• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.4
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• pp.1-8
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• 2008

RC beam of existing structures often encounter shear problems for various reasons. The shear failure of RC beam is sudden and brittle. Strengthening technique jacketing with external bonding of steel plates(or CFRP and CFS) with epoxy is many use to in practice. This study presents test results on strengthening shear deficient RC beams by external bonding of slit type steel plates. Test parameters are width, interval, length, thickness and angle of slit in steel plates. The purpose was to evaluate the reinforcing effects, failure modes and shear capacities for RC beams of strengthened with various slit type steel plates. The test result confirmed that all slit steel plates improved the stiffness and strength of the specimens significantly. Failure modes of SV series and SD series showed shear fractures and flexure fractures at ultimate state respectively. SD series were ductile rather than SV series.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.40-47
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• 2014

Recently the use of concrete post-installed set anchors has been increasing because this constructing method is flexible and easy to attach or fix structural members when we repair, reinforce, or remodel structures. Accordingly, designers and builders of Korea depend on foreign design codes since there are no exact domestic anchor design codes that they could credit. The anchor in plain concrete loaded in tensile exhibits various failure modes such as concrete breakout, splitting, steel failure, pull-out and side-face blowout, that depending on the tensile strength of the steel, the strength of concrete, embedment depth, interval, the edge distance and the presence of adjacent anchor. The objective is to investigate the effects of the variations like anchor embedment depth, interval and edge distance on pull-out fracture behavior of post-installed concrete set anchor embedded in plain concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.3
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• pp.177-183
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• 2023

Various failure modes occur in the concrete beams reinforced with GFRP(Glass Fiber Reinforced Plastic) under initial condition and repairing patterns. In this study, the failure behaviors of concrete beams restrengthened with GFRP sheet with slightly higher elastic modulus than concrete were investigated. For the tests, concrete beams with 24 MPa were manufactured, and the effects of initial notch, overlapping, end-strip reinforcement, and fiber anchors were analyzed on failure load. The cases of GFRP overlap around notch and the initial notch showed increasing failure loads similar to those of normal restrengthened case since the epoxy of the saturated GFRP sufficiently repaired the notch area. Compared to the control case without restrengthening of GFRP, the concrete with initial notch showed 0.78 of loading ratio and normal restrengthening showed 4.43~5.61 times of increasing ratio of failure loading, where interface-debonding from flexural crack were mainly observed. The most ideal failure behavior, break of GFRP, was observed when end-strip over 1/3 height from bottom and fiber anchor were installed, which showed increasing failure load over 150 % to normal restrengthening.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.2
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• pp.181-192
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• 2001

이 논문은 샌드위치식 강-콘크리트 복합구조체에서 상하 강판과 격벽으로 구성되는 셀의 형상비가 거동과 성능에 미치는 영향을 다루었다. 이 구조체에서 셀 형상비는 하중전달 메카니즘과 하중분배능력을 변화시킨다. 따라서 셀 형상비에 따라 부재의 응력수준과 하중저항능력이 변화한다. 이 연구에서는 셀 형상비가 이 구조체의 거동과 성능에 미치는 영향을 규명하기 위해, 두 종류의 샌드위치식 복합구조체에 대해 다양한 셀 형상비를 설정하여 비선형 구조해석을 수행하였다. 해석결과로부터 셀 형상비에 따른 하중전달 메카니즘과 부채 응력에서의 차이점을 도출하였으며, 이들 차이점을 바탕으로 셀 형상비가 전단성능, 휨성능, 하중저항성능에 미치는 영향을 분석하였고, 파괴모드와 연성에 미치는 영향에 대해서도 간략히 언급하였다. 연구결과, 셀 형상비가 증가함에 따라 하부 강판과 콘크리트의 응력수준이 낮아지는 결과를 나타내었다. 이것은 각 부재의 유효휨강성과 유효전단강성 증가를 나타내며, 따라서 구조체의 하중저항성능도 향상되는 것으로 판단된다. 특히 셀 형상비의 증가에 따른 성능향상에서 전단성능이 휨성능에 비해 더 큰 효과를 나타내며, 이러한 차이는 파괴모드와 연성에도 영향을 미칠 것으로 판단된다. 즉, 셀 형상비가 증가함에 따라 구조물의 거동 및 파괴모드는 점차적으로 전단에서 휨으로 변화하고, 이에 따라 구조물의 연성도 점차적으로 향상될 것으로 판단된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.289-295
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• 2008

The purpose of this study was to examine the flexural behavior of reinforced concrete beams strengthened with CFRP strips. A total of 12 rectangular beams were tested. Test variables in this study were the shapes, bonded length and the number of longitudinal layers of CFRP strips. From the experimental study, flexural capacity of the beams strengthened with CFRP strips significantly increased compared to the reinforced concrete beam without a CFRP strip. Maximum increase of ultimate strength was found about 120% more than the control beam. In this test, most of the strengthened beams failed suddenly due to the debonding of CFRP strips. It is also observed that the debonding of the strip was initiated in the flexural zone of the beam and propagated rapidly to the end of the beam. The ultimate tensile strains of CFRP strips in this test were occurred at the level of 36% of rupture tensile strength of the CFRP strip, and an analytical approach to compute the flexural strength of reinforced beams strengthened with CFRP strips based on the effective stresses was conducted.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.781-788
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• 2009

Mechanical properties of steel-concrete interface were evaluated on the basis of experimental observations. The properties included bond strength, unbounded and bonded friction angles, residual level of friction angle, mode I fracture energy, mode II bonded fracture energy and unbonded slip-friction energy under different levels of normal stress, and shape parameters to define geometrical shape of failure envelope. For this purpose, a typical type of constitutive model of describing steel-concrete interface behavior was presented based on a hyperbolic three-parameter Mohr-Coulomb type failure criterion. The constitutive model depicts the strong dependency of interface behavior on bonding condition of interface, bonded or unbounded. Values of the interface parameters were determined through interpretation of experimental results, geometry of failure envelope and sensitivity analysis. Nonlinear finite element analysis that incorporates steel-concrete interface as well as material nonlinearities of concrete and steel were performed to predict the experimental results.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.56-63
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• 1994

• Magazine of the Korea Concrete Institute
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• v.10 no.2
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• pp.137-146
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• 1998

본 연구에서는 콘크리트 속에서 인장과 전단을 받는 FRP 다우얼의 거동과 파괴를 예측할 수 잇는 수리적인 파괴 해석 모델을 개발하였다. 다우얼 파괴해석 모델은 다우얼 작용과 파괴기준에 대한 두 개의 하위 모델로 구성되어 있는데 이들을 수정, 결합하여 만들어졌다. 다우얼 작용에 대한 모델로는 BEF 모델을 기초로 하여 두가지의 지수를 새로이 정의, 사용하였는데 하나는 콘크리트지지 강성을 변화시키기 위한 변위 정도 지수이고 다른 하나는 긴장된 케이블의 반력을 고려하기 위한 인장 지수이다. 인장과 전단이 작용하는 FRP다우얼의파괴 모델로는 Tsai-Hill 파괴기준이 사용되었고 이 기준을 적용하기 위하여 파괴 계수를 정의하였다. 개발된 파괴 해석 모델은 긴장된 FRP다우얼의 극한 전단력과 극한 변위를 예측하는데 사용하였고, 해석결과는 여러 인장응력을 가진 FRP 다우얼의 시험결과와 비교하였다.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.225-228
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• 2008

In case of nonlinear analysis for reinforced concrete structure, the characteristics of the failure, which are depend on loading conditions, such as tension splitting, compression crushing and shear distortion should be considered. On the analytical evaluation for the failure behavior of these, the finite element techniques is the most widely used. After the maximum load, however, an analytical results by finite element technique are depending on the size of the element. In this study, integral nonlocal model which is one of those study for overcoming the element sensitivity and dependancy, used for the failure analysis of box culvert specimen. Comparing on the experimental and analytical results, validity and reliability of integral nonlocal model are investigate.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.773-780
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• 2009

Experiments on steel-concrete interface are performed to investigate and determine the mechanical roles and properties of interface parameters. The intrinsic different nature of bonded and unbonded interfaces are addressed based on the experimental observations that were obtained from two types of tests considering bonded and unbonded interfaces. The unbonded tests are performed for the specimens that are in unbonded when the initially bonded specimens are tested first. Four cases of lateral confinements including pure slip, and low and medium levels of lateral pressure are taken into account to investigate the effects of lateral confinements on interface behavior. It is shown that the maximum shear strengths, the levels of residual strengths and the Mode II fracture energy release rates are linearly related to the confinement levels. Based on the experimental evidences obtained from this study, the values of interface parameters required in a steel-concrete interface constitutive model will be presented in the companion paper.