• Computers and Concrete
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• 제14권3호
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• pp.327-345
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• 2014

This paper presents the application of multi-gene genetic programming (MGP) technique for modeling the bond strength of ribbed steel bars in concrete. In this regard, the experimental data of 264 splice beam tests from different technical papers were used for training, validating and testing the model. Seven basic parameters affecting on the bond strength of steel bars were selected as input parameters. These parameters are diameter, relative rib area and yield strength of steel bar, minimum concrete cover to bar diameter ratio, splice length to bar diameter ratio, concrete compressive strength and transverse reinforcement index. The results show that the proposed MGP model can be alternative approach for predicting the bond strength of ribbed steel bars in concrete. Moreover, the performance of the developed model was compared with the building codes' empirical equations for a complete comparison. The study concludes that the proposed MGP model predicts the bond strength of ribbed steel bars better than the existing building codes' equations. Using the proposed MGP model and building codes' equations, a parametric study was also conducted to investigate the trend of the input variables on the bond strength of ribbed steel bars in concrete.

• 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.

• Computers and Concrete
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• 제31권1호
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• pp.53-69
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• 2023

The rotational stiffness of a semi-rigid beam-to-column connection plays an important role in the reduction of the second-order effects in the precast concrete skeletal frames. The aim of this study is to present a detailed nonlinear finite element study to reproduce the experimental response of a semi-rigid precast beam-to-column connection composed by corbel, dowel bar and continuity tie bars available in the literature. A parametric study was carried using four arrangements of the reinforcing tie bars in the connection, including high ratio of the continuity tie bars passing around the column in the cast-in-place concrete. The results from the parametric study were compared to analytical equations proposed to evaluate the secant rotational stiffness of beam-to-column connections. The good agreement with the experimental results was obtained, demonstrating that the finite element model can accurately predict the structural behaviour of the beam-to-column connection despite its complex geometric configuration. The secant rotational stiffness of the connection was good evaluated by the analytical model available in the literature for ratio of the continuity tie bars of up to 0.69%. Precast beam-to-column connection with a ratio of the continuity tie bars higher than 1.4% had the secant stiffness overestimated. Therefore, an adjustment coefficient for the effective depth of the crack at the end of the beam was proposed for the analytical model, which is a function of the ratio of the continuity tie bars.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.531-546
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• 2022

Headed bars are often used when there is insufficient space for a straight or curved bar to be fully developed to ensure the transference of forces between steel and concrete in several types of connections between structural members. In such cases, the concrete breakout strength of the headed bars can be a critical point of the design and must be considered appropriately. This paper evaluates the tensile strength of headed bars embedded in reinforced concrete members, failing due to concrete breakout. Four experimental tests on headed bars embedded in slender concrete members are presented and discussed, showing that strength previsions from the design codes can be significantly conservative as they ignore the contribution from the flexural reinforcement. 3D finite element models were developed using Abaqus Unified FEA to simulate the tested specimens, and it was observed that they were able to reproduce the formation of the concrete cone accurately, besides the response and resistance observed in tests. Furthermore, the experimental, numerical, and design code resistances are compared and discussed. A new equation to evaluate the concrete cone strength of the tested headed bars is proposed, which takes into account parameters not explicitly considered in the current design equations.

• 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 1999년도 봄 학술발표회 논문집(I)
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• pp.647-652
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• 1999

The purpose of this study is to find the bond properties of deformed bars in hign-strength concrete by experimental and analytical method. In this study the following variables were adopted, i.e. (1) the compressive strength of concrete : 270, 400 and 600kg/$\textrm{cm}^2$ (2) the corrosion the bars : corroded and normal bars (3) the mixing ratio of natural and smashed fine aggregate : 7 : 3 and 5 : 5 (natural sand : smashed sand) For analytical method, the finite element analysis is performed. And the Pull-out test is performed as the experimental method.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.602-605
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• 2006

Locating reinforcing bars, in particular to know their accurate depths and horizontal distances, is very important in radar inspection of concrete structures. By the way, it is not easy for an accurate depth and horizontal distance estimation of reinforcing bars in concrete structures by the radar test. This problem can be solved by synthetic aperture radar method. To improve the vertical and horizontal resolution of reinforcing bars in concrete, synthetic aperture radar method was examined in this study.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.211-216
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• 2003

Coated bars are protecting reinforcing bars from corrosion and enhancing durabilities of reinforced concrete structures are tested to evaluate corrosion protection properties. Tests are performed based on the relevant standards of ACI and ASTM, such as chemical resistance, salt water spray, salt crack test and chloride permeability test with the main variable of the coating thickness. Three type materials are tested by Polyethylene, epoxy and bare bar. Test results show good chemical protection property and chloride permeability. Polyethylene coated bar is good coating material than any other materials.

• 전기의세계
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• 제30권6호
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• pp.366-374
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• 1981

In most cases, simulation of induction machines under dynamic conditions have been based on two-phase models using constant circuit parameters. Squirrel cage induction machines with double rotor bars which are made for high starting torgue have lower rotor bars of sufficient depth they cannot be accurately represented by a constant rotor resistance under all operating condition. In this paper, the circuit of three-phase symmetrical induction machines is represented in two-axis model by tensor. A method for simulating three-phase squirrel cage induction machines in a dynamic conditions is presented, and the current distribution in double rotor bars is calculated under dynamic conditions.

• 한국구조물진단유지관리공학회 논문집
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• 제22권1호
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• pp.72-80
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• 2018

초고층 및 장경간 등 대형 구조물에 대한 시공시 부재의 품질이 저하될 정도로 과다한 철근이 배근되고 있다는 문제점이 제기되고 있으며, 최근 건축되고 있는 초고층 건축물에서는 건물의 안정성과 내구성 등을 감안하여 사용 재료의 강도도 점차 증가하고 있다. 초고층 및 장경간 구조물의 시공에서 고강도 철근을 사용할 경우 기존의 일반 강도 철근에 비해 배근량 감소로 인하여 부재에서 배근 간격에도 여유를 줄 수 있어 시공성 향상, 공기단축, 접합부 상세가 간소화 되는 장점이 있다. 이 연구에서는 SD500, SD600 철근을 국내에서 설계되었거나 시공되어진 라멘 구조 형식의 지하주차장 건축물에 적용하여 각 부재별로 철근의 강도에 따른 순수 철근량에 대한 정착 및 이음 철근량 증감을 비교 분석한 결과 다음과 같은 결론을 얻었다. 계산된 철근의 정착 및 이음 물량은 사용철근의 강도가 증가함에 따른 정착 및 이음길이의 증가량과 순수 물량의 감소비율, 사용철근의 직경이 줄였을 때의 단면적 감소 등의 요인들에 의해 정착 및 이음 물량이 결정되었으며, 전체적으로 순수 물량에 대한 정착 및 이음 물량의 비율이 SD400대비 SD500의 경우는 증가하였지만 SD500대비 SD600의 경우는 감소하였다. 이는 보의 정착 및 이음 물량이 전체 정착 및 이음 물량에 미치는 영향이 크기 때문으로 판단된다. 한편 순수 물량에 대한 정착 및 이음 물량의 비율에서 SD400과 SD500의 차이와 SD400과 SD600의 차이가 미미하여 철근의 정착 및 이음 물량이 강도 증가에 따른 전체 철근 물량의 증감에는 큰 영향을 주지 않는 것으로 파악되었다.