• Coupled systems mechanics
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• 제9권5호
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• pp.433-454
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• 2020

In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures. The structural integrity of platform components under the maximum and minimum operating loads of environmental conditions is required for risk assessment and inspection plan development. In-place analyses have been executed to check that the structural member with all appurtenances robustness and capability to support the applied loads in either storm condition or operating condition. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The analysis includes interpretation of dynamic design parameters based on the available site-specific data, together with foundation design recommendations for in-place loading conditions. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have important effects on the results of the in-place analysis behavior. The result shows that the in-place analysis is quite crucial for safe design and operation of offshore platform and assessment for existing offshore structures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.532-539
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• 1996

Existing assessment methodologies present a considerable problem because of fuzzy situation of deterioration mechanism of concrete bridges; namely, qualitative, subjective or inconsistent. This paper discusses current assessment methods in aspect of uncertainty. The expert system, COBDA, is developed for consistent and fast assessment of deteriorantion of concrete bridges. Briefly introduced in this paper are the structure of expert system and several methodologies for decision making of deterioration situation and providing repair option. COBDA is configured by PROLOG for logic approach and expert system shell based on Bayesian subjective probability. The methodologies are illustrated and discussed by comparison of condition assessment results in a case study.

• Smart Structures and Systems
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• 제21권5호
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• pp.705-713
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• 2018

High-speed rail (HSR) has been in operation and development in many countries worldwide. The explosive growth of HSR has posed great challenges for operation safety and ride comfort. Among various technological demands on high-speed trains, vibration is an inevitable problem caused by rail/wheel imperfections, vehicle dynamics, and aerodynamic instability. Ride comfort is a key factor in evaluating the operational performance of high-speed trains. In this study, online monitoring data have been acquired from an in-service high-speed train for condition assessment. The measured dynamic response signals at the floor level of a train cabin are processed by the Sperling operator, in which the ride comfort index sequence is used to identify the train's operation condition. In addition, a novel technique that incorporates salient features of Bayesian inference and time series analysis is proposed for outlier detection and change detection. The Bayesian forecasting approach enables the prediction of conditional probabilities. By integrating the Bayesian forecasting approach with time series analysis, one-step forecasting probability density functions (PDFs) can be obtained before proceeding to the next observation. The change detection is conducted by comparing the current model and the alternative model (whose mean value is shifted by a prescribed offset) to determine which one can well fit the actual observation. When the comparison results indicate that the alternative model performs better, then a potential change is detected. If the current observation is a potential outlier or change, Bayes factor and cumulative Bayes factor are derived for further identification. A significant change, if identified, implies that there is a great alteration in the train operation performance due to defects. In this study, two illustrative cases are provided to demonstrate the performance of the proposed method for condition assessment of high-speed trains.

• 한국구조물진단유지관리공학회 논문집
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• 제16권6호
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• pp.93-101
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• 2012

교량에서의 바닥판은 통행차량의 쾌적하고 안전한 주행성 확보하는 역할을 가진다. 동시에 교통하중의 충격 등에 의한 마모 및 전단에 저항하여 상부 구조를 보호하거나 빗물 등의 기타 기상작용이나 화학약품 등 상판의 악영향으로부터 바닥판을 보호하는 역할을 한다. 현재 일반국도상 교량은 총6,248개소로서 이를 효과적으로 관리하기 위하여 현재 차량탑재형 GPR시스템의 도입이 검토되고 있다. 본 연구에서는 교량 및 터널 현황조서 및 기타 국토해양부의 자료를 바탕으로 교량의 재령별, 상부구조형식별, 지역별, 경간장별 바닥판 상태평가등급을 분석하였다. 결과적으로 교량 바닥판 조사 우선순위 결정인자로는 바닥판 상태평가등급, 상부구조 형식, 재령, 연장이 주요 인자인 것으로 도출되었다.

• 한국농공학회논문집
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• 제54권2호
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• pp.37-46
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• 2012

The change of rainfall pattern and hydrologic factors due to climate change increases the occurrence probability of agricultural reservoir water shortage. Water supply assessment of reservoir is usually performed current reservoir level compared to historical water levels or the simulation of reservoir operation based on the water budget analysis. Since each reservoir has the native property for watershed, irrigation district and irrigation water requirement, it is necessary to improve the assessment methods of agricultural reservoir water capability about water resources system. This study proposed a practical methods that water supply vulnerability assessment for an agricultural reservoir based on a concept of probabilistic reliability. The vulnerability assessment of water supply is calculated from probability distribution of water demand condition and water supply condition that influences on water resources management and reservoir operations. The water supply vulnerability indices are estimated to evaluate the performance of water supply on agricultural reservoir system, and thus it is recommended a more objective method to evaluate water supply reliability.

• 한국안전학회지
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• 제31권4호
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• pp.27-34
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• 2016

Process Safety Management (PSM) system was introduced since 1996 and it makes voluntarily organizing and managing chemical accident prevention system by company itself that contributes to reduce the chemical accidents. However, large or small scaled chemical accidents had occurred frequently in these days. This trend is brought up the necessity to analyze and improve PSM system. In this study, it was conducted by the questionnaire survey and workshop for prevention of major industrial accidents in PSM sites in order to collect extensive opinions from all walks of life and identify overall operation condition. It was proposed to establish improvement plan of implementing condition assessment in PSM system. By results of the study, company's voluntary safety management will be induced by improved PSM system and management plan and it expects to prevent the major industrial accidents.

• 한국안전학회지
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• 제21권1호
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• pp.105-113
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• 2006

The footing of a bridge is a very essential part that support the whole load induced by the bridge itself and the traffic as well. However, once a bridge is built, the footing is buried under soil so the footing is invisible from outside. Therefore, the safety or condition of the footing is very difficult to estimate. Not only the length of the imbedded part of the footings but also the type of footings are unknown once the design record is gone. Some nondestructive techniques can be used to evaluate invisible part of the footings but the results have not been successful yet. Using GPR (Ground Penetrating Radar), which has been used for the nondestructive evaluation in military purposes, the condition assessment of the footings have been successfully conducted in this research. The field evaluation and laboratory tests have been conducted to find effective factors in the condition assessment of the footings. The equipment and basic theory of the GPR has been presented. The field test results show that the GPR can be successfully used for the safety evaluation of the footings. More test results and field data are needed for more precise evaluation of the footings.

• 한국지진공학회논문집
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• 제25권6호
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• pp.283-292
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• 2021

In this study, a structural health monitoring system for cable-stayed bridges is developed. In the system, condition assessment of the structure is performed based on measured records from seismic accelerometers. Response indices are defined to monitor structural safety and serviceability and derived from the measured acceleration data. The derivation process of the indices is structured to follow the transformation from the raw data to the outcome. The process includes noise filtering, baseline correction, numerical integration, and calculation of relative differences. The system is packed as a condition assessment program, which consists of four major processes of the structural health evaluation: (i) format conversion of the raw data, (ii) noise filtering, (iii) generation of response indices, and (iv) condition evaluation. An example set of limit states is presented to evaluate the structural condition of the test-bed and cable-stayed bridge.

• Structural Monitoring and Maintenance
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• 제7권4호
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• pp.319-344
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• 2020

Inverse analysis of non-linear reinforced concrete bridge pier using recursive Gaussian filtering for in-situ condition assessment is the main theme of this work. For this purpose, minimum variance unbiased estimation using unscented sigma points is adopted here. The uniqueness of this inverse analysis lies in its approach for strain based updating of engineering demand parameters, where appropriate bound and constrained conditions are introduced to ensure numerical stability and convergence. In this analysis, seismic input is also identified, which is an added advantage for the structures having no dedicated sensors for earthquake measurement. First, the proposed strategy is tested with a simulated example whose hysteretic properties are obtained from the slow-cyclic test of a frame to investigate its efficiency and accuracy. Finally, the experimental test data of a full-scale bridge pier is used to study its in-situ condition in terms of Park & Ang damage index. Overall the study shows the ability of the augmented minimum variance unbiased estimation based recursive time-marching algorithm for non-linear system identification with the aim to estimate the engineering damage parameters that are the fundamental information necessary for any future decision making for retrofitting/rehabilitation.

• Geomechanics and Engineering
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• 제9권1호
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• pp.57-81
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• 2015

Water inrush and mud outburst always restricts the tunnel constructions in mountain area, which becomes a major geological barrier against the development of underground engineering. In view of the complex disaster-causing mechanism and difficult quantitative predictions of water inrush and mud outburst, several theoretical methods are adopted to realize dynamic assessment of water inrush in the progressive process of tunnel construction. Concerning both the geological condition and construction situation, eleven risk factors are quantitatively described and an assessment system is developed to evaluate the water inrush risk. In the static assessment, the weights of eight risk factors about the geological condition are determined using Analytic Hierarchy Process (AHP). Each factor is scored by experts and the synthesis scores are weighted. The risk level is ultimately determined based on the scoring outcome which is derived from the sum of products of weights and comprehensive scores. In the secondary assessment, the eight risk factors in static assessment and three factors about construction situation are quantitatively analyzed using fuzzy evaluation method. Subordinate levels and weight of factors are prepared and then used to calculate the comprehensive subordinate degree and risk level. In the dynamic assessment, the classical field of the eleven risk factors is normalized by using the extension evaluation method. From the input of the matter-element, weights of risk factors are determined and correlation analysis is carried out to determine the risk level. This system has been applied to the dynamic assessment of water inrush during construction of the Yuanliangshan tunnel of Yuhuai Railway. The assessment results are consistent with the actual excavation, which verifies the rationality and feasibility of the software. The developed system is believed capable to be back-up and applied for risk assessment of water inrush in the underground engineering construction.