• 한국지반공학회논문집
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• 제25권10호
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• pp.5-15
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• 2009

본 논문에서는 옥천 및 창녕지역에서 총 24회 수행한 암반앵커 현장인발시험의 결과를 나타내었다. 시험앵커의 정착깊이는 1~6m로 서로다른 암반내에 설치하였다. 앵커의 대부분은 고강도 이형철근인 SD40-D51mm를 사용함으로써 다른 파괴가 일어나기 전에 암반파괴가 먼저 일어나도록 유도하여 암반의 인발저항력을 파악하고자 하였으며, 일부에서는 SD40-D32mm앵커를 설치하여 앵커의 파괴도 아울러 살펴보았다. 많은 시험에서 파괴는 항복에 이르는 극한하중까지 관찰할 수 있었으며, 암반파괴형상은 암반이 들어올려지면서 방사상으로 균열이 발달하는 형태를 나타내었다. 또한 시멘트그라우트와 텐던사이의 부착강도를 평가하고자 방식쉬이스가 설치된 앵커에 대해 실내실험을 실시하였다. 실험결과 텐던-그라우트 사이의 부착강도는 그라우트 일축압축강도의 18~25%로 나타났으며, 방식쉬이스에 의한 부착력 감소는 무시할 수 있을 정도로 작게 나타났다.

• Structural Engineering and Mechanics
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• 제7권4호
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• pp.413-432
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• 1999

A macro-element model is developed to account for shear deformation and bond slip of reinforcement bars in the beam-column joint region of reinforced concrete structures. The joint region is idealized by two springs in series, one representing shear deformation and the other representing bond slip. The softened truss model theory is adopted to establish the shear force-shear deformation relationship and to determine the shear capacity of the joint. A detailed model for the bond slip of the reinforcing bars at the beam-column interface is presented. The proposed macro-element model of the joint is validated using available experimental data on beam-column connections representing exterior joints in ductile and nonductile frames.

• Steel and Composite Structures
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• 제13권5호
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• pp.473-487
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• 2012

An experimental study was performed to investigate the seismic performance of steel reinforced concrete (SRC) special-shaped columns. For this purpose, 17 steel reinforced concrete special-shaped column specimens under low-cyclic reversed load were tested, load process and failure patterns of the specimens with different steel reinforcement were observed. The test results showed that the failure patterns of these columns include shear-diagonal compression failure, shear-bond failure, shear-flexure failure and flexural failure. The failure mechanisms and characteristics of SRC special-shaped columns were also analyzed. For different SRC special-shaped columns, based on the failure characteristics and mechanism observed from the test, formulas for calculating ultimate shear capacity in shear-diagonal compression failure and shear-bond failure under horizontal axis and oblique load were derived. The calculated results were compared with the test results. Both the theoretical analysis and the experimental results showed that, the shear capacity of T, L shaped columns under oblique load are larger than that under horizontal axis load, whereas the shear capacity of +-shaped columns under oblique load are less than that under horizontal axis load.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.105-108
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• 2008

국외적으로 고강도 재료에 대한 연구가 활발히 진행되고 있는 반면 국내에서는 고강도 재료에 대한 연구가 미비한 실정이다. 일반적으로 RC 보의 전단 저항은 보강근의 전단 저항 보강근의 양($p_w$), 항복 강도($f_{wy}$)에 지배적인 영향($p_wf_{wy}$)을 받는다. 따라서 고강도 전단 보강을 사용하는 것으로 전단 보강근의 양을 저감시키는 효과가 있을 것으로 판단된다. 이에 본 연구는 고강도 보강근과 보통 강도 비 폐쇄형 횡 보강근의 혼용을 통한 전단 보강근의 양을 줄여 시공 능률향상과 부착성능 향상을 유도하여 부재내력을 증진하기 위한 실험적 연구를 수행하였다.

• Structural Engineering and Mechanics
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• 제32권2호
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• pp.251-267
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• 2009

Reinforced concrete (RC) structures consist of two different materials: concrete and steel bar. The stress transfer behaviour between the two materials through bond plays an important role in the load-carrying capacity of RC structures, especially when they subject to lateral load such as blast and seismic load. Therefore, bond and slip between concrete and reinforcement bar will affect the response of RC structures under such loads. However, in most numerical analyses of blast-induced structural responses, the perfect bond between concrete and steel bar is often assumed. The main reason is that it is very difficult to model bond slip in the commercial finite element software, especially in hydrodynamic codes. In the present study, a one-dimensional slide line contact model in LS-DYNA for modeling sliding of rebar along a string of concrete nodes is creatively used to model the bond slip between concrete and steel bars in RC structures. In order to model the bond slip accurately, a new approach to define the parameters of the one-dimensional slide line model from common pullout test data is proposed. Reliability and accuracy of the proposed approach and the one-dimensional slide line in modelling the bond slip between concrete and steel bar are demonstrated through comparison of numerical results and experimental data. A case study is then carried out to investigate the bond slip effect on numerical analysis of blast-induced responses of a RC column. Parametric studies are also conducted to investigate the effect of bond shear modulus, maximum elastic slip strain, and damage curve exponential coefficient on blast-induced response of RC columns. Finally, recommendations are given for modelling the bond slip in numerical analysis of blast-induced responses of RC columns.

• Structural Engineering and Mechanics
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• 제73권3호
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• pp.353-365
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• 2020

In the previous studies, the authors proposed the use of laminated veneer lumber - carbon fiber reinforced polymer (LVL-CFRP) composite beams for structural application. Bond strength of the LVL-to-CFRP interface and flexural strengthening schemes to increase the bending capacity subjected to positive and negative moment were discussed in the previous works. In this article, theoretical models are proposed to predict the moment capacity when the LVL-CFRP beams are subjected to negative moment. Two common failure modes - CFRP fracture and debonding of CFRP are considered. The non-linear model proposed for positive moment is modified for negative moment to determine the section moment capacity. For the debonding based failure, previously developed bond strength model for CFRP-to-LVL interface is implemented. The theoretical models are validated against the experimental results and then use to determine the moment-rotation behaviour and rotational rigidity to compare the efficacy of various strengthening techniques. It is found that combined use of bi- and uni-directional CFRP U-wrap at the joint performs well in terms of both moment capacity and rotational rigidity.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.387-392
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• 1999

The bond performance of prestressing strands is still not well understood and is still in controversy on the validity of the test results up to today, although it is a basic information to desing the prestressed pretensioned concrete beams. Different transfer length has been found for a product of the same company, but of the different production methods and factories in the United States. It is necessary to determine optimum transfer bond length of the domestic stands because the ultimate flexural and shear capacity in a section of prestressed concrete beams are evaluated under the assumption that the anchorage bond failure shall not happen. The transfer lenght of low-relaxation, Gr 270, and 1/2" seven-wire prestressing strands from four domestic companies will be evaluated by the concrete strain method. The recent concept of the 95% Maximum Average Strain Method suggested by Russel et al. will be considered to obtain the transfer length of domestic strands. It will be also evaluated if the domestic strands are conform to ACI 318-95.8-95.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.393-398
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• 1999

The main objective of this project is to define the ultimate bond performance of domestic prestressing strands in the precast prestensioned concrete beams. Eight specimens from four different companies were fabricated and tested in this study. Four-point loading tests were performed on the beams of domestic strands with an arbitrary anchorage length. The research has shown, that all seven specimens except one failed in bond are capable of developing their full flexural capacity and the strands within them are fully anchored even with the sudden transfer of frame cutting. Following results are summarized from the tests conducted. 1) All of the specimens are tested at an embedment lengths much shorter than those required by the ACI code, failed in flexure except one failed in bond. 2) It seems that the beam depth can not be an effective variable to estimate the bond length within these sections and length of specimens on this tests. 3) The development length with the stirrup space which are considered for correction factors in the equations of Russel and Paulsgrove, is fully accurate to determine the required length for the beam tested in this research.

• Computers and Concrete
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• 제1권4호
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• pp.401-416
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• 2004

This paper presents investigation of a three-dimensional (3-D) nonlinear finite element model analysis to examine the behavior of reinforced concrete beams strengthened with Carbon Fiber Reinforced Polymer (CFRP) composites to enhance the flexural capacity and ductility of the beams. Three-dimensional nonlinear finite element models were developed between the internal reinforcement and concrete using a smeared relationship. In addition, bond models between the concrete surface and CFRP composite were developed using a smeared bond for general analyses and a contact bond for sensitivity analyses. The results of the FEA were compared with the experimental data on full-scale members. The results of two finite-element bonding models showed good agreement with those of the experimental tests.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.579-584
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• 2003

For strengthening deteriorated concrete structures, externally bonded FRP sheets or plates using epoxy resins are widely used. For the external FRP composites to be effective in improving the performance of the structure, bond between FRP composites and concrete is required. In general, the most frequently observed failure mode in FRP strengthened concrete structures is debonding failure at the interfacial section between FRP and concrete. Therefore, it is very important to find out the interfacial behavior properties. This paper presents experimental results of the relationship of concrete and FRP sheet for some conditions including concrete compressive strength, concrete surface preparation to observe the bond behavior between concrete and FRP sheet and various anchorage types to increase the bond capacity of FRP sheet.