• Communications for Statistical Applications and Methods
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• v.27 no.6
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• pp.625-639
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• 2020

The gamma distribution is a flexible right-skewed distribution widely used in many areas, and it is of great interest to estimate the probability of a random variable exceeding a specified value in survival and reliability analysis. Therefore, the study develops a fixed-accuracy confidence interval for P(X > c) when X follows a gamma distribution, Γ(α, β), and c is a preassigned positive constant through: 1) a purely sequential procedure with known shape parameter α and unknown rate parameter β; and 2) a nonparametric purely sequential procedure with both shape and rate parameters unknown. Both procedures enjoy appealing asymptotic first-order efficiency and asymptotic consistency properties. Extensive simulations validate the theoretical findings. Three real-life data examples from health studies and steel manufacturing study are discussed to illustrate the practical applicability of both procedures.

• Geomechanics and Engineering
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• v.29 no.3
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• pp.331-338
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• 2022

Face stability analyses provides the most probable failure mechanisms and the understanding about parameters that need to be considered for the evaluation of ground movements caused by tunneling. After the Upper Bound Method (UBM) solution which can consider the influence of seepage forces and depth-dependent effective cohesion is verified with the numerical experiments, the probabilistic model is proposed to calculate the unbiased limiting tunnel collapse pressure. A reliability analysis of a shallow circular tunnel driven by a pressurized shield in a frictional and cohesive soil is presented to consider the inherent uncertainty in the input parameters and the proposed model. The probability of failure that exceeding a specified applied pressure at the tunnel face is estimated. Sensitivity and importance measures are computed to identify the key parameters and random variables in the model.

• Earthquakes and Structures
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• v.25 no.2
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• pp.79-87
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• 2023

Special moment resisting steel frame structures are now being used commonly in highly seismic regions as seismically reliable structures. However, a very important parameter describing the dynamics of steel structures during earthquake loading, Soil Structure Interaction (SSI), is generally neglected. In this study, the significance of consideration of flexibility of soil in being able to obtain a result closer to reality is asserted. The current paper focuses on calculation of seismic fragility curves special moment resisting steel frame structures under different earthquake loadings for fixed-base and SSI models. The observation of obtained fragility curves lead to the conclusion that the SSI has a considerable effect on component fragility for the steel structures, with its effects decreasing for higher peak ground acceleration. The results show that the structures when considered SSI have a higher probability of exceeding a damage limit state. This observation attests the role of SSI in the accurate study of structural performance.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.5
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• pp.305-318
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• 2012

Although the existing performance-based design method for the vertical breakwater evaluates an average sliding distance during an arbitrary time, it does not calculate the probability of the first occurrence of an event exceeding an allowable sliding distance(i.e. the first-passage probability). Designers need information about the probability that the structure is damaged for the first time for not only design but also maintenance and operation of the structure. Therefore, in this study, a time-dependent reliability design method based on a stochastic process is developed to evaluate the first-passage probability of caisson sliding. Caisson sliding can be formulated by the Poisson spike process because both occurrence time and intensity of severe waves causing caisson sliding are random processes. The occurrence rate of severe waves is expressed as a function of the distribution function of sliding distance and mean occurrence rate of severe waves. These values simulated by a performance-based design method are expressed as multivariate regression functions of design variables. As a result, because the distribution function of sliding distance and the mean occurrence rate of severe waves are expressed as functions of significant wave height, caisson width, and water depth, the first-passage probability of caisson sliding can be easily evaluated.

• Journal of Korea Spatial Information System Society
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• v.11 no.2
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• pp.89-98
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• 2009

As data stream is entered into system continuously and the memory space is limited, the data exceeding the memory size cannot be processed. In order to solve the problem, load shedding methods which drop a part of data to prevent exceeding the storage space have been researched. Generally, a traditional load shedding method uses random sampling with optimized rate according to data deviation. The method samples data not to distinguish those used in spatial query because the method uses only a random sampling with optimized rate according to data deviation. Therefore, the accuracy of query was reduced in u-GIS environment including spatial query. In this paper, we researched a new load shedding method improving accuracy of the query in u-GIS environment which runs spatial query and aspatial query simultaneously. The method uses a new sampling method that samples data having low probability used in query. Therefore proposed method improves spatial query accuracy and query processing speed as applying spatial filtering operation to sampling operator.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.478-484
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• 2019

The submarine cable for Yongsu wave power plant was cut in 2014 winter. This study investigated the probability of high-wave occurrence exceeding the 50-year return period and the underestimation of armor unit weight used to protect the cable. The observation data from KMA buoy and the hindcast wave data were reviewed to determine the return period of wave height during the winter. In order to investigate the armor unit weight of cable-protection, we calculated the required weight of armor unit using not only Design Standard for Harbor and Fishery Port, but also the previous researches for the wave with large incident angle. As a result, it appeared that the high wave exceeding the 50-year return period did not occur during the winter of 2014 and the armor unit weight of the cable protection was not sufficient to sustain the obliquely incident wave, which induced the cable protection failure.

• Earthquakes and Structures
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• v.11 no.3
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• pp.483-503
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• 2016

This study aims to evaluate seismic performance of existing low and mid-rise reinforced concrete buildings by comparing their displacement capacities and displacement demands under selected ground motions experienced in Turkey as well as demand spectrum provided in 2007 Turkish Earthquake Code for design earthquake with 10% probability of exceedance in 50 years for soil class Z3. It should be noted that typical residential buildings are designed according to demand spectrum of 10% probability of exceedance in 50 years. Three RC building sets as 2-, 4- and 7-story, are selected to represent reference low-and mid-rise buildings located in the high seismicity region of Turkey. The selected buildings are typical beam-column RC frame buildings with no shear walls. The outcomes of detailed field and archive investigation including approximately 500 real residential RC buildings established building models to reflect existing building stock. Total of 72 3-D building models are constructed from the reference buildings to include the effects of some properties such as structural irregularities, concrete strength, seismic codes, structural deficiencies, transverse reinforcement detailing, and number of story on seismic performance of low and mid-rise RC buildings. Capacity curves of building sets are obtained by nonlinear static analyses conducted in two principal directions, resulting in 144 models. The inelastic dynamic characteristics are represented by "equivalent" Single-Degree-of- Freedom (ESDOF) systems using obtained capacity curves of buildings. Nonlinear time history analysis is used to estimate displacement demands of representative building models idealized with (ESDOF) systems subjected to the selected ground motion records from past earthquakes in Turkey. The results show that the significant number of pre-modern code 4- and 7-story buildings exceeds LS performance level while the modern code 4- and 7-story buildings have better performances. The findings obviously indicate the existence of destructive earthquakes especially for 4- and 7-story buildings. Significant improvements in the performance of the buildings per modern code are also obvious in the study. Almost one third of pre-modern code buildings is exceeding LS level during records in the past earthquakes. This observation also supports the building damages experienced in the past earthquake events in Turkey.

• Journal of the Korean Geotechnical Society
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• v.32 no.11
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• pp.31-42
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• 2016

Usually the seismic stability analysis of slope uses the pseudostatic analysis considering the inertial force by the earthquake as a static load. Geostructures such as slope include the uncertainty of soil properties. Therefore, it is necessary to consider probabilistic method for stability analysis. In this study, the probabilistic stability analysis of slope considering the uncertainty of soil properties has been performed. The fragility curve that represents the probability of exceeding limit state of slope as a function of the ground motion has been established. The Monte Carlo Simulation (MCS) has been implemented to perform the probabilistic stability analysis of slope with pseudostatic analysis. A procedure to develop the fragility curve by the pseudostatic horizontal acceleration has been presented by calculating the probability of failure based on the Artificial Neural Network (ANN) based response surface technique that reduces the required time of MCS. The results showed that the proposed method can get the fragility curve that is similar to the direct MCS-based fragility curve, and can be efficiently used to reduce the analysis time.

• Earthquakes and Structures
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• v.24 no.4
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• pp.303-316
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• 2023

Rapid post-earthquake damage estimation of subway stations is particularly necessary to improve short-term crisis management and safety measures of urban subway systems after a destructive earthquake. The conventional Performance-Based Earthquake Engineering (PBEE) framework with constant earthquake occurrence rate is invalid to estimate the aftershock risk because of the time-varying rate of aftershocks and the uncertainty of mainshock-damaged state before the occurrence of aftershocks. This study presents a time-varying probabilistic seismic risk assessment framework for underground structures considering mainshock and aftershock hazards. A discrete non-omogeneous Markov process is adopted to quantify the time-varying nature of aftershock hazard and the uncertainties of structural damage states following mainshock. The time-varying seismic risk of a typical rectangular frame subway station is assessed under mainshock-only (MS) hazard and mainshock-aftershock (MSAS) hazard. The results show that the probabilities of exceeding same limit states over the service life under MSAS hazard are larger than the values under MS hazard. For the same probability of exceedance, the higher response demands are found when aftershocks are considered. As the severity of damage state for the station structure increases, the difference of the probability of exceedance increases when aftershocks are considered. PSDR=1.0% is used as the collapse prevention performance criteria for the subway station is reasonable for both the MS hazard and MSAS hazard. However, if the effect of aftershock hazard is neglected, it can significantly underestimate the response demands and the uncertainties of potential damage states for the subway station over the service life.

• Earthquakes and Structures
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• v.27 no.4
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• pp.331-344
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• 2024

The performance of reinforced concrete buildings subjected to earthquake excitations depends on the structural behaviour of the superstructure as well as the type of foundation and the properties of soil on which the structure is founded. The consideration of the effects due to the interaction between the structure and soil- foundation alters the seismic response of reinforced concrete buildings subjected to earthquake motion. Evaluation of the structural response of buildings for quantitative assessment of the seismic fragility has been a demanding problem for the engineers. Present research deals with development of fragility curve for building specific vulnerability assessment based on different damage parameters considering the effect of soil-structure interaction. Incremental Dynamic Analysis of fixed base and flexible base RC building models founded on different soil conditions was conducted using finite element software. Three sets of fragility curves were developed with maximum roof displacement, inter storey drift and plastic energy dissipated as engineering demand parameters. The results indicated an increase in the likelihood of exceeding various damage limits by 10-40% for flexible base condition with soft soil profiles. Fragility curve based on energy dissipated showed a higher probability of exceedance for collapse prevention damage limit whereas for lower damage states, conventional methods showed higher probability of exceedance. With plastic energy dissipated as engineering demand parameter, it is possible to track down the intensity of earthquake at which the plastic deformation starts, thereby providing an accurate vulnerability assessment of the structure. Fragility modification factors that enable the transformation of existing fragility curves to account for Soil-Structure Interaction effects based on different damage measures are proposed for different soil conditions to facilitate a congenial vulnerability assessment for buildings with flexible base conditions.