• Wind and Structures
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• v.7 no.5
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• pp.317-332
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• 2004

Wind tunnel experiments were conducted under highly turbulent and disturbed flow conditions over a solid/perforated plate with a long splitter plate in its plane of symmetry. The effect of varied level of perforation of the normal plate on fluctuating velocities and fluctuating pressures measured across and along the separation bubble was studied. The different perforation levels of the normal plate; that is 0%, 10%, 20%, 30%, 40% and 50% are studied. The Reynolds number based on step height was varied from $4{\times}10^3$ to $1.2{\times}10^4$. The shape and size of the bubble vary with different perforation level of the normal plate that is to say the bubble is reduced both in height and length up to 30% perforation level. For higher perforation of the normal plate, bubble is completely swept out. The peak turbulence value occurs around 0.7 to 0.8 times the reattachment length. The turbulence intensity values are highest for the case of solid normal plate (bleed air is absent) and are lowest for the case of 50% perforation of the normal plate (bleed air is maximum in the present study). From the analysis of data it is observed that $\sqrt{\overline{u^{{\prime}2}}}/(\sqrt{\overline{u^{{\prime}2}}})_{max}$, (the ratio of RMS velocity fluctuation to maximum RMS velocity fluctuation), is uniquely related with dimensionless distance y/Y', (the ratio of distance normal to splitter plate to the distance where RMS velocity fluctuation is half its maximum value) for all the perforated normal plates. It is interesting to note that for 50% perforation of the normal plate, the RMS pressure fluctuation in the flow field gets reduced to around 60% as compared to that for solid normal plate. Analysis of the results show that the ratio [$C^{\prime}_p$ max/$-C_{pb}(1-{\eta})$], where $C^{\prime}_p$ max is the maximum coefficient of fluctuating pressure, $C_{pb}$ is the coefficient of base pressure and ${\eta}$ is the perforation level (ratio of open to total area), for surface RMS pressure fluctuation levels seems to be constant and has value of about 0.22. Similar analysis show that the ratio $[C^{\prime}_p$ max/$-C_{pb}(1-{\eta})]$ for flow field RMS pressure fluctuation levels seems to be constant and has a value of about 0.32.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.405-413
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• 2017

In this paper, we study the biaxial buckling analysis of nonlocal MEE(magneto-electro-elastic) nano plates based on the first-order shear deformation theory. The in-plane electric and magnetic fields can be ignored for MEE(magneto-electro-elastic) nano plates. According to magneto-electric boundary condition and Maxwell equation, the variation of magnetic and electric potentials along the thickness direction of the MME plate is determined. In order to reformulate the elastic theory of MEE(magneto-electro-elastic) nano-plate, the nonlocal differential constitutive relations of Eringen is used. Using the variational principle, the governing equations of the nonlocal theory are discussed. The relations between nonlocal and local theories are investigated by computational results. Also, the effects of nonlocal parameters, in-plane load directions, and aspect ratio on structural responses are studied. Computational results show the effects of the electric and magnetic potentials. These computational results can be useful in the design and analysis of advanced structures constructed from MEE(magneto-electro-elastic) materials and may be the benchmark test for the future study.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.179-186
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• 2010

The bond between steel and concrete in reinforced concrete members is essential to resist external load, but the bond mechanism in reinforced concrete beams deteriorated by steel corrosion has not been clearly known yet. Most existing researches have dealt with the bond behavior of corroded steel under monotonic loading, but scarce are researches dealing with bond behavior of corroded steel under repeated loading. This study includes the experimental investigation on the bond behavior with respect to the various degrees of steel corrosion under repeated loading. According to the test results, the bond strength of corroded steel under monotonic loading increases as the rate of steel corrosion increases unless the splitting crack occurs. The slip versus number of load cycles relation was found to be approximately linear in double logarithmic scale, not only in specimens without steel corrosion but also in specimens with steel corrosion. The test results also show that the steel corrosion does not negatively affect the bond strength of corroded steel after repeated loading unless the splitting crack occurs. But the fatigue life decreases sharply after splitting crack occurs. This research will be helpful for the realistic durability design and condition assessment of reinforced concrete structures.

• Journal of the Economic Geographical Society of Korea
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• v.6 no.2
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• pp.443-470
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• 2003

This study is to consider economic, political, socio-cultural and environmental characteristics of the new urbanization process and its spatial structures and urban policy of Seoul in the 1990s. Some experimental findings which have been identified throughout this study can be summarized as follows. First of all, Seoul, the largest city in S.Korea has experienced a restructuring process of economy, which has been promoted by the development of producer services as well as knowledge- based or high tech industries. Secondly, the autonomy of Seoul has increased after the introduction of local self-government, with relatively higher self-management of local finance than other cities, strengthening the tendency of enterpreneurialism, empowering civil movements, and increasing the political participation of women. Thirdly, in the socio-cultural aspect, the material wants to gain a certain identity through consumption, using urban environments culturally, varying consuming attitudes and ways of leisure times in relation with the rapid development of transportation and information communication. Fourthly, in the environmental aspect, Seoul has tried to introduce the concept of sustainable development in terms of increasing wants on the quality of life, and to develop a pro-environmental eco-city with environmental rehabilitation, constructing green space and eco-park. Finally, in the spatial dimension, Seoul has shown a structuration of multi-centers, with highly spectacular urban landscapes and seemingly authentic urban planning. These results make us confirm that Seoul has been in the process of new urbanization which can be distinguished from the previous one.

• Journal of the Korean GEO-environmental Society
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• v.18 no.7
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• pp.13-20
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• 2017

Soil nailing is ground reinforcement method using the shear strength of ground and the pullout shear resistance force of nail. It is mainly used for reinforcement of cut slopes, earth retaining structures and retaining walls, etc. It may be designed considering the pullout resistance of nail in the case of earth retaining structure and retaining wall, but it should be designed considering not only pullout resistance but also shear and bending resistance in the case of slope. However, conservative designs considering only pullout resistance are being done and most of the studies are about increasing pullout resistance by improving of material, shape and construction method of nail. Actually, Shear bending deformations occur centering on the active surface in ground reinforced with the nail. The grout with relatively low strength is destroyed and separated from the reinforcing material. As a result, the ground is collapsed while reducing the frictional resistance rapidly. Therefore, it is necessary to develop the method to increase the shear resistance while preventing separation of nail and grout body. In this study, an experimental study was conducted on new soil nailing method which can increase shear resistance by forming protrusions through pressurized grouting after installing a packer on the outside of deformed bar.

• Journal of the Korea Concrete Institute
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• v.20 no.4
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• pp.469-475
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• 2008

It is obvious that chloride penetration through cracks can threaten the durability of concrete substantially, according to the previous studies of author. It was proposed that crack depth corrseponded with critical crack width from the surface is a crucial factor in view of durability design of concrete structures. It is now necessary to deal with chloride penetration through microcracks characterized with the mixing features of concrete. The purpose of this study is examining the effect of mix proportional features of concrete such as coarse aggregate, high strengtherize of concrete and reinforcement of steel fiber on chloride penetration through cracks. Although small size of coarse aggregate can lead to many microcracks in concrete, the cracks should not impact on chloride penetration directly. On the contrary, chloride should penetrate through cracks easily in concrete with a large size of coarse aggregate because mixrocracks are connected to each other. Second, high strength concrete has an excellent performance to resist with chloride penetration. However, for cracked high strength concrete, its performance is reduced upto the level of ordinary concrete. Finally, steel fiber reinforcement is effective to reduce chloride penetration through cracks because steel fiber reinforcement can lead to reduce crack depth significantly.

• Journal of the Korean Geosynthetics Society
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• v.19 no.1
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• pp.83-91
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• 2020

In this study, the characteristics of support behavior according to the change of ground condition of the cast-in-place pile and the large Caisson foundation, which are increasingly used as foundations of large structures and bridges. the allowable bearing capacity calculated using the yield load analysis method was analyzed to calculate similar allowable bearing capacity for each method. In addition, the allowable bearing capacity calculated by the ultimate load analysis method was found to have a large difference in bearing capacity for each method. Through this point, it can be usefully used as an empirical formula for evaluating the settlement characteristics of piles in future design and construction. In addition, as a result of examining the ground force distribution during sedimentation of large caissons, the section of the weathered rock layer showed almost constant ground force distribution as ground forces decreased after yield occurred at the base corner. And in the bed rock layer section, the foundation's center was transformed into a ground force in the form of a convex downward due to an increase in the ground resistance of the central part. Using these results, the theory previously presented by Fang (1991) and Kőgler (1936) was proved.

• Journal of the Korean Geotechnical Society
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• v.34 no.1
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• pp.37-46
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• 2018

Hollow prestressed concrete filled steel tube (HCFT) piles, which compose hollow PHC piles inside thin wall steel tubes, are developed. In order to investigate the strength characteristics of HCFT piles, flexural and shear tests were conducted on HCFT piles as well as PHC and steel pipe piles with the same diameter. Results of the test program showed that the flexural strength of HCFT piles was 2.88 and 1.19 times those of ICP and steel pipe piles with thickness of 12 mm, respectively, and its shear strength was 2.40 times that of steel pipe piles. The shear key attached to the inside of thin wall steel tube did not affect the flexural behavior of HCFT piles. It was also observed that the flexural strengths of HCFT piles with diameters of 450 and 500 mm were 35 to 63% higher than the sum of the flexural strengths of its components, respectively, because the strength of concrete in compressive zone increased by confining effect of thin wall steel tube on concrete. HCFT piles used as upper piles in hybrid composite piles might decrease the lateral displacement and increase the structural safety of structures subjected to lateral loads.

• Journal of the Korea Institute of Building Construction
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• v.15 no.2
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• pp.143-151
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• 2015

Many studies have investigated the airborne chlorides that can weaken the overall durability of the concrete structures due to the corrosion of steel materials, but most of the studies have aimed to examine weathering by exposing various construction materials to the actual oceanic environment. However, with the exposure test, it was difficult to find the threshold of precise corrosive amount of airborne chlorides due to diverse deteriorating environmental factors such as ultraviolet ray, acid rain, floating material from industrial pollution as well as airborne chlorides. Therefore, in this study, an airborne chloride simulator was set up, in oder to conduct a corrosion accelerating test for steels coated by five different finishing materials. As results, it was found that the corrosion began to be observed at $0.58{\sim}0.73mg/dm^2$ for no-coated steel, at $7.89{\sim}8.46mg/dm^2$for urethane-coated steel, at $57.95{\sim}69.48mg/dm^2$ for red lead-coated steel, and at $80.73{\sim}89.35mg/dm^2$ for stainless-coated steel, respectively. Hence, these specific data can be considered as the threshold ranges of corrosion for each coating material for steel.

• Korean Journal of Construction Engineering and Management
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• v.21 no.3
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• pp.28-38
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• 2020

The large-scaled and high-rise construction structures in recent years have increased high place work, leading to an increase in falling accidents (hereinafter, "accidents"). The need for prediction and management of unsafe acts of workers at construction sites has been raised as unsafe acts of workers are identified as the main cause of industrial accidents. This research aims at deriving the improvement effect of unsafe acts by presenting the relationship between unsafe acts of workers and accidents at construction sites as a probability. Unsafe acts of workers were derived based on the analysis of accident cases. In addition, surveys were conducted to calculate the probability of occurrence of accidents caused by unsafe acts (hereinafter, 'accident probability'). The Event Tree Analysis (ETA) was utilized to confirm the final probability according to the combination of unsafe acts and improvement effect. The accident probability by unsafe act was found to be the highest for working after drinking (95.41%) and to be the lowest for equipment and machine utilization (65.70%). The accident probability according to a combination of unsafe acts was the highest when all of the unsafe acts were conducted (13.23%) and was the lowest when none of the unsafe acts were conducted (0.00%).