• Structural Engineering and Mechanics
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• 제40권6호
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• pp.847-866
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• 2011

The objective of this study was to experimentally investigate the bond-related tension stiffening behavior of flexural reinforced concrete (RC) beams made with lightweight aggregate concrete (LWAC) under various high-cycle fatigue loading conditions. Based on strain measurements of tensile steel in the RC beams, fatigue-induced degradation of tension stiffening effects was evaluated and was, compared to reinforced normal weight concrete (NWC) beams with equal concrete compressive strengths (40 MPa). According to applied load-mean steel strain relationships, the mean steel strain that developed under loading cycles was divided into elastic and plastic strain components. The experimental results showed that, in the high-cycle fatigue regime, the tension stiffening behavior of LWAC beams was different from that of NWC beams; LWAC beams had a lesser reduction in tension stiffening due to a better bond between steel and concrete. This was reflected in the stability of the elastic mean steel strains and in the higher degree of local plasticity that developed at the primary flexural cracks.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.903-908
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• 2001

This paper deals with the estimation of the maximum flexural crack widths using minimum crack spacing for reinforced concrete members. The proposed method utilizes the conventional crack and bond-slip theories as well as bonding transfer length and effects of creep and shrinkage between the reinforcement and concrete. An analytical equation for the estimation of the maximum flexural crack width is formulated as a function of mean bond stress. The validity, accuracy and efficiency of the proposed method are established by comparing the analytical results with the experimental data and the major code specifications (e.g., ACI, CEB-FIP Model code, Eurocode 2, etc.). The analytical results of analysis presented in this paper indicate that the proposed method can be effectively estimated the maximum flexural crack width of the reinforced concrete members.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1993년도 가을 학술발표회 논문집
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• pp.173-178
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• 1993

In order to quantify the effect of transverse reinforcement on the bond splitting behavior of reinforcement monotonic loading tests of 8 slmply beams were carried out. The reinforcing details and material properties were so determined that the bond splitting failure proceded the shear and flexural failure. A bond splitting strength derived from the experimental data and it accounts for following parameters: 1) Concrete Strength 2) Transverse reinforcement ratio and shape 3) Thickness of concrete cover 4)Deformation of reinforcement

• 콘크리트학회논문집
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• 제17권6호
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• pp.903-910
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• 2005

최근 철근콘크리트 구조물의 보강 방법으로 고인장강도를 갖는 섬유복합체를 부재의 외부에 부착시켜 휨 내력을 증진시키는 부착식 보강공법이 널리 사용되고 있으나, 부착되는 섬유복합체의 박리에 의한 파괴강도를 예측하여 설계식에 반영하기 위한 연구는 미흡한 것이 사실이다. 보강재의 박리에 의한 파괴는 부재 전체의 취성적인 파괴를 유도하게 되므로, 부재의 보강설계를 위해서는 이에 대한 검토가 필수적으로 요구되어 진다. 본 연구에서는 보강재의 부착강도에 큰 영향을 미치는 유효부착길이의 개념을 도입하여, 기존 연구 결과로부터 부재의 부착강도를 좌우하게 되는 유효부착길이를 산정 하였으며, 이와 같은 유효부착길이에 의한 보강재의 박리하중을 산정할 수 있는 설계식을 제안하였다. 제안된 설계식은 기존 연구자들의 실험 연구결과와 비교하여 그 신뢰성을 검증하도록 하였으며, 기존 연구자들의 제안식과의 비교를 통하여 본 제안식의 타당성을 증명하였다.

• Computers and Concrete
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• 제17권3호
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• pp.305-322
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• 2016

The work is intended to demonstrate that the loss of bond between concrete and flexural steel which led in recent years a number of flat-slab structures to punching collapse under service loading conditions is also relevant to ultimate limit-state design. It is based on a comparative study of the results obtained from numerical experiments on flat slab-column sub-assemblages. The slabs were designed for punching either in compliance with the EC2 code requirements, which do not allow for such loss of bond, or in accordance with the compressive force-path method which considers the loss of bond between concrete and the flexural reinforcement in tension as the primary cause of punching. The numerical experiments are carried out through the use of a nonlinear finite element analysis package for which, although ample published evidence of its validity exists, additional proof of its suitability for the purposes of the present work is presented.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1990년도 봄 학술발표회 논문집
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• pp.108-115
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• 1990

This paper contains experimental studies on the flexural cracking behabior of PPC one-way slabs. Three post tensioned bonded PPC slabs with the same prestressing ratio and ultimate moment strength were tested. Based upon test results, this paper also presents the crack width prediction formula PPC slab. According to the crack theory developed mainly in Europe, crack width formula is given as the product of crack spacing and mean steel strain after decompression. Aaaaverage crack spacing formula is composed of many factors mainly such as concrete cover, concrete effective area in tension, sum of reinforcing bars perimeters and mixed reinforcements. In particular, it is very important to specify the bond characteristics of mixed reinforcements, since bond characteristics of PC bars are different from those of non-tensioned deformed bars. For this reason, a reduced bond coefficients for PS bars is employed in this study.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.84-87
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• 2004

Nominal flexural strength of RC members strengthened with FRP sheets is generally based on the tensile strength of composite materials obtained from coupon tests. This method is based on the assumption that bond failure does not occur until the FRP sheet reaches its rupture strength. According to the previous researches, however, bond failure often occurs before the FRP sheet reaches its rupture strength. Some attempts were made to control debonding failure by increasing the bonded length of sheet or wrapping the section around their side of the member(U-wrap). In this study, the flexural failure mechanism of RC beams strengthened with AFRP sheets with different bond lengths is investigated. Their strengthening details to prevent the premature debonding failure are also suggested and its effectiveness is verified.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.173-176
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• 2006

The one of the commonly reported failure mode of the RC beam strengthened with FRP was caused by the separation of the concrete cover, so called delamination. Therefore, ACI440 recommended that concrete cover delamination can be prevented in strengthened beams if bond length of FRP composite be exteneded over a point of cracking moment. In this study, the failure mode and the flexural performance of RC beam with different bond length of FRP are estimated. Each bonded length is calculated based on the point of cracking moment with addition or subtraction of specific length(=150mm). The results of this study show that mid-span debonding occurs in the specimen strengthened with CFRP strips which are bonded over the point of cracking moment, while concrete cover deliamination occurs at the termination point of CFRP in the specimen with less bonded length than the point of cracking moment region.

• 구강회복응용과학지
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• 제32권3호
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• pp.169-175
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• 2016

목적: 본 연구의 목적은 수종의 레진계 치아고정 재료의 굴곡강도와 탄성계수를 비교 분석하는 것이다. 연구 재료 및 방법: 레진계 치아고정 재료로 Super-Bond C&B (SB), G-FIX (GF), G-aenial Universal Flo (GU), Filtek Z350 XT (FZ)를 이용하여 각 군당 15개씩 총 60개의 시편을 제작하였다. 3점 굽힘 시험으로 측정된 값에 따라 굴곡강도와 탄성계수를 계산하였다. 실험값은 One-way ANOVA test로 분석하고, Scheffe's test로 사후 검정하였다. 결과: 본 연구의 결과 SB는 다른 재료들과 비교 시 가장 낮은 굴곡강도를 보였으며 GF, GU, FZ는 비슷하게 높은 굴곡강도를 보였다. 탄성계수의 경우 SB가 가장 낮은 값을 보였고 GF는 SB보다는 높지만 GU와 FZ보다는 낮은 탄성계수를 보였으며 GU와 FZ는 유의하게 높은 탄성계수를 보였다. 결론: 동요치 고정을 목적으로 새로 개발된 GU (G-FIX)는 유동성 복합 레진과 수복용 복합 레진과 같이 높은 강도를 보이며 잘 파절되지 않으면서도 상대적으로 유연한 성질을 보여 동요치 고정에 유리할 것으로 사료된다.

• 대한치과보철학회지
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• 제32권3호
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• pp.378-395
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• 1994

The purpose of this study was to investigate the effect of various metal surface treatments and adhesive systems on the flexural bond strength of composite resin to Au-Ag-Cu-Pd alloy. The specimens were divided into nine groups by the combinations of surface treatment methods and adhesive systems. The types of surface treatment in this study were alumina blasting only, alumina blasting-Sn plating, alumina blasting-heating and three kinds of adhesive system used in this study were Silicoater system(Heraeus Kulzer GmbH,Germany), Superbond C & B(Sun Medical Co.,Ltd.,Japan) and Cesead opaque primer(Kurary Co.,Ltd.,Japan). After surface treatments and adhesive systems were applied, each specimen was built up with Dentacolor composite resin (Heraeus Kulzer GmbH,Germany). Four-point flexural bond strength was measured by Instron universal testing machine (Model 4301,U.S.A.) and modes of failure were observed by SEM(JEOL,SSM-840A,Japan). The obtained results were as follows: 1. The group that was bonded with Superbond C & B after alumina blasting-heating shelved the highest bond strength with significant difference among the groups, except the group with Cesead opaque primer after alumina blasting-Sn plating(P<0.05). 2. In the groups bonded with Cesead opaque primer, there was significant difference only in the bond strength between the alumina blasting-Sn plating group and alumina blasting group, where the former showed a higher bond strength(P<0.05). 3. In the groups bonded with Silicoater system, there were no significant differences in bond strength regardless of the surface treatment method(P<0.05). 4. In SEM evaluation, the groups of high bond strength, especially bonded with Superbond C & B after alumina blasting-heating and Cesead opaque primer after alumina blasting-Sn plating, revealed mainly cohesive-adhesive failure, whereas the others showed the tendency of adhesive failure.