• Earthquakes and Structures
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• v.3 no.3_4
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• pp.365-381
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• 2012

Recent earthquakes have damaged some bridges located on the Pacific Coast of Mexico; these bridges have been retrofitted or rebuilt. Based on the fact that the Pacific Coast is a highly active seismic zone where most of the strong earthquakes in the country occur, one fertile and important area of research is the study of the vulnerability of both new and existent bridges located in this area that can be subjected to strong earthquakes. This work is focused on estimating the contribution of some parameters identified to have major influence on the seismic vulnerability of reinforced concrete bridges. Ten models of typical reinforced concrete (RC) bridges, and two existing bridges located close to the Pacific Coast of Mexico are considered. The group of structures selected for the study is based on two span bridges, two pier heights and two substructure types. The bridges were designed according to recent codes in Mexico. For the vulnerability study, the capacity of the structure was evaluated based on the FEMA recommendations. On the other hand, the demand was evaluated using a group of more than one hundred accelerograms recorded close to the subduction zone of Mexico. The results show that the two existent bridges analyzed show similar trends of behavior of the group of bridge models studied. In spite of the contribution that traditional variables (height and substructure type) had to the bridge seismic response, the bridge length was also found to be one of the parameters that most contributed to the seismic vulnerability of these RC medium-length bridges.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.24 no.2
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• pp.71-84
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• 2021

Restoration of DMZ has come up with the discussion on the peaceful use of the DMZ and the conservation plan of the army. In this study, we aim to identify soil characteristics of 108 sites to figure out environmental conditions around the iron fence of DMZ where vegetation has been removed repeatedly. Based on the soil characteristics and climate variables, hierarchy clustering was performed to categorize sites. As a result, we categorized 108 sites into 4 types: middle elevation region, lowland, East coast lowland, other areas. Group of 'other area' is only high in nutrient and clay proportion. Others are in igneous rock and metamorphic rocks with a high proportion of sand and lower nutrients than the optimum range of growth in Korean forest soil. The middle elevation region has a high altitude, low temperature. The east coast lowland has a high temperature in January and low precipitation. The lowland has a low altitude and high temperature. This category provides the environmental condition around the DMZ fence and can be used to select plants for restoration. The restoration project around the DMZ iron fence should satisfy the security of military plans, which means that functional restoration is prior to ecological restoration such as vegetation management under a power line. Additionally, improvement of soil quality and surface stability through restoration projects is required to enhance the resilience of the ecosystem in DMZ.

• Composites Research
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• v.33 no.6
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• pp.390-394
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• 2020

The carbon fiber has been damaged via tow spreading process for carbon fiber spread tow. The fiber damage is caused by friction between equipment and fibers or between fibers and fibers in the process of spreading. As a result, mechanical properties are decreased due to differences in process via material and equipment condition. Therefore, minimizing fiber damage have to be considered in the process. In this study, the change in carbon fiber pneumatic spreading process was observed by according to the filament count, sizing content of carbon fiber and process variables in spreading equipment (fiber tension at the beginning, air temperature in spreading zone, vacuum pressure in spreading zone). Tensile strength was evaluated using samples prepared under optimal conditions for each of the carbon fiber varieties, and mechanical properties were reduced due to damage on the carbon fiber.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.1-9
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• 2020

Using kerosene and liquid oxygen, 1.5-tonf class liquid-liquid pintle injector with rectangular two-row orifice was designed and manufactured. The combustion test of the pintle injector was carried out to verify the combustion performance and combustion stability under a supercritical condition which is the actual operation condition of the liquid rocket engine. The combustion test result showed that the pintle tip was damaged by the high temperature combustion gas in the high-mixed ratio recirculation zone of the combustion chamber. To solve this problem, the insert nozzle was installed in the pintle injector to increase cooling performance at the pintle tip. As a result of the hot firing test, installation of the insert nozzle, AR and BF had a great effect on pintle tip cooling performance.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.503-510
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• 2009

Latex modified concrete (LMC) is a successful polymer-portland cement concretes, which have been developed and used for many years, in overlaying bridge decks and resurfacing industrial floors. The excellent bond strength to substrate, easy application and high resistance to impact, abrasion, wear, aggressive chemicals and freeze-thaw deterioration have made this material used widely. The objective of this study was to determine experimentally the load-deflection response and ultimate strength of reinforced RC beams. The cracking patterns and the mode of failure were observed. Because of excellent bond strength and repairing effects, the RC beams repaired by LMC at compression or tension zone showed over 100% recovery from damaged structures. The RC beams overlaid by LMC showed significant improvement at load carrying capacity as overlay thickness increases. However, the beams repaired of tension zone without shear stirrups almost showed no strengthen effect, and indicated an interfacial failures. The interfacial behavior was estimated by numerical method adopting the concept of shear flow.

• Journal of Korean Society of Forest Science
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• v.79 no.1
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• pp.21-25
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• 1990

To investigate and analyze the change of the vegetation community structure between the severely damaged time (in 1980) and the restored time (in 1987) by the pine gall midge. Thecodoplosis japonensis, four plots with five subplots were sampled at Gwangju-gun of Kyongki-do. The total number of woody species per $500m^2$ changed 39 in 1980 to 41 in 1987. According to the damage restoring, the importance value of the genus Quercus as substituting in the severely damaged forest showed a slight decrease but the importance value of Carpinus laxiflora, Sorbus alnifolia and Styrax obassia increased. As to changes of the vegetation community structure for seven years, the diversity of vegetation structure has increased. The similarity indices between 1980 and 1987 were 52.9% and 51.9% in the understory and shrub stratum, respectively.

• Journal of Welding and Joining
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• v.14 no.5
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• pp.49-58
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• 1996

In Korea Gas Corporation, as one of the pipeline repairing methods, damaged pipelines are sometimes treated with a temporally employment of split sleeve. On conducting the repair process, circumferential fillet and longitudinal groove welding usually must be included. For the case of groove welding, a considerable amount of R&D have been carried out related to property changes, while few study on the property change in fillet welding has been conducted. In this paper, so as to confirm the specification of fillet welding in terms of safety and reliability, properties changed by fillet welding were investigated for two welding processes. Qualifying tests such as reviewing macrostructure and nick-break tests were performed according to API 1104 and ASME section IX. In addition, tensile properties and hardness were evaluated according to KS B0841 and BS 4515. The fillet weld prepared by the qualified procedure showed melting depth of 0.8∼1.3mm and heat affected zone of 2.8∼3.4mm length. No crack and lack of penetration were observed. And the results of hardness and nick-break tests satisfied code requirements. The area crossed by fillet and groove welding line was found to have minimal tensile strength.

• Steel and Composite Structures
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• v.11 no.5
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• pp.391-402
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• 2011

It is clear from the former researches on reinforced concrete filled steel tubular (RCFT) structures that RCFT structures have higher strength and deformation capacity than concrete filled steel tubular (CFT) structures. However, in the case of actual applications to large-scaled structures, the thin-walled steel tube must be used from the view point of economic condition. Therefore, in this study, compression tests of RCFT columns which were made by thin-walled steel tube or small load-sharing ratio in cooperation with high strength concrete were carried out, meanwhile corresponding tests of CFT, reinforced concrete (RC), pure concrete and steel tube columns were done to compare with RCFT. By the a series of comparison and analysis, characteristics of RCFT columns were clarified, and following conclusions were drawn: RCFT structures can effectively avoided from brittle failure by the using of reinforcement while CFT structures are damaged due to the brittle failure; with RCFT structures, excellent bearing capacity can be achieved in plastic zone by combining the thin-walled steel tube with high strength concrete and reinforcement. The smaller load-sharing ratio can made the reinforcement play full role; Combination of thin-walled steel tube with high strength concrete and reinforcement is effective way to construct large-scaled structures.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.248-255
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• 2006

Among a variety of influencing components, time-variant seepage and long-term underground motion are important to understand the abnormal behavior of tunnels. Excessiveness of these two components could be the direct cause of severe damage on tunnels. however, it is not easy to quantify the effect of these on the behavior of tunnels. These parameters can be estimated by using inverse methods once the appropriate relationship between inputs and results are clarified. Various inverse methods or parameter estimation techniques such as artificial neural network and least square method can be used depending on the characteristics of given problems. Numerical analyses, experiments, or monitoring results are frequently used to prepare a set of inputs and results to establish the back analysis models. In this study, a back analysis method has been developed to estimate geotechnically hard-to-known parameters such as permeability of tunnel filter, underground water table, long-term rock mass load, size of damaged zone associated with seepage and long-term underground motion. The artificial neural network technique is adopted and the numerical models developed in the firstpart are used to prepare a set of data for learning process. Tunnel behavior especially the displacements of the lining has been exclusively investigated for the back analysis.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.1
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• pp.43-48
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• 2020

At present, 24 nuclear power plants are in operation nationwide as the main power source responsible for about 27% of Korea's electricity, and five nuclear power plants are currently under construction. Issues of nuclear safety and reliability have always existed, but after the Fukushima accident, ensuring reliability has become an even more important issue for safety. Compared to other kinds of accidents, the initial response after a nuclear accident is more important than any other accident. Prior to accidents, it is important to be able to predict and judge the accident in advance for the sake of prevention. In this research, non-destructive inspection methods for existing pipe welds include radiographic, ultrasonic, magnetic particle practice, and liquid penetration testing. For this experiment, carbon steel pipes like that of the material used in nuclear pipes were adopted, and specimen welded to the flange (Flange) were manufactured. After testing, the weld specimen were not damaged through the infrared thermography (IRT) experiment. This study attempted to improve the safety of carbon steel pipes through a comparative analysis of finite element analysis.