• Journal of the Korean Society of Safety
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• v.30 no.6
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• pp.56-62
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• 2015

Recently, one of countermeasures against aging SOC infrastructures, performance-focused management including the serviceability, functionality, durability, and economics has been changed from the structural safety-focused evaluation has changed into The current inspection and diagnosis for the major SOC facilities in Korea has been carried out by the specific principle of details, and most of them checked by the visual inspection are focused on the repair and rehabilitation of the damaged structures, thus they are the preventive maintenance. However, the performance-focused management should be replaced for the effective and economic maintenance as wells as for the minimization of the damage. In this regard, this study the appropriacy of the current evaluation items about the concrete retaining wall, one of SOC infrastructures as the previous step forward the performance-focused management. In order to deduct the effective evaluation items in order, the entropy, analytic hierachy process (AHP), and promethee analysis were peformed and the results were compared and discussed.

• Smart Structures and Systems
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• v.19 no.4
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• pp.371-382
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• 2017

Concrete filled steel tubes are extensively applied in engineering structures due to their resistance to high tensile and compressive load and convenience in construction. But one major flaw, their vulnerability to environmental attack, can severely reduce the strength and life of these structures. Degradation due to corrosion of steel confining the concrete is one of the major durability problems faced by civil engineers to maintain these structures. The problem accelerates as inner surface of steel tube is in contact with concrete which serves as electrolyte. If it remains unnoticed, it further accelerates and can be catastrophic. This paper discusses a non-destructive degradation monitoring technique for early detection corrosion in steel tubes in CFST members. Due to corrosion, damage in the form of debonding and pitting occurs in steel sections. Guided ultrasonic waves have been used as a feasible and attractive solution for the detection and monitoring of corrosion damages in CFST sections. Guided waves have been utilized to monitor the effect of notch and debond defects in concrete filled steel tubes simulating pitting and delamination of steel tubes from surrounding concrete caused by corrosion. Pulse transmission has been used to monitor the healthy and simulated damaged specimens. A methodology is developed and successfully applied for the monitoring of concrete filled steel tubular sections undergoing accelerated chloride corrosion. The ultrasonic signals efficiently narrate the state of steel tube undergoing corrosion.

• Computers and Concrete
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• v.20 no.5
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• pp.583-593
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• 2017

Applications of fibre-reinforced polymer (FRP) composites for retrofitting, strengthening and repairing concrete structures have been expanded dramatically in the last decade. FRPs have high specific strength and stiffness compared to conventional construction materials, e.g., steel. Ease of preparation and installation, resistance to corrosion, versatile fabrication and adjustable mechanical properties are other advantages of the FRPs. However, there are major concerns about long-term performance, serviceability and durability of FRP applications in concrete structures. Therefore, structural health monitoring (SHM) and damage detection in FRP-retrofitted concrete structures need to be implemented. This paper presents a study on investigating the application of Rayleigh wave for detecting debonding defect in FRP-retrofitted concrete structures. A time-of-flight (ToF) method is proposed to determine the location of a debonding between the FRP and concrete using Rayleigh wave. A series of numerical case studies are carried out to demonstrate the capability of the proposed debonding detection method. In the numerical case studies, a three-dimensional (3D) finite element (FE) model is developed to simulate the Rayleigh wave propagation and scattering at the debonding in the FRP-retrofitted concrete structure. Absorbing layers are employed in the 3D FE model to reduce computational cost in simulating the practical size of the FRP-retrofitted structure. Different debonding sizes and locations are considered in the case studies. The results show that the proposed ToF method is able to accurately determine the location of the debonding in the FRP-retrofitted concrete structure.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.12
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• pp.7-14
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• 2019

A marine turning gear controls the position of the piston-crank mechanism by rotating the flywheel of the marine engine at a low speed, which is the main auxiliary machine that enables the disassembly and maintenance of the engine. In this study, the safety factor for surface durability and tooth bending strength was improved by the design modification of the marine turning gear based on the spur planetary gear. Angular velocity, torque, and efficiency of the turning gear were measured using a reliability evaluation tester, and a multibody dynamics model for analysis corresponding to the test results was developed. Finally, it was confirmed that the design improvements improved the tooth surface damage of the sun gear in the 3^rd reduction stage.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.7-8
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• 2017

Corrosion of reinforced concrete embedded in concrete is a deterioration phenomenon due to intrusion of embodied or Airborne chloride ions. Corrosion of a embedded steel increases the volume of the rebar and causes damage to the structure such as cracking and peeling of the concrete. This causes penetration of various corrosive factors and accelerates the corrosion of reinforcing bars, which has a serious effect on the durability of the structure. Researches on the corrosion phenomenon of these rebars by electrochemical methods have been carried out for a long time, but it is a lack of research in Korea. Therefore, in this study, one of electrochemical experimental methods, Tafel extrapolation method, was used to evaluate the performance of reinforcing bars according to the amount of NaCl and LiNO₂ added to concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.10a
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• pp.148-149
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• 2016

In this paper, the increase in chloride resistance of footing concrete at coastal area was evaluated by replacement of Mineral Admixture. In KBC 2009, the footing concrete's minimum specific concrete strength at coastal area is determined to 35MPa. However, this is criteria only based on the strength aspect. Thus, it is not considered to increase the chloride resistance by replacement of Mineral Admixture. According to the test results of chloride ions penetration resistance, 35MPa class concrete with OPC 100% shown inaccessible state. Low-strength (24~30MPa class) concretes with Mineral Admixture, however, presented better performances. In addition, chloride diffusion coefficient tests showed identical appearance. Therefore, the current KBC's chloride resistance criteria based on only concrete strength has to review for the reason it can cause many problems (ex. cost increases by growing concrete strength and the environmental issues by a lot of cement use).

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.148-148
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• 2017

Surface modification is a type of mechanical manipulation skills to achieve extensive aims including corrosion control, exterior appearance, abrasion resistance, electrical insulation and electrical conductivity of substrate materials by generating a protective surface using electrical, physical and chemical treatment on the surface of parts made from metallic materials. Such surface modification includes plating, anodizing, chemical conversion treatment, painting, lining, coating and surface hardening; this study conducted cavitation experiment to assess improvement of durability using anodizing. In order to observe surface characteristics with applied current density, the electrolyte temperature, concentration was maintained at constant condition. To prevent hindrance of stable growth of oxide layer due to local temperature increase during the experiment, stirring was maintained at constant speed. In addition, using galvanostatic method, it was maintained at processing time of 40minutes for 10 to $30mA/cm^2$. The cavitation experiment was carried out with an ultra sonic vibratory apparatus using piezo-electric effect with modified ASTM-G32. The peak-to-peak amplitude was $30{\mu}m$ and the distance between the horn tip and specimen was 1mm. The specimen after the experiment was cleaned in an ultrasonic bath, dried in a vacuum oven for more than 24 hours, and weighed with an electric balance. The surface damage morphology was observed with 3D analysis microscope. As a result of the study, differences were observed surface hardness and anti-cavitation characteristics depending on the development of oxide film with the anodizing process time.

• Tribology and Lubricants
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• v.25 no.4
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• pp.256-260
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• 2009

Fretting is a kind of wear which effects on reliability and durability. When machine parts are joined joint in parts such as a bolt or a rivet or a pin, fretting phenomenon is occurred by micro relative movement. When fretting occurs in joint parts, there is wear which is the cause of fatigue crack. Recently, although the ways of assessment of fatigue and damage tolerance are established, there is no way to evaluate fatigue crack initiation life by fretting phenomenon. Consequently, the prediction of life and prevention plan caused by fretting are needed to improve reliability. The objective of this paper is to predict fretting wear by using a experimental method and contact analysis considering wear process. For prediction of fretting wear volume, systematic and controlled experiments with a disc-plate contact under gross slip fretting conditions were carried out. A modified Archard equation is used to calculate wear depths from the contact pressure and stroke using wear coefficients obtained from the disc-plate fretting tests.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.2
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• pp.196-200
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• 1999

In the case that erosion and corrosion occurs in machinery and structure at the same time, the synergy effect by erosion-corrosion affects fatal effect to durability of machinery and structure. Therefore, in machinery and structure which use corrosion liquid, the study of the synergy effect of erosion-corrosion which affects metal material is requested. In this paper. the flow corrosion experiment about the effect of temperature change and liquid velocity change in sea water was carried out to study the characteristics of erosion-corrosion for tube material Cu heat exchanger The main results obtained are as follows. (1) Damage appearance of tube outside by erosion-corrosion becomes dull because electrode potentials of Cu tube is higher than electrode potential of STPG38 shell. (2) In the cooling system by sea water, the weight loss rate of Cu at tube outside liquid temperature of $70^{\circ}C$ is higher than that of temperature of $20^{\circ}C$. (3) In cooling system by sea water, the weight loss rate of Cu at liquid velocity of 5.1m/s is higher than that of velocity of 1.47m/s. But as the testing time passed, the weight loss rate of Cu at velocity of 5.1m/s is almost steady and becomes dull at velocity of 1.47m/s.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.141-145
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• 2007

The part in the structure that is most affected by changes of external temperature is the protective concrete layer that protects a waterproofing layer. Also, the waterproofing layer that is situated under or on the back of such a protective concrete layer is affected by temperature and the behavior of the protective concrete layer under the condition of consolidation or close adhesion. In particular, in many cases, the damage is serious mainly around the projection (such as a parapet), crack, and joint (expansion joint). However, there is no proper way of examining again the non-exposed waterproofing layer once it has been constructed. Therefore, there is an assessment only on the physical property of materials and the capability of the layer in construction, and there is no actual assessment in consideration of its environmental condition or the condition of the use of buildings after construction. Therefore, in order to create more pleasant buildings and to enhance the durability of structures, this study conducts research into the change of capability of non-exposed waterproofing material after the application of a static load and moving load on the waterproofing layer situated under or on the back of protective concrete.