• 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.

• Smart Structures and Systems
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• 제13권6호
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• pp.943-957
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• 2014

When subjected to fatigue loading, the main failure mode of partially prestressed concrete (PPC) structure is the fatigue fracture of tensile reinforcement. Therefore, monitoring and evaluation of the steel stresses/strains in the structure are essential issues for structural design and healthy assessment. The current study experimentally investigates the possibility of using fiber Bragg grating (FBG) sensors to measure the steel strains in PPC beams in the process of fatigue loading. Six full-scale post-tensioned PPC beams were exposed to fatigue loading. Within the beams, the FBG and resistance strain gauge (RSG) sensors were independently bonded onto the surface of tensile reinforcements. A good agreement was found between the recorded results from the two different sensors. Moreover, FBG sensors show relatively good resistance to fatigue loading compared with RSG sensors, indicating that FBG sensors possess the capability for long-term health monitoring of the tensile reinforcement in PPC structures. Apart from the above findings, it can also be found that during the fatigue loading, there is stress redistribution between prestressed and non-prestressed reinforcements, and the residual strain emerges in the non-prestressed reinforcement. This phenomenon can bring about an increase of the steel stress in the non-prestressed reinforcement.

• Structural Engineering and Mechanics
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• 제38권3호
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• pp.361-384
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• 2011

Earlier studies on hollow-circular rubber bearings, all of which are conducted for steel-reinforced bearings, indicate that the hole presence not only decreases the compression modulus of the bearing but also increases the maximum shear strain developing in the bearing due to compression, both of which are basic design parameters also for fiber-reinforced rubber bearings. This paper presents analytical solutions to the compression problem of hollow-circular fiber-reinforced rubber bearings. The problem is handled using the most-recent formulation of the "pressure method". The analytical solutions are, then, used to investigate the effects of reinforcement flexibility and hole presence on bearing's compression modulus and maximum shear strain in the bearing in view of four key parameters: (i) reinforcement extensibility, (ii) hole size, (iii) bearing's shape factor and (iv) rubber compressibility. It is shown that the compression stiffness of a hollow-circular fiber-reinforced bearing may decrease considerably as reinforcement flexibility and/or hole size increases particularly if the shape factor of the bearing is high and rubber compressibility is not negligible. Numerical studies also show that the existence of even a very small hole can increase the maximum shear strain in the bearing significantly, which has to be considered in the design of such annular bearings.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.593-598
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• 2002

Routinely, strength method for the determination of the nominal moment of reinforced concrete beam is assumed to also be suitable for strengthening beams with carbon fiber sheets since typically strengthening beams compromise 98% by volume of reinforced concrete. Flexural capacity of strengthening beam is absolutely dependent upon the type of reinforcement materials, amount of reinforcement, anchoring system, adhesion capacity between reinforcement material and concrete. Therefore, it might be incorrect to use strength method for analysis and design of strengthening beam without considering the differences in the load-deflection curves, mechanism of failure, state of stress distribution, failure strain of the reinforcement. An flexural analysis based on force equilibrium and strain comparability has been developed for strengthening beam. Systematic experimental investigations are compared with analytical results. Then, the adaptation of strength method for strengthening beam have also been discussed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.37-40
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• 2004

An experimental study was conducted to investigate the stress-strain behavior of confined concrete columns according to transverse reinforcement volumetric ratio. Uniaxial loading tests of eleven column specimens$(250\times100\times500mm)$ with rectangular section were conducted to study effect of confinement. The main variables in this test are transverse reinforcement volumetric ratio and cross tie arrangement. the results indicate that the strength and the ductility of confined concrete columns are subjected to transverse reinforcement volumetric ration and cross tie arrangement.

• Computers and Concrete
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• 제20권2호
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• pp.215-227
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• 2017

A finite element model (FEM) for predicting early-age behavior of reinforced concrete (RC) bridge deck slabs with fiber-reinforced polymer (FRP) bars is presented. In this model, the shrinkage profile of concrete accounted for the effect of surrounding conditions including air flow. The results of the model were verified against the experimental test results, published by the authors. The model was verified for cracking pattern, crack width and spacing, and reinforcement strains in the vicinity of the crack using different types and ratios of longitudinal reinforcement. The FEM was able to predict the experimental results within 6 to 10% error. The verified model was utilized to conduct a parametric study investigating the effect of four key parameters including reinforcement spacing, concrete cover, FRP bar type, and concrete compressive strength on the behavior of FRP-RC bridge deck slabs subjected to restrained shrinkage at early-age. It is concluded that a reinforcement ratio of 0.45% carbon FRP (CFRP) can control the early-age crack width and reinforcement strain in CFRP-RC members subjected to restrained shrinkage. Also, the results indicate that changing the bond-slippage characteristics (sand-coated and ribbed bars) or concrete cover had an insignificant effect on the early-age crack behavior of FRP-RC bridge deck slabs subjected to shrinkage. However, reducing bar spacing and concrete strength resulted in a decrease in crack width and reinforcement strain.

• 한국지반신소재학회논문집
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• 제2권1호
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• pp.39-45
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• 2003

보강토 지반에서 가장 중요한 부분은 보강재와 흙사이의 접촉부분으로서 이 부분의 전단강도 및 전단거동은 보강효과에 직접적인 영향을 미친다. 보강토 지반에서 접촉부분의 전단특성을 얻는 방법으로서 인발시험방법과 직접전단시험방법 등이 있다. 실제 보강토 구조물내에서 보강재와 흙사이에 인발이 되는 부분, 전단이 되는 부분 등이 존재한다. 전단이 되는 경우에도 보강재가 전혀 변형을 하지 않는 경우와 보강재 자체가 변형이 되는 경우 등으로 나눌 수 있다. 본 연구에서는 대형 전단시험기를 이용하여, 부직포/모래, 지오그리드/모래 등의 접촉면을 갖는 2종의 토목섬유를 이용하여, 토목섬유의 인장변형이 허용되는 자유조건과 인장변형이 억제되는 고정조건 등 두가지 방법으로 직접전단시험을 실시하였다. 실험결과 자유조건에 비해 고정조건으로 시험을 행한 경우가 마찰각이 더 컸다. 그리고 전단응력이 피크가 되는 전단변형의 크기는 자유조건의 경우가 더 큰 값을 가졌다. 잔류응력의 경우는 고정법의 경우가 컸지만 잔류응력비는 자유법의 경우가 더 큰 값을 가졌다.

• 한국구조물진단유지관리공학회 논문집
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• 제28권4호
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• pp.13-20
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• 2024

이 연구에서는 전단벽과 같은 면내 전단을 받는 경우에 대해, 종방향 보강근비를 2.96%로 일정하게 하고, 횡방향 보강근비를 0.30에서 2.98%까지 변화시켰을 때, CFRP 보강근을 사용한 콘크리트 부재의 거동특성을 MCFT 이론에 기반하여 평가하고, 철근을 사용한 콘크리트 부재의 경우와 비교하여 분석하고자 하였다. 보강근비 0.30에서 1.19% 사이에서는 CFRP 보강근을 사용한 경우가 철근을 사용한 경우보다 높은 전단강도를 보였으며, 그 이상의 1.79% 및 2.98%에서는 상대적으로 낮은 전단강도를 나타내었다. 최대전단변형률은 낮은 보강근비에서 철근을 사용한 경우가 더 크게 나타났으며, 0.97% 이상에서는 CFRP 보강근을 사용한 경우에 더 크게 나타났으며 보강근비가 커질수록 철근 대비 전단변형률 증가율이 더 크게 나타났다. 철근 및 CFRP 보강근의 기계적 성질 차이로 인해 발생하는 보강근에서의 변형률 차이 및 요소에서의 주변형률 차이 분석을 통해 보강근비 변화에 따른 철근 및 CFRP 보강근을 사용한 경우의 전단강도 및 전단변형률 변화를 비교하여 분석할 수 있었다.

• 대한토목학회논문집
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• 제37권2호
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• pp.277-287
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• 2017

이 연구는 한계상태설계법을 기반으로 하는 도로교설계기준에 의해 철근콘크리트 휨부재 설계 시 적용하는 균형철근비와 최대 철근량에 대한 규정을 검토한 것이다. 현행 도로교설계기준(한계상태설계법)에서는 휨부재 철근량 산정의 기준이 되는 균형철근비에 대한 명시적 규정이 없고, 휨모멘트 재분배 효과를 반영한 최대 중립축 깊이 및 콘크리트 단면적의 0.04배로서 최대 철근량을 산정한다. 그런데, 최대 중립축 깊이 규정에 의하면 최대 철근량이 적게 산정되어 단면을 크게 하여야 하며, 콘크리트 단면적의 0.04배라는 한계값이 적용될 경우에는 인장 철근의 변형률이 항복 변형률의 2배 이하로 되어 충분한 연성거동을 보장할 수 없는 문제점이 있다. 이 연구에서는 연성거동을 확보할 수 있는 휨부재 설계를 위한 사용 철근량 산정의 기준이 되는 균형철근비를 극한한계상태 검증 규정 및 재료 특성과 콘크리트 기준압축강도에 따른 극한한계변형률을 도입하여 설계 실무에 적용할 수 있도록 간편한 식으로 유도하였다. 그리고, 설계된 휨부재가 충분한 연성이 확보되도록 인장철근의 최소허용변형률을 항복변형률의 2배로 가정하고 철근의 기준항복강도 및 콘크리트 기준압축강도에 상관없이 만족할 수 있도록 최대 중립축 깊이 비 보정계수를 도입하여 수정하고, 이로부터 최대철근비를 산정할 수 있도록 하였다.

• Smart Structures and Systems
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• 제1권4호
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• pp.385-404
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• 2005

The paper presents a model to calculate reinforcement strain using measured crack width in members under applied tension, flexure, and/or shear stress. Crack mapping using a new type of distributed coaxial cable sensors for health monitoring of large-scale civil engineering infrastructure was recently proposed and developed by the authors. This paper shows the results and performance of such sensors mounted on near surface of two flexural beams and a large scale reinforced concrete box girder that was subjected to cyclic combined shear and torsion. The main objectives of this health monitoring study was to correlate the sensor's response to strain in the member, and show that magnitude of the signal's reflection coefficient is related to increases in applied load, repeated cycles, cracking, and reinforcement yielding. The effect of multiple adjacent cracks, and signal loss was also investigated. The results shown in this paper are an important step in using the sensors for crack mapping and determining reinforcement strain for in-situ structures.