• 대한토목학회논문집
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• 제11권4호
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• pp.1-8
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• 1991

최근에 피로하중을 받는 보나 기둥 구조물에 강섬유의 사용이 증가하는 추세이다. 예로서 교량, 고속도로, 비행장 그리고 빌딩 등이다. 본 연구에서는 강섬유를 혼입한 철근 콘크리트 보에 대하여 정적실험과 피로실험을 중점적으로 실시했다. 본 연구의 대상모형은 강섬유를 1% 또는 2% 포함한 경우, 스터럽이 있는 경우와 없는 경우로 구별하였다. 피로실험에 있어서 보의 파괴는 강섬유의 뽑힘이 아니라 절단에 있다는 사실을 확인할 수 있었으며, 강섬유 보강 콘크리트보의 해석적 적용성을 검토하기 위하여 실험의 결과치와 수치해석을 비교했는데 수치해석은 비선형 유한요소 프로그램(ADINA)을 사용했다.

• 한국강구조학회 논문집
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• 제25권4호
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• pp.379-388
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• 2013

본 연구에서는 신형상 U형 하이브리드 합성보의 내화성능평가를 실시하였다. 내화성능평가는 세라믹계의 뿜칠재와 내화페인트로 구분하여 내화시험을 수행하였다. 시험 변수는 피복재의 종류(뿜칠재와 페인트)와 내화시간(2시간, 3시간), 하중가력 유무(재하와 비재하), 뿜칠재 두께 등이다. 내화성능평가 합성보는 기존 철골보로 인정을 받은 제품에 비해 내화성능이 향상되는 것을 확인할 수 있다. 그러나 내화성능 향상에 대한 정량적인 평가는 합성보 형상과 관련한 다양한 변수가 조합되므로 지속적인 검토가 필요할 것으로 판단된다.

• 콘크리트학회논문집
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• 제11권5호
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• pp.119-130
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• 1999

Recently, as the building structure has been larger, higher, longer and more specialized, the demand of material with high-strength concrete for building has been increasing. In this research, silica-fume was used as an admixture in order to get a high-strength concrete. From the test result, High-strength concrete with cylinder strength of 1,200kgf/$\textrm{cm}^2$ in 28-days was produced and tested. The static test was carried out to measure the ultimate load, the initial load of flexural and diagonal cracking, crack patterns and fracture modes. The load versus strain and load versus deflection relations were obtained from the static test. The relation of cycle loading to deflections on the mid-span, the crack propagation and the modes of failure according to cycle number, fatigue life and S-N curve were observed through the fatigue test. Based on the fatigue test results, high-strength reinforced concrete beams failed to 57~66 percent of the static ultimate strength. Fatigue strength about two million cycles from S-N curves was certified by 60 percent of static ultimate strength.

• International Journal of Concrete Structures and Materials
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• 제10권sup3호
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• pp.87-96
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• 2016

This numerical study investigated the effects of different reinforcing details in beam-column joints on the blast resistance of the joints. Due to increasing manmade and/or natural high rate accidents such as impacts and blasts, the resistance of critical civil and military infrastructure or buildings should be sufficiently obtained under those high rate catastrophic loads. The beam-column joint in buildings is one of critical parts influencing on the resistance of those buildings under extreme events such as earthquakes, impacts and blasts. Thus, the details of reinforcements in the joints should be well designed for enhancing the resistance of the joints under the events. Parameters numerically investigated in this study include diagonal, flexural, and shear reinforcing steel bars. The failure mechanism of the joints could be controlled by the level of tensile stress of reinforcing steel bars. Among various reinforcing details in the joints, diagonal reinforcement in the joints was found to be most effective for enhancing the resistance under blast loads. In addition, shear reinforcements also produced favourable effects on the blast resistance of beam-column joints.

• 자원리싸이클링
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• 제20권1호
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• pp.46-53
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• 2011

폐콘크리트로부터 생산되는 순환골재는 천연골재에 비해 품질이 떨어지는 단점이 있어 이를 해결하는 것이 순환골재를 더 많이 재활용하는데 있어서 해결과제라 할 수 있다. 본 연구에서는 선행연구에서 사용된 콜로이달 실리카용액을 이용하여 순환골재의 품질개선에 효과적인 표면처리 방법을 도출하였다. 또한, 본 연구에서는 도출한 표면처리방법과 강섬유보강이 콘크리트의 특성에 미치는 영향을 파악하므로써 순환골재의 더 많은 재활용과 보다 인성적인 콘크리트의 제조를 위하여 5종류의 시험체의 강도 및 휨파괴시험 결과를 비교하여 고찰하였다.

• Steel and Composite Structures
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• 제15권6호
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• pp.623-643
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• 2013

Concrete filled steel tubular members (CFST) become a popular choice for modern building construction due to their numerous structural benefits and at the same time aging of those structures and member deterioration are often reported. Therefore, actions like implement of new materials and strengthening techniques become essential to combat this problem. The application of carbon fibre reinforced polymer (CFRP) with concrete structures has been widely reported whereas researches related to strengthening of steel structures using fibre reinforced polymer (FRP) have been limited. The main objective of this study is to experimentally investigate the suitability of CFRP to strengthening of CFST members under flexure. There were three wrapping schemes such as Full wrapping at the bottom (fibre bonded throughout entire length of beam), U-wrapping (fibre bonded at the bottom throughout entire length and extended upto neutral axis) and Partial wrapping (fibre bonded in between loading points at the bottom) introduced. Beams strengthened by U-wrapping exhibited more enhancements in moment carrying capacity and stiffness compared to the beams strengthened by other wrapping schemes. The beams of partial wrapping exhibited delamination of fibre and were failed even before attaining the ultimate load of control beam. The test results showed that the presence of CFRP in the outer limits was significantly enhanced the moment carrying capacity and stiffness of the beam. Also, a non linear finite element model was developed using the software ANSYS 12.0 to validate the analytical results such as load-deformation and the corresponding failure modes.

• Advances in concrete construction
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• 제10권4호
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• pp.319-332
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• 2020

The impacts of reinforcing concrete matrix with steel fibers, polypropylene fibers and recycled plastic fibers using different volume fractions of 0.15%, 0.5%, 1.5% and 2.5% on the compressive and tensile characteristics are experimentally investigated in the current research. Also, flexural behavior of plain concrete (PC) beams, shear performance of reinforced concrete (RC) beams and compressive characteristics of both PC and RC columns reinforced with recycled plastic fibers were studied. The experimental results showed that the steel fibers improved the splitting tensile strength of concrete higher than both the polypropylene fibers and recycled plastic fibers. The end-hooked steel fibers had a positive effect on the compressive strength of concrete while, the polypropylene fibers, the recycled plastic fibers and the rounded steel fibers had a negative impact. Compressive strength of end-hooked steel fiber specimen with volume fraction of 2.5% exhibited the highest value among all tested samples of 32.48 MPa, 21.83% higher than the control specimen. The ultimate load, stiffness, ductility and failure patterns of PC and RC beams in addition to PC and RC columns strengthened with recycled plastic fibers enhanced remarkably compared to non-strengthened elements. The maximum ultimate load and stiffness of RC column reinforced with recycled plastic fibers with 1.5% volume fraction improved by 21 and 15%, respectively compared to non-reinforced RC column.

• Earthquakes and Structures
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• 제12권1호
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• pp.55-65
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• 2017

Earthquake resilience of substations is essential for reliable and sustainable service of electrical grids. The majority of substation equipment consists of cylindrical porcelain components, which are vulnerable to earthquake shakings due to the brittleness of porcelain material. Failure of porcelain equipment has been repeatedly observed in recent earthquakes. Hence, proper seismic modelling of porcelain equipment is important for various limit state checks in both product manufacturing stage and detailed substation design stage. Sheds on porcelain core and cemented joint between porcelain component and metal cap have significant effects on the dynamic properties of the equipment, however, such effects have not been adequately parameterized in existing design guidelines. This paper addresses this critical issue by developing a method for taking these two effects into account in seismic modelling based on numerical and analytical approaches. Equations for estimating the effects of sheds and cemented joint on flexural stiffness are derived, respectively, by regression analyses based on the results of 12 pieces of full-scale equipment in 500kV class or higher. The proposed modelling technique has further been validated by shaking table tests.

• Earthquakes and Structures
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• 제15권3호
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• pp.275-283
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• 2018

Seismic strengthening is essential for existing bridge piers which are deficient to resist the earthquake. The concrete and CFRP jackets with a bottom-anchoring method are used to strengthen railway bridge piers with low reinforcement ratio. Quasi-static tests of scaled down model piers are performed to evaluate the seismic performance of the original and strengthened bridge pier. The fracture characteristics indicate that the vulnerable position of the railway bridge pier with low reinforcement ratio during earthquake is the pier-footing region and shows flexural failure mode. The force-displacement relationships show that the two strengthening techniques using CFRP and concrete jackets can both provide a significant improvement in load-carrying capacity for railway bridge piers with low reinforcement ratio. It is clear that the bottom-anchoring method by using planted steel bars can guarantee the CFRP and concrete jackets to work jointly with original concrete piers Furthermore, it can be found that the use of CFRP jacket offers advantages over concrete jacket in improving the energy dissipation capacity under lateral cyclic loading. Therefore, the seismic strengthening techniques by the use of CFRP and concrete jackets provide alternative choices for the large numbers of existing railway bridge piers with low reinforcement ratio in China.

• Architectural research
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• 제2권1호
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• pp.55-60
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• 2000

Recently, there is a great demand for precast reinforced concrete (RC) construction methods on the purpose of simplicity in construction. Nishimatsu Construction Company has developed a construction method with precast reinforced concrete members in medium-rise building. In this construction method, how to joint precast members, especially the anchorage of the main bar of beam, is important problem. In this study, the structural performance of exterior joints with precast members was investigated. The parameters of the test specimens are anchorage type of the main bar of beam (U-shape anchorage or anchorage plate) and the ratio of the column axial force to the column strength. Specimens J-3 and J-4 used U-shape anchorage and the ratio of the column axial force of specimen J-4 was higher. On the other hand, specimens J-5 and J-6 used anchorage plate, and the anchorage lengths are 15d and 18d, respectively. Experimental results are summarized as follows; 1) For the joints with beam flexural failure mode, it was found that the maximum strength of specimen with anchorage plate is equal to or larger than that of specimen with conventional U-shaped anchorage if the anchorage length of more than 15d would be ensured, 2) Each specimen shows stable hysteretic curves and there were no notable effects on the hysteretic characteristics and the maximum strength caused by the anchorage method of beam main bar and the difference of column axial stress level.