• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.298-304
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• 2017

The corrosion of reinforcements embedded in concrete causes some durability problems in reinforced and prestressed concrete structures. The epoxy coated reinforcements are one of the effective and reliable methods to prevent corrosion of reinforcements. However, it has been known that the epoxy coating reduces the bond capacity of reinforcement to concrete. This paper investigates the bond behaviors of epoxy coated reinforcements experimentally using direct pull-out test. Bond behaviors of epoxy coated bars for various reinforcement diameters of 10, 19 and 29mm and thicknesses of cover concrete of 1, 2, 3, and $4.5c/d_b$ (ratio of cover to bar diameter) are examined. Total 66 specimens were manufactured and tested according to the RILEM standard method. As the diameters of the epoxy coated reinforcements increase, the difference of bond strength between epoxy coated reinforcements and uncoated bars also increases. Epoxy coated bars showed more than 85% bond performance compared to those of uncoated bars. A new formular for estimating basic development length of epoxy coated reinforcement based on equilibrium equation is proposed using this experimental result.

• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.62-68
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• 2001

The purpose of this paper was to investigate the relations between the unbonded tendon stress and the influential parameters which were bonded reinforcement ratio, span/depth ratio, and loading type. To this end, first, the influence of parameters were examined with twenty eight test results obtained from references. Then, an experimental study was carried out with 21 test specimens. The investigation with previous and current tests revealed the followings; (1) The bonded reinforcement ratio and prestressing ratio were proved to be an important variables on the unbonded tendon stress. (2) The ratio of span to depth and type of loading affected partially the unbonded tendon stress although their effects varied depending on bonded reinforcement ratio. (3) AASHTO LRFD Code and Moon/Lim\`s design equation predicted the test results well with some safety margins.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.638-644
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• 2002

The stress-strain relationship of polymer concrete flexural member was evaluated using C-shaped polyester concrete specimen, the compressive strength of which is 1400 kgf/$\textrm{cm}^2$. Eccentric compression test was performed to estimate the parameters, ${\alpha}$, ${\beta}$1, ${\gamma}$ for equivalent rectangular stress block. The ultimate moment strength ware obtained from the bending test on reinforced polymer concrete beams which were prepared with S different tensile steel ratios with a shear span ratio of 4.0. These values were compared with theoretical ultimate moment strengths, which were obtained using the parameters ${\alpha}$=0.61 and ${\beta}$1=0.73 from stress-stain curves of C-shaped specimens. The results showed that, when tensile steel ratio was over 0.50 $\rho$b, the experimentally obtained moment strengths were well matched with theoretically calculated values. In order to develop accurate criteria for polymer concrete flexural members, however, many other expermental studies for parameter determination are necessary using C-shaped specimens which have various compressive strengths and different sizes.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.225-231
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• 1997

콘크리트 압축강도 및 전단스팬비의 변화에 의한 고강도 철근콘크리트 춤이 큰 보의 전단거동 및 내력특성을 파악하기 위한 실험적 연구를 하였다. 춤이 큰 보는 하중작용점과 하중지지점을 연결하는 사균열의 확대에 의해 취성전단파괴양상을 나타내었으며 하중작용점 하중 지지점의 콘크리트 압괴를동반하는 전단압축 및 전단인장파괴 형태로 최종파괴되었다. 전단스팬비가 감소함에 따라 사균열전단응력 및 최대전단응력은 크게 증가하였으며, ACI 및 CIRIA규준식은 부재의 최대전단응력을 비교적 정확하게 예측하고 있음을 파악하였다.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.149-160
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• 1999

This paper is a part of a research aimed at the verification of basic design rules of high-strength concrete columns. A total of 32 column specimens were tested to investigate structural behavior and strength of eccentrically loaded reinforced concrete tied columns. Main variables included in this test program were concrete compressive strength. steel amount, eccentricity, and slenderness ratio. The concrete compressive strength varied from 356 kg/$cm^2$ to 951 kg/$cm^2$ and the longitudinal steel ratios were between 1.13 % and 5.51 %. Test results of column sectional strength are compared with the results of analyses by ACI rectangular stress block, trapezoidal stress block, and modified rectangular stress block. Axial force-moment-curvature analysis is also performed for predicting axial load-moment strength and compared with the test results. The ACI rectangular stress block provides over-estimated column strengths for the lightly reinforced high strength column specimens. The calculated strengths by moment-curvature analyses are highly affected by $k_3$ values of the concrete stress-strain curve. Observed failure mode. concrete ultimate strain, and stress block parameters are discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.79-87
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• 1991

An efficient numerical procedure for material and geometric nonlinear analysis of reinforced concrete shells under monotonically increasing loads through their elastic, inelastic and ultimate load ranges is developed by using the finite element method. The 8-node Serendipity isoparametric element developed by the degeneration approach including the transverse shear deformation is used. A layered approach is used to represent the steel reinforcement and to discretize the concrete behavior through the thickness. The total Lagrangian formulation based upon the simplified Von Karman strain expressions is used to take into account the geometric nonlinearity of the structure. The material nonlinearities are taken into account by comprising the tension, compression, and shear models of cracked concrete and a model for reinforcement in the concrete; and also a so-called smeared crack model is incorporated. The steel reinforcement is assumed to be in a uniaxial stress state and is modelled as a smeared layer of equivalent thickness. This method will be verified a useful tool to account for geometric and material nonlinearities in detailed analysis of reinforced concrete concrete shells of general form through numerical examples of the sequential paper( ).

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.435-444
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• 2005

This paper predicted the shear behavior of reinforced concrete columns using Transformation Angle Truss Model (TATM) considered the effects of bending moment and axial force. Nine columns with various shear span- to-depth ratios and axial force ratios were tested to verify the theoretical results obtained from TATM. Fine linear displacement transducers (LVDT) were attached to a side of the column near the shear critical region to measure the curvature, the longitudinal and transverse axial deformations, and the shear deformation of the column. The test was terminated when the value of the applied load dropped to about $85\%$ of the maximum-recorded load in the post-peak descending branch. All the columns were failed in shear before yielding of the flexural steel. The shear strength and the stiffness of the columns increased, as the axial force increased and the shear span-to-depth ratio decreased. Shear stress-shear strain and shear stress-strain of shear reinforcement curves obtained from TATM were agreed well with the test results in comparison to other truss models (MCFT, RA-STM, and FA-STM).

• Magazine of the Korea Concrete Institute
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• v.7 no.1
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• pp.145-155
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• 1995

The purpose of this paper is to present an analysis method which can exactly analyze load-deflection relationships. crack propagations and stresses and strains of steel reinforccnlent and concrete in hehaviors of elastic, mclastic and ultlmate ranges of reinforced concretc beams under monotonically increasing loads. For these purposes, the material nonlinearities are taken into account by comprising the tension. compression and shear models of cracked concrete and a model for reinforcement in the concrete. Smeared crack model is used as a modeling of concrete. The steel reinforcement is assumed to be in an uniaxial stress state and modeled srncaretl layers of eqivalent thickness and line elernents for correct positiori arid behavior. For the verification of application and validity of the method proposed in this paper, several numerical examples are analyzed and compared with those from other researchers. As a results, this method shown in 3.5-15(%) error is correct.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.90-98
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• 2018

Recently, various reinforced concrete joints have been used in reinforced concrete structures. Therefore, it is important to grasp the tensile properties of the spliced rebar. In this study, uniaxial tensile tests were conducted on Grade 60 D22(#7), D29(#9), and two kinds of couplers manufactured according to ASTM A615 standard for evaluating ductility of coupler joints. The strain was measured using an image processing method more accurate and capable of measuring at various points freely. As the result of uniaxial tensile test, it was possible to calculate the stress-strain relationship and the longitudinal strain distribution according to the stress stages and it was founded that the average strain becomes lower as more occupying the coupler joint portions in the same gauge length. In addition, the empirical equations are proposed to account for the effect of the length of the coupler on the ultimate strain and the rupture strain.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.13-16
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• 2008

In a tension-controlled section, all steel tension reinforcement is assumed to yield at ultimate when using the strength design method to calculate the nominal flexural strength of members with steel reinforcement arranged in multiple layers. Therefore, the tension force is assumed to act at the centroid of the reinforcement with a magnitude equal to the area of tension reinforcement times the yield strength of steel. Because FRP materials have no plastic region, the stress in each reinforcement layer will vary depending on its distance from the neutral axis. Similarly, if different types of FRP bars are used to reinforce the same member, the stress level in each bar type will vary, and the member will show different behavior from our expectation. In this study, six high-strength concrete beam specimens reinforced with conventional steels, CFRP bars, and GFRP bars as flexural reinforcements were constructed and tested. The members reinforced with hybrid reinforcements showed higher stiffness, smaller crack width, and better ductility than the members reinforced with single type of FRP bars.