다양한 개구부 모서리 균열제어 상세를 갖는 벽체의 면내 전단거동

왕혜린,양근혁,윤현섭 대한건축학회 2023 대한건축학회논문집 Vol.39 No.5

This study examined the effect of different crack-control approaches at the opening corners on the in-plane shear response of reinforcedconcrete walls. The conventional diagonal bar arrangement, stress dispersion shell plate, and crack-control strip were considered at eachopening corner to mitigate the localized diagonal tension cracks at the re-entrants. Four wall specimens were tested under cyclic in-planelateral loads. Test results showed that the failure modes and lateral load-displacement relationship of wall specimens were marginally affectedby the crack-control approaches considered at the opening corners. Meanwhile, the crack-control strip was more promising than the otherapproaches in restricting the propagation of diagonal shear cracks at opening corners. The in-plane shear strength of walls with an openingcould be reasonably predicted by the ACI 3I8-I9 equation. 이 연구에서는 철근콘크리트 벽체의 면내 전단 거동에 대한 개구부 모서리에서의 균열제어 보강방법에 대한 영향을 검토하였다. 개구부 모서리에서는 국부적인 경사 균열을 완화하기 위해 기존의 경사철근, 응력분산 곡면판 및 균열제어 띠의 보강이 고려되었다. 4개의 벽체는 반복 면내 하중을 받도록 실험되었다. 실험결과 벽의 파괴모드 및 횡하중-횡변위 관계는 개구부 모서리 균열제어 보강재에 대한 영향이 미미하였다. 한편, 균열제어 띠는 개구부 모서리 경사균열 진전을 억제하는 데에 다른 보강재 대비 효과적이었다. 개구부가 있는 벽체의 면내 전단강도는 ACI 318-19의 따라 더 합리적으로 예측할 수 있었다.

철근콘크리트 보의 간접 균열제어를 위한 최대 철근간격 제안

이기열(Lee Kiyeol),이민희(Lee Minhi) 한국방재학회 2018 한국방재학회논문집 Vol.18 No.6

이 논문은 철근콘크리트 보의 균열폭을 직접 계산하지 않고 사용성능을 검토할 수 있는 간접균열제어의 방법인 최대 철근간격을 철근응력 수준별로 새롭게 제안한 것이다. 균열폭 이론에 기반한 계산식에 철근과 콘크리트의 부착특성과 균열거동을 반영한 균열간격 및 인장강화효과를 이용하여 철근간격을 계산할 수 있는 식을 유도하였다. 이 식으로부터 사용하중에 따른 철근응력 수준별로 단면깊이의 변화에 영향을 받지 않는 최대 철근간격을 새롭게 산정하였다. 이와 함께 콘크리트 압축강도의 증가를 반영할 수 있는 보정계수를 추가적으로 제안하였다. 제안된 최대 철근간격은 복잡한 균열폭 계산식을 대체할 수 있으며, 간접균열제어에 의한 철근콘크리트 보의 사용성능 검토의 적용성을 개선하였다. This paper proposes a maximum bar spacing according to the steel stress level as an indirect crack control for the verification of serviceability performance without calculating the crack width in a reinforced concrete beam. Based on the crack width theory, a new formulation that can calculate the bar spacing using the crack spacing and tension stiffening effect was derived by considering the bond characteristics and cracking behavior. From this equation, the maximum bar spacing, which is not affected by the change in section height, was newly calculated for each level of steel stress according to the service load. In addition, a correction factor was proposed to consider the increase in concrete strength. The proposed maximum bar spacing can replace the complex crack width calculation and improve the application and serviceability performance of reinforced concrete beams through indirect crack control.

습윤양생 장치를 이용한 아파트 측벽 균열제어에 관한 연구

김대건 ( Kim Dae-geon ),이동운 ( Lee Dong-woon ) 한국건축시공학회 2017 한국건축시공학회지 Vol.17 No.2

최근 국내 아파트의 외벽 거푸집공사의 경우 대부분 갱폼시스템을 통해 철근콘크리트 구조체를 시공하고 있다. 이러한 갱폼거푸집을 사용한 콘크리트의 경우는 거푸집 탈형후 외부환경에 노출되고 특히, 건조한 봄, 가을과 일사량이 높은 서중시기의 벽량이 많은 아파트 측벽에 다량의 균열이 발생되어지고 있다. 이에, 본 연구에서는 신축 아파트 건설현장 중심으로 균열량이 많은 아파트 측벽부분의 갱폼시스템에 습윤양생 자동설비장치를 적용하여 초기 콘크리트 양생에 필요한 수분을 공급함으로써 콘크리트의 품질확보와 다량의 측벽균열 저감을 통한 습윤양생 자동장치의 효율성 및 활용성을 검토하고자 하였는데, 그 결과, 양생 효과 및 낙수량 고려 시 습윤양생 자동장치에 0.3mm 사이즈의 노즐을 사용하여 살수양생을 실시할 경우, 자원낭비 없이 콘크리트의 품질향상 및 균열저감에 효과적인 것으로 판단되었다. In this study, moist curing equipment was used in the exist gang-form system. By achieving sufficient spray curing, the quality of the concrete was improved and the cracking occurred in building`s side wall was decreased. The following results could be made as the conclusion. For the compressive strength, all zones showed the similar results. Comparing with the zone without using moist curing equipment, the zone used moist curing equipment showed higher rebound hardness results. For the cracking, the zone utilized moist curing equipment showed the cracking averaged as 6.6m and the zone without using moist curing equipment showed the cracking averaged as 10.3m. The effectof reducing cracking by utilizing moist curing equipment is about 36%. Using moist curing equipment is considered as a good solution to reduce the cracking in the structure. Considering all the factors analysed, using moist curing equipment improved the quality of the concrete and decreased the cracking. When this equipment was used in the construction site, it is expected that the construction periodcan be shrunk and the ratio of defect caused by drying shrinkage can be decreased. In this research conditions, The 0.3mm sized moist curing equipment provided the most desirable results on concrete quality and preventing cracking.

노치 형상 및 장약조건의 변화에 따른 균열발생양상에 관한 연구

박승환(Seung-Hwan Park),조상호(Sang-Ho Cho),김승곤(Seung-Kon Kim),김광염(Kwang-Yeom Kim),김동규(Dong-Gyou Kim) 한국암반공학회 2010 터널과지하공간 Vol.20 No.1

암반발파에서 평활한 파단면을 확보하고 굴착손상영역을 제어하기 위하여 노치장약공을 이용한 균열제어 공법이 제안되었다. 본 연구에서는 노치형상과 장약조건이 균열발생 및 성장에 미치는 영향을 살펴보기 위하여 날개형 노치장약공을 갖는 발파모델을 구축하고 동적 파괴과정 해석법을 이용한 암반 파괴과정 해석을 수행하였다. 그 결과, 노치 길이가 증가함에 균열의 성장 길이가 증가하며 파단면의 거칠기가 감소하고 장약공 상하부에 손상균열의 발생이 억제되는 경향을 보였다. 해석결과로부터 노치 길이 및 개구 폭에 따른 응력집중계수의 변화 및 균열발생 양상을 비교 분석하여 균열제어에 미치는 영향인자에 대하여 고찰하였다. Crack-controlled blasting method which utilizes notched charge hole has been proposed in order to achieve smooth fracture plane and minimize the excavation damage zone. In this study, the blast models, which have a notched charge hole, were analyzed using dynamic fracture process analysis software to investigate the effect of the geometry of a notched charge hole and decoupling indexes of the charge hole on crack growth control in blasting. As a result, crack extension increased and damage crack decreased with the notch length. Ultimately, stress increment factors and resultant fracture patterns with different notch length and width were analyzed in order to examine the effect factors on the crack growth controlling in rock blasts using a notched charge hole.

비정질 강섬유보강콘크리트의 구속건조수축균열 특성

김선두(Kim, Seon-Du),최경규(Choi, Kyoung-Kyu),최세진(Choi, Se-Jin) 대한건축학회 2014 大韓建築學會論文集 : 構造系 Vol.30 No.7

In this study, free and restraint drying shrinkage tests of conventional and amorphous steel fiber-reinforced concrete were performed to investigate the shrinkage characteristics. To consider the effect of restraint condition of concrete on shrinkage cracking, three different test setups were used: ring type restraint test according to ASTM C 1581-04, dumbbell type restraint test according to KS F 2595, and modified dumbbell type restraint test with notches. Crack widths and strain profiles acquired from the tests were compared and investigated. The test results showed that the addition of amorphous steel fibers with 0.2-0.4% volume fraction into concrete resulted in 30% reduction of free drying shrinkage, 3-5 days delay of crack development time, and 20-60% reduction of crack width. Thus, it can be concluded that the amorphous steel fibers can be used for the purpose of crack control of concrete shrinkage cracking.

Statistical aspects of fatigue crack growth life of base metal, weld metal and heat affected zone in FSWed 7075-T651aluminum alloy

손혜정,Gunawan Dwi Haryadi,김선진 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.10

The statistical aspects of fatigue crack growth life of base metal (BM), weld metal (WM) and heat affected zone (HAZ) in friction stirwelded (FSWed) 7075-T651 aluminum alloy has been studied by Weibull statistical analysis. The fatigue crack growth tests were performedat room temperature on ASTM standard CT specimens under three different constant stress intensity factor range controls. Themain objective of this paper is to investigate the effects of statistical aspects of fatigue crack growth life on stress intensity factor rangesand material properties, namely BM, WM and HAZ specimens. In this work, the Weibull distribution was employed to estimate the statisticalaspects of fatigue crack growth life. The shape parameter of Weibull distribution for fatigue crack growth life was significantlyaffected by material properties and the stress intensity factor range. The scale parameter of WM specimen exhibited the lowest value atall stress intensity factor ranges.

Flexural and Shear Behavior of Steel Fiber Reinforced SCC Beams

Youcef Fritih,Thierry Vidal,Anaclet Turatsinze,Gérard Pons 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.6

This paper deals with the effect of steel fiber reinforcement on the behavior of Self-Compacting Concrete (SCC) beams. Bending tests were carried out to examine the effect of low fiber content (0.25% by volume) on the flexural behavior of beams with different amounts of steel rebar reinforcement. The study compares the behavior of reinforced concrete beams cast either with control SCC and the one of Fiber-Reinforced Self-Compacting Concrete (FRSCC). Fibers used were made of stainless amorphous metal. Their influence was studied through the global and local mechanical responses of the beams. The results show that fiber reinforcement allows the control of cracking to be improved. Yielding, ductility and load bearing capacity are not modified by the fiber reinforcement; its effects are limited to the kinetics and distribution of cracks. If it was observed that the used fiber content reduced stresses in the stirrups, they could not be considered as a solution to replace stirrups. However, their ability to transfer tensile stress through a crack provided greater beam stiffness, notably with a low steel bar reinforcement ratio. It was concluded that stainless steel fiber reinforcement is a suitable solution to control crack width in reinforced concrete elements in aggressive environments with respect to the limitations imposed by design codes such as the European code Eurocode 2.

Highly Complex Green Parts in Excellent Quality

Nies Norbert,Peters Detlef 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

SMS Meer GmbH, formerly Mannesmann and today part of the SMS Group, has been building powder presses since the early 1950s. The patents developed here in this field have long since documented the pioneering work carried out for the PM industry. The paper focuses on the challenge of reconciling the contradictory demands in the production of highly complex and crack-free PM parts. The process employed with the patented Controlled Punch Adapter (CPA) [1] counters possible cracking reliably and directly at the source. In this way is it possible to develop new and highly complex parts to series production maturity in a minimum of time even without simulation of the press cycle [2]. The quality data achieved in the production series, almost 100% crack and micro crack-free green parts with optimum density distribution over all press levels is unrivalled and thus gives the user a clear lead over the competition.

Crack‑free TiO2 films prepared by adjusting processing parameters via liquid phase deposition technique

Jie Li,Hai‑Yan Xu,Ai‑Guo Wang,Feng‑Jun Zhang,Dao‑Sheng Sun,Won‑Chun Oh 한국세라믹학회 2020 한국세라믹학회지 Vol.57 No.2

TiO2 thin films with controllable morphology and grain size were prepared via a liquid phase deposition (LPD) technique. The effects of the processing parameters including the ( NH4)2TiF6 concentration, solution pH, and ( NH4)2TiF6:H3BO3 molar ratio on the grain size and morphology of the films were investigated. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, and ultraviolet–visible spectroscopy. The results showed that the deposition parameters significantly affected the growth and nucleation velocities of the crystalline grains, which resulted in the formation of TiO2 films with different morphologies and grain sizes. The capillary stress among the grains of the film, which resulted in the cracking of the film, depended on the size of the grains. Thus, the cracking of the LPD-derived TiO2 films could be mitigated by adjusting the deposition parameters.

노치 장약공을 이용한 발파균열제어에 관한 수치해석적 연구

조상호 ( Sang Ho Cho ),박승환 ( Seung Hwan Park ),김광염 ( Kwang Yeom Kim ),나카무라유이치 ( Yuichi Nakamura ),카네꼬카츠히꼬 ( Katsuhiko Kaneko ) 대한화약발파공학회 2008 화약발파 Vol.26 No.1

터널 및 지하공동 폐기물 처분시설의 건설에서 여굴을 적게하고 굴착후 잔류암반의 안정성을 높이기 위하여 TBM 및 할암기 등의 기계적 굴착공법의 적용이 제안되고 있다. 그러나 기계적 굴착공법은 경비나 시공성, 현장 적용성에 있어서 많은 제약이 따르고 있다. 이러한 단점을 보안하기 위하여 고도의 정밀제어발파공법이 제안되고 있다. 특히 노치 장약 공을 이용하여 예정된 굴착면을 따라 정밀하게 파단면을 형성시키는 방법이 제안되고 있지만 아직까지 균열제어에 관련된 연구가 미흡한 실정이다. 본 연구에서는 동적 파괴과정해석코드를 이용하여 암반내 노치를 가진 발파공을 모델링하여 암반의 균열발생 메커니즘과 파괴과정을 수치해석적으로 검토하였다. Mechanical excavation techniques employing tunnel boring machines (TBM) and rock splitters have been proposed to minimize rock damage for tunnel and underground waste repository facilities. Such a mechanical excavation, however, is extremely expensive and not applicable in all cases. For these reasons, controlled blasting using notched charge holes have been suggested to achieve crack growth along specific directions and inhibit growth along other directions. This study introduces a dyanmic fracture process analysis code to simulate fracture processes of rock which has a notched charge hole.