• Title/Summary/Keyword: 짧은 균열

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Tension Lap Splice Length in High-Strength Concrete Flexural Members (고강도 콘크리트 휨부재의 인장 겹침이음길이에 관한 연구)

  • Lee, Gi-Yeol;Kim, Woo;Lee, Hwa-Min
    • Journal of the Korea Concrete Institute
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    • v.21 no.6
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    • pp.753-761
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    • 2009
  • This paper presents the test results of total 24 beam-end specimens to investigate the effect of high-strength concrete and cover thickness on the development resistance capacity in tensile lap splice length regions. Based on bond characteristics that an increase in concrete strength results in higher bond stress and shortening of the transfer length, cracking behavior that thin cover thickness induced a splitting crack easily and brittle crack propagation, current design code that development length provisions as uniform bond stress assumption was investigated apply as it. The results showed that as higher strength concrete was employed, not only development resistance capacity was influenced by cover thickness, but also more sufficient safety factor reserved shorter than the lap splice length provision in current design code. From experimental research results, high-strength concrete development length was not inverse ratio of $\sqrt{f_{ck}}$ but directly inverse of $f_{ck}$, and it is also said that there is a certain limit length of the embedded steel over which the assumption of uniform bond stress distribution is valid specially for high-strength concrete not having a same embed length such as normal-strength concrete in current design criteria hypothesis.

Technical Consideration for Production Data Analysis with Transient Flow Data on Shale Gas Well (셰일가스정 천이유동 생산자료분석의 기술적 고려사항)

  • Han, Dong-kwon;Kwon, Sun-il
    • Journal of the Korean Institute of Gas
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    • v.20 no.1
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    • pp.13-22
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    • 2016
  • This paper presents development of an appropriate procedure and flow chart to analyze shale gas production data obtained from a multi-fractured horizontal well according to flow characteristics in order to calculate an estimated ultimate recovery. Also, the technical considerations were proposed when a rate transient analysis was performed with field production data occurred to only $1^{st}$ transient flow. If production data show the $1^{st}$ transient flow from log-log and square root time plot analysis, production forecasting must be performed by applying different method as before and after of the end of $1^{st}$ linear flow. It is estimated by an area of stimulated reservoir volume which can be calculated from analysis results of micro-seismic data. If there are no bottomhole pressure data or micro-seismic data, an empirical decline curve method can be used to forecast production performance. If production period is relatively short, an accuracy of production data analysis could be improved by analyzing except the early production data, if it is necessary, after evaluating appropriation with near well data. Also, because over- or under-estimation for stimulated reservoir volume could take place according to analysis method or analyzer's own mind, it is necessary to recalculate it with fracture modeling, reservoir simulation and rate transient analysis, if it is necessary, after adequacy evaluation for fracture stage, injection volume of fracture fluid and productivity of producers.

Case study on the Distributed Multi-stage Blasting using Stemming-Help Plastic Sheet and Programmable Sequential Blasting Machine (전색보호판과 다단발파기를 이용한 다단식분산발파의 현장 적용 사례)

  • Kim, Se-Won;Lim, Ick-Hwan;Kim, Jae-Sung
    • Explosives and Blasting
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    • v.31 no.2
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    • pp.14-24
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    • 2013
  • The most effective way of the rock removing works in the downtown area is to removing rocks by splitting the rock by blasting with small amount of explosives in the hole. However environmental factors not only limit the applications but also increase the forbidden area. As this is a distributed multi-stage blasting method and to reduce vibration by applying the optimized precisioncontrol-blasting method, it is applicable in all situations. The process is to fix the stemming-help plastic sheet to the hole entrance when stemming explosives and insert detonator and explosive primer with same delay time, two or three sets. This method is more efficient in the downtown area where claims and dispute from vibration are expected. This method is easily usable by designing blast pattern even in the area where delay time blasting is difficult after multi-stage explosive stemming due to short length of blast hole (1.2~3.0m) and there is no detonator wire shortage or dead-pressure.

The effect of random spectrum on the fatigue life of hybrid metal matrix composites (랜덤하중이 하이브리드 금속복합재료의 피로수명에 미치는 영향)

  • 김성훈;배성인;송정일
    • Composites Research
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    • v.16 no.6
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    • pp.48-55
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    • 2003
  • This research makes comparisons of empirical fatigue-lives between AC8A A1 alloy and the metal matrix composites(A1/A12O3, A1/A12O3/A12O3p), and also includes comparisons of fatigue-lives between empirical fatigue-lives and estimated fatigue-lives from regular-periodic load testing, AE method to predict fatigue-crack initiation before visible in sight and SEM(scanning electron microscope) photographs of each material. According to the test results of the notched specimen. the fatigue life of the hybrid metal matrix composites and the metal matrix composites, which are more brittle than the base matrix was shorter than that of the base matrix under both types of loads. In addition, the fatigue-life estimated from the damage summation method and that from experiments at random loads were fairly identical.

Out-of-Plane Shear Strength Models of SC Wall (SC 벽체의 면외 전단강도 특성)

  • Hon, Sung-Gul;Lee, Kyuong-Jin;Park, Dong-Soo;Kim, Won-Ki;Lee, Dong-Hun
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.04a
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    • pp.225-228
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    • 2008
  • This paper presents out-of-plane shear strength models for composite wall with steel plates based on limit theorem in the framework of the plasticity theory. The formulas proposed by JEAG 4618 need to be reconsidered with a couple of limitations; ignoring the effect of bond stress generated by studs in the process of calculating arch action, illogically discriminating between concrete shear cracking strength and arch strength by algebraic relation in short shear span ratio(0-2.0). In most cases, reinforcement ratio is not sufficient to yield, as a result, arch strength is determined by accounting equilibrium including both bond strength and concrete compressive strength. We conducted experimental research assuming that SC wall is a continuous beam under the simplified loading patterns, changing main valuables involving the number of studs, stirrups. The results show good agreements with the formula and we quoted the test results of JEAG.

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Experimental Evaluation of Internal Blast Resistance of Prestressed Concrete Tubular Structure according to Explosive Charge Weight (프리스트레스트 콘크리트 관형 구조물의 폭발량에 따른 내부폭발저항성능에 관한 실험적 평가)

  • Choi, Ji Hun;Choi, Seung Jai;Yang, Dal Hun;Kim, Jang-Ho Jay
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.39 no.3
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    • pp.369-380
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    • 2019
  • When a extreme loading such as blast is applied to prestressed concrete (PSC) structures and infrastructures for an instantaneous time, serious property damages and human casualties occur. However, a existing design procedure for PSC structures such as prestressed containment vessel (PCCV) and gas storage tank do not consider a protective design for extreme internal blast scenario. Particularly, an internal blast is much more dangerous than that of external blast. Therefore, verification of the internal blast loading is required. In this paper, the internal blast resistance capacity of PSC member is evaluated by performing internal blast tests on RC and bi-directional PSC scaled down specimens. The applied internal blast loads were 22.68, 27.22, and 31.75 kg (50, 60, and 70 lbs) ANFO explosive charge at 1,000 mm standoff distance. The data acquisitions include blast pressure, deflection, strain, crack patterns, and prestressing force. The test results showed that it is possible to predict the damage area to the structure when internal blast loading occurs in PCCV structures.

Stress Distributions at the Dissimilar Metal Weld of Safety Injection Nozzles According to Safe-end Length and SMW Thickness (안전단 길이 및 동종금속용접부 두께 변화에 따른 안전주입노즐 이종금속용접부의 응력분포)

  • Kim, Tae-Jin;Jeong, Woo-Chul;Huh, Nam-Su
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.10
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    • pp.979-984
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    • 2015
  • In the present paper, we evaluate the effects of the safe-end length and thickness of the similar metal weld (SMW) of safety injection nozzles on stress distributions at the dissimilar metal weld (DMW). For this evaluation, we carry out detailed 2-D axisymmetric finite element analyses by considering four different values of the safe-end length and four different values of the thickness of SMW. Based on the results obtained, we found that the SMW thickness affects the axial stresses at the center of the DMW for the shorter safe-end length; on the other hand, it does not affect the hoop stresses. In terms of the safe-end length, the values of the axial and hoop stresses at the inner surface of the DMW center increase as the safe-end length increases. In particular, for the cases considered in the present study, the stress distributions at the DMW center can be categorized according to certain values of safe-end length.

Fatigue Evaluation of Precast Concrete Deck Connection using Ultra-High Performance, Fiber Reinforced Concrete (초고성능 섬유보강 콘크리트를 적용한 프리캐스트 바닥판 접합부의 피로성능 평가)

  • Lee, Jun-Ki
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.2
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    • pp.275-285
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    • 2015
  • This experimental study presents the fatigue evaluation of a precast deck connected using Ultra-High Performance, Fiber Reinforced Concrete (UHPFRC). Four types of two identical large-scale specimens were fabricated with simplified splice rebar details which had a short splice length of ten times rebar diameter. The flexural behavior of each type of specimens until failure was investigated and fatigue behavior of the same type of specimens was then evaluated using two-million cyclic loading. In the flexural tests, tensile rebars exhibited the deformation exceeding yielding strain but failure mode related to the splice details was not observed in spite of such a short splice length. In the fatigue tests, damage was not appreciably accumulated by the cyclic loading except initial flexural cracks and the stress variations in tensile rebars was less than the allowable stress range. These experimental results demonstrate that all types of specimens exhibited acceptable fatigue performance and indicate that enhanced mechanical properties of ultra-high performance material permits to use a simplified splice details along with short joint width.

Analyses of Scenarios Based on a Leakage of Highly Compressed Air and Fire Anticipated in CAES (Compressed Air Energy Storage) Facility (압축공기에너지저장 시설에서 발생 가능한 압축공기 유출 및 화재 시나리오 분석)

  • Yoon, Yong-Kyun;Ju, Eun-Hye
    • Tunnel and Underground Space
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    • v.25 no.6
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    • pp.568-576
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    • 2015
  • In this study, scenarios based on the leakage of highly compressed air and fire occurrence turned out to be high risks in an operation stage of CAES facility were constructed and estimated. By combining Bernoulli equation with momentum equation, an expression to calculate an impact force of a jet flow of compressed air was derived. An impact force was found to be proportional to the square of diameter of fracture and the pressure of compressed air. Four types of fire scenarios were composed to evaluate an effects that seasonal change and location of fire source have on the spread behavior of smoke. Smoke from the fire ignited in the vicinity of CAES opening descended more quickly below the limit line of breathing than one from the fire occurred 10 m away from CAES opening, which is expected to occur due to a propagation of wave front of smoke. It was shown that a rate of smoke spread of the winter fire is faster than one of the summer fire and smoke from the winter fire spreads farther than one of the summer fire, which are dependent on the direction of air flow into access opening. Evacuation simulation indicated that the required safe evacuation time(RSET) of the summer and winter fires are 262, 670 s each.

A Study on the Cyclic Hardening Property and the Low Cycle Fatigue Behavior of Marine Materials (박용재료(舶用材料)의 반복경화(反復硬化) 및 저(低)싸이클 피로특성(疲勞特性)에 관한 연구)

  • S.M. Cho;K. Horikawa
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.1
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    • pp.108-116
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    • 1991
  • In the non-linear behavior of many materials, there is difference between the monotonic behavior by static load and the cyclic behavior by cyclic load. In particular, the short fatigue cracks to propagate in elasto-plastic stress concentrations(notches), are governed significantly by the cyclic behavior of materials. Accordingly, it is needed to investigate and compare the monotonic and cyclic behavior of materials. In the pressent study, the stress-strain relations of materials by monotonic and cyclic load tests were examined for 2 kinds of steels(SS41, HT80) and 5 kinds of Al-alloys(A5083-O, A6N01-T5, A7N01-T4, A7016-T6, A7178-T6). And the constants for mechanical properties of the materials were determined by experimental results, Moreover, when a notch was subjected to cyclic load, the effect of cyclic hardening property of materials on the variation of stress-strain amplitude in the notch tip was discussed by the application of Neuber's rule and experiments for a center notched plate.

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