• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.4
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• pp.639-648
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• 1999

레이더법은 건축구조물에 대한 비파괴 검사의 대표적인 방법의 하나이다. 레이더법을 이용하는데 영향을 주는 요인들을 연구하고, 레이더로 측정된 결과들을 분석하기 위해서는 전자기파의 전파에 대한 수치적인 모델링을 통한 이론적인 접근이 필요하다. 콘크리트 시편에 전파되는 전자기파를 모델링 하기 위해 유한차분 시간영역법을 적용하고자 한다. 유한차분 시간영역법은 전자파 해석과 모델링을 통한 시뮬레이션에 매우 유용한 방법이다. 본 연구에서는 유한차분 시간영역법을 이용하여 두께가 다른 4개의 시편과 두께는 100㎜로 동일하고 피복두께가 다른 3개의 시편을 3차원으로 모델링 하였다. 두께 측정 모델링 결과에서는 계산영역의 셀간격과 입사파의 파장/콘크리트 시편의 두께값이 모델링의 정확성에 미치는 영향을 알 수 있었다. 철근이 있는 시편의 모델링에서는 0.08%∼0.5%의 오차로 철근의 위치를 확인할 수 있었다.

• Journal of the Korean Geophysical Society
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• v.9 no.4
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• pp.301-310
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• 2006

In this short paper, an elasto-plastic repair and retrofit element is developed for the investigation of the seismic performance of damaged reinforced concrete members. The developed element is capable of reflecting the increased characteristics due to both repair and retrofitting for degraded strength and stiffness of the members. The element having both birth and death time can freely be activated within the user-defined time intervals during static and dynamic time-history analysis. Comparative studies are conducted for reinforced concrete members being repaired and retrofitted. Analytical predictions including the developed element display reasonable correlation with experimental results. In short, it is concluded that the developed element is capable of providing salient features for the healthy assessment of seismic performance of RC members being repaired and retrofitted.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.107-115
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• 2003

Nondestructive testing was carried out in order to evaluate the structural integrity and construction quality of the slurry wall of the underground LNG storage tank. 9 test points were selected, and the wall thickness, rebar spacing, and compressive strength of the slurry wall were evaluated by stress wave impact-resonance method, GPR, sonic velocity, and rebound testing, respectively. As results, the wall thickness, rebar sparing and estimated compressive strength satisfy the design criteria.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.111-116
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• 2005

2-D and 3-D resistivity surveys were carried out at the Deok-In2 levee during the period of arid and rainy seasons to assess the waterproof effectiveness of sheet pile and grouting sections and detect the location of pipings. Inverted resistivity sections clearly indicated the boundaries of sheet pile and grouting sections and the locations of pipings observed at the ground surface. Besides, GPR survey was carried out to verify the rear cavity of culvert in levee which is thought to be the major cause of levee breakdown, But the quality of GPR data was very poor due to the steel reinforcements buried in the culvert. Because it is not easy to apply various geophysical surveys upon concrete structures, newly designed hydraulic response test was proposed to assess the continuity of rear cavity of culvert in this study.

• Journal of the Korean Geophysical Society
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• v.2 no.2
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• pp.135-142
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• 1999

Interpretations of 3-component magnetic logging data obtained for a reinforced bar as a model of the line of the magnetic dipoles are conducted using a least squared inversion technique. The length of the bar is 1.12 m, sampling interval is 0.05 m, the distance between the bar and the borehole is 0.3 m, and the top of the bar is fixed at 0 m of depth. The bar is set to be approximately vertical. Magnetic anomalies smoothed with FFT are used as input data for the inversion. For the interpretation of magnetic logging data the depth to the top, the length, the magnetic moment per unit length, the direction of the magnetization (declination and inclination), and the bearing and plunge of the line of magnetic dipoles are left as unknown parameters. The comparison of the results obtained from the individual inversion of the horizontal component or the vertical component of the magnetic anomalies, and those from the simultaneous inversion of horizontal and vertical component of the magnetic anomalies shows that there exist some disagreements between each inversion result. The depth to the bottom of the bar, which is actually 1.12 m, is estimated as 1.18 m, and the inclination of the magnetization is estimated as -76°by simultaneous inversion. The negative value of the inclination indicates that the strength of the remnant magnetization is much greater than that of the induced magnetization, so that the direction of the resultant magnetization points to the top of the bar.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.663-666
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• 1999

Ground Penetrating Radar (GPR) attached with 1 GHz center frequency antenna has been used to measure a dielectric constant of mortar, and to detect and locate a steel bar embedded inside laboratory size mortar specimens at various depth. Mortar specimens are made for the measurements with the dimensions of 100cm (width)$\times$100cm (length)$\times$14cm (depth). Each specimen has a 13mm diameter D13 steel bar at 2, 4, 6, 8, 10 and 12cm depth. In this paper, results of radar measurments are provided with a sample output, which successfully located the bar. It has been found that the reflected wave of the steel bar interacts with that of surface when the steel bar has the close distance to the surface.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.135-140
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• 2001

The radar method is becoming one of the major nondestructive testing (NDT) techniques for concrete structures. Numerical modeling of electromagnetic wave is needed to analyze radar measurement results and to study the influence of measurement parameters on the radar measurements. Finite difference-time domain (FD-TD) method is used to simulate electromagnetic wave propagation through concrete specimens. In the experiments, three concrete specimens are made with the dimensions of 100 cm (length) x 100 cm (wideth) x 14 cm (depth). Three specimens had a Dl6 steel bar at 8, 10, 12 cm depth.

• 한국터널공학회:학술대회논문집
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• 2005.04a
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• pp.202-212
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• 2005

배수식 방수방식으로 지하 30m에 건설된 NATM터널 통신구를 준공 7년후 완전방수식 방식으로 변경하였다. 터널 라이닝에 30m의 수압을 작용할 경우 발생하는 단면력을 구조검토하고 배근상태가 안전한가 분석하였다. 또한 라이닝의 시공단면을 확인하기 위하여 충격반향기법(Impact-Echo Method)탐사와 GPR탐사, 배근상태를 파악하기 위하여 철근탐지기를 사용하였다. 그 결과 30m 수압에 안전할 것이라는 판단하에 배면주입 방수공법을 적용 통신구를 완전방수 하였다. 그리고 배수식 통신구를 운용하는 비용과 완전방수공사비를 분석한 결과 배출되는 지하수량이 많은 경우 완전방수시공이 경제성이 있다고 분석되었다.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.663-666
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• 2003

Using numerical analysis modeling of Multi-electrode Array that could be applied to the corrosion state measurement of a reinforcing steel bar in concrete, the steel bar location inside concrete can be probed by the investigation of the change of the measured impedance from concrete surface determined by the electrical impedance of interface between the steel bar and concrete, the electrical resistivity of concrete, the array of electrodes and the relative location and diameter of the steel bar.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.191-194
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• 2008

The cavity behind the tunnel lining, caused by overbrake, might be cause a severe instability during tunnel construction. So backfill grouting is essentially required. GPR(Ground penetrating Radar) is widely used to identify the position and size of the cavity and to verify the effect of the backfill grouting. In this study, GPR survey with 450 MHz antenna was implied to access the effect of the backfill grouting before and after the work to the crown part of ○○ tunnel in Seoul respectively. The result of GPR survey conducted before the backfill, was revealed that cavities behind the lining were existed in the areas of 8 spans. Finally, from the GPR survey implied after backfilling, it was turned out that backfill grouting was successfully carried out. Also, GPR survey was ascertained the better contact between lining and rock base at arrangement of bar span.