• 한국건축시공학회지
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• 제17권2호
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• pp.149-155
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• 2017

본 연구에서는 겨울철 타설된 콘크리트 표면을 낮은 열전도율 재료로 덮어 주므로서 우수한 단열성을 갖으며, 높은 전용성으로 경제성까지 뛰어난 2중 버블시트에 의한 표면피복 양생공법에 대하여 검토하였다. 하지만, 벽식구조 건축물 시공의 경우 버블시트로 포설되는 슬래브 부분은 초기동해를 방지할 수 있지만, 노출 철근 부분의 경우 버블시트의 포설이 까다롭기 때문에 이 부분에 대한 양생법 변화는 초기동해 피해 여부와 관련하여 의구심이 제기되고 있다. 그러므로, 본 연구에서는 실제 시공중인 벽식구조 Apt 현장의 벽체부분을 동절기 저온 조건하에서 시공하는 것을 모사하여 각종 표면피복 양생방법 변화에 따른 매립 및 노출철근 부분의 위치별 온도 분포 특성을 분석하여 효율적인 양생방법을 제안하고자 하였다. 그 결과, 여러 양생방법 중 D방법의 양생이 가장 우수하게 초기동해를 방지할 수 있는 것으로 판명되었다. 그러나, 시공의 효율성 및 시공의 편리성 까지도 감안하면 철근과 철근의 간격부 만큼에 버블시트를 좁은 폭으로 잘라 덮어주는 B방법도 우수한 방법으로 추천된다.

• 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.

• 콘크리트학회논문집
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• 제17권5호
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• pp.829-834
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• 2005

A series of reinforced G109 type specimens was fabricated and pended with a 15 weight percent NaCl solution. Mix design variables included 1) two cement alkalinities (equivalent alkalinities of 0.32 and 1.08), 2) w/c 0.50 and 3) two rebar surface conditions (as-received and wire-brushed). Potential and macro-cell current between top and bottom bars were monitored to determine corrosion initiation time. Once corrosion was initiated, the specimen was ultimately autopsied to perform visual inspection, and the procedure included determination of the number and size of air voids along the top half of the upper steel surface. This size determination was based upon a diameter measurement assuming the air voids to be half spheres or ellipse. The followings were reached based upon the visual inspection of G109 specimens that were autopsied to date. First, voids at the steel-concrete interface facilitated passive film breakdown and onset of localized corrosion. Based upon this, the initiation mechanism probably involved a concentration cell with contiguous concrete coated and bare steel serving as cathodes and anodes, respectively. Second, the corrosion tended to initiate at relatively large voids. Third, specimens with wire-brushed steel had a lower number of voids at the interface for both cement alkalinities, suggesting that air voids preferentially formed on the rough as-received surface compared to the smooth wire brushed one.

• 콘크리트학회논문집
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• 제20권6호
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• pp.681-687
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• 2008

이 연구는 적외선 열화상을 이용하여 철근의 부식을 정량적으로 파악하는 기법을 개발하는 것이다. 연구 진행 과정에서 전기적 가열방법이 실험 데이터에 지대한 영향을 끼치는 것을 발견했다. 가열접촉 방법에 대한 여러 실험적 연구를 통하여 실험 데이터의 신뢰성 확보와 효율적인 연구를 추구하였다. 사각어스클램프를 이용하여 철근을 가열하였을 때 철근의 온도변화를 통해 집게어스클램프보다 표면저항이 적다는 것을 입증하였다. 또한 접촉 방법의 표준화를 위해 토크렌치를 활용한 실험을 진행하였다.

• Structural Engineering and Mechanics
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• 제67권1호
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• pp.45-52
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• 2018

Several techniques have been developed for shear strengthening of reinforced concrete (RC) members by using fiber reinforced polymer (FRP) composites. However, debonding of FRP retrofits from concrete substrate still deemed as a challenging concern in their application which needs to be scrutinized in details. As a result, this paper reports on the results of an experimental investigation on shear strengthening of RC beams using near surface mounted (NSM) FRP reinforcing bars. The main objective of the experimentation was increasing the efficiency of shear retrofits by precluding/postponing the premature debonding failure. The experimental program was comprised of six shear deficient RC beams. The test parameters include the FRP rebar spacing, inclination angle, and groove shape. Also, an innovative modification was introduced to the conventional NSM technique and its efficiency was evaluated by experimental observation and measurement. The results testified the efficiency of glass FRP (GFRP) rebars in increasing the shear strength of the test specimens retrofitted using conventional NSM technique. However, debonding of FRP bars impeded exploiting all retrofitting advantages and induced a premature shear failure. On the contrary, application of the proposed modified NSM (MNSM) technique was not only capable of preventing the premature debonding of FRP bars, but also could replace the failure mode of specimen from the brittle shear to a ductile flexural failure which is more desirable.

• 복합신소재구조학회 논문집
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• 제5권4호
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• pp.24-35
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• 2014

An experimental study on the structural behavior of connection types between approach slab and integral abutment has been done for three typical bar connections. Typical hinge style reinforcing bar detail for its connection is preferred in order to accommodate rotation of the approach slab among engineers. However, the straight horizontal bars can be used as connection detail accomodate structural capacity. Total six specimens with three types of rebar detail are tested for direct tensile and bending load. The characteristic structural behaviors are carefully monitored and all the strain gauge data obtained are analyzed. It is shown that the structural performance of all the specimens well exceed its design allowance. Several design suggestions are given based on careful reviews on the experiment.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.1081-1084
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• 2008

고강도 콘크리트의 적용 확대에 반해, 현행 철근의 정착 및 이음 산정식은 70MPa 미만의 콘크리트로 한정되어 있으며, 50MPa 이상에서는 압축이음길이가 인장이음보다 길어지는 현상이 발생하는 등 관련 기술이 미비한 상태이다. 본 연구에서는 고강도 콘크리트에서 콘크리트 압축강도, 철근간격, 직교방향 보강 철근의 위치와 보강량에 따른 철근 압축이음내력 특성을 평가하였다. 압축이음된 22mm 철근을 주근으로 가지는 총 64개의 기둥 실험체를 제작하여, 단조 일축 압축 하중을 파괴 시 까지 재하하여 실험을 수행하였다. 실험결과 콘크리트의 압축강도, 압축 이음 길이, 철근간격 및 직교방향 보강 철근 등이 철근의 압축이음 내력을 결정하는 주요한 요소로 작용하는 것으로 분석되었다.

• Structural Engineering and Mechanics
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• 제59권5호
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• pp.867-883
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• 2016

In this paper, the effects of steel-fiber and rebar reinforcements on the ultimate bearing strength of the local anchorage zone were investigated based on experiments and comparisons between test results and design-equation predictions (AASHTO 2012, NCHRP 1994). Eighteen specimens were fabricated using the same anchorage device, which is one of the conventional anchorage devices, and two transverse ribs were used to secure an additional bearing area for a compact anchorage-zone design. Eight of the specimens were reinforced with only steel fiber and are of two concrete strengths, while six were reinforced with only rebars for two concrete strengths. The other four specimens were reinforced with both rebars and steel fiber for one concrete strength. The test and the comparisons between the design-equation predictions and the test results showed that the ultimate bearing strength and the section efficiency are highly affected by the reinforcement details and the concrete strength; moreover, the NCHRP equation can be conservatively applied to various local anchorage zones for the prediction of the ultimate bearing strength, whereby conditions such as the consideration of the rib area and the calibration factor are changed.

• Earthquakes and Structures
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• 제24권2호
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• pp.97-109
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• 2023

This experimental study investigates the effectiveness of applying carbon fiber reinforced polymer (CFRP) jackets for the retrofit of short reinforced concrete (RC) columns with inadequate transverse reinforcement and stirrup spacing to longitudinal rebar diameter equal to 12. RC columns scaled at 1/3, with round and square section, were subjected to axial compression up to failure. A damage scale is introduced for the assessment of the damage severity, which focusses on the extent of buckling of the longitudinal rebars. The damaged specimens were subsequently repaired with unidirectional CFRP jackets without any treatment of the buckled reinforcing bars and were finally re-tested to failure. Test results indicate that CFRP jackets may be effectively applied to rehabilitate RC columns (a) with inadequate transverse reinforcement constructed according to older practices so as to meet modern code requirements, and (b) with moderately buckled bars without the need of previously repairing the reinforcement bars, an application technique which may considerably facilitate the retrofit of earthquake damaged RC columns. Factors for the estimation of the reduced mechanical properties of the repaired specimens compared to the respective values for intact CFRP-jacketed specimens, in relation to the level of damage prior to retrofit, are proposed both for the compressive strength and the average modulus of elasticity. It was determined that the compressive strength of the retrofitted CFRP-jacketed columns is reduced by 90% to 65%, while the average modulus of elasticity is lower by 60% to 25% in respect to similar undamaged columns jacketed with the same layers of CFRP.

• Corrosion Science and Technology
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• 제23권3호
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• pp.195-202
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• 2024

A zinc mesh sacrificial anode cathodic protection method is recently being developed to protect the reinforced concrete structure in a marine environment. However, comprehensive information regarding the cathodic protection technology applied to reinforced concrete test specimens utilizing zinc mesh sacrificial anodes remains limited. Particularly, no research has investigated the effective range of sacrificial anode cathodic protection in a reinforced concrete structure regarding the transmission of protection current from zinc mesh sacrificial anode to the reinforced concrete structure, particularly concerning effects of temperature variations. This study examined the distribution of potential and current using a long single rebar and several segment reinforcing bars inside a horizontal beam. Vertical pile specimens were applied with a zinc mesh sacrificial anode to simulate concrete bridges or harbor structures. To check the effect of cathodic protection, cathodic protection potential and current of the reinforced concrete specimens were measured and 100 mV depolarization criterion test was performed. It was confirmed that effect of cathodic protection varied depending on resistivity and temperature. The cathodic protection test of pile specimens revealed that the maximum reachable range of cathodic protection current was 10 cm from the waterline as observed in the experiment.