• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.79-86
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• 2010

This study was performed to evaluate the flexural behavior of Hybrid fiber sheet (HFC) and Hybrid fiber bar (HFB) strengthened reinforced concrete (RC) beams. According to test results, Hybrid fiber reinforcement strengthened RC beams showed approximately 60 to 200% higher reinforcing effects than that of un-reinforced specimens. In addition, the reinforced beams showed the ideal failure pattern, which is failed presenting the ductile behavior after yielding of the reinforcing bar. More specifically, in the case of HFB reinforced RC beams, the difference with puttying method was not apparent since HFB beams reinforced using the injection of epoxy and bonding of putty showed the similar failure patterns.

• Magazine of the Korean Society of Agricultural Engineers
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• v.24 no.3
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• pp.100-107
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• 1982

최근 철근 콘크리트 구조물의 지진하중 및 이와 유사한 진동하중에 대한 내진안전성 문제가 대두되어 이에 관한 모형공식체의 진동실험 및 실존구조물의 동적구조특성의 해석 등에 의한 내진성 향상을 위한 보강방법이 강구되고 있다. 본 연구에서는 진동하중에 파괴되기 쉬룬 철근 콘크리트 보와 기둥이 상호 교차되는 죠인트 구역의 동적파괴거동을 확인하기 위하여 "L"형 철근 콘크리트 죠인트와 부재를 제작, 모의지진하중 조건하에서의 동적 응답특성을 구명하고자 반복하중에 따른 joint구역과 보 및 기둥의 동적파괴거동을 고찰하였다. 특히 내진구조물 설계에 주요 요소인 연성(m)이 0.5, 1.0, 3.0일 때 각각 3회씩 그리고 m=5.0일 때 부재가 완전히 파괴될 때까지 4회 반복하여 반복하중을 작용시키면서 이때의 부재의 극한강도 및 그 변형성능을 LVDT System을 사용하여 조사분석하였으며, 파괴성상은 물론 배근효과에 대하여도 이를 구명하고자 노력하였다. 본 연구 결과 무엇보다도 부재의 강성과 내력의 향상 및 신축만곡, 전단변형 등의 변형성능의 개선 그리고 보의 휨파괴에 대한 보강 및 joint구역의 전단보강은 내진구조물 설계를 위하여 중요 사항임을 확인하였다.

• 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.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.323-326
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• 2009

콘크리트의 보강재로 높은 인장 강도와 비부식성, 비자기성, 비전기성 등의 장점을 갖는 FRP의 사용에 대한 연구가 활발히 진행되고 있다. 하지만 FRP가 갖는 낮은 탄성계수와 취성적 성질로 인해 기존 설계방법을 적용하기에는 문제가 있다. 본 연구에서는 보강비 변화에 따른 AFRP 보강 콘크리트 보의 구조 실험을 수행하여 FRP 보강근을 사용한 콘크리트 부재의 휨 성능 연구에 대한 기초적 자료를 제공하고자 하였다. 각 실험체의 결과 데이터를 비교 분석한 결과 균형보강비를 기준으로 저보강 실험체는 FRP의 파단에 의해 급격한 파괴양상을 보인 반면에, 과보강 실험체는 콘크리트가 압괴하는 파괴 징후를 보이며 파괴에 도달하였다. FRP 보강근을 사용한 보 부재의 설계에 균형보강 이상의 설계가 요구되며, 과보강의 경우 고강도 콘크리트의 사용이 요구되는 것으로 분석되었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.89-96
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• 2008

The purpose of this study is to investigate the flexural strengthening effectiveness for the beams reinforced with NSM CFRP strips. To accomplish this objective, concrete T beams were made and tested. From this study, it is found that the flexural stiffness and strength of the beams reinforced with NSM strips were significantly improved compared to the beams without CFRP strip. The maximum increase of flexural strength was 247%. Failure of the beam reinforced with NSM was initiated by a part of separation of NSM strips along the longitudinal direction, and the second failure of strips was investigated. After the first rupture of the NSM strips, the load dropped suddenly and the second rupture was succeeded. This result shows that a perfect composite reaction with NSM strips and concrete is possible in the beam reinforced with NSM CFRP strips the NSM strips and Near surface mounted(NSM) is one of the most recent and promising strengthening techniques for reinforced concrete structures.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.689-697
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• 2002

The dynamic loads and load-point displacements of concrete three-point bend (TPB) specimens had been measured. The average crack velocities measured with strain gages were 0.16 ㎜/sec ∼ 66 m/sec. The fracture energy for crack extension was determined from the difference of the kinetic energy for the load-point velocity and the strain energy without permanent deformation from the measure external work. For all crack velocities, there were micro-cracking for 23 ㎜ crack extension, stable cracking for 61 ㎜ crack extension at the maximum strain energy, and then unstable cracking. The unstable crack extension was arrested at 80 ㎜ crack extension except the tests of 66 m/sec crack velocity. The tests less than 13 ㎜/sec crack velocity and faster than 1.9 m/sec showed static and dynamic fracture behaviors, respectively. In spite of much difference of the load and load-point displacement relations for the crack velocities, the crack velocities of dynamic tests did not affect on fracture energy rate during the stable crack extension due to the reciprocal action of kinetic force, crack extension and strain energy. During stable crack extension, the maximum fracture resistances of the dynamic tests was 147％ larger than that of the static tests.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.199-208
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• 2010

In order to substitute FRP bar for steel bar in new structures, it is necessary to establish a reliable design code. But relatively little research has been conducted on the material in Korea. So, a total of 22 beam specimens (18 GFRP reinforced concrete and 4 conventional steel reinforced concrete) were constructed and tested. In the first phase of the experiment, it was carried out to observe flexural behavior, and collect deflection and crack data. In order to eliminate of the uncertainty by the shear reinforcements and induce flexural failure mode, any stirrup were not used and only shear span-depth ratio were adjusted. However, almost beams were broken by shear and the ACI 440.1R, CSA S806, which were used to design test beams, showed considerable deviation between prediction and test results of shear strengths. Therefore in the second phase of the study, shear failure modes and behavior were observed. A standard specimen had dimensions of 3,300 mm long ${\times}$ 800 mm wide ${\times}$ 200 mm effective depth. Clear span and shear span were 2,800 mm, 1,200 mm respectively. Control shear span-depth ratio was 6.0. Four-point bending test over simple support was conducted. Variables of the specimens were concrete compressive strength, type and elastic modulus of reinforcement, shear span-depth ratio, effective reinforcement ratio, the effect of bundle placing method and cover thickness.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.4 s.70
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• pp.417-426
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• 2005

Recent days composite bridge dock is gaining attraction due to many advantages such as light weight, high strength, corrosion resistance, and high durability. In this study, composite deck models of hat, box and triangular section type wore fabricated with VARTM Process. For these models, three point flexural tests wore carried out both in strong and weak axis. The experimental results were compared with each other to determine efficient section profile. It has been demonstrated that composite sandwich deck has strong potentials to be used as bridge deck in the new construction and rehabilitation works.

• Journal of Korean Society of Steel Construction
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• v.14 no.2
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• pp.357-364
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• 2002

The study performed a series of flexural tests on Closed Cold-Formed Steel Sections for stud, joist, and roof truss. Results were compared with analytical values. Each 2.4-m long and 0.9-m wide specimen consisted of two steel beams set at 0.46 m interval. The steel beams were attached to the specimens using either plaster board or ply wood. Another specimens did not use any attachment material. Positive and negative bending tests were conducted to investigate the composite behavior, including the effects of plaster board or ply wood on the buckling behavior of steel beam. Full-scale roof truss tests were also performed to study the buckling behavior and failure mode of the truss members.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.57-66
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• 2015

This paper is a preliminary study to apply the lightweight concrete slabs reinforced with GFRP (glass fiber reinforced polymer) bars to the bridge deck slabs or some other concrete structures. So, some different behaviors between the conventional steel reinforced concrete slab and the lightweight concrete slab reinforced with GFRP bars were investigated. For this purpose, a number of slabs were constructed and then the three point bending test and numerical analysis for these slabs were performed. The flexural test results showed that the lightweight concrete slabs reinforced with GFRP bars were failed by the shear failure due to the over-reinforced design. The weight and failure load of the GFRP bar reinforced lightweight concrete slabs were 72% and 58% of the steel reinforced concrete slab with the same dimensions, respectively. Results of the numerical analysis for these slabs using a commercial program, midas FEA, showed that the load-deflection curve could be simulated well until the shear failure of the slabs, but the applied loads and the deflections continuously increased even beyond the shear failure loads.