• Journal of Korea Water Resources Association
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• v.53 no.1
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• pp.29-43
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• 2020

The purpose of this study is to propose the design criteria and detailed design model by reviewing the issues related to geometry, formation process, destruction process, hydraulic function, restoration and ecological function of the step-pool from the existing research results, to apply the step-pool sequences to river restoration. Based on the analysis and review results, the design criteria for the structure and size of the step-pool are presented as ratio of the step spacing and the channel width, ratio of the unit step slope and channel slope, and ratio of step height and the particle size. To ensure structural stability of the step, stability analysis method of overturning based on the keystone theory was proposed as a design criterion. As a detailed design concept, a layout model was proposed by applying the imbricating structure of keystones and arch stones to the planar, longitudinal and transverse configurations of the step-pool.

• Journal of Korean Association for Spatial Structures
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• v.5 no.3 s.17
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• pp.91-100
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• 2005

The paper presents a direct method for the diplacement control and stiffness redesign using displacement and response force contribution factors. At first, these two kinds of factors are derived and the relationship between them is examined. An equation to evaluate the change of displacement according to the change of each member stiffness is proposed. For the statically determinate structures, the proposed equation gives the exact solution with no approximation. But it has some error in case of statically indeterminate structures because the redistribution of response forces is neglected in the equation. However, the equation may be very useful even for statically indeterminate structures because it provides the relationship between the member stiffness and the global displacement. The proposed method is expected to be useful for the displacement control of large space or hi-rise building structures where the stiffness design governs the design result.

• Korean Journal of Crystallography
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• v.7 no.1
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• pp.57-63
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• 1996

The compound titanium (III) pyrophosphate, KTiP2O7 has been prepared and the crystal structure of the compound has been determined by the X-ray diffraction techniques. It crytallizes in the space group P21/a of the monoclinic system with four formula units in a cell of dimensions a=8.210(3), b=10.292(2), c=7.434(1)Å and β=106.71(2)°. The structure consists of the framework possessing corner-sharing octahedral TiO6 and pyrophosphate groups. As a result, a tunnel structure has been constructed and the K+ cations reside inside the tunnel. KTiP2O7 is isostructural with other trivalent metal pyrophosphates such as KAlP2O7 and RbTiP2O7 but the size difference of the alkali metals causes the variation in the structure. The classical charge balance of the compound can be described as [K+][Ti3+][P24O74-].

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.1
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• pp.57-67
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• 2007

The service life of concrete structure is to a great extent influenced by crack developed at early ages of concrete material. Especially, hydration heat is a main cause of thermal cracking at mass concrete structures. The thermal cracking of massive structure is analyzed of the thermal cracking index which was presented Concrete Standard Specifications. The thesis analyzed the thermal cracking index which considered various variable (cement type, height of casting, curing condition, concrete mixing temperature, the unit cement content) at internal restricted mass concrete. The analysis result is denoted increase and decrease rate of thermal cracking index whenever the variables change. The results is helped to understand thermal cracking every time structures is designed and constructed. And I think that it is useful economic and stable design of mass concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.2
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• pp.19-30
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• 2012

Due to the fact that the social environment is improved and the urban development is stabilized, the demand of new construction of apartment becomes slowdown. Accordingly, there are many researches to lengthen the service life of the existing apartment through the remodeling and its importance is continuously rising. However, reliable design specifications and guidelines for the design of remodeling with partial demolition are not provided yet in Korea. Specially, in the apartment remodeling, slab collapse accidents take major portion in all accidents that reported by Korean Government. It is very important to prevent intial crack of slab because intial crack could cause severe accident like collapse of all structure in a short period of time. The purpose of this study is to develop structural guidelines that could guarantee the structural safety and serviceability of slab structure and could be adopted in Korean remodeling with partial demolition. There are mainly two components to determine structural behavior of slab structure. One is the shape of slab structure and the other is load which is resisted by the slab structure. In this study, the weight per unit volume of concrete debris and concrete strength are estimated through the analysis of previous researches to recognize the relationship between the shape of slab and load that loaded on the slab. Accordingly, approximately 300 pieces of floor plan are collected and analyzed. The finite element analysis is conducted using these analyzed and estimated results. From the finite element analysis results, the limited stacking height of debris is suggested and the stacking method is also discussed. In addition, to find the relationship between movement of demolition equipment and structural behavior of slab, the static and dynamic loading tests are conducted. From the results of loading tests, the impact factor which will be considered in the remodeling design could be estimated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.839-847
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• 2012

Numerical simulations for channel flows with $Re_{\tau}$ = 180, 395 and 590 have been performed to investigate the hairpin packet formation process in wall-bounded turbulent flows. Using direct numerical simulation databases, the initial flow fields are given by the conditionally averaged flow field with the second quadrant event specified at the buffer layer. By tracking the initial vortex development, the change in the initial vortex to an ${\Omega}$-shaped vortex and th generation of a secondary hairpin vortex were found to occur with time scales based on the wall units. In addition, at the time when the initial vortex has grown to the channel center, the inclination angle of the hairpin vortex packet is approximately $12{\sim}14^{\circ}$, which is similar for all three Reynolds numbers. Finally, numerical simulations of the evolution of two adjacent hairpin vortices have been performed to examine the interaction between the adjacent vortex packets.

• Journal of the Korean Society for Railway
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• v.17 no.4
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• pp.245-250
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• 2014

This paper, as a study for the serviceability design of railway bridges with concrete track, presents the effects of design parameters of tracks and bridges on the forces acting on the rail supports of the track. To calculate the forces acting on the track, an unequal spacing discrete supported model with different spacing of rail supports was induced. Design parameters are the rail support spacing of expansion joints above abutments or piers of bridges, the distance from the support of a girder to the last rail support on the end of the girder, and the number of additional rail supports. The causes of the displacement of track are axial force, unit vertical displacement, and unit rotation. From the analysis, the maximum compressive force and the maximum uplifting force acting on the rail supports were determined and the effects of the rail support spacing on the forces acting on the track were presented.

• Journal of Korea Water Resources Association
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• v.33 no.3
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• pp.315-330
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• 2000

The GIUH (Geomorphologic Instantaneous Unit Hydrograph) is to be applied to the ungauged or insufficiently gauged basins. For tIris purpose, an accurate estimation of the charactenstlc velocity is one very important part, but any proper method for this has not been developed yet. In case that we have enough rainfall and runoff clata, the estimation of the characteristic velocity may be an easy job, but it is out of the purpose of the GIUH. Remindmg that the purpose of GIUH the characterisbc veloclty should be estimated based on the geomorpholog1c analysis and also be snnple for easy apphcation. In tIris research analysis cmd application of the GruH was given to several sub-basins in Wi-stream river basin, Gono, Donggok and Hyoryung. After deriving the characteristic velocity througn a optimizatlOn process with real data, it is compared w1th several velOCIties der1ved from geOlnoI1Jhoclimatic instantaneous unit hydrograph theory and several other concentration time formulae. The estimated charactenstic velocities using Kerby, Kim, KInematic Wave, and Brasby- Williams formulae found to g1ve the appropriate results. Hmvever, as the Kerby, and the Kinematic Wave require user's decision of the IvIanning's n value, the K1m and the Braby-Williams seem to be more applicable and recommended as characteristic velocity formula.

• Journal of Korea Water Resources Association
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• v.51 no.1
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• pp.19-33
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• 2018

This study proposed a rainfall-runoff model for the purpose of real-time flood warning in urban basins. The proposed model was based on the shot noise process, which is expressed as a sum of shot noises determined independently with the peak value, decay parameter and time delay of each sub-basin. The proposed model was different from other rainfall-runoff models from the point that the runoff from each sub-basin reaches the basin outlet independently. The model parameters can be easily determined by the empirical formulas for the concentration time and storage coefficient of a basin and those of the pipe flow. The proposed model was applied to the total of three rainfall events observed at the Jungdong, Guro 1 and Daerim 2 pumping stations to evaluate its applicability. Summarizing the results is as follows. (1) The unit response function of the proposed model, different from other rainfall-runoff models, has the same shape regardless of the rainfall duration. (2) The proposed model shows a convergent shape as the calculation time interval becomes smaller. As the proposed model was proposed to be applied to urban basins, one-minute of calculation time interval would be most appropriate. (3) Application of the one-minute unit response function to the observed rainfall events showed that the simulated runoff hydrographs were very similar to those observed. This result indicates that the proposed model has a good application potential for the rainfall-runoff analysis in urban basins.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5D
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• pp.655-664
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• 2008

Lean Construction recommends implementing site production management by measuring the reliability of daily production tasks, collecting the causes for failure of incomplete tasks, and identifying problems in the existing process based on the collected data. Although many research projects have been performed to introduce Lean Construction in Korea, there are not many cases in which day-to-day site production operations has been stringently evaluated based on such methods. This paper introduces three cases in which such techniques were implemented on a residential, civil infrastructure and plant project. On each project, process maps were created with the superintendents and daily production meetings were held for two weeks. Consequently, the average PPC for the three projects was 79% for PPC and 16% for PAT. In addition, the majority of the failures were due to 'Directive/Plan' and 'Prerequisites.' The results show that project stakeholders (owners, contractors, etc.) lack the ability to plan ahead and keep to their plans, and also lack the capability to synchronize workflow between themselves. The results also reveal that project participants need to be more proactive in solving process problems on site and also need to be better educated in Lean concepts and methodologies.