• 한국구조물진단유지관리공학회 논문집
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• 제26권4호
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• pp.81-90
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• 2022

이 연구에서는 일방향 콘크리트 슬래브를 대상으로 하여, 철근을 사용한 경우와 CFRP 보강근을 사용한 경우에 대해 보강근 사용량에 따른 휨강도와 처짐 및 균열폭을 비교하여 평가하였으며, CFRP 보강근 콘크리트 슬래브의 휨설계의 지배적인 성능과 효율적인 휨설계 방안에 대해 검토하였다. CFRP 보강근을 사용한 콘크리트 슬래브는 철근을 사용한 경우에 비해 동일한 보강근량에서 더 큰 설계휨강도를 얻을 수 있는 반면, 처짐 및 균열폭은 상대적으로 훨씬 크게 발생한다. CFRP 보강근을 사용한 콘크리트 슬래브에서는 최대균열폭이 설계의 지배적인 요인으로 작용하는 것으로 확인하였으며, 효율적 휨설계를 위해서는 허용균열폭을 0.7 mm로 완화하여 적용할 필요가 있으며, 작은 직경의 보강근 적용을 검토할 필요가 있음을 제시하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권4호
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• pp.11-19
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• 2022

본 연구에서는 기계식 커플러의 이음성능을 향상시키기 위해 다른 접합방식을 가진 두 가지의 새로운 커플러를 개발하였다. 두 가지 방식의 기계식 이음장치에 대하여 응력 해석을 수행하였다. 커플러의 재료특성, 접합방식, 내부 조임쇠의 경사길이를 변수로 최대 인장강도의 영향성을 분석하기 위해 일축인장시험을 수행하였다. 일축인장시험결과를 만족하는 시험체를 대상으로 KS D 0249에 의거하여 정적내력시험 및 반복하중 시험을 수행하였다. 이에 대한 연구결과는 다음과 같다. (1) 커플러의 인장강도와 내부 조임쇠의 경사길이는 최대 인장강도에 영향을 끼친다. (2) 연결 방식에 따라 접합된 철근의 강성, 슬립량, 강성감소율에 영향이 있다. 연구결과는 새롭게 제안된 향상된 기계식 이음장치의 현장 적용에 대한 가능성을 검증하였다.

• Computers and Concrete
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• 제29권 6호
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• pp.407-418
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• 2022

This paper numerically investigates the effect of changes in the mechanical properties (displacement, strain, and stress) of the ultra-high-performance concrete (UHPC) without rebar and the reinforced concrete (RC) using steel re-bars. This reinforced concrete is mostly used in the concrete bridge decks. A mixture of sand, gravel, cement, water, steel fiber, superplasticizer, and micro silica was used to fabricate UHPC specimens. The extended finite element method as used in the ABAQUS software is applied for considering the mechanical properties of UHPC, RC, and ordinary concrete specimens. To calibrate the ABAQUS, some experimental tests have been carried out in the laboratory to measure the direct tensile strength of UHPC by the compressive-to-tensile load converting (CTLC) device. This device contains a concrete specimen and is mounted on a universal tensile testing apparatus. In the experiments, three types of mixed concrete were used for UHPC specimens. The tensile strength of these specimens ranges from 9.24 to 11.4 MPa, which is relatively high compared with ordinary concrete specimens, which have a tensile strength ranging from 2 to 5 MPa. In the experimental tests, the UHPC specimen of size 150×60×190 mm with a central hole of 75 mm (in diameter)×60 mm (in thickness) was specially made in the laboratory, and its direct tensile strength was measured by the CTLC device. However, the numerical simulation results for the tensile strength and failure mechanism of the UHPC were very close to those measured experimentally. From comparing the numerical and experimental results obtained in this study, it has been concluded that UHPC can be effectively used for bridge decks.

• Structural Engineering and Mechanics
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• 제20권6호
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• pp.673-693
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• 2005

A general step-by-step simulation for the time-dependent analysis of segmentally-erected prestressed concrete box-girder bridges is presented. A three dimensional finite-element model for the balanced-cantilever construction of segmental bridges, including effects of the load history, material nonlinearity, creep, shrinkage, and aging of concrete and the relaxation of prestressing steel was developed using ABAQUS software. The models included three-dimensional shell elements to model the box-girder walls and Rebar elements representing the prestressing tendons. The step-by-step procedure allows simulating the construction stages, effects of time-dependent deformations of materials and changes in the structural system of the bridges. The structural responses during construction and throughout the service life were traced. A comparison of the developed computer simulation with available experimental results was conducted and good agreement was found. Deflection of the bridge deck, changes in stresses and strains and the redistribution of internal forces were calculated for different examples of bridges, built by the balanced-cantilever method, over thirty-year duration. Significant time-dependent effects on the bridge deflections and redistribution of internal forces and stresses were observed. The ultimate load carrying capacities of the bridges and the behavior before collapse were also determined. It was observed that the ultimate load carrying capacity of such bridges decreases with time as a result of time-dependent effects.

• 한국구조물진단유지관리공학회 논문집
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• 제23권6호
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• pp.61-69
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• 2019

본 연구에서는 단일강섬유와 하이브리드강섬유로 보강된 UHPC의 휨강도 및 연성을 평가하기 위해 세 개의 휨파괴형 보에 대한 4점 가력 실험을 수행하였다. 실험 결과 단일섬유로 보강된 UHPC보다 하이브리드 섬유로 보강된 UHPC가 강도 및 연성 모든 측면에서 더 우수한 구조성능을 보유한 것으로 나타났다. 설계시의 안전성에 대해 평가하기 위하여, K-UHPC 구조설계지침에서 제공하는 방법에 따라 실험체의 강도와 연성을 평가해본 결과 현재의 재료모델은 강도에 대해서는 보수적으로 평가할 수 있으나 연성에 대해서는 과대평가하는 것으로 나타났다.

• 복합신소재구조학회 논문집
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• 제6권1호
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• pp.30-37
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• 2015

The need to consider torsion in the design of members of a structure has recently been increasing; therefore, many studies on torsion have been carried out. Recent research was focused on the torsional performance of concrete according to the reinforcing materials used. Of particular interest, are torsion studies of beams made of SFRC(steel fiber reinforced concrete), and there has been increasing use of SFRC at construction sites. In contrast, research on the composite PVA-ECC (polyvinyl alcohol-engineered cementitious composite) has only covered its mechanical performance, though it exhibits excellent tensile-strain performance (better than SFRC). Therefore, research on the torsion of concrete beams retrofitted using PVA-ECC is lacking. In this study, the behavior characteristics and performance of reinforced-concrete beams retrofitted by PVA-ECC was investigated experimentally. The experimental results show that the resistance to torsional cracking is increased by PVA-ECC. In addition, the strain on the rebar of the specimen was found to be reduced.

• Earthquakes and Structures
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• 제18권4호
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• pp.451-466
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• 2020

In this paper, the effect of Engineered Cementitious Composites (ECC) on the lateral strength of a bearing unreinforced Masonry (URM) wall, was experimentally and numerically investigated. Two half scale solid walls were constructed and were tested under quasi-static lateral loading. The first specimen was an un-retrofitted masonry wall (reference wall) while the second one was retrofitted by ECC mortar connected to the wall foundation via steel rebar dowels. The effect of pre-compression level, ECC layer thickness and one or double-side retrofitting on the URM wall lateral strength was numerically investigated. The validation of the numerical model was carried out from the experimental results. The results indicated that the application of ECC layer increases the wall lateral strength and the level of increment depends on the above mentioned parameters. Increasing pre-compression levels and the lack of connection between the ECC layer and the wall foundation reduces the influence of the ECC mortar on the wall lateral strength. In addition, the wall failure mode changes from flexure to the toe-crashing behavior. Furthermore, in the case of ECC layer connected to the wall foundation, the ECC layer thickness and double-side retrofitting showed a significant effect on the wall lateral strength. Finally, a simple method for estimating the lateral strength of retrofitted masonry walls is presented. The results of this method is in good agreement with the numerical results.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 춘계 학술논문 발표대회
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• pp.7-8
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• 2017

Corrosion of reinforced concrete embedded in concrete is a deterioration phenomenon due to intrusion of embodied or Airborne chloride ions. Corrosion of a embedded steel increases the volume of the rebar and causes damage to the structure such as cracking and peeling of the concrete. This causes penetration of various corrosive factors and accelerates the corrosion of reinforcing bars, which has a serious effect on the durability of the structure. Researches on the corrosion phenomenon of these rebars by electrochemical methods have been carried out for a long time, but it is a lack of research in Korea. Therefore, in this study, one of electrochemical experimental methods, Tafel extrapolation method, was used to evaluate the performance of reinforcing bars according to the amount of NaCl and LiNO₂ added to concrete.

• 한국구조물진단유지관리공학회 논문집
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• 제4권4호
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• pp.149-160
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• 2000

As systematic methodologies are required for the evaluation on the durability of reinforced concrete structure, it is necessary to study and examine every factor which deteriorates the durability of structures. This paper aims to define factors affecting rebar corrosion and to establish a basis for a prediction of serviceability, regarding a state of harmful corrosion as a state when crack begins on the surface of concrete. The study results are followings; The corrosive current has changed by types of mixture, and this property enables the evaluations of corrosion resistance by mixture and concrete cover. The specimen using AE superplasticizer has better corrosion-resistance properties than non-AE specimen, as well those having low W/C and high unit cement weight. The procedure for calculation of durable year in this study is able to use as an indicator to establish mixture factors such as unit cement weight, W/C, amount of admixture, etc.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.247-259
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• 2017

This paper presents a fatigue assessment model that was developed for corroded reinforced concrete (RC) beams strengthened using prestressed carbon fiber-reinforced polymer (CFRP) sheets. The proposed model considers the fatigue properties of the constituent materials as well as the section equilibrium. The model provides a rational approach that can be used to explicitly assess the failure mode, fatigue life, fatigue strength, stiffness, and post-fatigue ultimate capacity of corroded beams strengthened with prestressed CFRP. A parametric analysis demonstrated that the controlling factor for the fatigue behavior of the beams is the fatigue behavior of the corroded steel bars. Strengthening with one layer of non-prestressed CFRP sheets restored the fatigue behavior of beams with rebar at a low corrosion degree to the level of the uncorroded beams, while strengthening with 20- and 30%-prestressed CFRP sheets restored the fatigue behavior of the beams with medium and high corrosion degrees, respectively, to the values of the uncorroded beams. Under cyclic fatigue loading, the factors for the strengthening design of corroded RC beams fall in the order of stiffness, fatigue life, fatigue strength, and ultimate capacity.