• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.6
• /
• pp.164-172
• /
• 2008

The heat of hydration for early aged mass concrete induces high temperature with the hydration. 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 current prevention methods for hydration cracking show some limitations for the control of thermal gradients, and these limitations could make micro and macro cracks in surface and core of concrete. Especially cooling methods can decrease the increasing hydration temperature, but it can not prevent the problem while decreasing temperature. Consequently heating pipes are added simultaneously with the cooling pipes in order to control the temperature gradients between core and surface of the concrete, followed by the finite element analysis (FEA). Based on the FEA, the proposed method using cooling pipe and heating pipes together has been found to be an effective alternative in thermal gradient control, in terms of controlling temperature induced cracks significantly.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.4
• /
• pp.109-120
• /
• 2007

In this study, a bridge maintenance system is developed to generate performance-based optimum maintenance strategy by considering the life-cycle cost. A multi-objective combinatorial optimization problem is formulated to generate a tradeoff maintenance scenarios which satisfies the balance among the conflicting objectives such as the performance and cost during the bridge lifetime and a genetic algorithm is applied to the system. By using the developed program, this study proposes a process of optimum maintenance scenario applying to the steel girder bridge of national road. The developed system improves the current methods of establishing the bridge maintenance strategy and can be utilized as an efficient tool to provide the optimum bridge maintenance scenario corresponding to the various constraints and requirements of bridge agency.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.2
• /
• pp.121-130
• /
• 2008

Recently, we can see an increasing amount of dam damage or failure due to aging, earthquakes occurrence and unusual changes in weather. For this reason, dam safety is gaining more importance than ever before in terms of disaster management at a national level. Therefore, the government is trying to come up with an array of legal actions to secure consistent dam safety. Other dam management organizations are also taking various institutional and technical measures for the same purpose. In this study, Dam Safety Management System, KDSMS, has developed for consistent and efficient dam safety management. The KDSMS consists of dam and reservoir data, a hydrological information system, a field inspection and data management system, a instrumentation and monitoring system including earthquake monitoring, a field investigation and safety evaluation system, and a collective information system. The KDSMS is a kind of enterprise management system which has been developed to deal with safety management of each field, research center, and headquarter office and their correlation as well as detailed safety information management.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.5
• /
• pp.109-115
• /
• 2008

As structures are getting super-rise and large-sized, introducing the construction methods such as prefabrication of bar-meshes and complex method are being actively discussed to pursue the high quality of reinforced concrete, the simplification of field works, and the reduction of duration, as well as the study on how to connect reinforcing rods, which occurs while applying the same methods, is in progress Also, the pressure welded joint is a kind of method that heats the ends of reinforced bars locally and joint them, and after the pressure welding, the vulnerable part in the reinforced bar occur. Thus, in the construction field, the throughout quality control is necessary because of the delayed duration and the lowered construct ability. In this study, of the traditional lap splice method and the mechanical splice one, the screw coupler, we tried to look into through experiments the prefabrication method of bar-meshes, a typical joint method usually used for the joint parts for PSC structures applying the reinforced bar with its big diameter, and a newly-developed up-set coupler method. And we also examined the characteristic of tensile.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.6 s.58
• /
• pp.166-175
• /
• 2009

An experimental study was carried out to estimate the flexural performance of steel fiberreinforced self-compacting concrete. Seven slabs with three different steel fiber-reinforced concretes were prepared to make beam specimens. After proper curing period, each slab was cut to five beams with a diamond saw. The beam specimen was tested with displacement control method to obtain load-deflection curve. As the results, the self-compacting concrete beam showed higher flexural strength, ductility and toughness index compared to the normal concrete beam. This means that steel fiber-reinforced self-compacting concrete can be used more widely in the field of architecture and civil engineering because of its self-compactability and good mechanical properties.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.6 s.58
• /
• pp.135-147
• /
• 2009

In order to develop the ultra high strength concrete over 400Mpa at 28 day, Low-heat portland cement, ferro-silicon, silica-fume and steel fiber were mixed and tested under the special autoclave curing conditions. Considering the influence of Ultra high strength concrete. normal concrete is used as a comparison with low water-cement ratio possible Low-heat portland cement. Additionally, as a substitution of aggregates, we analyzed the compressive strength of Ferro Silicon by making the states of mixed and curing conditions differently. In addition, SEM films testified the development of C-S-H hydrates of Type III & Type IV, and tobermolite, zonolite due to the high temperature, high pressure of autoclave curing. Fineness of aggregate, filler and reactive materials in concrete caused 420Mpa compressive strength at 28day successfully.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.1 s.53
• /
• pp.69-77
• /
• 2009

An underwater structure is made to put with serious damage state by special environmental factors. If this damage phenomena persist, as for the structure, it is generated a structural serious problem because of the corrosion of a reinforcing bar and the loss of the concrete cut end. Repair work of an underwater structure is very harder than repair work in land, and it is actual that certification about a maintenance effect is uncertain. And the existing repair method is applied to a structure damaged with you without verification of a repair effect by a foreign reward and experience. In this study, a repair method about an underwater structure was proposed and observed a behavior characteristic and interface failure of an specimens. and comparison analyzed an effect of a proposed maintenance method.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.5 s.57
• /
• pp.133-141
• /
• 2009

50 year-old masonry buildings which had been constructed using lime mortar have caused lots of problems because of using different material, cement mortar, when they repair them. Also, there is little information on structural capacities and details of masonry buildings built using lime mortar. In addition, it is difficult to evaluate the structural capacities of the buildings which were often constructed by untrained labors. To preserve the original masonry construction, the study on their construction materials and methodologies has to be carried out. This paper provides basic information for establishing standard details of masonry works using lime mortar in order to overcome these problems when cultural properties are repaired or retrofitted. To do this, compression tests of lime mortar were preformed with the parameters of mixing ratios, mixing material, curing time and curing conditions etc. Based on the test results, the differences between lime mortar and cement mortar were specified and the structural characteristics of lime mortar were also presented in this paper.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.3 s.55
• /
• pp.110-118
• /
• 2009

The tunnel structure is widely used for transportation in the mountain area. To reduce the duration of construction and thus the expense, a tunnel excavation is often performed simultaneously with a tunnel lining in in-situ. However, cracking of the tunnel lining may occur arising from the vibrating impact in the excavation process. The present study concerns the role of steel fiber and nylon fibers in tunnel lining concrete to reduce the vibrating impact. As a result it was found that both the nylon fiber and steel fiber improved the durability and physical properties of concrete.

• Korean Journal of Culture and Social Issue
• /
• v.17 no.1
• /
• pp.81-113
• /
• 2011

This study investigates leisure activity, involvement and self-concept in cyberspace of various age groups of adolescents. A total of 1,388 students (elementary school=337, middle school=326, high school=361, university=364, consisting of 696 male and 692 female) participated in the study. The results are as follows. First, although the vast majority of adolescents (96.9%) had a computer at home, majority of adolescents visited Internet cafe. Second, 70.3% of adolescents visited Internet cafe to play Internet games, followed by engaging in information search, chatting, and participated in cyber community. Third, on average adolescents spent 5.43 hours per week playing Internet games, with more males playing Internet games than female adolescents. As for information search, the weekly average was 2.60 hours, with university students spending more time than the other groups. As for chatting, the weekly average was 1.69 hours, with no significant differences among the groups. The weekly average of Internet use was 9.65 hours, with older groups spending more time. The weekly average use of computer was 10.91 hours, with older groups spending more time and more males using more computer than females. Fourth, as for self-concept in cyberspace, elementary and middle school students reported that they had fun, while high school and university students reported that they were the same as in the regular daily life. In addition, adolescents reported that they spent leisure activity in cyberspace and they become a fictional character in cyberspace. Fifth, when they played Internet games, regardless of age and gender, adolescents reported that they had fun, followed by that they were absorbed, that they became aggressive, and that they were the same as in the regular daily life. Sixth, when they chatted on Internet, regardless of age and gender, adolescents reported that they had fun, followed by that they were not interested, that they were the same as in the regular daily life, and that they do not chat on Internet. Seventh, when they interacted with their friends on Internet, regardless of age and gender, majority of adolescents reported that they had fun, followed by that they conversed, that they were the same as in the regular daily life, and that they felt closer. These results indicate that Korean adolescents view Internet as a place to spend their leisure time and that they enjoyed spending time on Internet.