• International Journal of Concrete Structures and Materials
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• v.6 no.3
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• pp.199-207
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• 2012

Concrete is an economical construction material and for that reason it is widely used in buildings and infrastructures. The use of deicing salts, expansion joint failure, and freeze-thaw cycles have led to concrete bridge girders experiencing corrosion of steel reinforcement and becoming unsafe for driving. The goal of this research is to assess the effectiveness of current and possible repair techniques for the end region of damaged prestressed concrete girders. To do this, three American Association of State Highway and Transportation prestressed concrete girders were tested to failure, repaired, and retested. Three different repair materials were tested including carbon fiber, glass fiber, and surface mounted rods. Each different repair material was also tested with and without injected epoxy. Comparisons were then made to determine if injecting epoxy had a positive effect on stiffness and strength recovery as well as which repair type regained the largest percentage of original strength.

• Journal of the Korean Society of Safety
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• v.28 no.5
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• pp.21-26
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• 2013

Delamination of cover concrete due to re-bar corrosion is a critical damage reducing structural safety of reinforced concrete structures. Therefore, it should be detected and evaluated to provide appropriate maintenance to recover structural integrity. Impact-echo method, which utilizes thickness vibration characteristics of delaminated concrete section, is effective for detection and evaluation of small areal size delamination. However, it may not be applicable for large areal size delamination in which flexural vibration modes are dominated. In this study, applicability of vibration mode shapes of delaminated concrete section is investigated for visualization of delamination region in concrete structures. Numerical and experimental modal tests are performed to estimate mode shapes of delaminated concrete section and linear absolute summation technique is proposed for effective visualization of delamination region based on estimated mode shapes.

• Journal of the Korean Society of Safety
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• v.33 no.3
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• pp.33-38
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• 2018

Defects in piping caused by corrosion or external impact of underground piping can lead to high risk of rupture of the piping due to high pressure. Flammable gas can be immediately ignited when discharged from piping, causing a jetfire. The damage of the radiant heat not only threatens the health of the workers who work in the industry but also the health of the people living in the neighboring residential areas. It is important to prevent and prepare before an accident occurs. In this study, three types of flammable gas underground piping accident scenarios were investigated, and the ranges of influence were determined using Phast ver7.2. and finally regression models were formulated to predict the ranges using excel and Matlab.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.134-138
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• 1995

The reinforced concrcte structure were once belicved to have permanent durability. However, it is now spoiled by durability failure caused by the corrosion of embeded steel reingorcement carbonation. alkali-aggregate reaction and salt attack Recently. salt damage has been also spreading. Salt damage is found in concrete structures built using seasands or certain admixtures containing calcium chlorides and in coastal structures frequently caught in seawater spray or blown by seawind It is the aim of this study to investigate the performance and application of new repair system for the exterior wall according to the durability improvement in the RC structures.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1248-1253
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• 2007

Urban transit or subway stations generally service for a long period of several decades. And, the urban transit or subway is public transportation which lots of people takes every day. During the service time, they are inevitably damaged from environmental corrosion, material aging, fatigue, and the coupling effects with long-term loads and extreme loads. The included damage accumulates and performance degenerates due to the above factors. They would inevitably reduce the resisting capacity of station against the disaster; even they result in collapse with the structural failure under extreme loads. And, if disaster such as earthquake, fire, etc. happens, it causes huge property damage and threatens the human lives. Because of these above reasons, the intelligent health surveillance system should be researched and developed for ensuring the safety of station. In this paper, the research plans of the intelligent health surveillance system of urban transit station are presented. And also, the development or establishment directions of this system are suggested.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.2
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• pp.33-41
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• 2012

The component cooling water heat exchangers are critical components in a nuclear power plant. As the operation years of the heat exchanger go by, the maintenance costs required for continuous operation also increase. Most heat exchangers have carbon steel shells, tube support plates and flow baffles. The titanium tube is susceptible to flow induced vibration. The damage on carbon steel tube support rod and titanium tube around cooling water entrance area is inevitable. Therefore, analysis of internal flow around the component cooling water entrance and tube channel is a good opportunity to seek for failure prevention practice and maintenance method. The numerical study was carried out by FLUENT code to find out the causes of tube failure and its location.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.60-61
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• 2013

For reinforced concrete structures located in a sea environment, the Impressed Current Cathodic Protection (ICCP) is mostly used as a signature method to prevent steel corrosion. For this research, specimens to which the ICCP is applied were manufactured under the assumption of two following cases the specimens are exposed to various salt damage environments (submerged zone, tidal zone), and deteriorative factors (crack) occur in concrete. For the specimens manufactured, an enhancement experiment for deterioration was conducted through regular cycle change under the temperature between 15 ~ 70℃ with 70 ~ 90% humidity. Afterwards, the method effect was verified through a half-cell method and application of the ICCP derived from salt damage environments was investigated.

• Journal of KIBIM
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• v.8 no.4
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• pp.13-22
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• 2018

Future performance prediction of bridges is challenging task for structural engineers. Well-organized information from design, construction and operation stages is essential for the assessment of structures. Digital twin model is a new concept to realize more reliable data platform for management of infrastructures. Damage history including degradation of material, cracking, corrosion, etc. needs to be accumulated in the digital model. The digital model is linked to the analysis model for the assessment of structural performance considering changed mechanical properties of structural components. In this paper, initial definition digital twin model of a PSC-I girder bridge is proposed.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.883-889
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• 2014

It is generated for cavitation erosion due to the local static boiling by pressure differentials in high speed rotating fluid environment. The cavitation is influenced by various elements such as pressure, velocity, temperature, pH of fluid and medium. In particular, the damage of material is accelerated due to the electrochemical corrosion by $C1^-$ and cavitation erosion due to cavities in seawater. In this paper, hence, it investigated for martensite stainless steel the damage behavior with applied current density and cavitation time in natural seawater solution. Less damage depth at the cavitation condition was observed than static condition as a result of galvanostatic experiment. Furthermore, it was shown that dramatic increase of weightloss, damage rate and damage depth after 3 hour of cavitation test.

• Journal of Surface Science and Engineering
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• v.45 no.6
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• pp.264-271
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• 2012

Due to the good corrosion resistance and machinability, copper alloy is commonly employed for shipbuilding, hydroelectric power and tidal power industries. The Cu alloy, however, has poor durability, and the seawater application at fast flow condition becomes vulnerable to cavitation damage leading to economic loss and risking safety. The HVOF(High Velocity Oxygen Fuel) thermal spray coating with WC-10Co4Cr were therefore introduced as a replacement for chromium or ceramic to minimize the cavitation damage and secure durablility under high-velocity and high-pressure fluid flow. Cavitation test was conducted in seawater at $15^{\circ}C$ and $25^{\circ}C$ with an amplitude of $30{\mu}m$ on HVOF WC-10Co4Cr coatings produced by thermal spray. The cavitation at $15^{\circ}C$ and $25^{\circ}C$ exposed the substrate in 12.5 hours and in 10 hours, respectively. Starting from 5 hours of cavitation, the coating layer continued to show damage by higher than 160% over time when the temperature of seawater was elevated from $15^{\circ}C$ to $25^{\circ}C$. Under cavitation environment, although WC-10Co4Cr has good wear resistance and durability, increase in temperature may accelerate the damage rate of the coating layer mainly due to cavitation damage.