• 산업기술연구
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• 제25권A호
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• pp.39-47
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• 2005

Air void systems in hardened concrete has an important influence on concrete durability such as freeze-thaw resistance, water permeability, surface scaling resistance. Linear traverse method and point count method described at ASTM are the routine analysis of the air void system that have been widely used to estimate the spacing factor in hardened concrete. Recently, many concretes often have a spacing factor higher than the generally accepted $200-250{\mu}m$ limit for the usual range of air contents. This study is proposed to estimate the plane spacing factor by calculation of simplicity. The plane spacing factor need two parameters that are air content and numbers of air voids in the hardened concrete. Those obtained from the standard air-void system analysis of the ASTM C 457. The equation is valid for all values of paste-to-air ratio because the estimation of paste content is unnecessary at the using ASTM C 457. The plane spacing factor yields a similar estimate of the standard spacing factor.

• 한국해양공학회지
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• 제7권2호
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• pp.103-113
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• 1993

X-ray diffraction analysis technique was used for the fatigue damage analysis and fatigue life prediction in Al 7075-T651 alloy. The tensile test, fatigue strength and fatigue crack propagation test with change of stress ratio were carried out. As a result, half-value breadth was increased with the plastic deformation in the specimen increasint at all test conditions. In particular, half-value breadth at the surface of the specimens fractured by fatigue was increased as stress intensity factor range and effective stress intensity factor range were increased. In addition, the good relationship between half-value breadty and diffraction pattern was shown.

• 터널과지하공간
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• 제8권4호
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• pp.287-295
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• 1998

흙 사면의 안정성 해석에는 한계평형법이 널리 사용되고 있다. 그러나 절 리가 발달한 암반사면의 파괴는 절리의 거동에 지배를 받으므로 절리의 방향성과 파괴특성이 동시에 고려되어야 한다. 본 논문에서는 이러한 암반사면의 안정성해석을 위하여 임의방향으로 발달한 두 조의 절리군을 고려할 수 있는 편재절리모델을 사용하여 사면과 절리의 상대적인 방향성이 사면의 안전율에 어떠한 영향을 주는지 살펴보았다. 이를 위하여 이미 개발된 바 있는 비등방 탄소성 모델을 사면안정 해석에 적용할 수 있도록 수정하였으며, 안전율 계산 routine을 상용프로그램인 FLAC인 FISH macro 언어를 사용하여 작성하였다. 개발된 모델의 검증을 위하여 1요소에 대한 직접전단시험을 수치해석적으로 수행하였고, 안전율이 1인 흙사면을 선택하여 서로 수직인 2조의 절리군이 발달한 암반의 안정성 해석을 수행하여 Culmann의 평면파괴해와 비교하였다. 또한 UDEC에 의한 해석을 수행하여 사면파괴양상을 비교하였다. 절리의 간격이 충분히 작을 경우 편재절리모델은 정확한 결과를 나타내어 절리암반사면의 설계 및 안정성 해석에 활용될 수 있을 것으로 생각된다.

• 한국지반공학회논문집
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• 제30권11호
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• pp.5-15
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• 2014

사면파괴로 인한 피해사례가 늘어남에 따라 사면을 안전하게 설계하고 시공하는 것은 대단히 중요하다. 현재 실무에서 주로 사용되는 한계평형해석은 간단한 계산에 의해 안전율을 산정할 수 있지만 활동면을 미리 가정한다는 단점이 있다. 한편 유한차분해석 시 전단강도감소기법을 이용하여 안전율 산정이 용이해짐에 따라 설계 시 이용되는 빈도가 점차 증가하고 있다. 따라서 본 연구에서는 두 가지 해석방법의 비교를 통해 합리적인 쏘일네일링 설계방안의 제안을 목적으로 한다. 이를 위해 평면파괴 예상구간에 쏘일네일링 보강 시 보강패턴에 따른 보강효과를 비교해보았다. 그 결과 네일의 각도와 간격에 따른 보강효과는 동일하게 나타났다. 하지만 네일 길이가 증가함에 따라 한계평형해석의 경우 안전율이 증가하였지만 유한차분해석의 경우 안전율의 변화가 없었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 가을 학술발표회 논문집
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• pp.303-310
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• 2002

Overbreak occurred inevitably in a tunnel excavation, Is the main factor for increasing cost and time in tunnel projects. Furthermore the damage to the remained rock mass related to the overbreak can give rise to a serious safety problem in tunnels. As a rule of thumb, causes for the overbreak are inaccuracy in drilling, the wrong design of blasting and selection of explosives, and heterogeneity in rock mass. Specially, the geological features of the rock mass around periphery of an excavation are very important factors, so a lot of researches have been conducted to describe these phenomena. But the quantitative geological classification of the rock mass for the overbreak and the method for decreasing the amount of the overbreak have not been established. Besides, the technical improvement of the charge method is requested as explosives for the smooth blasting have not functioned efficiently. In this study, the working face around periphery of an excavation has been continuously sectionalized to 5∼6 parts, and the new Blastability Index for the overbreak based on 6 factors of RMD(Rock Mass Description), UCS(Uniaxial Compressive Strength) JPS(Joint Plane Spacing), JPO(Joint Plane Orientation), JPA(Joint Plane Aperture) and FM(Filling Material) is proposed to classify sections of the working face. On the basis of this classification, the distance between contour holes and the charging density are determined to minimize the overbreak. For controlling the charging density and improving the function of explosives, the New Deck Charge(N.D.C) method utilizing the deck charge method and detonation transmission in hole has been developed.

• Steel and Composite Structures
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• 제22권6호
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• pp.1417-1443
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• 2016

Cellular and castellated steel beams are used to obtain higher stiffness and bending capacity using the same weight of steel. In addition, the beam openings may be used as a pass for different mechanical fixtures such as ducts and pipes. The aim of this study is to investigate the effect of different parameters on both elastic and inelastic critical buckling stresses of steel web plates with openings. These parameters are plate aspect ratio; opening shape (circular or rectangular); end distance to the first opening; opening spacing; opening size; plate slenderness ratio; steel grade; and initial web imperfection. The web/flange interaction has been simplified by web edge restraints representing simply supported boundary conditions. A numerical parametric study has been performed through linear and nonlinear finite element (FE) models, where the FE results have been verified against both experimental and numerical results in the literature. The web plates are subject to in-plane linearly varying compression with different loading patterns, ranging from uniform compression to pure bending. A buckling stress modification factor (${\beta}$-factor) has been introduced as a ratio of buckling stress of web plate with openings to buckling stress of the corresponding solid web plate. The variation of ${\beta}$-factor against the aforementioned parameters has been reported. Furthermore, the critical plate slenderness ratio separating elastic buckling and yielding has been identified and discussed for two steel grades of DIN-17100, namely: ST-37/2 and ST-52/3. The FE results revealed that the minimum ${\beta}$-factor is 0.9 for web plates under uniform compression and 0.7 for those under both compression and tension.

• Geomechanics and Engineering
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• 제13권4호
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• pp.535-570
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• 2017

There are only few cases where cause and location of failure of a rock structure are limited to a single discontinuity. Usually several discontinuities of limited size interact and eventually form a combined shear plane where failure takes place. So, besides the discontinuities, the regions between adjacent discontinuities, which consist of strong rock and are called material or rock bridges, are of utmost importance for the shear strength of the compound failure plane. Shear behaviour of persistent and non-persistent joint are different from each other. Shear strength of rock mass containing non-persistent joints is highly affected by mechanical behavior and geometrical configuration of non-persistent joints located in a rock mass. Therefore investigation is essential to study the fundamental failures occurring in a rock bridge, for assessing anticipated and actual performances of the structures built on or in rock masses. The purpose of this review paper is to present techniques, progresses and the likely future development directions in experimental testing of non-persistent joint failure behaviour. Experimental results showed that the presence of rock bridges in not fully persistent natural discontinuity sets is a significant factor affecting the stability of rock structures. Compared with intact rocks, jointed rock masses are usually weaker, more deformable and highly anisotropic, depending upon the mechanical properties of each joint and the explicit joint positions. The joint spacing, joint persistency, number of rock joint, angle of rock joint, length of rock bridge, angle of rock bridge, normal load, scale effect and material mixture have important effect on the failure mechanism of a rock bridge.

• 한국농공학회지
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• 제30권1호
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• pp.38-49
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• 1988

This paper presented as follows results of laboratory model tests with various shaped footings on soil bed reinforced with the strips on the base of behaviour of soil structure according to the loads and triaxial test results reinforced with geotextiles. Their parameters studied were the effects on the bearing capacity of a footing of the first layer of reinforcement, horizontal and vertical spacing of layers, number of layers, tensile strength of reinforcement and iclination load to the vertical 1.Depending on the strip arrangement, ultimate bearing capacity values could be more improved than urreinforced soil and the failure of soil was that the soil structure was transfered from the macrospace to microspase and its arrangement, from edge to edge to face to face. 2.The reinforcement was produced the reinforcing effects due to controlling the value of factor of one and permeable reinforcement was never a barrier of drainage condition. 3.Strength ratio was decreased as a linear shape according to increment of saturation degree of soil used even though at the lower strength ratio, the value of M-factor was rot influenced on the strength ratio but impermeable reinforcement decreased the strength of bearing capacity. 4.Ultimate bearing capacity under the plane-strain condition was appeared a little larger than triaxial or the other theoretical formulars and the circular footing more effective. 5.The maximum reinforcing effects were obtained at U I B=o.5, B / B=3 and N=3, when over that limit only acting as a anchor, and same strength of fabric appeared larger reinforcing effects compared to the thinner one. 6.As the LDR increased, more and more BCR occurred and there was appeared a block action below Z / B=O.5, but over the value, decrement of BCR was shown linear relation, and no effects above one. 7.The coefficient of the inclination was shown of minimum at the three layers of fabrics, but the value of H / B related to the ultimate load was decreased as increment of inclination degree, even though over the value of 4.5 there wasn't expected to the reinforcing effects As a consequence of the effects on load inclination, the degree of inclination of 15 per cent was decreased the bearing capacity of 70 per cent but irnproved the effects of 45 per cent through the insertion of geotextile.

• 한국지반공학회논문집
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• 제16권4호
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• pp.63-70
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• 2000

불연속성 암반의 강도특성이나 변형특성에 대한 해석중 가장 중요한 점은 불연속면의 정량적인 파악과 조사방법에 있다. 그러나, 실질적으로 불연속면의 조사 인자들이 암반의 역학적인 특성과의 관계에 대하여는 분명한 해답을 내릴 수 없는 단계에 있다. 본 연구에서는 첫째로 불연속면의 현장 조사 항목 중 절리밀도, 절리길이, 절리 간격을 변화시키면서 암반의 탄성계수와의 상호관계를 밝히고 둘째로, 불연속성 암반의 탄성계수에 직접적인 관계를 가지며 불연속성 암반의 탄성계수를 정리할 수 있는 새로운 인자를 제안하는 것이 목적이다. 해석방법으로는 불연속성 암반의 기본모델로써 난수발생법에 의하여 불연속면을 발생시킨 기본단위구조를 가정하고 이를 균질화법과 유한요소법을 이용한다. 이들 방법을 통한 수치해석으로 불연속성 암반의 탄성계수를 구한다. 그 결과 불연속면의 조사항목과 탄성계수와의 상호관계성 뿐만 아니라 불연속성 암반의 탄성계수와 선형적인 관계를 가지는 새로운 파라메타로써 영향면적률을 제안한다.