• Geotechnical Engineering
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• v.10 no.4
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• pp.67-82
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• 1994

In this study, a reinforced clay model based on the limit equilibrium of forces under direct shear was proposed to predict shear strength increase in clays induced by the steel inclusion. The model accounted for the effects of orientation of inclusion, length, bonding stress between clay and indclusion and passive soil resistance 1 induced by the inclusion movement, on the behavior of reinforced clays. In order to compare with the theoretical predictions, direct shear tests were performed using a direct shear apparatus formed of an open shear box. Also pull-out tests were conducted to determine the bonding stress between the inclusion and clay. From the experimental results, the increase or decrease in shear strength of reinforced clay samples was found to depend on the orientation of inclusionas well as water content of clay samples. From the comparison of theoretical predictions and experimental results, it was found that the theore tical model predicted reasonably well the influence of orientation of the inclusion as well as passive soil resistance induced by the inclusion movement on the mechanical behavior of reinforced clays.

• Journal of the Korean Society for Railway
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• v.14 no.3
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• pp.240-247
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• 2011

Finite element analysis was undertaken to investigate the effect of freezing force of water unexpectedly penetrated into inserts used in railway sleeper on pullout capacity of anchor bolts for fixing base-plate onto concrete sleeper. Based on the in-situ investigation and measurement of geometry of railway sleeper and rail-fastener, the railway sleeper was modeled by 3D solid elements. Nonlinear and fracture properties for the finite element model were assumed according to CEB-FIP 1990 model code. And the pullout maximum load of anchor bolt obtained from the model developed was compared with experimental pullout maximum load presented by KRRI for verification of the model. Using this model, the effect of position of anchor bolt, amount of fastening force applied to the anchor bolt, and compressive strength of concrete on pull-out capacity of anchor bolts installed in railway sleeper was investigated. As a result, it is found that concrete railway sleepers could be damaged by the pressure due to freezing of water penetrated into inserts. And the pullout capacity of anchor bolt close to center of railway is slightly greater than that of the others.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.2
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• pp.175-182
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• 2020

The application of epoxy coated reinforcements is increased as a means to prevent a corrosion of reinforcements embedded in reinforced concrete structures, However, epoxy coating may reduce the bond capacity between concrete and reinforcement, which results a longer development length and lap splice length. This paper aims to the possibility of modification in lap splice length from reduction of basic development length which was confirmed using a direct pull out test. Total 36 beam specimens were tested to compare the lap splice properties of normal and epoxy coated reinforcements with beam-end test for various lap lengths and diameters of reinforcements. According to the results on failure modes, deformations, and crack widths of this experiments, the modification factor of 1.2 should be used, though the direct bond capacity is assured through direct pull out test.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.158-158
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• 2011

통상 교량구조물은 차도부와 보도부 및 그 부속시설로서 난간 및 연석부 등으로 구성되는데, 자동차 전용도로의 경우 보도부가 설치되지 않게 되고, 국내의 국도 및 지방도상의 많은 교량이 차도부와 보도부의 별도의 구분이 없이 보행자가 연석부 위로 통행하거나 여의치 않을 경우 난간에 기대어 통행하는 경우가 일반적이어서 안전사고의 위험에 직접 노출되는 경우가 많다. 이에 국토해양부에서는 최근 "도로의 구조 및 시설기준에 관한 규칙"을 개정하여 국내의 보행자 관련 교통사고로 인한 사망자가 전체 교통사고 사망자의 약 절반을 차지하는 실정을 고려하여 보행자의 안전한 통행로 확보를 통해 보행공간의 근본적인 개선이 불가피한 실정임을 시사 하였다. 이에 국내에서는 교량 보도부의 확장에 대한 관심이 높은 실정이며, 현재 보도부 확장에 대한 시공이 활발하게 이뤄지고 있다. 그러나 기존 교량에 보도부를 신설 혹은 확장함에 있어서 보도부 부재의 설치 간격 및 필요한 앵커볼트의 수량 및 부재의 성능 평가에 대한 기준이 명확하게 이뤄지지 않은 상태에서 설치되어져 왔었다. 기존에 시공되던 H-형강의 브라켓 단면의 경우 브라켓 단면의 중량이 커서 안정성 및 시공성이 떨어지며 과다한 앵커볼트의 체결 및 브라켓 단면의 과다설계로 인한 공사기간 및 비용의 증대를 가져오는 문제점이 있었다. 이에 본 연구에서는 교량 보도부의 확장 및 신설에 있어서 보도부 부재의 설치간격의 적정성 및 브라켓의 최적화를 위한 브라켓의 성능평가 시험을 수행하였다. 브라켓의 성능평가 시험은 1차 2차 3차 시험으로 나누어 진행되었으며, 1차시험은 H-형강의 브라켓단면을 원형강관으로서의 대체 가능성을 확인하였고, 2차 시험에서는 원형강관의 브라켓 단면의 앵커볼트수량의 최적화에 대한 시험을 수행하였으며, 3차 시험은 최적화된 브라켓 단면에 프리스트레싱의 도입으로 반력 및 인발력의 감소효과를 확인하는 연구를 수행하였다. 본 연구의 수행결과 기존의 설계 및 시공방법이 과다 설계가 이뤄졌음을 판단하였고, 브라켓 단면의 최적화를 통하여 기존 시공방법에 비해 시공성, 안전성, 경제성을 높일수 있을 것으로 판단된다.

• International Journal of Highway Engineering
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• v.6 no.1 s.19
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• pp.47-56
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• 2004

To determine the pure bond strength between substrate and its overlayed concrete material, a direct pull-off test method was introduced by using a bi-material cylinder with which a penny-shaped crack was mountained at its interface. First, to evaluate the stress magnification or concentration at the interface, the energy release rates of a penny-shaped interface crack in remote tension loading on a bi-material cylinder were determined in terms of different modulus ratios and undonded area ratios(crack ratios) using a commercial finite element program. Then the energy release rates were calibrated as non-dimensional values in consideration of structural dimensions and applied forces. And to evaluate whether this new pull-off test method gives sound test results, three different sizes of unbended area ratios were incorporated along their interface in bi-material cylinders(sulphur polymer concrete + old concrete). Test results showed that all specimens were broken off at their interfaces as intended. Also the FEM analyses and test results indicated that a bi-material specimen with unbended area ratio of 0.4$\sim$0.6 is suitable for best accurate testing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.149-156
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• 2021

FRP has been proposed to replace the steel as a reinforcement in the concrete structures for addressing the corrosion issue. However, FRP-Rebar does not behave in the same manner as steel because the properties of FRP are different. For example, FRP-Rebar has a high tensile strength, low stiffness, and linear elastic behavior which results in a difference bonding mechanism to transfer the load between the reinforcement and the surrounding concrete. Therefore, bonding behavior between FRP-Rebar and concrete has to be investigated using the bonding test. So, Pull-out test has been used to estimate bond behavior because it is simple. However, the results of pull-out test have a difference with flexural-boding behavior of FRP-Rebar concrete member. So, it is needed to evaluate the real fleuxral-bonding behavior. In this study, the evaluation method to flexural-bonding behavior of FRP-Rebar concrete member was reviewed and compared. It was found that the most accurate evaluation method for the fleuxral-bonding behavior of FRP-Rebar concrete member was splice beam test, however, the size and length of specimen have to increase than other test method and the design and analysis of splice beam is complex. Meanwhile, characteristics of concrete could be reflected by using arched beam test, unlike hinged beam test which is based on the ignored change of moment arm length in equilibrium equation. However, the possibility of shear failure exists before the flexural-bonding failure occur.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.128-135
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• 2010

Polymer-modified cement mortar(PCM) has been widely used for strengthening of the concrete structures due to its excellent physical properties such as high strength and durability. Adhesive strength or behavior, on the other hands, between PCM and concrete is very important in strengthening the concrete member using PCM. Therefore the adhesive failure mechanism between PCM and concrete should be fully verified and understood. This study was performed to evaluate adhesive strength of PCM to the concrete by the direct pull-out test. In the direct pull-out tests, the adhesive strength under the various pre-treatment conditions such as immersion, thunder shower, freezing and thawing are evaluated. Also, the field direct pull-out test are performed to investigate the adhesive strength of mock-up test specimens. In the results of the test, the adhesive strength value by field test are lower than those of the standard curing condition. From these comparison and investigation, field test result was similar with the thunder shower test result. The results of the test was used to evaluate the korean industrial standard of polymer modified cement mortars for maintenance in concrete.

• Journal of the Korean Geosynthetics Society
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• v.21 no.3
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• pp.61-69
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• 2022

In this study, a large-scale direct shear test was performed to evaluate the shear characteristics of the pile-soil interface according to the fines content and confining pressure conditions as a reasonable evaluation method of the pullout resistance performance of pile considering the soil conditions. It was found that the shear stress was greatly generated under the conditions of high normal stress and low fines content. In addition, the maximum shear stress was found to be rather large under the conditions of the same normal stress and fines content, when pile surface had high roughness. The internal friction angle decreased at the pile-soil interface, when the fines content in the ground increased. On the other hand, the cohesion decreased under the condition of high fines content. And the internal friction angle and cohesion were large regardless of the fines content in the model ground, when the roughness of the pile surface was high.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1089-1092
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• 2008

The bond behavior between concrete and reinforcement is a important requirement for reinforced concrete constructions. For practical application, it is very important to study bond behavior of reinforcing bars in recycled fine aggregate concrete. Therefore, pull-out test in order to investigate the bond behavior between recycled fine aggregate concrete and deformed bars was performed. Recycled fine aggregate concrete replacement ratios (i.e., 0% and 100%) and positions of deformed bars (i.e., vertical and horizontal position) were considered as variables in this study. Test results were compared with the bond strength requirement recommended by CEB-FIP code. Based on the test results, It was found that the bond strength between the recycled fine aggregate concrete and deformed bars were influenced by both recycled fine aggregate concrete replacement ratios and positions of deformed bars. The reduction of bonded area at the soffit of horizontal reinforcement caused by concrete bleeding was observed in H type specimen. So, Only V type and HB specimen satisfied the bond strength requirement recommended by CEB-FIP code.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.06a
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• pp.145-154
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• 2003

When a nail pulled out in dense, granular soil, the soil in the vicinity of the nail tends to dilate, but its dilatancy results in a normal stress concentration at the soil/nail interface, thereby increasing the pull-out resistance of the inclusion. It is thought to be occurring within the resistance zone where the soil mass is at stationary state and the reinforcement are held in position by the soil, due to the friction or bond. In this paper, A series of direct shear and interface tests were conducted by using so called‘Constant Normal Stiffness Test Apparatus’which was modified and improved from the conventional direct shear box test rig. Unlikely the normal shear box test, this enables to simulate the different constraint effects of surrounding soil during shear under the conditions of constant stress and volume, constant normal stiffness. The aim of the research programme is to get better understanding of pull-out bond mechanism, thus to explore the possibility of evaluating the pull-out bond capacity of soil/reinforcement at the preliminary design stage from the laboratory test.