• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.585-593
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• 2010

On the basis of the strain-based shear strength model developed in the previous study, a strength model was developed to predict the direct punching shear capacity and unbalanced moment-carrying capacity of interior and exterior slab-column connections. Since the connections are severely damaged by flexural cracking, punching shear was assumed to be resisted mainly by the compression zone of the slab critical section. Considering the interaction with the compressive normal stress developed by the flexural moment, the shear strength of the compression zone was derived on the basis of the material failure criteria of concrete subjected to multiple stresses. As a result, shear capacity of the critical section was defined according to the degree of flexural damage. Since the exterior slab-column connections have unsymmertical critical sections, the unbalanced moment-carrying capacity was defined according to the direction of unbalanced moment. The proposed strength model was applied to existing test specimens. The results showed that the proposed method predicted the strengths of the test specimens better than current design methods.

• Journal of Korean Society of Steel Construction
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• v.25 no.5
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• pp.531-541
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• 2013

This paper investigated the structural capacity of the CT shear connectors, which is a kind of the perfobond rib and functions as an anchor transferring the tension force in the joint between a composite PHC wall pile and a bottom slab. The direct pull-out test was performed for various specimens. From failure modes and load-displacement curves, it was found that transverse rebars should be placed to holes in a web to restrict pull-out failure of CT shear connectors. The results of additional tests for specimens with transverse rebars and various support lengths indicated that all specimens were failed by the tension failure of PHC pile before pull-out failure of CT shear connector and concrete pull-out failure. Thus, the CT shear connector could endure the tension force between the PHC wall pile and the bottom slab.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.89-97
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• 2006

This study investigated the effect of relative density on the thickness of shear zone. Digital image processing was used to measure the thickness of shear zone under plane strain conditions. A suitable epoxy resin was injected into the sample and the thickness of the shear zone was investigated. Four independent condition samples were prepared and the thickness of the shear zone was measured. The results indicated that the thickness of shear zone increases as the initial density of sample increases, and during the shear, the void ratios of the shear zone were changed, but the thickness of shear zone was not changed. In addition, the result of measurement of the thickness showed that the thickness of shear zone was almost fixed before critical state, but beyond critical state, the thickness of shear zone sharply increases as relative density increases.

• Proceedings of the KSR Conference
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• 2002.05a
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• pp.177.1-182
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• 2002

본 연구는 합성교량의 경우 브라켓이나 가로보에 사용되고 비합성교량의 경우 연결재로 사용되는 스랩앵커를 Push-Out Test를 하여 실험으로 얻은 특성을 실제 소수주형모델에 적용하여 FEM해석을 통하여 거동특성을 파악 하고자 한다. 일반적으로 전단연결재 실험의 경우 콘크리트 슬래브와 강재 주형 사이에 직접 길이 방향 전단력을 작용시킬 수 있을 뿐 아니라 실험의 편리함 때문에 주로 Push-out 실험이 많이 이용되고 있다. 본 실험에서는 BS-5400에 제시된 바에 근거하여 실험체를 제작하였다. 이 실험을 통하여 탄성구간에서의 강성(k) 값을 알아내어 3D FEM 해석에 적용한다. 이때 콘크리트 바닥판과 강재와의 연결을 축 방향으로는 특정한 강성 값을 넣을 수 있는 Joint Element를 사용하여 연결시키고, 1경간 단순지지와 2경간 연속교에 대하여 연구를 수행하는데, 1경간 단순지지의 경우에는 Joint Element에 여러 강성 값과 실험을 통해 얻은 강성 값을 적용하여 합성거동을 파악하고 강성 값에 따른 합성정도를 규명하고자 한다. 또한 2경간 연속교에서는 슬랩앵커의 강성 값을 적용하여 많이 문제시되고 있는 내부지점부에 슬랩앵커를 사용하였을 때 슬래브의 인장응력이 어떤 변화양상을 나타내는지 파악 하고자한다.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.565-578
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• 2019

Basic friction angles of Hwangdeung granite, Berea sandstone, Jeongsun marble, Hongcheon gneiss, Pungam shale and Eumseong sandy shale were measured by direct shear test, tilt test and pull test. Characteristics of basic friction angle and the accuracy of test methods were compared and the optimal method in measuring basic friction angle was suggested. Although basic friction angles might be measured accurately by direct shear test, the test apparatus is expensive and procedures are complicated. Tilt tests which is the suggested method for measuring basic friction angle by International Association for Rock Mechanics also provided similar basic friction angles measured by direct shear test. However, the error measured for the same rock type is higher than 7° and values by repeated measurements in one sample show different trends, such as increasing or decreasing or almost constant as measurements continued. The difference measured in one gneiss sample is higher 12°, indicating that tilt test may be not a reliable method for measuring basic friction angle. Not only pull test provided accurate and consistent results under low normal stresses, but also test apparatus is simple and inexpensive and procedure is not complicated, indicating that pull test may be the optimal method for measuring basic friction angle.

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.159-168
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• 2011

In the present study, an improved design method was developed for the punching shear strength of interior slabcolumn connections and column footings with and without shear reinforcement. In the evaluation of the punching shear strength, the possible failure mechanisms of the connections and column footings were considered. The considered failures modes were inclined tensile cracking of concrete, yielding of shear re-bars, and concrete crushing of compression zone/strut. The punching shear applied to the concrete critical section was assumed to be resisted mainly by the compression zone. The punching shear strength of the concrete compression zone was evaluated based on the material failure criteria of the concrete subjected to the compressive normal stress and shear stress. For verification of the proposed design method, its prediction was compared with the existing test results. The result showed that the proposed method predicted the strengths of the test specimens better than the current design methods of the KCI code for both the shear reinforced and unreinforced cases.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2C
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• pp.89-98
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• 2006

In this study, the iron and aluminium electrode was put in marine clay which was taken from south coast in Korea to increase the undrained shear strength by inducing the densification and cementation between clay particles and precipitation which was developed by electrode decomposition. For raising the cementation rate and reducing treatment time, high electric current( 2.5A) was applied in each electrode at semi-pilot scale soil box with marine clay. After the tests, the undrained shear strength was measured at designated points using cone penetration test device and sampling was conducted simultaneously in order to measure water content, pH and electric conductivity which would be the key for configuring the cementation effects indirectly. The iron electrode decomposition test results show that the water content adjacent to anode section decreased in 35% and increased in 13% at cathode section. The measured shear strength however, was increased considerably comparing to initial shear strength because of cementation effect between iron ions and soil particles. In case of aluminium electrode decomposition test, the distribution of measured shear strength and degree of improvement were more homogeneous than iron electrode decomposition test.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.93-105
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• 2017

This study presents direct shear tests, model tests, and numerical simulations to assess the effect of reduction of soil strength because of saturation during formation of ground cave-in caused by damaged sewer pipe lines. The direct shear test results show that the saturation affects the cohesion of soil significantly although it does not influence the friction angle of soil. To experimentally reproduce ground cave-in, the model tests were performed. As ground cave-ins were accompanied with extreme deformation, conventional finite element method has difficulty in simulating them. The present study relies on generalized interpolation material point method, which is one of meshless methods. Although there are differences between the model test and numerical simulation caused by boundary conditions, incomplete saturation, and exclusion of groundwater flow, similar ground deformation characteristics are observed both in the model test and numerical simulation.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.328-336
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• 1999

To characterize the hydro-mechanical behavior of a rock joint, a rotary shear testing apparatus was devised in this study. Shear stress was driven by twisting the end of a sample in the rotary shear testing apparatus. The test results show that the rotary shear test underestimates the peak shear strength of a rock joint. The torque is known as a function of the radial distance from the axis of rotation, resulting in the radial variation of the shear stress. Fluid flow through rock joints is mainly dependent on the Joint roughness, contact area, initial aperture. To examine the dependency, the relationship between the hydraulic and the mechanical apertures for shear-flow was established by measuring the initial aperture. It shows that the mechanical aperture and the hydraulic aperture increase linearly with the dilatancy. The difference between the hydraulic and mechanical apertures describes the deviation from the behavior predicted by the parallel plate model.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.772-781
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• 2020

A direct shear member resists external forces through the shear transfer of reinforcing bars placed at the concrete interface. The current concrete structural design code uses empirical formulas based on the shear friction analogy, which is applied to the horizontal shear of concrete composite beams. However, in the case of a member with a large amount of reinforcing bars, the shear strength obtained through the empirical formula is lower than the measured value. In this paper, the limit state of newly constructed composite beams on an existing concrete girder is defined using stress field theory, and material constitutive laws are applied to gain horizontal shear strength while considering the tension-stiffening and softening effects of concrete struts. A simplified method of calculating the shear strength is proposed, which was validated by comparing it with the related design code provisions. As a result, it was confirmed that the method generally shows a similar tendency to the experimental results when the shear reinforcing bar yields, unlike the regulations of the design code, where differences in the predicted value of shear strength occur according to the shear reinforcement ratio.