• Geomechanics and Engineering
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• 제15권6호
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• pp.1173-1182
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• 2018

The coal wall, gob-side backfill, and gangues in goaf, constitute the support system for Gob-side entry retaining (GER) in coal mines. Reasonably allocating and utilizing their bearing capacities are key scientific and technical issues for the safety and economic benefits of the GER technology. At first, a mechanical model of GER was established and a governing equation for coordinated bearing of the coal-backfill-gangue support system was derived to reveal the coordinated bearing mechanism. Then, considering the bearing characteristics of the coal wall, gob-side backfill and gangues in goaf, their quantitative design methods were proposed, respectively. Next, taking the No. 2201 haulage roadway serving the No. 7 coal seam in Jiangjiawan Mine, China, as an example, the design calculations showed that the strains of both the coal wall and gob-side backfill were larger than their allowable strains and the rotational angle of the lateral main roof was larger than its allowable rotational angle. Finally, flexible-rigid composite supporting technology and roof cutting technology were designed and used. In situ investigations showed that the deformation and failure of surrounding rocks were well controlled and both the coal wall and gob-side backfill remained stable. Taking the coal wall, gob-side backfill and gangues in goaf as a whole system, this research takes full consideration of their bearing properties and provides a quantitative basis for design of the support system.

• 한국강구조학회 논문집
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• 제29권5호
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• pp.341-352
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• 2017

강구조물을 접합하는 대표적인 두 가지 방법으로는 용접접합과 볼트접합이 있다. 이중 잘 접합된 볼트접합은 지압메카니즘에 의한 강도상승과 연성거동을 기대할 수 있다. 이러한 볼트접합부의 연성능력을 충분히 활용하기 위해 본 연구에서는 합리적인 단일볼트접합부의 힘-변형관계 및 지압강도 산정식을 제안하고자 하였다. 볼트접합부의 경계조건 및 기하학적인 요소를 고려하여 체계적으로 단일볼트 실험을 수행하였다. 현행 설계기준의 볼트접합부의 지압강도 산정식의 모순점을 해결하기 위해 새로운 지압강도 설계식 및 변형한계 산정식을 제안하였다. 또한 접합부의 강성, 강도, 기하학적 조건 등을 반영할 수 있는 힘-변형관계식을 제안하였다. 본 연구에서 제시한 지압강도식 및 힘-변형관계식은 현행설계기준보다 합리적으로 실험결과를 예측하였다.

• Steel and Composite Structures
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• 제22권4호
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• pp.797-820
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• 2016

This paper simulates the hysteretic behavior of steel reinforced recycled concrete (SRRC) columns under cyclic loads using OpenSees software. The effective fiber model and displacement-based beam-column element in OpenSees is applied to each SRRC columns. The Concrete01 material model for recycled aggregate concrete (RAC) and Steel02 material model is proposed to perform the numerical simulation of columns. The constitutive models of RAC, profile steel and rebars in columns were assigned to each fiber element. Based on the modelling method, the analytical models of SRRC columns are established. It shows that the calculated hysteresis loops of most SRRC columns agree well with the test curves. In addition, the parameter studies (i.e., strength grade of RAC, stirrups strength, steel strength and steel ratio) on seismic performance of SRRC columns were also investigated in detail by OpenSees. The calculation results of parameter analysis show that SRRC columns suffered from flexural failure has good seismic performance through the reasonable design. The ductility and bearing capacity of columns increases as the increasing magnitude of steel strength, steel ratio and stirrups strength. Although the bearing capacity of columns increases as the strength grade of RAC increases, the ductility and energy dissipation capacity decreases gradually. Based on the test and numerical results, the flexural failure mechanism of SRRC columns were analysed in detail. The computing theories of the normal section of bearing capacity for the eccentrically loaded columns were adopted to calculate the nominal bending strength of SRRC columns subjected to vertical axial force under lateral cyclic loads. The calculation formulas of horizontal bearing capacity for SRRC columns were proposed based on their nominal bending strength.

• 한국지반공학회논문집
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• 제20권3호
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• pp.85-96
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• 2004

본 연구는 점토층위의 모래지반에 위치하는 표면기초의 극한지지력에 대해 이론적으로 조사하였다. 실용적인 적용을 위하여 표면기초의 지지력에 관한 연구들에 대한 검토와 논의가 제시되며, 한계해석(Limit Analysis)의 운동학적 접근방법을 이용하여 정해의 극한 지지력이 계산되었다. 운동학적 해는 상한값이며 해의 정확성은 파괴메카니즘의 형상에 달려 있다. 이러한 방법은 설계도표를 만드는데 편리할 뿐만 아니라 물성치의 영향을 추정할 수 있다. 본 연구에서는 범용 유한요소해석 프로그램인 ABAQUS를 사용하여 탄소성 이론에 근거하여 극한지지력을 계산하였다. 운동학적 방범으로 계산된 결과와 유한요소 해석, 한계평형론에 근거한 몇몇 알려진 식들(Yamaguchi, Meyerhof와 Okamura 등)에 의한 결과를 비교하였다. 아울러, 운동학적 방법에 의한 제안식과 유한요소해석 결과와 한계평형해석 결과의 유효성에 대하여 검증하였다.

• Structural Monitoring and Maintenance
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• 제9권1호
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• pp.29-42
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• 2022

In mountainous areas of China, concrete poles with connectors are widely employed in power transmission due to its convenience of manufacture and transportation. The bearing capacity of the poles must have degenerated over time, and most of the steel connectors have been corroded. Carbon fiber reinforced polymer (CFRP) offers a durable, light-weight alternative in strengthening those poles that have served for many years. In this paper, the bearing capacity and failure mechanism of CFRP sheet strengthened existing reinforced concrete poles with corrosion steel connectors were investigated. Four poles were selected to conduct flexural capacity test. Two poles were strengthened by single-layer longitudinal CFRP sheet, one pole was strengthened by double-layer longitudinal CFRP sheets and the last specimen was not strengthened. Results indicate that the failure is mainly bond failure between concrete and the external CFRP sheet, and the specimens fail in a brittle pattern. The cross-sectional strains of specimens approximately follow the plane section assumption in the early stage of loading, but the strain in the tensile zone no longer conforms to this assumption when the load approaches the failure load. Also, bearing capacity and stiffness of the strengthened specimens are much larger than those without CFRP sheet. The bearing capacity, initial stiffness and elastic-plastic stiffness of specimen strengthened by double-layer CFRP are larger than those strengthened by single-layer CFRP. Weighting the cost-effective effect, it is more economical and reasonable to strengthen with single-layer CFRP sheet. The results can provide a reference to the same type of poles for strengthening design.

• 한국지반공학회지:지반
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• 제13권6호
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• pp.139-146
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• 1997

기초파괴는 일반적으로 변형이 집중되어 하나 또는 그 이상의 파괴면이 발생되어, 기초의 관입과 더불어 파괴면은 점진적으로 형성된다. 본 논문의 목적은 수치적으로 기초의 극한지지력 및 진행성 파괴거동을 파악할 수 있는가 하는 가능성을 검토하는데 있다. 대변형이론과 변형률 연화이론을 사용하여 비배수 상태인 점토지반의 기초에 대한 진행성 파괴거동에 대하여 분석하였다. 본 논문에서는 기초의 진행성 파괴과정과 완전한 하중 변위곡선을 해석하기 위한 수치해석 방법에 대하여 논하였다. 해석결과, 띠기초의 피크 이후의 지반파괴거동 및 진행성 파괴과정에 대한 명확한 수치적 해석가능성을 보여주었다.

• 한국기계가공학회지
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• 제6권1호
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• pp.43-49
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• 2007

Multi-function and miniaturization of the medical equipment and tele-communication systems need small and high precision machined parts. For the economic machining of the small size workpiece it should be machined by small and high precision machine tools with high speed machining. The belt type driving system in turning lathe has a limitation of spindle speeds because of the vibrations from driving mechanism, built-in type of driving mechanism is used to reduce the vibration. However, the main spindle of the built-in motor is connected directly to the motor, so the heat generation of the motor and bearing makes bad influence of the accuracy of machine tools. In this study, the analysis of heat generation from motor and bearings supporting main spindle and experiment were carried out. The results of theoretical simulation of temperature and deformation of the main spindle are good agreement with those of measured.

• Biomolecules & Therapeutics
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• 제22권4호
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• pp.341-346
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• 2014

Paeonol is a major phenolic micromolecular component of Moutan cortex Radicis, a traditional Chinese Medicine. It has shown antitumor effects in previous studies; however, the underlying mechanisms remain unknown. This study investigated the mechanism by giving treatments of placebo, cyclophosphamide, paeonol of 150 and 300 mg/kg to 4 groups of mice bearing EMT6 breast cancer. Apoptosis in tumor cells were confirmed by morphology analysis, including hematoxylin, eosin staining and TUNEL staining. The results showed that the weight of EMT6 breast tumor was significantly reduced in the groups treated with both 150 and 300 mg/kg of paeonol. Immunohistochemical and Western blot results showed that the expression of Bcl-2 was down-regulated while the expression of Bax, caspase 8 and caspase 3 was up-regulated respectively. These results suggest that paeonol exhibits antitumor effects and the mechanism of the inhibition is via induction of apoptosis, regulation of Bcl-2 and Bax expression, and activation of caspase 8 and caspase 3.

• 한국지반신소재학회논문집
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• 제9권1호
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• pp.13-20
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• 2010

본 연구에서는 얕은기초의 파괴거동과 전체적인 하중-변위 관계를 묘사하는 방법에 대하여 기술하였다. 제안한 방법에 의하여 얕은기초의 최고점 이후의 거동과 점진적인 파괴과정을 비교적 명확히 기술하는 것이 가능함을 보여주었다. 유한요소 수치해석법으로 얕은 기초지반에 대하여 마찰각과 체적팽창각을 달리하여 지지력계수 $N_{\gamma}$을 계산하였다. 일반적으로 적용하는 관련 흐름법칙과 거친 기초조건에 의한 지지력계수 $N_{\gamma}$값은 실제 흙거동인 비관련 흐름법칙과 약간 미끈한 기초조건에 대해서는 불안전한 설계가 되는 것을 보여주었다.

• 산업기술연구
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• 제18권
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• pp.7-16
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• 1998

This paper is an experimental study of investigating the reinforcing effect and the behavior of cohesionless slope installed with reticulated root pils. Reduced scale model tests with plane strain conditions were performed to study the behavior of the strip footing located on the surface of cohesionless slopes reinforced with root piles. Model tests were carried out with Jumunjin Standard Sand of 45% relative density prepared by raining method to have an uniform slope foundation during tests. Slope of model foundation was 1 : 1.5 and a rigid model slop. Parametric model tests were performed with changing location of model footing, arrangements of root piles and angles of pile installation. On the other hands, the technique with camera shooting was used to monitor sliding surface formed with discontinuty of dyed sand prepared during formation o foudation. From test results, parameters affecting the behavior of model footing were analyzed qualitatively to evaluate their effects on the characteristic of load - settlement, ultimate bearing capacity of model footing and failure mechanism based on the formation of failure surface.