• Journal of the Korean Society for Railway
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• v.20 no.1
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• pp.64-75
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• 2017

The role of a track subgrade is to provide bearing capacity and distribute load transferred to lower foundation soils. Track subgrade soils are usually compacted by heavy mechanical machines in the field, such that sometimes they are attributed to progressive residual settlement during the service after construction completion of the railway track. The progressive residual settlement generated in the upper part of a track subgrade is mostly non-recoverable plastic deformation, which causes unstable conditions such as track irregularity. Nonetheless, up to now no design code for allowable residual settlement of subgrade in a railway trackbed has been proposed based on mechanical testing, such as repetitive triaxial testing. At this time, to check the DOC or stiffness of the soil, field test criteria for compacted track subgrade are composed of data from RPBT and field compaction testing. However, the field test criteria do not provide critical design values obtained from mechanical test results that can offer correct information about allowable permanent deformation. In this study, a test procedure is proposed for permanent deformation of compacted subgrade soil that is used usually in railway trackbed in the laboratory using repetitive triaxial testing. To develop the test procedure, an FEA was performed to obtain the shear stress ratio (${\tau}/{\tau}_f$) and the confining stress (${\sigma}_3$) on the top of the subgrade. Comprehensive repetitive triaxial tests were performed using the proposed test procedure on several field subgrade soils obtained in construction sites of railway trackbeds. A permanent deformation model was proposed using the test results for the railway track.

• The KIPS Transactions:PartC
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• v.9C no.4
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• pp.531-542
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• 2002

An input and output buffering ATM switch conventionally operates in either Queueloss mode or Backpressure mode. Recently, a new mode, which is called Hybrid mode, was proposed to overcome the drawbacks of Queueloss mode and Backpressure mode. In Hybrid mode, when both the destined output buffer and the originfted input buffer are full, a cell is dropped. This thesis analyzes the cell loss rate and the cell delay of Queueloss, Backpressure and Hybrid modes in a switch adopting output-port expansion scheme under uniform traffic. Output-port expansion scheme allows only one cell from an input buffer to be switched during one time slot. If several cells switch to a same destined output port, the number of maximum transfer cells is restricted to K (Output-port expansion ratio). The simulation results show that if an offered load is less than 0.9, Hybrid mode has lower cell loss rate than the other modes; otherwise, Queueloss mode illustrates the lowest cell loss rate, which is a different result from previous researches. However, the difference between Hybrid and Queueloss modes is comparably small. As expected, the average cell delay in Backpressure mode is lower than those of Queueloss mode and Hybrid mode, since the cell delay due to the retransmission of higher number of dropped cells in Backpressure mode is not considered.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.3
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• pp.30-37
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• 2023

The PSCB girder bridge is a closed cross-section in which the top and bottom flanges and the web are integrated, and the structural characteristics are generally different from the bridges in which the girder and the floor plate are separated, so a maintenance plan that reflects the characteristics of the PSCB girder bridge is required. As a result of analyzing damage types by collecting detailed safety diagnosis reports of highway PSCB girder bridges, most of the deterioration and damage occurring during use is concentrated on the top flange. In particular, cracks in the bridge direction on the underside of the top flange occurred in about 70 % of the PSCB girder bridges to be analyzed, and these cracks were judged to be caused by indirect loads such as heat of hydration and drying shrinkage rather than structural cracks caused by external loads. In order to improve durability and reduce maintenance costs of PSCB girder bridges in use, it is necessary to control restraint drying shrinkage cracks from the design stage. Therefore, in this paper, the cracks caused by drying shrinkage under restraint, which is the main cause of cracks under the flanges of the top part of the PSCB girder bridge, were directly calculated using the Gilbert Model, and the influencing factors such as the amount of reinforcing bars, diameter and spacing of reinforcing bars were analyzed. As a result of the analysis, it was found that the crack width caused by restraint drying shrinkage exceeded the allowable crack width of 0.2 mm for reinforcing bars with a reinforcing bar ratio of 0.01 or less based on the H16 reinforcing bar and a reinforcing bar with a diameter greater than H19 based on the reinforcing bar ratio of 0.01. Finally, based on the results of the crack width review, a method for controlling the crack width of the top flange of the PSCB girder bridge was proposed.

• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.438-446
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• 2001

Recently, porous concrete has been used for the purpose of decreasing the load of earth environment. It consists solely of cement, water and uniform-sized coarse aggregate. And its fundamental properties will be considerably affected by the physical properties of aggregate because the aggregate occupies for the most part in its mix proportion. For such a reason, this study was carried out to investigate the influence of the sizes and kinds of aggregate for the fundamental properties of porous concrete. It showed that the fundamental properties of porous concrete were the similar value in all sizes of aggregate except in the case of using the 2.5∼5㎜ aggregate and were varied according to the kinds of aggregate. In particular, compressive strength of porous concrete using 2.5∼5㎜ aggregate was more higher than that using other aggregate, and its void ratio and coefficient of permeability was lower. And the maintenance capacity of permeability of porous concrete was varied by the sizes and the kinds of aggregate. In particular, it was greatly decreased in case of using the 2.5∼5㎜ aggregate. And unlike dynamic modulus of elasticity of ordinary concrete, that of porous concrete was very high value in early ages and was slowly increased after that time.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.392-402
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• 2020

We investigated the concentrations of acid volatile sulfide (AVS), ignition loss (IL), total organic carbon (TOC), total nitrogen (TN), and metallic elements (As, Cd, Cr, Cu, Fe, Hg, Mn, Pb, and Zn), in August 2015, to determine the spatial distribution and pollution status of organic matter and metals in the surface sediment of Jinju Bay, a spraying shellfish farming area, Korea. The concentrations of organic matter and metallic elements were significantly higher in the southern part of the bay than in the mouth and center of the bay. The C/N ratio (5.7~8.0) in the sediment represents the dominance of organic matter of oceanic origin in the surface sediment of the study area. The concentrations of AVS, TOC, and metals (As, Cd, Cr, Cu, Hg, Pb, and Zn) were much lower than the values of the sediment quality guidelines applied in Korea. Based on the results of the pollution load index (PLI) and ecological risk index (ERI), the metal concentrations in the surface sediment of Jinju Bay have a weakly negative ecological effect on benthic organisms although the sediments with high metal pollution status are distributed in the southern parts of the bay, with high dense shellfish farming areas. Thus, the surface sediments in Jinju Bay are not polluted with organic matter and are slightly polluted with metallic elements.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.149-160
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• 1999

This paper is a part of a research aimed at the verification of basic design rules of high-strength concrete columns. A total of 32 column specimens were tested to investigate structural behavior and strength of eccentrically loaded reinforced concrete tied columns. Main variables included in this test program were concrete compressive strength. steel amount, eccentricity, and slenderness ratio. The concrete compressive strength varied from 356 kg/$cm^2$ to 951 kg/$cm^2$ and the longitudinal steel ratios were between 1.13 % and 5.51 %. Test results of column sectional strength are compared with the results of analyses by ACI rectangular stress block, trapezoidal stress block, and modified rectangular stress block. Axial force-moment-curvature analysis is also performed for predicting axial load-moment strength and compared with the test results. The ACI rectangular stress block provides over-estimated column strengths for the lightly reinforced high strength column specimens. The calculated strengths by moment-curvature analyses are highly affected by $k_3$ values of the concrete stress-strain curve. Observed failure mode. concrete ultimate strain, and stress block parameters are discussed.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.1 s.47
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• pp.41-49
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• 2006

Through the 1982 Urahawa-ohi and the 1995 Kobe earthquakes, a number of bridge columns were observed to develop a flexural-shear failure due to the bond slip as a consequence of premature termination of the column longitudinal reinforcement. Because the seismic behavior of RC bridge piers is largely dependent on the performance of the plastic hinge legion of RC bridge piers, it is desirable that the seismic capacity of RC bridge pier is to evaluate as a curvature ductility. The provision for the lap splice of longitudinal steel was not specified in KHBDS(Korea Highway Bridge Design Specification) before the implementation of 1992 seismic design code, but the lap splice of not more than 50%, longitudinal reinforcement was newly allowed in the 2005 version of the KHBDS. The objective of this research is to investigate the distribution and ductility of the curvature of RC bridge column with the lap splice of longitudinal reinforcement in the plastic hinge legion. Six (6) specimens were made in 600 mm diameter with an aspect ratio of 2.5 or 3.5. These piers were cyclically subjected to the quasi-static loads with the uniform axial load of $P=0.1f_{ck}A_g$. According to the slip failure of longitudinal steels of the lap spliced specimen by cyclic loads, the curvatures of the lower and upper parts of the lap spliced region were bigger and smaller than the corresponding paris of the specimen without a lap splice, respectively. Therefore, the damage of the lap spliced test column was concentrated almost on the lower part of the lap spliced region, that appeared io be failed in flexure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.3
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• pp.103-110
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• 2022

The purpose of this study is to experimentally evaluate the stiffness and strength reduction according to the reinforcing bar details of the vertically divided reinforced concrete shear walls. To confirm the effect of reducing strength and stiffness according to vertical division, four real-scale specimens were fabricated and repeated lateral loading tests were performed. As a result of the experiment, it was confirmed that the strength and stiffness were decreased according to the vertical division. In particular, as the stiffness reduction rate is greater than the strength reduction rate, it is expected that safety against extreme strength can be secured when the load is redistributed according to vertical division. As a result of checking the crack pattern, a diagonal crack occurred in the wall subjected to compression control among the divided walls. It was confirmed that two neutral axes occurred after division, and the reversed strain distribution appeared in the upper part, showing the double curvature pattern. In future studies, it is necessary to evaluate the stiffness reduction rate considering the effective height of the wall, to evaluate additional variables such as wall aspect ratio, and to conduct analytical studies on various walls using finite element analysis.

• Journal of agriculture & life science
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• v.50 no.3
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• pp.31-41
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• 2016

This study was conducted to develop a handy earth auger for use in sloppy and rugged forest terrains in order to reduce labor cost which comprises a major part of the production costs in forest afforestation projects. The first prototype is developed consist of two parts, the soil-digging screw and the battery power source. The specifications of the first prototype screw are: length of 170mm, a top diameter of 60mm, bottom diameter of 47mm, 23° angle for each helix, and a 50mm awl-head tip. The use of a single line of screw was selected for reduced weight. In addition, a power source of rotary DC Motor(WD-6G2425, WONILL, Korea) with a maximum torque of 30kgf-cm, rotation of 20-30rpm, K6G30C decelerator with a reduction ratio of 30:1 which could be used with no load for 48 was operated. In consideration of its weight, a lithium battery was utilized in line with the goal of developing a lightweight auger. In order to evaluate the performance of the first prototype, test sites were selected as 6 areas. The rotational force was found to be highest in area A(Solid area), followed by areas F(Mounted slope 40° area) and E(Mounted slope 30° area). It was also observed that in general, the rotational force increased along with the increase in soil depth with the maximum rotational force recorded at 10cm.

• Journal of Wetlands Research
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• v.21 no.2
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• pp.140-146
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• 2019

In order to manage non-point sources, the paradigm of the system should be changed so that the management of non-point sources will be systematized from the beginning of the use and development of the land. It is necessary to change the method of national subsidy support and poeration plan for the non-point source management area. In order to increase the effectiveness of the non-point source reduction project, it is necessary to provide a minimum support ratio and to provide additional support according to the performance of the local government. A new system should be established to evaluate the performance of non-point source reduction projects and to monitor the operational effectiveness. It is necessary to establish the related rules that can lead the local government to take responsible administration so that the local governments faithfully carry out the non-point source reduction project and achieve the planned achievement and become the sustainable maintenance. Alternative solutions are needed, such as problems with the use of $100{\mu}m$ filter in automatic sampling and analysis, timely acquisition of water sampling and analysis during rainfall, and effective management of non-point sources network operation management. As an alternative, it is necessary to consider improving the performance of sampling and analysis equipment, and operate the base station. In addition, countermeasures are needed if the amount of pollutant reduction according to the non-point source reduction facility promoted by the national subsidy is required to be used as the development load of the TMDLs. As an alternative, it is possible to consider supporting incentive type of part of the maintenance cost of the non-point source reduction facility depending on the amount of pollutants reduction.