• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.105-113
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• 2007

In the current research, an algorithm of performance-based seismic retrofit design of reinforced concrete columns using FRP jacket has been proposed. For exact prediction of the nonlinear flexural analysis or FRP composite RC members, multiaxial constitutive laws of concrete and composite materials have been presented. For seismic retrofit design, an algorithm of direct displacement-based design method (DDM) proposed by Chopra and Goel (2001) has been newly applied to determine the design thickness of FRP jacket in seismic retrofit of reinforced concrete columns. To compare with the displacement coefficient method (DCM), the DDM gives an accurate prediction of the target displacement in highly nonlinear region, since the DCM uses the elastic stiffness before reaching the yield load as the effective stiffness but the DDM uses the secant stiffness.

• Journal of the Korea Concrete Institute
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• v.25 no.5
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• pp.529-537
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• 2013

The aim of the current study is to develop a nonlinear isoparametric layered frame finite element (FE) analysis of FRP strengthened reinforced concrete (RC) beam or column members by a force-based FE formulation. In sections, concrete is modeled in the triaxial stress-strain relationship state and the FRP sheet is modeled as layered composite materials in two-dimension. The element stiffness matrix derived by the force-based FE has the force-interpolation functions without assuming the displacement shape functions. A lateral load test of RC column strengthened by GFRP sheets was analyzed by the developed force-based FE model. From comparative studies of the experimental and analysis results, it was shown to compare with the stiffness FE method that the force-based FE analysis could give more accurate predictions in the overall lateral load-deflection response as well as in nonlinear deformations and damages in the column plastic hinge region.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.6
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• pp.315-329
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• 2018

Recently, RC transfer slab systems have been used widely to construct high-rise wall-type apartments for securing parking space or public space. However, it is problem that the design method and structural performance evaluation method developed for thin RC flat slab are still used in the design of the transfer slab whose thickness is very thick and therefore structural behavior is expected to be different from RC flat slab. Thus, for the rational design of the transfer slab, the ultimate shear behavior of the RC transfer slab system is required to be analyzed properly. Accordingly, in the present study, the two-way shear behavior of the transfer slab was analyzed using nonlinear FEM according to various design parameters such as thickness of the transfer slab, strength of concrete, shear span ratio, and reinforcement ratio. In addition, the two-way shear strength evaluations of RC transfer slab by the existing evaluation methods were verified by comparing those with the results of nonlinear FEM analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.267-279
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• 2009

A numerical model that can simulate the nonlinear behavior of ultra high strength fiber reinforced concrete (UHSFRC) structures subjected to monotonic loading is introduced. The material properties of UHSFRC, such as compressive and tensile strength or elastic modulus, are different from normal strength reinforced concrete. The uniaxial compressive stress-strain relationship of UHSFRC is designed on the basis of experimental result, and the equivalent uniaxial stress-strain relationship is introduced for proper estimation of UHSFRC structures. The steel is uniformly distributed over the concrete matrix with particular orientation angle. In advance, this paper introduces a numerical model that can simulate the tension-stiffening behavior of tension part of the axial member on the basis of the bond-slip relationship. The reaction of steel fiber is considered for the numerical model after cracks of the concrete matrix with steel fibers are formed. Finally, the introduced numerical model is validated by comparison with test results for idealized UHSFRC beams.

• Economic Analysis
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• v.24 no.3
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• pp.1-36
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• 2018

When it comes to explaining the relationship between inventory investment and business fluctuations, the production smoothing theory and the stock-out avoidance theory take contradictory stances. Decision-making related to inventory investments of corporations is thought to be influenced by both motives, but the relative sizes or directions of their respective influences can differ depending upon the phase of the business cycle. Against this backdrop, this paper differs from existing studies in that it theoretically tests the relative significances of the production smoothing and stock-out avoidance motives in the inventory investment dynamics, while placing its analytical focus on determining the existence and patterns of the asymmetric dynamics of inventory investment over the business cycle phases. To this end this paper sets up a non-linear model that is expanded from the existing linear inventory investment model, and checks whether its predictive power is better than that of the existing model. The results of analysis confirm the nature of the asymmetric dynamics of inventory investment over the business cycle phases. A stock-out avoidance motive appears but there is no significant production smoothing motive in boom times. In downturns, in contrast, the stock-out avoidance motive is insignificant, but a quality of asymmetric dynamics in which changes in inventory cause the deepening of recessions, due to the non-convexity of production costs proposed by Ramey (1991), is detected. This paper confirms that a model considering the asymmetric dynamics of inventory investment can have better predictive power than one that does not consider it, through within-sample and out-of-sample predictions and various predictive power tests. These research results are expected to be useful for economic forecasting, through their enhancement of the understandings of the inventory investment dynamics and of the nature of its business cycle destabilization.

• Journal of Intelligence and Information Systems
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• v.22 no.4
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• pp.19-43
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• 2016

This study examines the causes of the Asian exchange rate crisis and compares it to the European Monetary System crisis. In 1997, emerging countries in Asia experienced financial crises. Previously in 1992, currencies in the European Monetary System had undergone the same experience. This was followed by Mexico in 1994. The objective of this paper lies in the generation of useful insights from these crises. This research presents a comparison of South Korea, United Kingdom and Mexico, and then compares three different models for prediction. Previous studies of economic crisis focused largely on the manual construction of causal models using linear techniques. However, the weakness of such models stems from the prevalence of nonlinear factors in reality. This paper uses a structural equation model to analyze the causes, followed by a neural network model to circumvent the linear model's weaknesses. The models are examined in the context of predicting exchange rates In this paper, data were quarterly ones, and Consumer Price Index, Gross Domestic Product, Interest Rate, Stock Index, Current Account, Foreign Reserves were independent variables for the prediction. However, time periods of each country's data are different. Lisrel is an emerging method and as such requires a fresh approach to financial crisis prediction model design, along with the flexibility to accommodate unexpected change. This paper indicates the neural network model has the greater prediction performance in Korea, Mexico, and United Kingdom. However, in Korea, the multiple regression shows the better performance. In Mexico, the multiple regression is almost indifferent to the Lisrel. Although Lisrel doesn't show the significant performance, the refined model is expected to show the better result. The structural model in this paper should contain the psychological factor and other invisible areas in the future work. The reason of the low hit ratio is that the alternative model in this paper uses only the financial market data. Thus, we cannot consider the other important part. Korea's hit ratio is lower than that of United Kingdom. So, there must be the other construct that affects the financial market. So does Mexico. However, the United Kingdom's financial market is more influenced and explained by the financial factors than Korea and Mexico.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1164-1168
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• 2010

수자원이 우리 생활의 전반적으로 중요한 역할을 차지하면서 댐의 효율적인 운영과 안정적인 용수공급에 대한 연구는 지속적으로 수행되어지고 있다. 1990년대 이후 비선형적인 특성을 잘 모의하는 장점을 가진 인공신경망(ANN)을 이용하여 유입량 예측에 대한 많은 연구가 수행되었다. 하지만 ANN 모형을 포함한 회귀모형은 월 강우 및 유입량의 예측에 대해 간편하게 사용을 할 수 있지만, 예측의 정확성에 한계를 가지고 있다. 본 연구에서는 ANN 모형과 회귀모형의 예측오차를 후처리 과정을 통하여 오차를 줄임으로써 예측모형의 성과를 향상시키는 방법을 제안하였다. 연구지역은 금강수계의 대청댐 유역으로, 1982년 9월부터 2005년 12월에 해당하는 유역 내 11개 지점의 강우관측소에서 관측한 월 강우와 댐 유입량을 수집하여 모형을 구축하였다. 강우량과 유입량 자료에 대해 자기상관함수와 교차상관함수를 이용하여 입력변수를 결정하였고, 정규화를 통한 전처리 과정을 거쳐 ANN 모형과 회귀모형을 이용한 예측모형을 구축하였으며, 예측성과의 향상을 위하여 군집 분석을 이용하여 오차를 재조정하였다. 이러한 오차 후처리 과정을 포함한 모형은 RMSE와 상관계수를 이용하여 비교 평가한 결과, 예측성과를 약 40% 정도 향상시켰다.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.6
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• pp.45-53
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• 2011

The purpose of this study was to propose a design procedure for a damped structure with a friction damper for an existing structure. The target displacement of the damped structure was determined using the maximum displacement of the existing structure. The displacement of the damped structures was predicted using a proposed equation for the inelastic displacement ratio. For this study, we conducted a nonlinear response history analysis using 80 earthquake ground motions to verify the validity of the proposed design procedure by comparing the responses of the damped and undamped structures. Based on the dynamic analysis results, it was concluded that the predicted displacement of the damped structure using the proposed design procedure matched well with the analysis results.

• Magazine of the Korea Concrete Institute
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• v.2 no.2
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• pp.73-80
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• 1990

The current analytical techniques for R/C elements under severe dynamic repeated loads, like earth¬quake or impact, have two major problems; one is that the effects of strain rate are not considered and the other one is the current analytical model was developed based on flexural behavior only. This study develops computer software that can idealize the flexural and shear behavior of R/C elements using several parameters and also can consider the effects of strain rate. The analytical results using the developed technique were compared with serveral experimental results and they were generally satisfied.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.137-140
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• 2010

본 논문에서는 국내 지진발생 시 비보강 조적조 건축물의 손상상태 예측 및 내진성능 평가를 위해 기존건축물을 대상으로 역량스펙트럼 해석을 수행하였다. 이는 지진피해를 보다 상세하게 예측하고 건축물의 거동을 파악하기 위한 방법으로 국내 설계 지진하중과 부재의 비선형 특성을 적용하여 해석을 수행하였으며 해석 결과는 구조물의 손상상태에 따라 Slight, Moderate, Extensive, Complete 등으로 구분하여 평가하였다. 그 결과 대부분의 건축물에서 약간의 구조적 피해(Slight)와 보통의 구조적 피해(Moderate) 정도로 나타났으며, 일부 건축물에서 심각한 구조적 피해(Extensive)가 발생하는 것으로 예측되었다. 이전 연구에서 비보강 조적조 건축물의 내진성능평가를 위해 구조내진판정지표를 사용하여 내진성능을 판정하였으며 대부분의 비보강 조적조 건축물이 내진성능을 만족하지 못하였다. 본 연구에서는 기존 건축물에 구조내진 판정지표를 적용하고 그 결과를 바탕으로 역량스펙트럼 해석을 함에 따라 보다 상세한 구조물의 피해정도를 예측할 수 있었다.