Stochastic Model for Service Life Prediction of RC Structures Exposed to Carbonation using Random Field Simulation

나웅진,권성준,Samit Ray Chaudhuri,Masanobu Shinozuka 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.1

Deterioration of Reinforced Concrete (RC) structures is related to the corrosion of reinforcement since it propagates to structural degradation. In urban or underground conditions, carbonation-initiated corrosion in reinforcement is reported. In this paper, a stochastic model for predicting service life of RC structure subjected to carbonation is proposed through Monte Carlo simulation method with the spatial variation of material, geometric properties of RC structures, and environmental factors. This model can take into account the spatial variation of uncertain parameters by generating non-Gaussian and multi-dimensional random fields using spectral representation method. To estimate the temporal variation of the probability to exceed a pre-defined serviceability, timedependent reliability analyses are performed. Spatial reliability indicators such as the mean and standard deviation of the area are calculated through 20-sample with 4-variable full-factorial realization. It is evaluated that there exists large variation in predicted service life and quality control for concrete is required during construction for the service life. Based on these results, design and construction considerations are provided.

지진 위험도를 고려한 도로 교통망의 내진보강 우선순위 결정

나웅진,박태원 한국지진공학회 2008 한국지진공학회논문집 Vol.12 No.6

본 논문은 캘리포니아지역에 위치한 고속도로망을 대상으로 하여, 도로망내에 있는 교량의 내진보강 우선순위를 결정하는 방법에 관한 연구이다. 내진보강 우선순위 결정은 지진공학 분야에서 매우 중요한 이슈 중의 하나이며, 정부나 도로 관리청의 의사결정권자는 예산 배정 과정에서 이와 같은 문제에 항상 직면하게 된다. 본 연구는 특정지역의 고속도로망을 대상으로 어떻게 내진보강 우선순위를 결정할 것인가에 관한 방법론을 보여주고 있다. 우선순위 결정을 위하여 구조물의 지진 취약도, 도로망상에 위치한 각각 연결로의 중요도에 대한 개념이 먼저 소개되었다. 도로망상 각각의 교차로를 잇는 연결로를 지진 보강의 대상 단위로 하여 도로망의 내진 성능에 대한 시뮬레이션을 수행하였으며, 추가 소요되는 교통 지체시간을 각각의 시뮬레이션 경우에 대하여 측정함으로써 내진보강에 의한 효과를 평가하였다. 또한, 지진 위험도의 확률적인 특성을 반영하기 위하여 확률론적 시나리오 지진을 도입하였다. 본 연구의 결과에서 알 수 있듯이 우선순위의 의미는 이해관계자의 주요 관심 사항에 따라 다르게 정의될 수 있고, 각각 다른 우선순위 결과를 보여주게 된다. 본 연구는 교통망의 효과적인 내진보강을 위한 우선순위 결정 과정에 도움이 될 수 있는 일반적인 지침을 제공할 것으로 기대된다. This research focuses on the issue of seismic retrofit prioritization based on the Caltrans' highway network serving Los Angeles and Orange counties. Retrofit prioritization is one of most important problems in earthquake engineering, and it is a problem that most decision makers face in the process of resource allocation. This study demonstrates the methods of prioritized resource allocation in the process of retrofitting a regional highway network. For the criteria of a retrofit ranking, seismic vulnerability and the importance of network link are first introduced. Subsequently, link-based seismic retrofit cases are simulated, investigating the effects of the seismic retrofit in terms of seismic performance, such as driver's delay. In this study, probabilistic scenario earthquakes are used to perform a probabilistic seismic risk analysis. The results show that the retrofit prioritization can be differently defined and ranked depending on the stakeholders. This study provides general guidelines for prioritization strategy for the effective retrofitting of a highway network system.

습염식 제설제 적정 사용량 산정

나웅진,장진환 한국도로학회 2022 한국도로학회논문집 Vol.24 No.5

PURPOSES : Snow removal is one of the principal components in winter road maintenance. The two commonly used methods are mechanical removal and chemical removal. Mechanical removal pushes accumulated snow off the roadway using snow plows. Chemical removal involves the application of chemicals such as NaCl2 (salt), CaCl2, MgCl2, etc., to liquefy the snow on the road. However, chemicals are known to pose negative effects on the environment and road infrastructure, so it is emphasized that only an appropriate amount of chemicals should be applied. Hence, in this study, extensive field experiments were performed to determine the appropriate amounts of chemicals required for each road surface temperature group. METHODS : The experiments were carried out at a road weather proving ground, located in Yeoncheon where road weather (including snowfall) can be artificially created. Four surface temperature groups were predetermined, according to the characteristics of de-icing chemicals on snow. For each temperature group, four different amounts of pre-wetted salt were applied to find the optimal rate for each group. RESULTS : As a consequence, the amount of recommended chemicals for each temperature group was found to be an average of 27.2g/ m2, which is 7.7g/m2 (22%) lower than the corresponding amount presented in the current Korean guidelines. CONCLUSIONS : Applying the results of this study to snow and ice control tasks enables the minimization of the negative impacts of de-icing chemicals, but still maintaining road safety and mobility.

핵비등이탈 현상 재구성을 위한 조건부 적대적 생성 신경망 활용

나웅진(UngJin Na),최문희(Moonhee Choi),이석용(SeockYong Lee),박세현(SeHyeon Park),조항진(HangJin Jo) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11

Understanding the nuances of the departure from nucleate boiling (DNB) is paramount for ensuring the safety and functionality of high thermal flux systems. The DNB, characterized by a sudden drop in heat transfer, remains a challenge to pinpoint due to its intricate nature. Many techniques aim to decode these complexities, but obtaining detailed data often demands excessive resources. This study presents a novel approach using conditional generative adversarial networks (cGANs) to reinterpret thermal data during DNB. We utilize paired images: total reflection visualizations and infrared thermometry from flow boiling experiments. Our method not only reveals links between phase interface dynamics and thermal patterns but also streamlines traditionally labor-intensive experimental setups related to infrared imaging.

기존 문헌을 활용한 일반국도상 교량 바닥판의 상태 현황 분석

오광진,나웅진,이장원,이준구 한국구조물진단유지관리학회 2012 한국구조물진단학회 학술발표회논문집 Vol.2012 No.1

In this research, the comparison and Analysis of domestic Bridge Deck on General National Road has been performed with major variations of Superstructure type, Span Lengths, Located Resion and Ages by using ‘the current status of road bridge and tunnel’ that is provided by MLTM(Ministry of Land, Transport and Maritime Affairs).

수중부재의 파력산정에 관한 고찰

오재택,나웅진,O, Jae-Taek,Na, Ung-Jin 한국해안해양공학회 2011 해안과 해양 Vol.4 No.1

Energy harvesting techniques for remote corrosion monitoring systems

김세환,나웅진 국제구조공학회 2013 Smart Structures and Systems, An International Jou Vol.11 No.5

An Remote Corrosion Monitoring (RCM) system consists of an anode with low potential, the metallic structures against corrosion, an electrode to provide reference potential, and a data-acquisition system to ensure the potential difference for anticorrosion. In more detail, the data-acquisition (DAQ) system monitors the potential difference between the metallic structures and a reference electrode to identify the correct potential level against the corrosion of the infrastructures. Then, the measured data are transmitted to a central office to remotely keep track of the status of the corrosion monitoring (CM) system. To date, the RCM system is designed to achieve low power consumption, so that it can be simply powered by batteries. However, due to memory effect and the limited number of recharge cycles, it can entail the maintenance fee or sometimes cause failure to protect the metallic structures. To address this issue, the low-overhead energy harvesting circuitry for the RCM systems has designed to replenish energy storage elements (ESEs) along with redeeming the leakage of supercapacitors. Our developed energy harvester can scavenge the ambient energy from the corrosion monitoring environments and store it as useful electrical energy for powering local data-acquisition systems. In particular, this paper considers the energy harvesting from potential difference due to galvanic corrosion between a metallic infrastructure and a permanent copper/copper sulfate reference electrode. In addition, supercapacitors are adopted as an ESE to compensate for or overcome the limitations of batteries. Experimental results show that our proposed harvesting schemes significantly reduce the overhead of the charging circuitry, which enable fully charging up to a 350-F supercapacitor under the low corrosion power of 3 mW (i.e., 1 V/3 mA).

손상과 소성을 고려한 콘크리트 변형률 국소화의 유한요소해석

송하원,나웅진 한국전산구조공학회 1997 전산구조공학 Vol.10 No.3

The strain localization of concrete is a phenomenon such that the deformation of concrete is localized in finite region along with softening behavior. The objective of this paper is to develop a plasticity and damage algorithm for the finite element analysis of the strain-localization in concrete. In this paper, concrete member under strain localization is modeled with localized zone and non-localized zone. For modeling of the localized zone in concrete under strain localization, a general Drucker-Prager failure criterion by which the nonlinear strain softening behavior of concrete after peak-stress can be considered is introduced in a thermodynamic formulation of the classical plasticity model. The return-mapping algorithm is used for the integration of the elasto-plastic rate equation and the consistent tangent modulus is also derived. For the modeling of non-localized zone in concrete under strain localization, a consistent nonlinear elastic-damage algorithm is developed by modifying the free energy in thermodynamics. Using finite element program implemented with the developed algorithm, strain localization behaviors for concrete specimens under compression are simulated. 콘크리트에 발생하는 변형률 국소화는 연화거동에 수반하여 변형이 국부적으로 집중되는 현상으로 이를 유한요소해석 할 수 있는 일관된 알고리즘을 개발하는 것이 본 연구의 목적이다. 변형률 국소화현상이 발생한 콘크리트는 변형률이 집중되는 국소화영역과 그외의 영역인 비국소화영역으로 크게 구분할 수 있으며 국소화영역에서는 연화현상을 포함하는 탄소성거동을 하게 되며 비국소화영역은 손상제하거동을 수반하게 된다. 변형률 국소화현상이 진행중인 콘크리트의 국소화영역을 모델링하기 위하여 열역학적으로 정식화된 전형적인 소성모델에 콘크리트의 극한응력 이후에 비선형 연화로 표현되는 소성거동을 고려할 수 있는 일반화된 Drucker-Prager모델을 도입하였으며 소성이론식의 적분을 위해 return-mapping 알고리즘을 사용하고 일관된 알고리즘을 전개하였다. 또한, 콘크리트의 비국소화영역의 모델링을 위하여 열역학적 자유에너지함수를 수정하여 비선형 탄성 및 손상의 일관된 알고리즘을 전개하였다. 개발된 알고리즘에 의한 유한요소해석을 통해 압축을 받는 콘크리트 부재의 변형률 국소화 현상을 해석하였다.

Prediction of Repairing Time for RC Columns with Crack and Joint under Carbonation based on Probabilistic Approach

권성준,나웅진 한국콘크리트학회 2011 International Journal of Concrete Structures and M Vol.5 No.1

Carbonation in RC (reinforced concrete) structure is considered as one of the most critical deteriorations in urban cities. Although RC column has one mix condition, carbonation depth is measured spatially differently due to its various environmental and internal conditions such as sound, cracked, and joint concrete. In this paper, field investigation was performed for 27 RC columns subjected to carbonation for eighteen years. Through this investigation, carbonation distribution in sound, cracked, and joint concrete were derived with crack mappings. Considering each related area and calculated PDF (probability of durability failure) of sound, cracked, and joint concrete through Monte Carlo Simulation (MCS), repairing timings for RC columns are derived based on several IPDF (intended probability of durability failure) of 1, 3, and 5%. The technique of equivalent probability including carbonation behaviors which are obtained from different conditions can provide the reasonable repairing strategy and the priority order for repairing in a given traffic service area.

연속압출공법에 의한 PC Box Girder 교량의 최적화에 관한 연구

변근주,나웅진,송하원,안창모 연세대학교 산업기술연구소 1996 논문집 Vol.28 No.1