• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.5A
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• pp.369-378
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• 2011

In this paper, the response analysis of RC(Reinforced Concrete), SC(Steel-Plate Concrete) containment buildings subjected to a large aircraft impact is performed using Autodyn-3D as Hydrocode. Until now, the impact load in the analysis of aircraft impacts has been applied to target structures at the local area by using the impact load-time history function of Riera. However in this paper, the results of aircraft crash are analyzed by using an aircraft model similar to Boeing 767 and verified by comparing the generated history of the aircraft crash against the rigid target with another history by using the Riera's function. To estimate the resistivity of the impact, the response and safety of SC containment buildings, this study is performed by comparing the four cases of plane concrete, reinforced concrete, bonded containment liner plate at reinforced concrete, and SC structure. Thus, the different behaviors between SC and RC structures when they are subjected to the extreme impact load could be anticipated. Consequently, the improved safety is expected by replacing RC structure with SC structure for nuclear power plants.

• Journal of the Korean Geotechnical Society
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• v.27 no.7
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• pp.17-33
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• 2011

Recently, the utilization of recycled aggregates for backfilling a power transmission pipeline trench has been considered due to the issues of eco-friendly construction and a lack of natural aggregate resource. It is important to identify the physical and thermal properties of domestic recycled aggregates that can be used as a backfill material. This paper evaluated thermal properties of concrete-based recycled aggregates with various particle size distributions. The thermal properties of the recycled aggregates and river sand provided by local vendors were measured using the transient hot wire method and the transient needle probe method after performing the standard compaction test. The needle probe method considerably overestimated the thermal resistivity of recycled aggregates especially at the dry of optimum water content because of experiencing disturbance while the needle probe is being inserted into the specimen. Similar to silica sand, the thermal resistivity of recycled aggregates decreased when the water content increased at a given dry density. Also, this paper evaluated some of the existing prediction models for the thermal resistivity of recycled aggregates with the experimental data, and developed a new prediction model for recycled aggregates. This study shows that recycled aggregates can be a promising backfill material substituting for natural aggregates when backfilling the power transmission pipeline trench.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.56 no.2
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• pp.104-108
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• 2007

This paper deals with an approach to the reduction of potential rise according to the buried depth of structure. In order to analyze the surface potential rise of structure, an electrolytic tank which simulates the semi-infinite earth has been used. The potential rise has been measured and analyzed for types of structure using an electrolytic tank experimental apparatus in real time. The structure models were designed through reducing real buildings and fabricated with four types on a scale of one-one hundred sixty. When a test current flowed through structure models, potential gradient was the highest value in case of the outline frame type(structure model A). The distributions of surface potential rise are dependent on the resistivity and absorption percentage in concrete attached to structure model.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.8
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• pp.371-377
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• 2005

This paper Presents the Potential gradient characteristics of structure grounding electrode when a test current flows through grounding electrode. In order to analyze the potential gradient of ground surface on structure grounding electrode, the reduced scale model has been used. The potential gradient has been measured and analyzed for types of structure using the hemispherical grounding simulation system in real time. The structures were designed through reducing real buildings and fabricated with four types on a scale of one-one hundred sixty. The supporter was made to put up with weight of structure and could move into vertical, horizontal, rotary direction. When a test current flowed through structure grounding electrodes, ground potential rise was the lowest value at electric cage type(type B). According to resistivity and absorption percentage In concrete attached to structure, the potential distribution of ground surface appeared differently.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.11a
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• pp.111-114
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• 2005

This paper presents a comparison of experimental value by hemispherical grounding simulation system and calculated value by CDEGS program for ground potential rise of structure. When a test current flowed through structure grounding electrodes, ground potential rise was measured and analyzed for types of structure using the hemispherical grounding simulation system in real time, and was computed by means of CDEGS program. The model structures were designed and fabricated with two types on a scale of one-one hundred sixty. When the experimental data were compared with the theoretical values, the similar profile was shown. Therefore, the confidence of measurement was obtained. The distributions of ground surface potential are dependent on the resistivity and absorption percentage in concrete attached to structure.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.342-346
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• 2006

This paper describes ground surface potential rises and touch voltage. The more soil resistivity of upper layer is lower, the more ground surface potential rise is increased. Ground surface potential rise is increased as the buried depth of ground rod in lowered. Ground surface potential rises were measured in the test site and compared with results by CDEGS program. Touch voltages according to the separation distance of ground rod were measured in four directions. Touch voltages were remarkably changed by separation distance and contact position.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.57-65
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• 2022

This study investigated the electromechanical response of smart ultra-high performance fiber reinforced concretes (S-UHPFRCs) under flexural loading to evaluate the self-sensing capacity of S-UHPFRCs in both tension and compression region. The electrical resistivity of S-UHPFRCs under flexural continuously changed even after first cracking due to the deflection-hardening behavior of S-UHPFRCs with the appearance of multiple microcracks. As the equivalent bending stress increased, the electrical resistivity of S-UHPFRCs decreased from 976.57 to 514.05 kΩ(47.0%) as the equivalent bending stress increased in compression region, and that did from 979.61 to 682.28 kΩ(30.4%) in tension region. The stress sensitivity coefficient of S-UHPFRCs in compression and tension region was 1.709 and 1.098 %/MPa, respectively. And, the deflection sensitivity coefficient of S-UHPFRCs in compression region(30.06 %/mm) was higher than that in tension region(19.72 %/mm). The initial deflection sensing capacity of S-UHPFRCs was almost 50% of each deflection sensitivity coefficient, and it was confirmed that it has an excellent sensing capacity for the initial deflection. Although both stress- and deflection-sensing capacity of S-UHPFRCs under flexural were higher in compression region than in tension region, S-UHPFRCs are sufficient as a self-sensing material to be applied to the construction field.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.48-56
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• 2022

Controlling the setting time of cementitious materials is one of the most important factors in securing early-age performance of concrete structures. Recently, the use of retarding admixtures, which enable the inhibition of some hydration products to control the securing time due to average temperature rise is suggested. Although various non-destructive evaluation methods have been proposed to evaluate cement hydration and hardening of cement-based materials to overcome the limitations of Vicat needle test, experimental research is still required to use the non-destructive evaluation method with added retarding admixtures. In this study, measurements of electrical resistivity and ultrasonic wave velocity in early-aged cement pastes were performed according to the addition of retarding admixture(tartaric acid). The setting time of the cement pastes was evaluated by obtained rising time of the both non-destructive measurements. As a result, the possibility of evaluating the setting delay in cement pastes was confirmed through comparative analysis with the initial and final setting times by Vicat test. In addition, X-ray diffraction results at the rising time of electrical resistivity showed a key hydration product affecting the setting delay.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.62-69
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• 2023

This study investigated the electromechanical properties of cement based smart repair materials (SRMs) according to the different amounts of fine steel slag aggregates (FSSAs). SRMs can self-diagnose the quality of repairing and self-sense the damage of repaired zone. The replacement ratios of FSSAs to sand for SRMs were 0% (FSSA00), 25% (FSSA25), and 50% (FSSA50) by sand weight. The electrical resistivity of SRMs generally decreased as the compressive stress of SRMs increased: the electrical resistivity of FSSA25 at the age of 7 hours decreased from 78.16 to 63.68 kΩ-cm as the compressive stress increased from 0 to 22.37 MPa. As the replacement ratio of FSSAs by weight of sand increased from 0% to 25%, the stress sensitivity coefficient (SSC) of SRM at the age of 7 h increased from 0.471 to 0.828 %/MPa owing to the increased number of partially conductive paths in the SRMs. However, as the replacement ratio of FSSAs further increased up to 50%, the SSC decreased from 0.828 to 0.649 %/MPa because some of the partially conductive paths changed to continued conductive ones. SRMs are expected to self-sense the quality and future damage of repaired zone only by measuring the electrical resistivity of the repaired zone in addition to fast recovery in the mechanical resistance of structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.102-109
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• 2016

This paper presents mechanical properties and chloride diffusivity of the recycled aggregate concretes(RAC) in which natural coarse aggregate was replaced by recycled coarse aggregate(RCA) by compressive strength levels(20, 35, 50 MPa). A total of 9 RAC were produced and classified into three series, each of which included three mixes designed with three compressive strength levels of 20 MPa, 35 MPa and 50 MPa and three RCA replacement ratios of 0, 50 and 100%. Engineering properties of RAC were tested for slump test, air content, compressive strength, chloride penetration depth and chloride diffusion coefficient. The test results indicated that the workability of RAC could be improved or same by RCA replacement ratios, when compared with that containing no RCA. This is probably because of the RCA shape improving the workability of RAC. Also, the test results showed that the compressive strength was decreased by 9~10% as the RCA replacement ratios increase. Furthermore, the result indicated that the measured chloride diffusion coefficient increases by 144% with the increase of the RCA replacement. In the case of the concrete having low level compressive strength, the increase of chloride diffusion coefficient tends to be higher when using the RCA. However, the trend of chloride diffusion coefficient in high level compressive strength concrete is similar to that obtained in general concrete. This is because that the effect of the RCA replacement could be a decrease with increase of compressive strength. Therefore, an advance on the admixture application and mix ratio control are required to improve the chloride resistivity when using the recycled aggregate in large scale.