• Geotechnical Engineering
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• v.12 no.6
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• pp.51-64
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• 1996

After the model open-ended pile attached with strain gages was driven into a pressure chamber, in which the saturated microfine sand was contained, the static compression loading test was performed for that pile. Based on the test results, ultimate pile capacity was determined. Then, either simulated earthquake shaking or sinusoidal shaking was applied to the pile with the sustained certain level OP ultimate pile load. Then, pile capacity degradations characteristics during shaking were studied. Pile capacity degradation during two different shakings were greatly different. During the simulated earthquake shaking, capacity degradation depended upon the magnitude of applied load. When the load applied to the pile top was less than 70% of ultimate pile capacidy, pile capacity degradation rate was less than 8%, and pile with the sustained ultimate pile load had the degradation rate of 90%. Also, most of pile capacity degradation was reduced in outer skin friction and degradation rate was about 80% of ultimate pile capacity reduction. During sinusoidal shaking, pile capacity degradation did not depend on the magnitude of applied load. It depended on the amplitude and the frequency , the larger the amplitude and the fewer the frequency was, the higher the degradation rate was. Reduction pattern of unit soil plugging (once depended on the mode of shaking. Unit soil plugging force by the simulated earthquake shaking was reduced in the bottom 3.0 D, of the toe irrespective of the applied load, while reduction of unit soil plugging force by sinusoidal shaking was occurred in the bottom 1.0-3.0D, of the toe. Also, the soil plugging force was reduced more than that during simulated earthquake shaking and degradation rate of the pile capacity depended on the magnitude of the applied load.

• The Journal of Engineering Geology
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• v.23 no.1
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• pp.19-27
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• 2013

Deformation of a slope at a coal waste depot and the natural slope under the depot was surveyed and investigated at Dogye village in Samcheock city, Gangwon Province. To investigate the behaviors of the slopes, wire sensors and a rain gauge were installed on the crest of the waste depot slope and inclinometers were installed in the natural slope. The results of deformation monitoring at the crest of the waste depot slope using wire sensors revealed increased deformation with increasing cumulative rainfall. The results of monitoring horizontal deformation of the natural slope revealed that maximum horizontal deformation was also affected by cumulative precipitation. However, the groundwater level at the natural slope showed no change with rainfall. These measurements confirm that deformation at coal mine waste depots is closely related to precipitation, indicating that self-loading at such depots increases with rainfall infiltration, thus causing deformation of the waste depot slope. In addition, increasing the self-load of the coal mine waste depot may cause deformation of the underlying natural slope.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.3
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• pp.219-232
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• 2013

This paper presents a microstrip antenna which recovers its resonant frequency and impedance shifted automatically by the approach of other objects such as hands. This can be used for telemetry sensor applications in the ultrahigh frequency(UHF) industrial, scientific, and medical(ISM) band. It is the key element that an frequency-reconfigurable antenna could be electrically controlled. This antenna is miniaturized by loading the folded plates at both radiating edges, and varactor diodes are installed between the radiating edges and the ground plane to control the resonant frequency by adjusting the DC bias asymmetrically. Using this voltage-controlled antenna and the micro controller peripheral circuits of reading the returned level, the antenna is designed and fabricated which recovers its resonant frequency and impedance automatically. Designed frequency auto recovering antenna is conformed to be recovered within a few seconds when the resonant frequency and impedance are shifted by the approach of other objects such as hand, metal plate, dielectric and so on.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.477-485
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• 2010

Various monitoring sensors are used to predict and detect structural damage. Smart sensors, such as glass-fiber sensors, PZT, and MEMS, among others, have replaced traditional sensors. They are now being used in many areas. This study aims to predict the damage by measuring the PZT voltage attached on the specimen by the applied impact load. In the experiment to detect damages in beam connection, simple $H-400{\times}200{\times}8{\times}13$ beams were spliced with bolts. The results of FFT between PZT sensor and accelrometer were compared to measure the sensitivity of the PZT sensor. The damage to the beam was presumed by loosening the bolt, and then the damage measurement was accompanied. Secondly, a steel $PL600{\times}65{\times}5.8$ plate beam was fabricated for the purpose of experimenting on damage measurement. Impact loading test on three different locations was carried out. Damage width varied between 6~42mm on both sides by cutting, using a steel saw. The ratio of frequencies before and after the damage was computed to quantify the damage level by using FFT, and the change in mode pattern with the increased damage was investigated to measure the damage.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.51-63
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• 2011

Surface of fine-size exposed aggregate portland cement concrete pavements(FS-EAPCC) is consist by exposed coarse aggregate to remove upper 2~3mm mortar of concrete slabs. Advantages of FS-EAPCC are maintaining low-noise and adequate skid-resistance level during the performance period. However, FS-EAPCC is required rational management criteria for field application, since it is early stage for application. Design construction and quality control criteria of FS-EAPCC was temporary laboratory tests which including optimum mix and exposing method, selection of adequate aggregate, resistance against, environmental loading and etc. However, these criteria need to be validated base on field application. In this study, experimental constructions were performed and construction procedure and quality control criteria were suggested based on the performance of the FS-EAPCC.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.55-68
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• 1991

In this study, Mixed coordination method was selected to optimize the shape of the truss structures which takes multi-loading condition, allowable stress, buckling stress, displacement constraints into consideration. The structure was devided into substructures by Goal coordination method and the substructures were optimized by model coordination method which used two-level technique. Therefore the number of design variables and constrints can be decreased considerable. Under the condition of the same disign, the weight of truss structures can be decreased more considerable by means of optimizing even the shape of truss than by means of optimizing the section of truss while fixing geometrical configuration of it, even though there might be a little difference according to the early geomatrical shape of the truss and the design condition. Thus, the shape optimization of truss structures which utilize the results of this study can be helpful to the economical design of truss structures.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.667-675
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• 2012

Flat plate are being used more in buildings requiring a high level of technical installations or in buildings needing changeable room arrangements during their life time such as office buildings. The main problem in flat plate is its weak resistance against a punching failure at its slab-column connections. Therefore, in this research, an experimental study on full-scale interior slab-column connection was performed. Three types of shear reinforcements were tested to prevent brittle punching shear failure that could lead to collapse of the structure. A series of four flat plate specimens including a specimen without shear reinforcement and three specimens with shear reinforcements were tested. The slabs were tested up to failure using monotonic vertical shear loading. The presences of the shear reinforcements substantially increased punching shear capacity and ductility of the interior slabcolumn connections. The test results showed that a slab that did not have enough bond length failed before shear reinforcement yielded due to anchorage slip. Also, FEM analyses were performed to study an effect of slab thickness and concrete compressive strength on the flat plate slab. The analytical study results were used to propose a method to calculate performance capacity of shear reinforcement in slab-column connection.

• Korean Journal of Construction Engineering and Management
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• v.21 no.2
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• pp.47-58
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• 2020

The ICEC (Index of Construction Engineer's Competency) quantifies the competence of construction engineers using such parameters as experience, education, and qualifications and assigns four technical grades (expert, advanced, intermediate, and beginners) to construction engineers according to their scores for the efficient management and loading of technical personnel. However, as of 2020, the seventh year since its implementation, ICEC has shown many problems in its application, unlike its intended purpose. So institutional supplementation is required to provide improvement measures that can cope with the changing labor market environment and complement the current ICEC. Therefore, this study examined the current status of the career management system after the introduction of the ICEC, suggested a career index proportional to the competence of construction engineers from the beginner to the expert level, and developed an effective capability evaluation model I²CEC. The improved model presented in this study provides a means to comprehensively judge the performance, experience, and the professional work abilities of construction management engineers. Furthermore, the results of this study are expected to contribute to the development of efficient manpower and career management systems for enhancing the competitiveness of the domestic construction industry.

• Journal of Wetlands Research
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• v.17 no.1
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• pp.11-18
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• 2015

As the seriousness of water pollution resulted from nitrogen is being magnified, research has been conducted to reduce nitrogen in sewage as well as wastewater. Particularly research on innovative nitrogen removal methods that are based on the reaction of nitritation and are economically feasible and eco-friendly has been receiving attention. However, research on the applicability and efficiency of the methods based on the reaction of nitritation has not been completely done yet. Accordingly, the current study has analyzed the characteristics of sewage flowing into municipal wastewater treatment plants, primary clarifier supernatant, recycled water, and livestock wastewater and also operated a laboratory-level reactor. The result shows that recycled water and livestock wastewater contain higher-concentration nitrogen than other kinds of sewage, so they increase nitrogen loading in the water treatment line. And the result of operating a reactor shows that because of ammonium nitrogen low concentration, sewage and primary clarifier supernatant do not induce the reaction of nitritation. Also, there exist differences in the conditions of retention time inducing the reaction of nitritation by the types of sewage, and this seems to be attributed to organic compound and ammonium nitrogen concentration. Among the kinds of sewage inducing the reaction of nitritation, anaerobic digester supernatant indicates the highest efficiency.

• Journal of Environmental Health Sciences
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• v.28 no.5
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• pp.77-85
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• 2002

The objective of this study was to evaluate the performances of the ASBR under critical conditions of solid-liquid separation, caused by extremely high solids concentration, for wider application of the ASBR to various wastes. The ASBRs and completely-mixed daily-fed control runs were operated using a municipal mixed sludge at 35$^{\circ}C$ and 55$^{\circ}C$. Conversion of completely-mixed daily-fed reactor to sequencing batch mode and changes in HRT of all ASBRs were easily achieved without adverse effect, regardless of digestion temperature. Solids accumulation was remarkable in the ASBRs, and directly affected by settleable solids concentration of the feed sludge. Noticeable difference in solids-liquid separation was that flotation thickening occurred in the mesophilic ASBRs, while gravity thickening was a predominant solid-liquid separation process in the thermophilic ASBRS. Solids profiles at the end of thickening step dramatically changed at solid-liquid interface, and slight difference in solids concentrations was observed within thickened sludge bed. Organics removals based on subnatant or supernatant after thickening always exceeded 80% in all reactors. Thickened sludge volume and gas production of the ASBRs affected mutually. Gas production increased as thickened sludge accumulated, and continuous gas evolution during thickening could cause thickened sludge to expand or resuspend. Thickened sludge volume exceeding a predetermined withdrawal level resulted in loss of organic solids as well as biomass during withdrawal step, leading to decrease in gas production ind SRT. Such an adverse mutual effect was significant in gravity thickening, while it was not sensitive in flotation thickening. Changes in organic loading had no significant effect on organic removals and gas production after build-up of solids in the ASBRs.