• 대한치과기공학회지
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• 제33권1호
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• pp.1-6
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• 2011

Purpose: To examine the shear bond strengths of zirconia and veneering ceramic according to their surface processing. Methods: The test samples were divided into three groups: one without zirconia surface processing, one sandblasted, and one sandblasted then 3% etched. Then veneering ceramic was fired on all test samples, and their shear bond strengths were measured. Results: The test samples of the control group (Z1) showed the lowest shear bond strengths of $21.82{\pm}1.02$ MPa. The shear bond strengths of Z2 and Z3 ($28.25{\pm}0.72$ and $26.23{\pm}0.82$ MPa, respectively) were relatively higher than those of the control group. The fracture surface of the control group showed adhesive fractures while the test groups had relatively large numbers of cohesive fractures. Conclusion: The shear bond strength was high in the test groups with surface processing while the fracture surfaces showed compound fractures of adhesive and cohesive fractures.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.777-783
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• 2006

The coarse grained materials are used in various construction field such as express way back fill, Dam etc. Especially, for dam construction, a huge mount of rock fill materials are needed, so around domestic stony mountains are generally developed to produce materials. Not an accurate theory, but design criteria is based on empirical factors that were constructed in advance for design of dam especially Concrete Face Rockfill Dam(CFRD). Considering the post facts, the modified design criteria are essential in the future with more theoretical and experimental ways. In this study, large scale direct shear tests are performed with various relative density conditions on coarse grained material of Yecheon area to compare test results and general CFRD design factors.

• 한국지반공학회논문집
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• 제34권6호
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• pp.61-73
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• 2018

쏘일네일 보강지반에 전단변형이 발생하면 쏘일네일 주변지반에는 수동토압이 유발되고, 전단변형의 증가는 주변지반의 토압 변화와 쏘일네일의 변형 및 부재력 변화를 야기한다. 본 연구에서는 대형 직접전단시험기를 이용하여 쏘일네일의 수직방향으로 전단변형을 유발하면서 쏘일네일의 전단거동을 실험적으로 분석하였으며, 수치해석을 통해 검증하였다. 전단면에서 이격된 쏘일네일의 정착부 길이(6D, 8D, 10D, 12D) 변화를 변수로 전단시험을 실시하였다. 연구결과, 전단변형의 지속적인 증가는 그라우트의 손상을 유발함을 확인하였으며, 정착부 길이변화에 따른 영향을 확인하였다. 모형시험과 수치해석을 통해 분석된 쏘일네일의 전이길이는 0.2~0.22m로 기존 연구에서 제시한 0.1m보다 크게 증가하였으며, 전단영역은 전단면에서 0.6m까지의 범위로 확인되었다.

• Geomechanics and Engineering
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• 제30권1호
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• pp.27-44
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• 2022

Gravelly soil is a kind of special geotechnical material, which is widely used in the subgrade engineering of railway, highway and airport. Its mechanical properties are very complex, and will greatly influence the stability of subgrade engineering. To investigate the mechanical properties and failure mechanism of gravelly soils, this paper introduced and verified a new discrete element method (DEM) of gravelly soils in large scale direct shear test, which considers the actual shape and broken characteristics of gravels. Then, the stress and strain characteristics, particle interaction, particle contact force, crack development and energy conversion in gravelly soils during the shear process were analyzed using this method. Moreover, the effects of gravel content (GC) on the mechanical properties and failure characteristics were discussed. The results reveal that as GC increases, the shear stress becomes more fluctuating, the peak shear stress increases, the volumetric strain tends to dilate, the average particle contact force increases, the cumulative number of cracks increases, and the shear failure plane becomes coarser. Higher GC will change the friction angle with a trend of "stability", "increase", and "stability". Differently, it affects the cohesion with a law of "increase", "stability" and "increase".

• Structural Engineering and Mechanics
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• 제80권5호
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• pp.595-608
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• 2021

To investigate the mechanical behavior of large stud shear connector embedded in hybrid fiber-reinforced concrete (HFRC), a refined 3D nonlinear finite element (FE) model incorporating the constitutive model of HFRC was developed using ANSYS. Firstly, the test results conducted by the authors (He et al. 2017) were used to validate FE model of push out tests. Secondly, a total of 27 specimens were analyzed with various parameters including fiber volume fractions of HFRC, diameter of studs and HFRC strength. Finally, an empirical equation considering the contribution of steel fiber (SF) and polypropylene fiber (PF) was recommended to estimate the ultimate capacity of large stud shear connector embedded in HFRC.

• Geomechanics and Engineering
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• 제11권5호
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• pp.713-723
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• 2016

Shear wave velocities of three selected sandy soils subject to drained triaxial compression test were continuously measured using the bender elements. The shear wave velocity during isotropic compression, as widely recognized, increased as confining pressure increased and they were correlated well. However, during drained shearing, the mean effective stress could no further provide a suitable correlation. The shear wave velocity during this stage was almost constant with respect to the mean effective stress. The vertical stress was found to be more favorable at this stage (since confining stress was kept constant). When sample was attained its peak stress, the shear wave velocity reduced and deviated from the previously existed trend line. This was probably caused by the non-uniformity induced by the formation of shear band. Subsequently, void ratios computed based on external measurements could not provide reasonable fitting to the initial stage of post-peak shear wave velocity. At very large strain levels after shear band formation, the digital images revealed that sample may internally re-arrange itself to be in a more uniform loose stage. This final stage void ratio estimated based on the proposed correlation derived during pre-peak state was close to the value of the maximum void ratio.

• Steel and Composite Structures
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• 제42권4호
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• pp.477-487
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• 2022

The shear stiffness of headed-stud shear connectors has no unified definition due to the nonlinear characteristics of its load-slip relationship. A unified framework was firstly adopted to develop a general expression of shear load-slip equation for headed-stud shear connectors varying in a large parameter range based on both force and energy balance. The pre- and post-yield shear stiffness were then determined through bilinear idealization of proposed shear load-slip equation. An updated and carefully selected push-out test database of 157 stud shear connectors, conducting on studs 13~30mm in diameter and on concretes 30~180 MPa in cubic compressive strength, was used for model regression and sensitivity analysis of shear stiffness. An empirical calculation model was also established for the stud shear stiffness. Compared with the previous models through statistical analysis, the proposed model demonstrates a better performance to predict the shear load-slip response and stiffness of the stud shear connectors.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1252-1258
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• 2005

The coarse grained materials which is produced in the domestic stony mountains are used as principle materials in the construction sites such as dams, ports, pavement structures and etc. Despite using of various fields like this, There is few apparatuses to experiment these materials in the country. some design parameters of the structures until these days was used from the result of former research abroad. Hereupon, We have developed the large scale direct shear test apparatus and we conduct research in order to get a shear strength of the coarse grained materials from the domestic stony mountains in Kyuong-gi, Choong-chung and Kyoung-sang province. As results of the test, it was revealed that the internal friction was ranging from $38.6^{\circ}$ to $44.5^{\circ}$ and the cohesion was from $1.1kg/cm^2$ to $1.7kg/cm^2$ depending on the local rock conditions.

• KCI Concrete Journal
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• 제12권1호
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• pp.91-99
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• 2000

A new type of retrof=t anchor bolt that uses deformed reinforcing bars and a commercial adhesive was developed and then an experimental study was carried out to determine the behavior of the anchors in direct shear. The steel-to-concl몫ete interface was tested. Plain concrete slabs with about 20-MPa compressive strength were used for 23 direct shear tests performed Test variables were anchor diameters (D16, D22. and D29) and edge effect. Three different shear tests were completed: simple shear, edge shear where anchors were pulled against the concrete core, and edge shear where anchors were pushed against the concrete cover In the simple and the edge shear tests where the anchors were pulled against the core, the theoretical dowel strength determined by (equation omitted) was achieved but with relatively large displacements. The shear resistances increased with the increasing displacements. In the edge shear test where the anchors were pushrd against the cover, the peak shear strengths signif=cantly lower than the theoretical dowel strength were determined due to cracks developed in concrete when the edge distance was 80 mm. The peak strengths were about 50% of the dowel strength for Dl6 bar. and about 25% or less of the dowel strength for D22 and D29 bars. Test results revealed that the edge shear where the anchor was pushed against the cover controled.

• 한국구조물진단유지관리공학회 논문집
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• 제21권6호
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• pp.67-73
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• 2017

최근 초고층 빌딩과 같은 대형 구조물의 증가로 인하여 기초의 허용 지지력 확보를 위한 대구경 말뚝의 수요가 급속히 증가하고 있다. 이 연구에서는 기성 대구경 PHC말뚝의 전단성능을 향상시키기 위하여 속채움 콘크리트와 전단철근을 사용하여 대구경 합성 PHC말뚝을 제작하였다. 제작된 시험체는 KS규격의 전단강도 시험방법에 따라 수행하였고 변위제어 방법으로 진행하였다. 전단시험을 통하여 F 시험체는 휨균열과 경사균열이 발생한 이후 급작스런 수평균열이 발생하였으나, FT 시험체는 수평균열의 발생 없이 말뚝의 전 지간에 걸쳐 휨균열과 전단 경사균열이 일정 패턴으로 발생하였다. 또한, 대구경 합성 PHC말뚝의 최대하중은 PHC말뚝과 비교할 경우, F 시험체의 경우 2.9배, FT 시험체의 경우 3.3배 이상으로 크게 향상된 것을 확인하였다. FT 시험체의 높은 전단 저항 능력은 전단철근의 배근으로 인하여 대구경 합성 PHC 말뚝이 우수한 합성거동을 하였고, 발생한 전단균열의 성장을 효과적으로 제어하였기 때문인 것으로 판단된다.