• 화약ㆍ발파
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• 제22권3호
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• pp.1-12
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• 2004

암석 파쇄도는 노천의 벤치발파에서 생산성을 좌우하는 요소이다. 벤치발파에서 암석 파쇄도는 여러 가지 조건의 영향을 받게 되는데, 특히 암반의 불연속면 조건과 자연상태 암반 블록의 크기는 큰 영향을 미치는 것으로 알려져 있다. 이 연구에서는 석회석을 생산하는 3개 노천광산에서 발파조건 뿐 아니라 암반의 불연속면 조건과 자연상태 암반 블록크기를 면밀히 조사하여 이들 조건이 암석 파쇄도에 미치는 영향을 검토하였다. 분석 결과 암반의 불연속면 조건과 발파조건은 복합적인 상호작용에 의해 영향을 미치는 것으로 밝혀졌으며, 특히 자연상태 암반 블록의 크기는 암석 파쇄도에 가장 큰 영향을 미치는 것으로 나타났다. 암석 파쇄도는 암반의 불연속면 조건 중 주절리군의 방향에 의해서도 영향을 받는 것으로 확인되었는데, 주절리군의 방향이 벤치 앞쪽 자유면과 $30^{\circ}$의 경사를 이룰 때 파쇄물의 평균크기가 가장 작게 되는 것으로 나타났다. 이런 현상은 발파로 만들어진 탄성파의 전파경로 차이에 기인하는 것으로 판단된다.

• International Journal of Concrete Structures and Materials
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• 제3권1호
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• pp.63-69
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• 2009

This paper provides the engineer with a simple design method dealing with situations arise where in-situ reinforced concrete joints are cast between hollow core units. Using finite element method, hollow core slabs with wide in-situ RC joints under point load and line loads are analysed. In addition, some important behavioural characteristics of the floor slab subjected to line and point loads are investigated. In-situ reinforced concrete joint causes reduction of load distribution for remote units because distance to the remote units from the point of load is increased, while the portion of load distribution carried by loaded unit increases. Also, it was turned out load distribution factors for point load and line loads are almost same. Finally, we suggest a simple analytical method, which can determine load distribution factors using normalized deflections by regression analysis for design purposes.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 지반공학 공동 학술발표회
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• pp.639-648
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• 2005

Up to now, practical engineers applying simplicity value of rockfall block weight suggested in design manual without considering in-situ rockfall block weight which reflect joint characteristics. However, the size of rockfall block varies with joint spacing of discontinuities and influences over rockfall analysis results. In this paper, we estimate realistic rockfall block weight distribution using statistical invariances of joint spacing derived from scan-line survey result. And, we study whether this distribution is applicable in practical rockfall analysis directly. As the results of this study, rockfall analysis results that using rockfall block weight distribution estimated from scan-line survey show resonable and realistic outcomes.

• 한국터널지하공간학회 논문집
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• 제6권4호
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• pp.303-314
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• 2004

본 연구에서는 터널을 굴착할 때 절리가 있는 암반의 역학적 거동특성을 실험적으로 규명하고자 하였다. 절리와 터널의 이격거리, 측압계수를 변화시키며 실험을 수행하였다. 터널주변에 수직절리가 있는 경우 천단부와 수직절리 반대편의 어깨부에서 가장 큰 영향이 발생되며 측압이 작을 경우에는 천단부 보다 절리 반대편 측벽부에서 접선 방향의 응력이 크게 증가된다. 반면 $45^{\circ}$의 경사절리가 있는 경우 발생하는 압축응력은 절리면 방향의 터널 좌측부가 무절리 상태의 3배정도로 터널의 안정성에 큰 영향을 미치는 것으로 나타났다.

• 산업기술연구
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• 제23권A호
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• pp.69-81
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• 2003

Numerical analysis is important for the design, construction and maintenance of large caverns. The rock mass contains generally discontinuities such as faults, joints and fissures. The mechanical behavior and geometric characteristics of these discontinuities would have a significant impact on the stability of the caverns. In this research the Distinct Element Method(DEM) was used to analyze the structural stability of the large cavern. The Barton-Bandis Joint Model (B-B J.M) was used as a constitutive model for the joint. In addition, two different cases 1) analysis with a support system and 2) analysis with no support system, were analyzed to optimize a support system and to investigate reinforcing effects of a support system. The most significant parameters of in-situ stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. Displacement (horizontal, joint shear), maximum joint opening, maximum and minimum principal stresses, range of relaxed zone, rockbolt axial forces and shotcrete stresses were calculated at each excavation stage. As a result of analysis the calculated values proved to be under the allowable value Rockbolts also proved to be an efficient support measure to control joint shear displacement which had significant effects on extending the relaxed zone. As a consequence, the structural stability of the cavern was assured with an appropriate support system.

• International Journal of Railway
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• 제3권1호
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• pp.1-6
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• 2010

The steel plate-girder bridges with concrete gravity piers have possibilities of overturning by lateral inertial force which can be reproduced by sudden earthquake attack. This paper explores an overturning mechanism of existing concrete gravity pier onto the sandy soil in the event of lateral push-over load by in-situ experimental observation. The in-situ push-over experiment for pier with earth anchors between spread footing and rock beds exhibits a reasonable enhancement of ductility against overturning. In unanchored system, a flexural crack at cold joint of concrete pier is not developed because of the over-turning of the pier. This leads a global instability (rotation) of pier-footing system with relatively low stresses in pier itself. While a lateral load is persistently increased in anchored system, the successive flexural cracking failure at cold joint is observed even after the local shear failure of soil due to redistribution of stress equilibrium between soil and pier structure as long as a tensile action of anchor cable is active.

• 한국재료학회지
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• 제18권1호
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• pp.38-44
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• 2008

The micro-structural changes, strength characteristics, and micro-fractural behaviors at the joint interface between a Sn-4.0wt%Ag-0.5wt%Cu solder ball and UBM treated by isothermal aging are reported. From the reflow process for the joint interface, a small amount of intermetallic compound was formed. With an increase in the isothermal aging time, the type and amount of the intermetallic compound changed. The interface without an isothermal treatment showed a ductile fracture. However, with an increase in the aging time, a brittle fracture occurred on the interface due mainly to the increase in the size of the intermetallic compounds and voids. As a result, a drastic degradation in the shear strength was observed. From a microshear test by a scanning electron microscope, the generation of micro-cracks was initiated from the voids at the joint interface. They propagated along the same interface, resulting in coalescence with neighboring cracks into larger cracks. With an increase in the aging time, the generation of the micro-structural cracks was enhanced and the degree of propagation also accelerated.

• 대한기계학회논문집A
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• 제27권8호
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• pp.1388-1397
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• 2003

Since the reliability of adhesively bonded joints for composite structures is dependent on many parameters such as the shape and dimensions of joints, type of applied load, and environment, so an accurate estimation of the fatigue life of adhesively bonded joints is seldom possible, which necessitates an in-situ reliability monitoring of the joints during the operation of structures. In this study, a self-sensor method for adhesively bonded joints was devised, in which the adhesive used works as a piezoelectric material to send changing signals depending on the integrity of the joint. From the investigation, it was found that the electric charge increased gradually as cracks initiated and propagated in the adhesive layer, and had its maximum value when the adhesively bonded joint failed. So it is feasible to monitor the integrity of the joint during its lifetime. Finally, a relationship between the piezoelectric property of the adhesive and crack propagation was obtained from the experimental results.

• Journal of Mechanical Science and Technology
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• 제20권3호
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• pp.310-318
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• 2006

In this study, we investigate the feasibility of in-situ crack propagation by using a double cleavage drilled compression (DCDC) specimen showing a slow crack velocity down to 0.03 mm/s under 0.01 mm/s of displacement control. Finite element analysis predicted that the DCDC specimens would show at least 4.3 fold delayed crack initiation time than conventional tensile fracture specimens under a constant loading speed. Using DCDC specimens, we were able to observe the in-situ crack propagation process in a particle reinforced transparent polymer composite. Our results confirmed that the DCDC specimen would be a good candidate for the in-situ observation of the behavior of particle reinforced composites with slow crack velocity, such as the self-healing process of micro-particle reinforced composites.

• 한국구조물진단유지관리공학회 논문집
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• 제6권1호
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• pp.241-254
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• 2002

Though there are many kinds of type in the expansion joint of bridges, Transflex joint was usually used from 1970's to 1980's. But it made of rubber is needed to exchange to new one often because of the breakage by wheel load. This study performed the safety estimation which is to exchange the transflex joint to finger joint kept the part of situ-cast-concrete. The standard of finger joint is same as that of transflex joint, we investigated the safety of finger joint with experimental results and FEM (Finite element method) analysis.