plastic Limit Loads of Thinned Elbows Observed During Real-Scale Failure Test Under Combined Load (감육엘보 실증실험에서의 탄성 및 소성 한계하중 거동 고찰)

  • Lee, Sung-Ho;Lee, Jeong-Keun;Park, Chi-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.9
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    • pp.1293-1298
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    • 2010
  • In most power plants, wall thinning in carbon-steel pipes due to flow-accelerated corrosion is one of the major aging phenomena, and it reduces the load-carrying capacity of the piping system. Various types of wall-thinning defects were manufactured in real-scale elbows, and monotonic in-plane bending tests were performed under internal pressure to evaluate the failure behavior of the elbows. In this paper, the behavior of elastic and plastic limit leads of locally thinned elbows in a real-scale failure test is presented. The loads determined on the basis of TES (twice elastic slope) were considered to be the limit loads of locally thinned elbows so that the integrity of the thinned elbows could be maintained, even when a small amount of plastic deformation might have occurred.

Development of a Short-term Failure Assessment of High Density Polyethylene Pipe Welds - Application of the Limit Load Analysis - (고밀도 폴리에틸렌 융착부에 대한 단기간 파손 평가법 개발 - 한계하중 적용 -)

  • Ryu, Ho-Wan;Han, Jae-Jun;Kim, Yun-Jae;Kim, Jong-Sung;Kim, Jeong-Hyeon;Jang, Chang-Heui
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.4
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    • pp.405-413
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    • 2015
  • In the US, the number of cases of subterranean water contamination from tritium leaking through a damaged buried nuclear power plant pipe continues to increase, and the degradation of the buried metal piping is emerging as a major issue. A pipe blocked from corrosion and/or degradation can lead to loss of cooling capacity in safety-related piping resulting in critical issues related to the safety and integrity of nuclear power plant operation. The ASME Boiler and Pressure Vessel Codes Committee (BPVC) has recently approved Code Case N-755 that describes the requirements for the use of polyethylene (PE) pipe for the construction of Section III, Division 1 Class 3 buried piping systems for service water applications in nuclear power plants. This paper contains tensile and slow crack growth (SCG) test results for high-density polyethylene (HDPE) pipe welds under the environmental conditions of a nuclear power plant. Based on these tests, the fracture surface of the PENT specimen was analyzed, and the fracture mechanisms of each fracture area were determined. Finally, by using 3D finite element analysis, limit loads of HDPE related to premature failure were verified.