• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.2
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• pp.65-72
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• 2000

콘크리트 구조물이 지진 등으로 손상을 입었을 때 그 내부 상태를 파악하는 일은 구조물의 안전성 판단에 필요한 중요 과정중 하나이다 손상도 파악에 사용되는 비파괴 검사 방법 중 레이더법은 현재 콘크리트 부재의 두께와 매립된 철근 및 공동 탐사에 적용되고 있다 레이더법은 다른 비파괴 검사 방법에서와 마찬가지로 측정된 신호의 처리와 해석에 따라 그 결과가 좌우된다 . 이논문에서는 상용 레이더 시스템에서 얻어지는 화상 데이트터를 개선하는 방법을 개발하여 철근이 매립된 콘크리트 시편에 적용하였다 실험에 사용된 기편의 크기는 1,000mm(길이)$\times$600mm (폭) $\times$140mm(두께) 이고 철근의 매립깊이는 표면으로부터 철근 중심까지 60mm 이다 레이더 실측 실험에서 철근의 수평배근 간격을 60 90, 120, 150 mm 로 변화시켜 간격탐사가능성을 시험하였다 결과적으로 상용 시스템에 비해 샹상된 판별효과를 나타냈으며 배근 간격이 90, 120, 150mm 인 시편에서 그 간격을 정확히 찾아내었다.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.393-396
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• 2008

This paper presents the experimental results on the fire performance of high strength concrete(HSC) column made with different tie spacing. Three HSC columns measuring 305${\times}$305mm in cross section were prepared to evaluate the effect of tie spacing with 150, 210, 300mm, respectively. Compressive strength was 69MPa at test. As a result, the fire performance of HSC columns was greatly influenced by tie spacing. The fire resistance increases with decreasing the tie spacing.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.87-98
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• 2011

Crack formations are inevitable in reinforced concrete structures. To estimate crack widths, empirical formulae are used widely and indirect crack controling methods of limiting bar spacing and bar diameter are also used due to their simplicity. In EC2, the characteristic crack width is calculated by multiplying maximum crack spacing and average strain. In this study, limit values of maximum bar spacing and bar diameter are examined as the material characteristics are varied. Two models of tension stiffening effect and maximum crack spacing and their effects are evaluated. The obtained results are compared with the values obtained using KCI method. The results showed that a significant difference is found when two tension stiffening effect are employed, and an under-estimation is found when 2nd order tension stiffening effect and maximum crack spacing limit from Part II were implemented. Therefore, a rational indirect crack control method attained using the tension stiffening effect of 2nd order form is needed. Also, a consistency in serviceabiliy analysis in flexural members needs to be secured. In order to achieve these goals, two crack controling models are suggested.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.95-104
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• 2007

This study was focused on the effect of concrete strength and lateral ties of concrete columns subjected to eccentric compressive loads. The twenty-four concrete columns with $200mm{\times}200mm$ square cross-section were tested. The main variables were concrete strength, spacing and configuration of lateral ties, and eccentricity ratios. From the experiment, the followings were investigated ; 1) In all cases, it was observed that the increase of concrete compressive strength led to the decrease of ductility. Also, as the eccentricity ratios increased, the effect of ductility enhancement by lateral ties decreased. 2) As the ties spacing decreased from 100mm to 30mm, the magnitude of axial load acting on the concrete column showed an enhancement of 1.1~1.2 times and the descending curve after a peak moment presented a smooth decline. 3) The high-strength concrete columns required a design of lateral ties to increase the volumetric ratios and density of tie spacing to sustain a proper strength and ductility. Accordingly, regardless of concrete strength, the current AIK design code to specify the maximum tie spacing of concrete columns was proven to lead to the poor strength and ductility for seismic design. Therefore, it is necessary to develop a new seismic design code that connects volumetric ratios and tie spacing of concrete columns with concrete strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1081-1084
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• 2008

Column specimens were constructed with main parameters significantly affecting the strength of the compression lap splice, such as lap length, spacing of lapped bars, amount and location of transverse reinforcements, and concrete strength. An experimental study has been conducted with column specimens in concrete strength of 40 to 60 MPa. Diameters of lapped reinforcing bars are 22 mm. An axial load was monotonically applied to the column specimens. All specimens failed in a brittle sudden manner and cover concrete was blasted out at maximum load. Compression lap splice strengths of specimens were evaluated from strains measured at the beginning of the lap length. Effects of the main parameters on the strengths of compression lap splice are assessed. Similarly to strengths of tension lap slice, the compression splice strength is found to be affected by lap length, spacing of lapped bars, transverse reinforcements.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.81-88
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• 1999

In order to properly evaluate the shear strength of reinforced concrete circular columns due to the transverse shear reinforcement, the average of fractions of forces generated along the circular transverse hoops across the shear failure plane in the loading direction is calculated. For this, the center-to-center diameter of circular transverse hoops. spacing and the crack angle measured to the column longitudinal axis are considered. Using these variables, an equation representing the effective section area of circular transverse shear steel is proposed. The study result shows that the constant parameter. used for the calculation of the effective section area of circular hoops over the last 10 years, should not universally be applied any more. The use of the constant parameter may not seriously do harm to the evaluation of shear strength for circular columns with non-seismically designed transverse hoop reinforcement, since it gives slightly conservative results. However. for well-confined circular columns with close spacing or circular steel jacketing. it gives about 20% overestimation of the shear capacity contributed by the transverse hoop steel.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.4
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• pp.103-111
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• 1985

Presented is a study on the determination of crack width and crack spacing in the reinforced concrete flexural members. The derivation of crack width and crack spacing is based on the recently developed cracking theory. The new prediction formulas for the crack widths and crack spacings are proposed. An experiment for the reinforced concrete beams was conducted to compare with the proposed formulas. The comparisons of the present prediction formulas with our tests and other test data show good agreement. The present crack width formula has been also compared with the well-known ACI formula originally proposed by Gergely & Lutz. It was found that the present crack width formula shows better correlation with test data than that of Gergely & Lutz.

• Magazine of the Korea Concrete Institute
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• v.7 no.6
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• pp.216-223
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• 1995

This research is aimed to investigate the influence of the structural parameters on dowel action of reinforcing bars in reinforced concrete members. I~ollowing the previous research, $^{(3.6)}$ a total of forty two specimens were tested to scrutinize the dowel action of reinforcing bars. Concrete cover, reinforcing bar size and bar distance were taken as main test variables for constant compressive strength of concrete. ]+om the test results, the structural behavior of all specimens was almost linear up to failure load. It is seen that dowel force increases as concrete cover increases. Reinforcing bar size and bar distance hardly affects dowel force. It is found that the dowel forces obtained by this experimental research is relatively close to that of regression analysis results and White's equation.

• Magazine of the Korea Concrete Institute
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• v.4 no.3
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• pp.113-121
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• 1992

본 논문에서는 철근콘크리트 부재의 뽐힘부착거동을 규명하기 위하여 일련의 포괄적인 실험 및 이론 연구를 수행하였다. 실험의 주요변수는 콘크리트의 압축강도, 철근간격 및 덮개, 그리고 철근의 부착길이 등을 선정하였다. 본 연구결과 철근 콘크리트의 부착강도는 뿐만아니라 부착길이, 철근의 덮개 등에 따라 큰 영향을 받는 것으로 나타났으며, 본 연구에서는 이들의 영향을 정량적으로 도출하였다. 또한, 본 연구에서는 철근콘크리트의 부착강도식을 새롭게 제안하였으며, 부착응력-슬립관계식도 유도하여 제시하였다.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.371.2-371
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• 1999