• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.40-48
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• 2017

RC flat plates may be governed by a serviceability as well as a strength condition, and a construction sequence and its impact on the distributions of gravity loads among slabs tied by shores are decisive factors influencing short and long term behaviors of flat plate. Over-loading and tensile cracking in early-aged slabs significantly increase the deflection of a flat plate system under construction, and a reshoring work may be helpful in reducing slab deflections by controlling the vertical distributions of loads in a multi-shored flat plate system. In this study, a effect of reshoring works on short and long term deflections of flat plate systems are analyzed. The slab construction loads with various reshoring schemes and slab design and construction conditions are defined by a simplified method, and the practical calculation of slab deflections with considering construction sequences and concrete cracking and long term effects is applied. From parametric studies, the reshoring works are verified to reduce slab deflections, and the optimized conditions for the reshoring works and slab design and constructions are discussed.

• Journal of the Korean Geotechnical Society
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• v.30 no.7
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• pp.41-53
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• 2014

This study examined the magnitude and distribution of the earth pressure on the support system in a jointed rock mass by considering different joint shear strength, rock type, and joint inclination angle. The study particularly focused on the effect of joint cohesive strength for a certain condition. Based on a physical model test (Son and Park, 2014), extended parametric studies were conducted considering rock-structure interactions based on the discrete element method, which can consider the rock and joint characteristics of rock mass. The results showed the earth pressure was strongly affected by the joint cohesive strength as well as the rock type and joint inclination angle. The study indicated that the effect of joint cohesive strength was particularly significant when a rock mass was under the condition of joint sliding. This paper investigates the magnitude of joint cohesive strength to prevent a joint sliding for each different condition. The test results were also compared with Peck's earth pressure, which has been frequently used for soil ground. The comparison indicated that the earth pressure in a jointed rock mass can be significantly different from that in soil ground. This study is expected to provide a better understanding of the earth pressure on the support system in a jointed rock mass.

• Journal of Periodontal and Implant Science
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• v.36 no.3
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• pp.591-600
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• 2006

Purpose: This study assessed the impact of self-reported periodontal health on the oral health-related quality of life among elderly Koreans. Methods: Four hundred twenty one elderly Koreans in Seoul and suburban areas were selected with a cluster (institution) sampling method, and were requested to take oral examinations and finish questionnaires on the Oral Health Impact Profile-14(OHIP-14). and self-reported periodontal health status, such as periodontal symptoms, self-rated periodontal health and periodontal treatment need. As the dependent variable, OHIP-14 showed a positive skewed distribution (skewness: 1.17), we transformed to square-root form to apply parametric analyses. Bivariate analysis by t-test and ANOVA, and multivariate analysis with the two-level regression model accounting clusters were implemented. Results: Mean age of the subjects was 74.6 years and 66.5% were women. Fourteen items of OHIP-14 were summarized to one factor explaining 78.6% of total variance and produced the Chronbach alpha coefficient of 0.92. Results from the multivariate model, adjusting for age, sex, type of institutions, ability to pay, and number of teeth present, showed significantly lower OHIP-14 with reporting less than 3 periodontal symptoms (p(O.OOO1), rating their own periodontal health as above average level (p=O.0144), and thinking they don't need any periodontal treatments in the near future (p=O.0148), than their counterparts. The intraclass-corrrelation estimated by the final model was 0.028. Conclusion: This study demonstrates a significant association between self-reported periodontal health status and the oral health-related quality of life.

• Journal of the Korean Data and Information Science Society
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• v.26 no.6
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• pp.1353-1366
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• 2015

These days Shewhart control chart for evaluating stability of the process is widely used in various field. But it must follow strict assumption of distribution. In real-life problems, this assumption is often violated when many quality characteristics follow non-normal distribution. Moreover, it is more serious in multivariate quality characteristics. To overcome this problem, many researchers have studied the non-parametric control charts. Recently, SVDD (Support Vector Data Description) control chart based on RBF (Radial Basis Function) Kernel, which is called K-chart, determines description of data region on in-control process and is used in various field. But it is important to select kernel parameter or etc. in order to apply the K-chart and they must be predetermined. For this, many researchers use grid search for optimizing parameters. But it has some problems such as selecting search range, calculating cost and time, etc. In this paper, we research the efficiency of selecting parameter regions as data structure vary via simulation study and propose a new method for determining parameters so that it can be easily used and discuss a robust choice of parameters for various data structures. In addition, we apply it on the real example and evaluate its performance.

• Survey Research
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• v.4 no.2
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• pp.63-86
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• 2003

The objective of this study was to investigate the existence of starting point bias in the bidding game contingent valuation elicitation technique when determining willingness to pay (WTP) for improving the qualify of running water in Seoul and its vicinity. Of all existing contingent techniques, the bidding game most closely mimics the normal price taking behavior in local markets. Three different starting points (low, medium and high) were used to determine WTP and the existence of starting point bias in the meanwhile respectively. The respondents were randomly assigned to the three different starting point groups in order to ensure homogeneity, so that any variation seen in WTP could be attributed to the starting point effects. And a pretested interviewer-administered questionnaire used to elicit WTP. Non-parametric test and the logit model were used to analyze the data for evidence of starting point bias. In this instance, the high starting point group had a high WTP, and low starting point group had a low WTP. This means there exist starting point bias in estimating WTP by bidding game in this instance. This finding might signal that people may actually be making up their minds on the maximum amount they are willing to pay for running water service as a bidding iterating is going on and is influenced by the starting point used in the bidding game. The problem of slaking point bias can be avoided if the respondent is asked directly for the maximum WTP without payment cards or a bidding game. But such a question is perceived as being very difficult to answer and this leads to problems of non-response and being unrealistic.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.115-124
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• 2004

According to Sagong and Paik (2003), the side resistance of rock socketed drilled shafts is affected by rock quality, types, uniaxial compressive strength, and confining stress. Their approach based upon the Hoek-Brown criterion provides reasonable predictions of the side resistance. In this study, we propose an equation to calculate the side resistance considering size effects of the shafts and investigate the influence of drilled shaft diameter on the side resistance. A new method employs the modified Hoek-Brown criterion together with an empirical size effect of rock core. From the previous field tests, 12 pile load test results were collected and compared with prediction calculated from the equation proposed in this study. In a given condition, similar results between measurement and estimate are observed. From the parametric study on the GSI, confining stress, uniaxial compressive of intact rock and pile size, it is shown that uniaxial compressive strength is the most influential parameter on the side resistance. Though pile size shows the least influence on the resistance, the size effect is apparent as rock quality increases.

• Proceedings of KOSOMES biannual meeting
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• 2007.05a
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• pp.203-210
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• 2007

This paper treats optimal route safety assessment system at seaway based on weather forecasting data through INMARSAT. Since early times, captain have been sailing to select the optimum route considering the weather, ship loading status condition and operational scheduling empirically. However, it is rare to find digitalized onboard route support system whereas weather facsimile or wave and swell chart are utilized for the officer, based on captain's experience. In this paper, optimal route safety assessment system which is composed of voyage efficiency and safety component is introduced. Optimum route minimized ETA(estimated time of arrival) and fuel consumption that shipping company. and captain are requiring to evaluate for efficient voyage considering speed loss and power increase based on wave added resistance of ship. In the view point of safety, seakeeping prediction is performed based on 3 dimensional panel method Basically, the weather forecast is assumed to be prepared previously in order to operate this system.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.4
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• pp.203-214
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• 2010

This study numerically investigates the wave control of 2-rowed Impermeable Rectangular Submerged Dike(IRSD) with an object of how to control short-period and solitary waves simultaneously based on the Bragg resonance phenomenon that elevates the wave control performance. The boundary integral method using Green formula and the 3-D one-field Model for immiscible TWO-Phase flows (TWOPM-3D) by 3-D numerical wave flume have been used for the numerical predictions for short-period and solitary waves, respectively. These numerical models were verified through the comparisons with the previously published numerical results by other researchers. Through the parametric tests of numerical experiments for short-period waves, an optimum model of 2-rowed IRSD of a lowest transmission coefficient has been found. Furthermore, the performances of 3-D wave control for solitary waves were evaluated for the various free board, crown widths and gap distance between dikes, and have been compared with those of a single-rowed IRSD. Numerical results show that a 2-rowed IRSD with a less cross sectional area than 1-rowed one improves the wave attenuation performances when it is compared to that of single-rowed IRSD. Within the test frequency ranges of the numerical simulations conducted in this study, 2-rowed IRSD with an optimum gap distance shows an outstanding improvement of the wave attenuation up to 58% compared to that of single-rowed IRSD.

• Journal of Korea Water Resources Association
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• v.48 no.9
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• pp.711-717
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• 2015

This paper attempts to measure the economic benefits of advanced water treatment in five cities (Goyang, Paju, Gumi, Gimcheon, Chilgok), which are supplied water from Goyang and Gumi filtration plant. We used the dichotomous choice contingent valuation method to estimate WTP. Parametric interval-data model are used to obtaining the mean WTP estimates. The results show that the mean of additional WTP for advanced water treatment services were estimated to be KRW 231.3 and KRW 231.2 per $m^3$ using model with covariates and without covariates, respectively. Given the water supplies of Goyang and Gumi filtration plants ($59.675m^3/y$ and $93.734m^3/y$), the economic benefits of those advanced water treatments can be expected to be KRW 13.8 billion and KRE 21.68 billion. And the calculated B/C ratios are 3.7 and 2.1 when a lifespan of facility is 10 years. Advanced water treatment should be introduced in terms of the economic benefits and costs. Thus, this results can be useful in water policy decision-making.

• Magazine of the Korea Concrete Institute
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• v.8 no.5
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• pp.111-122
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• 1996

The effects of external restraint on the thermal stresses i n mass concrete are investigated through a series of parametric study. Two major factors affecting the degree of external restraint such as the ratio of length to height of the placed structure (L/H) and the elastic modulus of base structure ($E_r$) are employed as the parameters in a condition which a placing height H is 1.0m. Various conditions of I,/H and E, are analysed by a FEM program and the relationship between these two parameters is examined. The shape of stress distribution due to the external restraint is shown as linearity on the height direction of the section, and is influenced by L/H, $E_r$, and strength development of placed concrete. The external restraint can be devided by two part. One is an axial restraint and the other is a flexural restraint. When the level of external restraint is low, the structure behavior is mainly governed by flexural restraint, otherwise it is dependent on axial restraint. Comparing the calculated stress by the method of the ACI 207 committee with a finite element analysis, the fbrmer overestimates the external restraint stress when the degree of external restraint is weak, and underestimates when it is strong.