• Earthquakes and Structures
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• v.25 no.1
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• pp.57-67
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• 2023

The buckling of longitudinal reinforcements under seismic loading accelerates the degradation of the bearing capacity of reinforced concrete columns. The traditional hysteretic constitutive model of reinforcement, which does not consider buckling, usually overestimates the seismic performance of pier columns. Subsequent researchers have also proposed many models including the buckling effects. However, the accuracy of these hysteretic constitutive models proposed for simulating the buckling behavior is inadequate. In this study, based on their works, the influence of historical events on buckling is considered, the path of the re-tensioning phase is corrected by adjusting the boundary lines, and the positions of the onset buckling point and compressive buckling path during each buckling deformation are corrected by introducing correction parameters and a boundary line. A modified hysteretic constitutive model is obtained, that can more accurately reflect the buckling behavior of reinforcements. Finally, a series of hysteresis tests of reinforcements with different slenderness ratios were then conducted. The experimental results verify the effectiveness of the proposed modified model. Indicating that the modified model can more accurately simulate the equivalent stress-strain relationship of the buckling reinforcement segment.

• The Journal of the Korea Contents Association
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• v.18 no.11
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• pp.353-368
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• 2018

The purpose of this study is to examine the effect of private tutor's job stress on the organizational commitment and turn-over intention and to verify the mediating effect of the organizational commitment. The questionnaire survey was peformed for 332 private tutors in special education region in Seoul. The collected data were used as a model of path coefficients obtained through analysis of structure equation model(SEM) and hypothesis verification. The result of the verification is as follows. First, both stress by student and stress by administrative support showed statistically significant negative effects on the organizational commitment. Second, the private tutor's organizational commitment showed a statistically significant negative effects on the turn-over intention. Third, both stress by task and stress by conflict in organization showed statistically significant positive effects on the turn-over intention. Fourth, even if both stress by student and stress by administrative support showed statistically no significant effects on the turn-over intention, they showed statistically significant effects on the turn-over intention with the mediating effect of the organizational commitment. It was confirmed that the turn-over intention can be decreased by relief of the private tutor's job stress and enhancement of the organizational commitment. In this process, it is meaningful to verify the role and function of the private tutor's organizational commitment.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.2
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• pp.177-189
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• 2012

Sediment load deposited in sewers and manholes reduces not only the capacity of pipes but also the efficiency of the whole sewer system. This causes the inundations of the low places and overflows at manholes, Moreover, sulfides and bad odor can occur due to deposited sediment with organic loads in manholes. Movements of sediment load in manholes are complicated depending on manhole size, location, inside structure, sediment load type, and time. Therefore, it is necessary to understand the movements of sediment load in manholes by experiments. In this study, experiments were implemented by a square manhole with straight path to measure deposited sedimentation quantity. The experimental apparatus was consisted of a high water tank, an upstream tank, test pipes, a sediment supplier, a manhole, and a downstream tank to measure the experimental discharge. The quantity of deposited sediment load was measured by different conditions, such as the inflow condition of sediment(continuous and certain period), the amount of inflow sediment, discharge, and the type of sediment. Jumoonjin sand(S=2.63, D50=0.55mm), general sand(GS, S=2.65, D50=1.83mm) and anthracite (S=1.45, D50=0.80mm) were employed for the experiment. The velocities in inflow pipe were 0.45 m/s, 0.67 m/s, and 0.9 m/s. Sediment load movement and sedimentation quantity in manhole were influenced by many factors such as velocity, shear stress, viscosity, amount of sediment, sediment size, and specific gravity. Suggested regression equations can estimated the quantity of deposited sediment in the straight path square manholes. The connoted equations that were evaluated through the experimental study have velocity range from 0.45 to 0.9m/sec. The study results illustrates that appropriation of design velocity ragne between 1.0 and 2.0m/sec could implement to maintain and manage manholes.

• Journal of the Korean GEO-environmental Society
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• v.8 no.3
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• pp.59-65
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• 2007

Excess pore pressures in low permeability soils may not dissipate quickly enough and decrease the effective stresses inside the soil, which in turn may cause a reduction of the shear strength at the interface between the soil and the reinforcement in MSE walls. For this condition the dissipation rate of pore pressures is most important and it varies depending on wall size, permeability of the backfill, and reinforcement length. In this paper, a series of numerical analysis has been performed to investigate the effect of those factors. The results show that for soils with a permeability lower than $10^{-3}cm/sec$, the consolidation time gradually increases. The increase in consolidation time indicates the decrease in effective stress thus it will result in decrease in pullout capacity of the reinforcement as verified by the numerical analyses. It is also observed that larger consolidation time is required for longer reinforcement length (longer drainage path).

• The Journal of the Korea Contents Association
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• v.10 no.4
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• pp.359-366
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• 2010

The purpose of this study is to examine the influence of the leisure constraint of a private security guard on his/her task stress and life satisfaction. The subjects of this study were chosen among the private security guards working in Seoul based private security firms in 2009, and by going through judgement sampling, 300 cases were applied in the final analysis. Collected data went through factor analysis, reliability analysis, regression analysis, and path analysis by using SPSSWIN 17.0. In reference with the reliability of the questionnaire, Cronbach's $\alpha$ was over .600. The conclusion of this study is as following. Firstly, the leisure constraint of a private security guard affects his/her task stress. In other words, when peripheral and individual constraint increase, task stress is intensified, while task stress winds down when interpersonal constraint decreases. Secondly, the leisure constraint of a private security guard affects life satisfaction. That is, when individual constraint goes down, life satisfaction is improved. Thirdly, the task stress of a private security guard affects life satisfaction. when compensation and career development increase, life satisfaction rises. On the other hand when task characteristic is weakened, life satisfaction gets lower. Fourthly, the leisure constraint of a private security guard has a causal influence on task stress and life satisfaction. Accordingly, it becomes apparent that the task stress is a significant variable which intermediates the relation between leisure constraint and life satisfaction.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2009.06a
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• pp.187-187
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• 2009

Opening of fractures induced by shear dilation or normal deformation can be a significant source of fracture permeability change in fractured rock, which is important for the performance assessment of geological repositories for spent nuclear fuel. As the repository generates heat and later cools the fluid-carrying ability of the rocks becomes a dynamic variable during the lifespan of the repository. Heating causes expansion of the rock close to the repository and, at the same time, contraction close to the surface. During the cooling phase of the repository, the opposite takes place. Heating and cooling together with the, virgin stress can induce shear dilation of fractures and deformation zones and change the flow field around the repository. The objectives of this work are to examine the contribution of thermal stress to the shear slip of fracture in mid- and far-field around a KBS-3 type of repository and to investigate the effect of evolution of stress on the rock mass permeability. In the first part of this study, zones of fracture shear slip were examined by conducting a three-dimensional, thermo-mechanical analysis of a spent fuel repository model in the size of 2 km $\times$ 2 km $\times$ 800 m. Stress evolutions of importance for fracture shear slip are: (1) comparatively high horizontal compressive thermal stress at the repository level, (2) generation of vertical tensile thermal stress right above the repository, (3) horizontal tensile stress near the surface, which can induce tensile failure, and generation of shear stresses at the comers of the repository. In the second part of the study, fracture data from Forsmark, Sweden is used to establish fracture network models (DFN). Stress paths obtained from the thermo-mechanical analysis were used as boundary conditions in DFN-DEM (Discrete Element Method) analysis of six DFN models at the repository level. Increases of permeability up to a factor of four were observed during thermal loading history and shear dilation of fractures was not recovered after cooling of the repository. An understanding of the stress path and potential areas of slip induced shear dilation and related permeability changes during the lifetime of a repository for spent nuclear fuel is of utmost importance for analysing long-term safety. The result of this study will assist in identifying critical areas around a repository where fracture shear slip is likely to develop. The presentation also includes a brief introduction to the ongoing site investigation on two candidate sites for geological repository in Sweden.

• Journal of the Korean Applied Science and Technology
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• v.40 no.3
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• pp.462-475
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• 2023

This study is descriptive research to identify the effect of COVID-19 stress on premenstrual syndrome in female college students and the mediating effect of depression and coping with premenstrual syndrome. The data were collected through an on-line survey for 20 days from November 11 to November 30, 2021, targeting female college students attending C College located in S city. As a result of analyzing a total of 161 data, COVID-19 stress was positively correlated with premenstrual syndrome(r=.383, p<.001) and depression(r=.436, p<.001), and coping with premenstrual syndrome had a positive correlation only in premenstrual syndrome(r=.190, p=.016). As a result of verifying the mediating effect of depression and coping with premenstrual syndrome between COVID-19 stress and premenstrual syndrome, COVID-19 stress had a significant direct effect on premenstrual syndrome(β=4.907, p=.002), and depression(β=6.780, p<.001), and depression had a significant direct effect on premenstrual syndrome(β=.383, p=<.001), coping with premenstrual syndrome had a direct effect on premenstrual syndrome(β=4.292, p=.030) respectively. The indirect effect of verifying the mediating effect in the relationship between COVID-19 stress and premenstrual syndrome confirmed that there was a statistically significant effect only in the path via depression(95% CI, 1.282 to 4.140). Therefore, it is necessary to develop an intervention strategy to reduce depression and alleviate premenstrual syndrome symptoms by controlling related stress, such as COVID-19 stress, in preparation for the outbreak of new infectious diseases and pandemic situations such as COVID-19.

• Geotechnical Engineering
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• v.10 no.4
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• pp.83-102
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• 1994

For estimation of Ko value depending upon the stress history of dry sand, a new type of Ko oedometer apparatus is devised, and the horizontal earth pressure is accurately measured. For this study, 2 types of one-cyclic Ko loading/unloading models have been studied experimentally using four relative densities of the sand. The results obtained in this test are as follows Kon, the coefficient of earth pressure at rest for virgin loading is a function of the angle of internal friction of the sand and is determined as Kon=1-0.914 sin, Kou the coefficient of earth pressure at -rest for virgin unloading is a function of K. and overconsolidation ratio(OCR), and is determined as Kou : Kon(OCR)". The exponent u, increases as the relative density increases. Ko,, the coefficient of earth pressure at rest for virgin reloading decreases in hyperbola type as the vertical stress, cv', increases. And, the stress path at virgin reloading lends to the maximum prestress point, independent upon the value of the minimum unloading stress. The gradient of this curve, mr, increases as OCR increases.ases.

• Journal of Power System Engineering
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• v.13 no.6
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• pp.95-101
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• 2009

The generator for gas turbine power generation consists of the rotor which generates magnetic field, the winding coil which is the path for the field current and the wedge and retaining ring which prevents the radial movement of the coil. Relatively severe deformation was observed at the coil end section during the inspection of the generator for peaking-load operation, and the thermal-electricity and the centrifugal force were evaluated by the simple modeling of the windings to find the cause. But the simulation stress was not sufficient to induce the coil plastic deformation. The analysis result seems to be applicable to the base-load generators which runs continuously without shut down up to a year, but there had been more deformation than simulated for the generator which is started up and shut down frequently. The cause of the coil deformation was the restriction of the expansion and shrinkage. The restriction occurs when the winding coil shrinks, and the stress overwhelms the yield stress and cause the plastic deformation. The deformation is accumulated during the start-ups and shut-downs and the thermal growth occurs. The factors which induce the coil restriction during the expansion and shrinkage should be reduced to prevent the unallowable deformation. The resolutions are cutting off the field current earlier during the generator shut-down, modifying the coil end section to remove the stress concentration and making the insulation plate inserted between the coil end section and the retaining ring have the constant thickness.

• Magazine of the Korea Concrete Institute
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• v.7 no.3
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• pp.175-186
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• 1995

The determination of the stress intensity factors is investigated by sur-face integral method around the crack tip of the nlass~vc: concrete structure. The surface integral met hod is naturally derived from the standal-ci path integral J. Howevcr. In the J integral method, pressure in the crack-face and body forces can not be considered, while this theory has advantage of ccmsidering many kind of forces, so t.his theory will be useful in investigating more accurate strt:ss states around crack tip. Furthermore. t h~s rrlethod can elerninate unntussary process of using singular elements and fine mesh around crack tip which is used 11; modelling the singularity around crack tip. A computer program for determming $K_I$, $K_{II}$ is tfcvulopcd by applying this theory. $K_I$, $K_{II}$ values usmg X noded isoparametric elements which was proved and variation of the stress intensity factor was investigated by application of darn structures.