• Earthquakes and Structures
• /
• 제10권4호
• /
• pp.867-891
• /
• 2016

This paper addresses numerically the behavior of steel structures under Fire-after-Earthquake (FAE) loading. The study is focused on a four-storey library building and takes into account the damage that is induced in structural members due to earthquake. The basic objective is the assessment of both the fire-behavior and the fire-resistance of the structure in the case where the structure is damaged due to earthquake. The combined FAE scenarios involve two different stages: during the first stage, the structure is subjected to the ground motion record, while in the second stage the fire occurs. Different time-acceleration records are examined, each scaled to multiple levels of the Peak Ground Acceleration (PGA) in order to represent more severe earthquakes with lower probability of occurrence. In order to study in a systematic manner the behavior of the structure for the various FAE scenarios, a two-dimensional beam finite element model is developed, using the non-linear finite element analysis code MSC-MARC. The fire resistance of the structure is determined using rotational limits based on the ductility of structural members that are subjected to fire. These limits are temperature dependent and take into account the level of the structural damage at the end of the earthquake and the effect of geometric initial imperfections of structural members.

• 한국농공학회지
• /
• 제40권2호
• /
• pp.140-147
• /
• 1998

Since a structure carries out its given functions and purposes while it is always resisting against the external load, the capacity of the resistance in the structure within the range that will not collapse the structure itself becomes the important factor in the design of the structures. Therefore, many suggestions were proposed and noted for determining method of the collapse load. Some of the methods from the suggestions have been commonly used due to the considerations on their distinctive advantages such as the compactness of the conceptions and the convenience in the computation. However, in case when the variation becomes huge in the materials and load, the results would carry(have or contain) many uncertain elements. On the other hand, load incremental method which regards the characteristics of the probability must be more attainable method even though it might complicate the calculation. This study intends to develop a finite element model that uses the probabilistic load incremental method to estimate the collapse load, and also to compare the result of the analysis with the linear load incremental method and Turkstra's Rule.

• Nuclear Engineering and Technology
• /
• 제33권3호
• /
• pp.270-282
• /
• 2001

A simple measure of uncertainty importance based on normalized metric distance to quantify the entire change of cumulative distribution functions (CDFs) has been developed for use in probability safety assessments (PSAs). The metric distance measure developed in this study reflects the relative impact of distributional changes of inputs on the change of an output distribution, white most of the existing uncertainty importance measures reflect the magnitude of relative contribution of input uncertainties to the output uncertainty. Normalization is made to make the metric distance measure a dimensionless quantity. The present measure has been evaluated analytically for various analytical distributions to examine its characteristics. To illustrate the applicability and strength of the present measure, two examples are provided. The first example is an application of the present measure to a typical problem of a system fault tree analysis and the second one is for a hypothetical non-linear model. Comparisons of the present result with those obtained by existing uncertainty importance measures show that the metric distance measure is a useful tool to express the measure of uncertainty importance in terms of the relative impact of distributional changes of inputs on the change of an output distribution.

• 한국환경과학회지
• /
• 제15권9호
• /
• pp.887-895
• /
• 2006

Through this research of the analysis on the frequency flood discharges regarding basin property factors, a linear regression system was introduced, and as a result, the item with the highest correlation with the frequency flood discharges from Nakdong river basin is the basin area, and the second highest is the average width of basin and the river length. The following results were obtained after looking at the multi correlation between the flood discharge and the collected basin property factors using the data from the established river maintenance master plan of the one hundred twenty-five rivers in the Nakdong river basin. The result of analysis on multivariate correlation between the flood discharges and the most basic data in determining the flood discharges as basin area, river length, basin slope, river slope, average width of basin, shape factor and probability precipitation showed more than 0.9 of correlation in terms of the multi correlation coefficient and more than 0.85 for the determination coefficient. The model which induced a regression system through multi correlation analysis using basin property factors is concluded to be a good reference in estimating the design flood discharge of unmeasured basin.

• Computers and Concrete
• /
• 제7권5호
• /
• pp.455-468
• /
• 2010

This paper presents a prediction and simulation method of tensile stress-strain curves of Engineered Cementitious Composites (ECC). For this purpose, the bridging stress and crack opening relations were obtained by the fiber bridging constitutive law which is quantitatively able to consider the fiber distribution characteristics. And then, a multi-linear model is employed for a simplification of the bridging stress and crack opening relation. In addition, to account the variability of material properties, randomly distributed properties drawn from a normal distribution with 95% confidence are assigned to each element which is determined on the basis of crack spacing. To consider the variation of crack spacing, randomly distributed crack spacing is drawn from the probability density function of fiber inclined angle calculated based on sectional image analysis. An equation for calculation of the crack spacing that takes into quantitative consideration the dimensions and fiber distribution was also derived. Subsequently, a series of simulations of ECC tensile stress-strain curves was performed. The simulation results exhibit obvious strain hardening behavior associated with multiple cracking, which correspond well with test results.

• 품질경영학회지
• /
• 제43권3호
• /
• pp.373-382
• /
• 2015

Purpose: In this paper, we developed a reliability index (RI) to efficiently compare reliability of products based on the design, development and production information such as reliability tests, quality, product life-cycle management. RI also can be applied to reliability prediction of a novel product as well as comparison evaluation among existing products. Methods: For evaluating RI, we proposed evaluation process which is composed of five steps. Target modules are selected based on warranty data and correlation analysis. Scores of selected target modules are calculated by scoring function. Finally, weights of RI model are determined by optimization method. Results: This paper presented an empirical analysis based on failure data of mobile devices. In this case study, we demonstrated that there is a direct correlation between evaluated RI and field failure probability of each product. Conclusion: We proposed the index for comprehensive and effective assessment of product reliability level. From the procedure of this study, we expected to be applied for reliability estimation of novel products and deduction of field failure-related factors.

• 한국측량학회지
• /
• 제34권6호
• /
• pp.547-557
• /
• 2016

Due to threats caused by social disasters, operating surveillance devices are essential for social safety. CCTV, infrared cameras and other surveillance equipment are used to observe threats. This research proposes a method for searching for the optimum location of surveillance sensors. A GA (Genetic Algorithm) was used, since this algorithm is one of the most reasonable and efficient methods for solving complex non-linear problems. The sensor specifications, a DEM (Digital Elevation Model) and VITD (Vector Product Interim Terrain Data) maps were used for input data. We designed a chromosome using the sensor pixel location, and used elitism selection and uniform crossover for searching final solution. A fitness function was derived by the number of detected pixels on the borderline and the sum of the detection probability in the surveillance zone. The results of a 5-sensor and a 10-sensor were compared and analyzed.

• Journal of Communications and Networks
• /
• 제15권3호
• /
• pp.266-275
• /
• 2013

The exact closed-form expressions for outage probability and bit error rate of spectrum sharing-based multi-hop decode-and-forward (DF) relay networks in non-identical Rayleigh fading channels are derived. We also provide the approximate closed-form expression for the system ergodic capacity. Utilizing these tractable analytical formulas, we can study the impact of key network parameters on the performance of cognitive multi-hop relay networks under interference constraints. Using a linear network model, we derive an optimum relay position scheme by numerically solving an optimization problem of balancing average signal-to-noise ratio (SNR) of each hop. The numerical results show that the optimal scheme leads to SNR performance gains of more than 1 dB. All the analytical expressions are verified by Monte-Carlo simulations confirming the advantage of multihop DF relaying networks in cognitive environments.

• 근관절건강학회지
• /
• 제23권1호
• /
• pp.61-69
• /
• 2016

Purpose: The purpose of this study was to determine the effect of the Tai Chi exercise program (Sun style 31 forms) on fatigue, anxiety, and sleep patterns in nursing students. Methods: A quasi-experimental study with a non-equivalent control group pretest-posttest design was used. Nursing students who participated in this study were assigned to an experimental group (n=24), and a control group (n=26). The experimental group participated in Tai Chi exercise program for 60 minutes per session, and 3 times a week for 7 weeks. The Tai Chi exercise program consisted of 10 minutes for warm-up, 45 minutes for main session, and 5 minutes for cooling down exercises. The data were collected prior and after the intervention using self-administered questionnaires. Data were analyzed using descriptive statistics, $x^2$-test, Fisher's exact probability, t -test, and the general linear model. Results: After the application of the program, the experimental group showed a significant difference in fatigue (F=20.62, p<.001), anxiety (F=16.96, p<.001), and sleep pattern (F=15.70, p<.001) scores. Conclusion: These findings show that the Tai Chi exercise program can be an effective nursing intervention to improve sleep pattern and to reduce fatigue and anxiety in nursing students.

• 한국식생활문화학회지
• /
• 제34권2호
• /
• pp.159-167
• /
• 2019

The purpose of this study is to provide basic information to improve understanding of contemporary kimchi culture in Korea. Many Koreans are now purchasing kimchi at markets, while the proportion of self-preparation is gradually decreasing. This commodification tendency of kimchi is considered to be associated with changes in consumer's behavior and attitude. In this study, a linear regression and a logistic regression model were used to identify relationships between kimchi consumption behavior and household characteristics. The results showed that the probability of kimjang activity was positively related with family size, possession of a kimchi refrigerator, self-preparation practice, and the intensity of sharing behavior. I also found that kimchi consumption volume per capita of 'purchasing' household was greater than that of 'self-preparing ' or 'sharing-dependent' households, and that the number of family members was inversely related with kimchi consumption volume per capita. The inverse relationship between family size and kimchi consumption volume per capita is considered to be contrary to the widespread thoughts in Korea, which have been developed while experiencing kimchi preparation and consumption in traditional extended families. I think that the relationship comes from differences in menu varieties, which appear to vary with family size. This issue will be investigated in subsequent studies.