• KCI Concrete Journal
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• 제11권3호
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• pp.181-189
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• 1999

An experimental study was performed on the Pull-out behavior of 90-deg standard hooks from the exterior beam-column connections. the effects of the number of hooked bars and fiber reinforcement of the joint area were investigated with the following conclusions : (1) Under the pull-out action of hooked bars. the damage and cracking of joint area the number of hooks pulling out from a joint increases; (2) Substitution of the transverse column (confining) reinforcement with steel fibers at the joint region effectively reduces the extent of cracking in exterior joints caused by the pull-out of hooked bars; (3) The pull-out strength and post-peak ductility of hooked bars are adversely influenced by the increase in number of hooks pulling out from an exterior joint. Current hooked bar anchorage design guidelines may be improved by considering the effect of the number of hooked bars on anchorage conditions at the exterior joints; and (4) The strength and ductility of hooked bars under pull-out forces are positively influenced by substituting the conventional confining reinforcement of exterior joints with steel fibers . The application of steel fibers to the exterior joints is an effective technique for improving the anchorage conditions of hooked bars, and also for reducing the congestion of reinforcement in the beam-column connections.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 춘계 학술논문 발표대회
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• pp.11-12
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• 2016

The contemporary buildings are becoming super-taller gradually as the industry evolves. Accordingly, winter concrete also became an important element for the year-round construction since shortening of a construction duration became important. Accordingly, this research team once developed a double bubble sheet as concrete cover curing compound during winter. But since there is no proper countermeasure for the exposed reinforcement bars, it is worried that the concrete can be damaged by exposed frozen reinforcement bars at a low temperature during the initial period. Therefore, in this study, it is intended to review the temperature history of the reinforcement bars depending on changes of the covering methods of the exposed reinforcement bars by using bubble sheets.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2013년도 춘계 학술논문 발표대회
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• pp.71-72
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• 2013

This study investigates the effect of the diameters of reinforcement bars located in an euro-form before placing concrete in a cold weather condition. The diameters of reinforcement bars with 13 mm, 19 mm, 25 mm and 32 mm were prepared for the experimental tests. Results showed that the larger the size of the diameter of the bars, the higher were the temperature drop. However, this study found that its effect on the temperature drop of the bars was insignificant.

• International Journal of Concrete Structures and Materials
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• 제18권3E호
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• pp.151-159
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• 2006

A total of 32 pullout tests were performed for the multiple headed bars relatively deeply embedded in reinforced concrete column-like members. The objective was to determine the minimum embedment depth that was necessary to safely design exterior beam-column joints using headed bars. The variables for the experiment were embedment depth of headed bar, center-to-center distance between adjacent heads, and amount of supplementary reinforcement. Regular strength concrete and grade SD420 reinforcing steel were used. The results of the test the indicated that a headed bar embedment depth of $10d_b$ was not sufficient to have relatively closely installed headed bars develop the pullout strength corresponding to the yield strength. All the experimental variables, influenced the pullout strength. The pullout strength increased with increasing embedment depth and head-to-head distance. It also increased with increasing amount of supplementary reinforcement. For a group of closely-spaced headed bars installed in a beam-column joint, it is recommended to use column ties at least 0.6% by volume, 1% or greater amount of column main bars, and an embedment depth of $13d_b$ or greater simultaneously, to guarantee the pullout strength of individual headed bars over 125% of $f_y$ and ductile load-displacement behavior.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.203-208
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• 2001

Objectives of this study included design of head and evaluation of the pullout performance of the headed reinforcement that can be used to replace standard hooks in the building exterior beam-column joints. Results of 36 pullout tests are presented. Test variables included reinforcing bar diameters (16-25mm), embedment depth (6-7db), transverse reinforcement, and single-vs.-group pullout behavior. The square head designed had gross area of 4Ab and thickness of db. The headed reinforcement made of Dl6 bars developed pullout strengths close to the bar yield strength, but larger bars developed strengths smaller than the yield strengths. The pullout resistance increased with decreasing spacing of the transverse reinforcement. Use of column ties with 6.0-db spacing improved the pullout performance of the headed bars without causing difficulties in fabricating the specimens. The comparison of the pullout performances between the headed bars and the standard hooks revealed that strengths, stiffnesses, and ductile behaviors are about the same.

• 콘크리트학회논문집
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• 제16권4호
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• pp.451-458
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• 2004

본 연구는 재래 철근과 Fiber Reinforced Polymer 보강재를 사용한 Hybrid Reinforcement System의 기본 개념과 적용성에 대해 기술하고 있다. 콘크리트 교량상관은 보로서 지지되고 상하 두층의 보강재로 인장보강되어 있다. HRS를 이용한 콘크리트 교량상판에서는 보 지지점 부근의 부모멘트에 대한 상부 인장력은 FRP 봉으로 저항하고 보 지지점 중앙부근의 하부인장력은 재래의 철근으로 저항한다. HRS를 이용한 콘크리트 교량상판은 FRP 봉은 비 부식성이고, 부식되기 쉬운 철근은 교량상판 위로부터 가급적 멀리하여 부식물질의 침투를 막을 수 있는 장점이 있다. HRS를 이용한 콘크리트 교량상판은 또한 극한상태에서 충분한 연성을 가지고 있다. 그 이유는 1) FRP봉은 철근보다 탄성계수가 낮고 파단시의 최대 변형률이 크며, 2) 충분한 FRP 보강량을 사용하면 극한변형률을 낮출 수 있으며, 3) 부모멘트 구간의 일부를 비부착시켜 극한 변형률을 낮출 수 있다. 실험 연구 결과 보통의 FRP보강비의 범위에서는 FRP 및 HRS 콘크리트 슬래브는 FRP봉의 파단이 아니라 콘크리트의 압축에 의해 파피됨을 보여주고 있다. 그러므로 HRS를 이용한 연속 콘크리트 교량상관에서는 정모멘트부의 하부철근이 먼저 항복하여 소성힌지를 형성하고 나중에 부보멘트나 정모멘트부의 콘크리트가 압축파괴되어 FRP 콘크리트 슬래브에 비하여 상당한 소성에너지를 소모한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.929-934
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• 2002

Eight full-scale columns were constructed and tested under monotonic axial compression loading to investigate the influence of headed bars on the confinement of the concrete. One column represented a column with no transverse reinforcement and another column had poor detailing and little confinement. A third column contained seismic hoops and crossties, which represented current detailing practice for significant confinement. A fourth column test is conducted to investigate the response with the seismic crossties replaced by headed bars. Two column specimens were constructed and tested with all of the transverse reinforcement provided by headed bars. These six specimens enabled an assesment of the effectiveness of headed bars in confining the concrete. It was found that the use of headed bars improved the confinement of the columns. Two additional specimens were constructed without any transverse reinforcement. These columns were later retrofitted, by drilling horizontal holes in the columns, adding special headed bars (one head fixed and the other head threaded) and then filling the drilled holes with epoxy. These retrofitted specimens with these added headed bars provided insight into the rehabilitation of older structures containing poorly detailed columns. All of the test specimens were instrumented to determine strain localization during failure and to monitor the strain in the longitudinal and transverse reinforcement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.1091-1096
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• 2003

Pullout tests of single headed bars using plain concrete blocks indicate that the embedment depth of $10d_b$ is in general required for the headed bars to develop pullout strength equivalent to 125% of bar yield strength. In this experimental study, test results of multiple headed bars installed in reinforced concrete column sections are presented. Test variables included embedment depth, column main reinforcement ratio, and spacing of column ties. 2D29 bars were pulled out at one time from normal strength concrete. Test results indicated that the embedment depths, column tie spacings, and column main reinforcement ratios all influenced the pullout strengths of the headed bars. When the embedment depth was not sufficient, narrow tie spacings especially resulted in increased pullout strengths of the headed bars. Test results also indicated that the embedment depth of 15㏈ was sufficient for the closely spaced two headed bars (head-to-head spacing =$6d_b$) to develop pullout strength equivalent to 125% of the bar yield strength.

• KCI Concrete Journal
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• 제14권3호
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• pp.102-110
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• 2002

Results of an experimental study on the pullout behavior of the headed reinforcement are presented. A total of 48 pullout tests was performed to evaluate pullout strengths and load-displacement behaviors in pullout of the headed bars. The square steel heads had gross area of 4 $A_{b}$ and thickness of $d_{b}$ The test program consisted of three pullout test groups: Simple and Edge pullout tests using plain concrete slabs, comparison of pullout performances between the standard hooks and the headed reinforcement, and pullout tests of headed reinforcement using reinforced concrete columns. Test variables included concrete strengths ( $f_{c}$' = 27.1MPa, 39.1MPa), reinforcing bar diameters (D16~D29), embedment depths (6 $d_{b}$~12 $d_{b}$), edge conditions, column reinforcement, and single-vs.-multiple bar pullout. Test results revealed that the heads effectively provided the pullout resistances of the deformed bars in tension. The load-displacement behaviors were similar between the 90-degree hooks and the headed reinforcement. When a multiple number of headed bars installed with small head-to-head spacings was pulled out, reinforcement designed to run across the concrete failure surface in a direction parallel to the headed bars helped improve the pullout performances of the headed reinforcement.t.ement.t.

• Structural Engineering and Mechanics
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• 제69권4호
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• pp.399-405
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• 2019

The present study assessed the reliability-based reinforcement ratio of FRP reinforced concrete structure applying recycled coarse aggregate (RCA) concrete. The statistical characteristics of FRP bars and RCA concrete were investigated from the previous literatures and the mean value and standard deviation were employed for the reliability analysis. The statistics can be regarded as the material uncertainty for configuring the probability distribution model. The target bridge structure is the railway bridge with double T-beam section. The replacement ratios of RCA were 0%, 30%, 50%, and 100%. From the probability distribution analysis, the reliability-based reinforcement ratios of FRP bars were assessed with four cases according to the replacement ratio of RCA. The reinforcement ratio of FRP bars at RCA 100% showed about 17.3% higher than the RCA 0%, where the compressive strength at RCA 100% decreased up to 27.5% than RCA 0%. It was found that the decreased effect of the compressive strength of RCA concrete could be compensated with increase of the reinforcement ratio of FRP bars. This relationship obtained by the reliability analysis can be utilized as a useful information in structural design for FRP bar reinforced concrete structures applying RCA concrete.