• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.677-685
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• 2006

Control of the temperature difference across a section is an effective strategy to minimize the hydration-heat-induced cracks for the structures where internal restraint is dominant. The domestic code, however, overestimates probability of the crack occurrence judging from the foreign codes and construction experiences of real structures. Therefore, the background of the equation presented in the domestic code was investigated step by step to examine validity of the equation, and, as a result, it was found that the equation is established on a basis of simple elastic model where the change of elastic modulus in an early age is not considered. An advanced assessment strategy was proposed taking into account the hypoelastic model which corresponds to an incremental constitutive equation. The presented procedure resulted in an increased crack index, i.e. decreased crack risk, the value of which depends on various conditions of the mix and structures. Also, a prediction equation of the temperature difference was proposed which can readily consider the effect of the curing condition and ambient temperature in a hand calculation. For further study, the assessment equation may be more classified to strictly consider the characteristics of the mix and structures if the analytical and experimental data are accumulated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.69-78
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• 1991

This paper concentrates on the analysis of deflection of the reinforced concrete flexural members under monotonic loading. Concrete is treated as an orthotropic nonlinear material. The concept of equivalent strain and crack strain are used to establish independent stress-strain relationships in the directions of orthotropy. Steel is modeled as an elstoplastic material, and von Mises failure criterion is applied. The finite element computer program for the nonlinear analysis of the deflection of RC flexural members under monotonic loading is developed. The accuracy and reliability of the numerical procedure is demonstrated by the FEM analysis and experiments of the under reinforced concrete beams over the entire loading range up to failure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.299-305
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• 1994

An experimental test section was placed in Pangyo-Guri Expressway to monitor the performance of CRCP(Continuously Reinforced Concrete Pavement). So far early-age behaviors of the test section have been monitored for about two years. The purposes of this paper are to analyze the early-age behavior and temperature pattern of the test section and to compare the results with those of similar test sections placed in Houston. As results of this study, following findings were obtained. The results of Pangyo-Guri test section were generally better than those of Houston test sections in terms of the early-age crack patterns. Type II cement was more effective than type I cement in controlling the early-age cracking. Afternoon placement was more effective than morning construction in controlling the early-age cracking in summer season.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.703-710
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• 1994

A nonlinear FEM analysis of steel members under very-low-cycle loading has been performed in conjunction with experimental works. This analysis is an FEM tracing toward cracking of steel members under cyclic loads such as a strong earthquake. After verifying the procedure by comparing global hysteretic behaviors from the analytical and experimental results, the local stress-strain hysteresis at critical sections for large cyclic deformations was traced by the numerical analysis. Local strain history was discussed in relation to cracking. Based on the experimental and analytical results, a new approach to seismic safety assessment for steel members was proposed in this paper.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.99-107
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• 1993

In this study, material nonlinear finite element program is developed to analyze reinforced concrete shell of arbitrary geometry considering tension stiffening effects. This study is capable of tracing the load-deformation response and crack propagation, as well as determining the internal concrete and steel stresses through the elastic, inelastic and ultimate ranges in one continuous computer analysis. The cracked shear retention factor is introduced to estimate the effective shear modulus including aggregate interlock and dowel action. The concrete is assumed to be brittle in tension and elasto-plastic in compression. The Drucker-Prager yield criterion and the associated flow rule are adopted to govern the plastic behavior of the concrete. The reinforcing bars are considered as a steel layer of equivalent thickness. A layered isoparametric flat finite element considering the coupling effect between the in-plane and the bending action was developed. Mindlin plate theory taking account of transverse shear deformation was used. An incremental tangential stiffness method is used to obtain a numerical solution. Numerical examples about reinforced concrete shell are presented. Validity of this method is studied by comparing with the experimential results of Hedgren and the numerical analysis of Lin.

• Journal of Soil and Groundwater Environment
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• v.10 no.4
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• pp.33-44
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• 2005

On the basis of a stepwise and careful integration of various field and laboratory methods the analysis of groundwater flow characterization was performed with five boreholes (BH-1, -2, -3, -4, -5) on a pilot site of Natural Forest Park in Guemsan-gun, Chungcheongbook-do, Korea. The regional lineaments of NW-SE are primarily developed on the area, which results in the development of many fractures of NW-SE direction around boreholes made in the test site for the study. A series of surface geological survey, core logging, geophysical logging, tomography, tracer tests, and heat-pulse flowmeter logging were carried out to determine fracture characteristics and fracture connectivity between the boreholes. In the result of fracture connectivity analysis BH-1 the injection well has a poor connectivity with BH-2 and BH-3, whereas a good with BH-4 and BH-5. In order to analyse the hydraulic connectivity between BH-1 and BH-5, in particular, a conspicuous groundwater outflux in the depth of 12 m and influx in the depth of 65 m and 70 m, but partly in/outflux occurred in other depths in BH-5 were observed as pumping from BH-1. On the other hand, when pumping from BH-5 the strong outflux in the depths of 17 m and 70 m was occurred. The spatial connectivity between the boreholes was examined in the depth of 15 m, 67 m, and 71 m in BH-1 as well as in the depth of 15 m, 17 m, 22 m, 72 m, and 83 m in BH-5.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2007.04a
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• pp.431-434
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• 2007

빗물 및 폐수가 흘러가는 하수관은 자연 유하식으로 하수가 흘러갈 수 있도록 설계되어있는 관의 특성상 침전물이 많이 발생하며, 집중호우로 발생하는 다량의 빗물이 빠른 유속으로 관을 흐르기 때문에 관내부를 손상시키는 요인으로 작용하고 있다. 이에 본 연구에서는 관 내부를 촬영할 수 있는 궤도차량을 통해 동영상 자료를 획득하고 영상의 이미지 보정 단계를 거쳐 그래픽 파일로 변환한후 관련 정보를 입력, 저장하는 시스템 개발을 본 연구의 주요 범위로 한다. 이미지보정은 동영상을 거리의 함수를 가지는 이미지 파일로 변환하고 각각의 획득된 이미지를 영상정합기법을 사용하여 하나의 연속된 이미지 형태로 저장하여 영상 해석을 통해 균열, 침전등의 사항을 도출하여 도출된 사항은 지리정보 체계와 연동할 수 있는 파일 체계를 갖추도록 개발하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.1
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• pp.25-32
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• 1989

A finite element program for material nonlinear fracture analysis of reinforced concrete shell was developed. This method can be used to trace the load-displacement response and crack propagation through the elastic and inelastic ranges. A layered isoparametric flat finite element considering the coupling effect between the in-plane and the bending action was developed. Mindlin plate theory taking account of transverse shear deformation was used. The validity of the present program was proved by comparing the numerical results with Hedgren's experimental data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.806-812
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• 1988

When laser interference method is used to measure stress intensity factor with experiment, crack molded from teflon crack molding method is better than the crack manufactured through fatigue test. It is known that center distance between two indentations which is best for detecting the laser interference fringe order is about 80.mu.m with photodetector used in this research. Errors with measurement of stress intensity factor through laser interference are between 2% and 11%, therefore, experimental process and method developed in this research can be used with obtaining the more precision experimental data for stress intensity factors.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.168-173
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• 2001

배전용 애자는 전기적, 열적, 기계적 스트레스 등 내 외부 서지에 의한 균열이 서서히 발생되며 장시간 사용시 절연파괴에 의한 지락사고로 진전되는 경우가 많다. 이러한 사고로 인하여 순간정전이나 장시간 정전에 의한 피해를 최소화하기 위해 열화된 애자를 조기에 검출함으로써 전력공급의 신뢰성 향상을 기하고자 한다. 이를 위해 열화된 애자에서 나타나는 물리적 현상에 의해 변화되는 주파수 스펙트럼 분포 해석을 통해 방전 전자파가 갖는 주기성 파형(120Hz)을 검출하여 열화된 애자를 탐지 추적하는 장치를 개발하고자 한다.