• Structural Engineering and Mechanics
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• 제74권3호
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• pp.351-363
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• 2020

Based on the dynamic tests of recycled aggregate concrete (RAC) short columns confined by the hoop reinforcement, the dynamic failure mechanism and the mechanical parameters related to the constitutive relation of confined recycled aggregate concrete (CRAC) were investigated thoroughly. The fracturing sections were relatively flat and smooth at higher strain rates rather than those at a quasi-static strain rate. With the increasing stirrup volume ratio, the crack mode is transited from splitting crack to slipping crack constrained with large transverse confinement. The compressive peak stress, peak strain, and ultimate strain increase with the increase of stirrup volume ratio, as well as the increasing strain rate. The dynamic confining increase factors of the compressive peak stress, peak strain, and ultimate strain increase by about 33%, 39%, and 103% when the volume ratio of hoop reinforcement is increased from 0 to 2%, but decrease by about 3.7%, 4.2%, and 9.1% when the stirrup spacing is increased from 20mm to 60mm, respectively. This sentence is rephrased as follows: When the stirrup volume ratios are up to 0.675%, and 2%, the contributions of the hoop confinement effect to the dynamic confining increase factors of the compressive peak strain and the compressive peak stress are greater than those of the strain rate effect, respectively. The dynamic confining increase factor (DCIF) models of the compressive peak stress, peak strain, and ultimate strain of CRAC are proposed in the paper. Through the confinement of the hoop reinforcement, the ductility of RAC, which is generally slightly lower than that of NAC, is significantly improved.

• 콘크리트학회지
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• 제11권2호
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• pp.197-208
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• 1999

고강도 콘크리트는 기둥부재에서 그 사용효과가 극대화될 것이 예상되지만, 아직 고강도 콘크리트를 사용한 기둥의 연성특성과 최대강도효과에 대한 구체적인 자료가 부족한 실정이다. 띠근 보강된 콘크리트 기둥은 삼축압축상태가 되며, 고강도 콘크리트의 연성을 증가시키므로 이에 대한 많은 연구가 필요하다. 본 연구에서는 축하중을 받는 띠근보강 고강도 콘크리트 기둥부재의 횡보강효과에 의한 극한강도와 변형율 특성에 대하여 정성적 평가와 정량적 평가를 수행하는 것을 목적으로, 삼축압축상태하의 콘크리트 파괴이론과 기존의 실험결과들을 활용한 통계적기법을 이용하였다. 그 결과 콘크리트 강도, 띠근의 항복강도 및 간격비, 체적비 등을 변수로 고려하는 띠근의 횡보강응력 산정식, 최대압축강도 추정식 그리고 변형율 특성식을 제안하였다. 또한 제안된 식들은 실험결과를 적절히 예측하고 있음을 확인하였다.

• 한국지반공학회논문집
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• 제19권6호
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• pp.379-385
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• 2003

기존의 섬유보강성토제체의 설계에서 보강재의 변형을 고려하지 않고 연직응력을 보강재의 인장강도로 사용함으로써, 흙구조물의 파괴응력에 대응하는 보강재의 한계응력산정과 그에 따른 보강재의 규격결정이 불가능했다. 보강재에 의해 보강된 성토제체의 파괴면에서 보강재와 흙의 거동은 초기응력단계에서는 일체로서 거동하지만 응력의 증가에 따라 변형량의 차이가 증가한다. 이러한 문제는 흙구조물의 보강재설계에서 중요한 요소로서 보강효과에 큰 영향을 미칠 수 있다. 본 연구에서는 연약지반위에 PET Mat로 보강한 성토제체의 보강재 설계 시 파괴면상의 보강재 설치위치에서 흙과 보강재의 변형량을 고려한 설계방법을 제시하였다. 연구결과에 의하면, 허용안전율을 확보하는 범위내에서 예상파괴면상의 보강재 설치위치에서의 보강재의 인장강도는 흙의 응력 이상이어야 하며, 흙의 변형링${\Delta S}$과 보강재의 변형량${\Delta G}$이 일체로 거동하는 보강재의 소요인장강도를 보강재의 설계인장강도로서 결정하는 것이 합리적이고 경제적인 것으로 평가되었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.257-258
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• 2006

The $I_c$ degradation behaviors of externally-reinforced Bi-2223 superconducting tapes under pressurized liquid nitrogen were investigated. Tapes with different thickness of reinforcement layers were compared and the results showed that when the bending strain was calculated at the outer surface, the tape with the thicker reinforcement showed a better bending strain tolerance of $I_c$, but when the bending strain was calculated at the outermost filament, the $I_c$ degradation behavior became identical for all tapes. $I_{c0}$ decreased with the increase of applied pressure. After depressurization to atmospheric pressure from 1 MPa, the $I_c$ was completely recovered to its initial values. Ballooning occurred after a thermal cycle.

• 콘크리트학회논문집
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• 제23권1호
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• pp.67-75
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• 2011

이 연구에서는 UHPCC에서 강섬유 혼입률이 압축거동에 미치는 영향에 관한 연구를 수행하였으며, 그 결과로부터 UHPCC에 적용가능한 압축거동 모델을 제시하고자 하였다. 섬유혼입률 0~5 vol.%에 대해 실험을 수행한 결과, 섬유혼입률이 증가함에 따라 압축강도 및 그 때의 극한변형률 및 탄성계수가 증가하는 경향을 확인할 수 있었다. 이와 같은 결과는 100 MPa 이하의 강섬유보강 콘크리트에 대한 기존 연구 결과들과 비교했을 때, 압축강도는 섬유보강효과가 거의 동일한 경향을 나타내는 반면, 극한변형률과 탄성계수에 대한 섬유보강효과는 상대적으로 훨씬 적게 나타났다. 섬유혼입률이 증가함에 따른 UHPCC의 압축강도, 극한변형률 및 탄성계수의 변화를 섬유보강지수(RI)를 이용한 선형관계식으로 표현하였다. UHPCC의 압축거동에 대한 섬유보강효과는 거동의 형상에 전혀 영향을 미치지 않으며, 다만 압축강도와 그 때의 극한변형률 및 탄성계수에 영향을 미치는 점을 고려하여 UHPCC의 압축응력-변형률 관계를 제시하였다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.345-352
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• 2005

The purpose of this study is to analyze the stress-strain behavior of confined concrete columns with rectangular section. Uniaxial concentric loading tests of nineteen concrete columns with rectangular section ($150{\times}100$, $250{\times}100$, $350{\times}100\;mm$) were conducted. The main variables are transverse reinforcement volumetric ratio and spacing, cross tie arrangement, cross-section aspect ratio, and concrete strength. From the present experiments, it was found that the increase of transverse reinforcement ratio increases the maximum stress and ductility ratio and the reduction of the spacing of transverse reinforcement also increases the ductility and effective confinement. The increase of the aspect ratio of the cross-section does not influence much the stress-strain behavior of rectangular columns within the aspect ratio range of 3.5. The effect of concrete strength on ductility is also discussed.

• Steel and Composite Structures
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• 제34권5호
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• pp.671-679
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• 2020

The new energy-based criterion, named Reinforcement Strain Energy Density (ReiSED), is proposed to investigate the fracture behavior of the cracked orthotropic materials in which the crack is embedded in the matrix along the fibers. ReiSED is an extension of the well-known minimum strain energy density criterion. The concept of the reinforced isotropic solid as an advantageous model is the basis of the proposed mixed-mode I/II criterion. This model introduces fibers as reinforcements of the isotropic matrix in orthotropic materials. The effects of fibers are qualified by defining reinforcement coefficients at tension and shear modes. These coefficients, called Reduced Stress (ReSt), provide the possibility of encompassing the fiber fraction in a fracture criterion for the first time. Comparing ReiSED fracture limit curve with experimental data proves the high efficiency of this criterion to predict the fracture behavior of orthotropic materials.

• 한국농공학회지
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• 제45권2호
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• pp.58-67
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• 2003

Over the last decade fiber-reinforced polymer (FRP) reinforcement consisting of glass, carbon, or aramid fibers embedded in a resin such as vinyl ester, epoxy, or polyester has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. But reinforcing rebar for concrete made of FRP rebar has linear elastic behavior up to tensile failure. For safety a certain plastic strain and an elongation greater than 3% at maximum load is usually required for steel reinforcement in concrete structures. The same should be required for FRP rebar. Thus, the main object of this study was to develop new type of hybrid FRP rebar Also, this study was evaluated to the mechanical properties of Hybrid FRP rebar. The Manufacture of the hybrid FRP rebar was achieved by pultrusion, and braiding and filament winding techniques. Tensile and interlaminar shear test results of Hybrid FRP rebar can provide its excellent tensile strength-strain behavior and interlaminar stress-strain behavior.

• Earthquakes and Structures
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• 제9권6호
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• pp.1233-1250
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• 2015

The behavior of reinforced concrete (RC) columns made from high strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength transverse reinforcing bars and three with normal-strength transverse reinforcement, were tested under double curvature bending load. The effects of yielding strength and ratio of transverse reinforcement on the cracking patterns, hysteretic response, shear strength, ductility, strength reduction, energy dissipation and strain of reinforcement were studied. The test results indicated that all specimens failed in splitting failure, and specimens with high-strength transverse reinforcement exhibited better seismic performance than those with normal-strength transverse reinforcement. It also demonstrated that the strength of high-strength lateral reinforcing bars was fully utilized at the ultimate displacements. Shear strength formula of short concrete columns, which experienced a splitting failure, was proposed based on the Chinese concrete code. To enhance the applicability of the model, it was corroborated with 47 short concrete columns selected from the literature available. The results indicated that, the proposed method can give better predictions of shear strength for short columns that experienced a splitting failure than other shear strength models of ACI 318 and Chinese concrete codes.

• KIEAE Journal
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• 제8권5호
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• pp.61-68
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• 2008

For the recycling of the resources and the preservation of the environment, this study's purpose is to measure flexural behavior of the reinforced concrete beams with the major variables like concrete strength, replacement ratio of the recycled aggregate and the waste foundry sand and the tension reinforcement ratio and to present the data of the recycled aggregate used for the structure design. The experiment on the flexural behavior resulted in the followings. The ultimate strength of recycled R/C beam was manipulated proportionate to the tension reinforcement ratio, however the strength instantly decreased after passing the ultimate load due to the destroyed concrete of the compression side. The deflection at the maximum load varied from the tension reinforcement ratio by 5.5 times. The test specimen with the tension reinforcement ratio less than $0.5{\rho}b$ showed constant curve without change in the load from the yield to the ultimate load in contrast to the distinctive plastic region where the displacement was rising. Although the strain of main tension steel with the reinforcement ratio indicate different, the design of recycled concrete member can be applied for current design code for reinforced concrete structure as the ratio of tension reinforcement district the under the reinforcement ration in a balanced strain condition.