• Earthquakes and Structures
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• v.26 no.4
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• pp.261-267
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• 2024

With the increase in the exploitation depth of offshore oil and gas, it is possible to control the global buckling of deep-sea pipelines by the snake lay method. Previous studies mainly focused on the analysis of critical buckling force and critical temperature of pipelines under the snake-like laying method, and pipelines often suffer structural failure due to seismic disasters during operation. Therefore, seismic action is a necessary factor in the design and analysis of submarine pipelines. In this paper, the seismic action of steel pipes in the operation stage after global buckling has occurred under the active control method is analyzed. Firstly, we have established a simplified finite element model for the entire process cycle and found that this modeling method is accurate and efficient, solving the problem of difficult convergence of seismic wave and soil coupling in previous solid analysis, and improving the efficiency of calculations. Secondly, through parameter analysis, it was found that under seismic action, the pipe diameter mainly affects the stress amplitude of the pipeline. When the pipe wall thickness increases from 0.05 m to 0.09 m, the critical buckling force increases by 150%, and the maximum axial stress decreases by 56%. In the pipe soil interaction, the greater the soil viscosity, the greater the pipe soil interaction force, the greater the soil constraint on the pipeline, and the safer the pipeline. Finally, the pipeline failure determination formula was obtained through dimensionless analysis and verified, and it was found that the formula was accurate.

• Steel and Composite Structures
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• v.51 no.4
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• pp.441-456
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• 2024

This paper aims to develop Machine Learning (ML) algorithms to predict the buckling resistance of cold-formed steel (CFS) channels with restrained flanges, widely used in typical CFS sheathed wall panels, and provide practical design tools for engineers. The effects of cross-sectional restraints were first evaluated on the elastic buckling behaviour of CFS channels subjected to pure axial compressive load or bending moment. Feedforward multi-layer Artificial Neural Networks (ANNs) were then trained on different datasets comprising CFS channels with various dimensions and properties, plate thicknesses, and restraining conditions on one or two flanges, while the elastic distortional buckling resistance of the elements were determined according to the Finite Strip Method (FSM). To develop less biased networks and ensure that every observation from the original dataset has the chance of appearing in the training and test set, a K-fold cross-validation technique was implemented. In addition, the hyperparameters of the ANNs were tuned using a grid search technique to provide ANNs with optimum performances. The results demonstrated that the trained ANNs were able to predict the elastic distortional buckling resistance of CFS flange-restrained elements with an average accuracy of 99% in terms of coefficient of determination. The developed models were then used to propose a simple ANN-based design formula for the prediction of the elastic distortional buckling stress of CFS flange-restrained elements. Finally, the proposed formula was further evaluated on a separate set of unseen data to ensure its accuracy for practical applications.

• Land and Housing Review
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• v.2 no.4
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• pp.367-377
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• 2011

This paper investigates the determination factors' variation of real estate price after sub-prime financial crisis, in korea, using a VAR model. The model includes land price, housing price, housing rent (Jensei) price, which time period is from 2000:1Q to 2011:2Q and uses interest rate, real GDP, consumer price index, KOSPI, the number of housing construction, the amount of land sales and practices to impulse response and variance decomposition analysis. Data cover two sub-periods and divided by 2008:3Q that occurred the sub-prime crisis; one is a period of 2000:1Q to 2008:3Q, the other is based a period of 2000:1Q to 2011:2Q. As a result, Comparing sub-prime crisis before and after, land price come out that the influence of real GDP is expanding, but current interest rate's variation is weaken due to the stagnation of current economic status and housing construction market. Housing price is few influenced to interest rate and real GDP, but it is influenced its own variation or Jensei price's variation. According to the Jensei price's rapidly increasing in nowadays, housing price might be increasing a rising possibility. Jensei price is also weaken the influence of all economic index, housing price, comparing before sub-prime financial crisis and it is influenced its own variation the same housing price. As you know, real estate price is weakened market basic value factors such as, interest rate, real GDP, because it is influenced exogenous economic factors such as population structural changes. Economic participators, economic officials, consumer, construction supplyers need to access an accurate observation about current real estate market and economic status.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.4
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• pp.225-232
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• 2024

This study focuses on the determination of the fracture mode in composite laminates using deep learning. With the increase in the use of laminated composites in numerous engineering applications, the insurance of their integrity and performance is of paramount importance. However, owing to the complex nature of these materials, the identification of fracture modes is often a tedious and time-consuming task that requires critical domain knowledge. Therefore, to alleviate these issues, this study aims to utilize modern artificial intelligence technology to automate the fractographic analysis of laminated composites. To accomplish this goal, scanning electron microscopy (SEM) images of fractured tensile test specimens are obtained from laminated composites to showcase various fracture modes. These SEM images are then categorized based on numerous fracture modes, including fiber breakage, fiber pull-out, mix-mode fracture, matrix brittle fracture, and matrix ductile fracture. Next, the collective data for all classes are divided into train, test, and validation datasets. Two state-of-the-art, deep learning-based pre-trained models, namely, DenseNet and GoogleNet, are trained to learn the discriminative features for each fracture mode. The DenseNet models shows training and testing accuracies of 94.01% and 75.49%, respectively, whereas those of the GoogleNet model are 84.55% and 54.48%, respectively. The trained deep learning models are then validated on unseen validation datasets. This validation demonstrates that the DenseNet model, owing to its deeper architecture, can extract high-quality features, resulting in 84.44% validation accuracy. This value is 36.84% higher than that of the GoogleNet model. Hence, these results affirm that the DenseNet model is effective in performing fractographic analyses of laminated composites by predicting fracture modes with high precision.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.15 no.4
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• pp.69-81
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• 2020

This study is to identify the effect of seniors in their 40s and 50s on their entrepreneurial intentions through attitude on entrepreneurship, subjective norms, and perceived behavioral control by utilizing the integrated model of the theory of planned behavior and self-determination theory. Also, in this process, we tried to analyze moderating effect of entrepreneurship education for seniors. An online survey was conducted for seniors in their 40s and 50s living in Seoul and Gyeonggi province, out of the total 284 questionnaire responses, 243 valid questionnaires were used in the study. Research analysis utilized SPSS 24, AMOS 23 structural equation model and Professor Hayes' Process 3.4 to analyze moderating effect. The results of the study were summarized as follows. First, autonomous motivation had a positive influence on attitude toward entrepreneurship, subjective norms and perceived behavioral control. But controlled motivation didn't have the significant influence on attitude, subjective norms and perceived behavioral control. Second, attitude toward entrepreneurship, subjective norms and perceived behavioral control had positive influence on entrepreneurship intention. Third, as a result of analyzing moderating effect of entrepreneurship education for seniors, the significant moderating effect was verified between attitude and entrepreneurship intention. Also the significant moderating effect was verified between subjective norms and entrepreneurship intention. On the other hand, no significant moderating effect was proved between perceived behavioral control and entrepreneurship intention. The implication of this study is that for retired seniors planning to enter into entrepreneurship, the result can contribute to the development of a entrepreneurship support program that can increase new startup creation, survival and sucess by diagnosing autonomous and controlled motivation for entrepreneurship. In addition, by providing entrepreneurship education as well as re-employment training in the senior outplacement program, the study can contribute to widening the opportunities for seniors to second career after retirement.

• KDI Journal of Economic Policy
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• v.31 no.1
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• pp.169-206
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• 2009

This study stems from a question, "How should we understand the pattern of the Korean economy after the 1990s?" Among various analytic methods applicable, this study chooses a Structural Vector Autoregression (SVAR) with long-run restrictions, identifies diverse impacts that gave rise to the current status of the Korean economy, and differentiates relative contributions of those impacts. To that end, SVAR is applied to four economic models; Blanchard and Quah (1989)'s 2-variable model, its 3-variable extensions, and the two other New Keynesian type linear models modified from Stock and Watson (2002). Especially, the latter two models are devised to reflect the recent transitions in the determination of foreign exchange rate (from a fixed rate regime to a flexible rate one) as well as the monetary policy rule (from aggregate targeting to inflation targeting). When organizing the assumed results in the form of impulse response and forecasting error variance decomposition, two common denominators are found as follows. First, changes in the rate of economic growth are mainly attributable to the impact on productivity, and such trend has grown strong since the 2000s, which indicates that Korea's economic growth since the 2000s has been closely associated with its potential growth rate. Second, the magnitude or consistency of impact responses tends to have subsided since the 2000s. Given Korea's high dependence on trade, it is possible that low interest rates, low inflation, steady growth, and the economic emergence of China as a world player have helped secure capital and demand for export and import, which therefore might reduced the impact of each sector on overall economic status. Despite the fact that a diverse mixture of models and impacts has been used for analysis, always two common findings are observed in the result. Therefore, it can be concluded that the decreased rate of economic growth of Korea since 2000 appears to be on the same track as the decrease in Korea's potential growth rate. The contents of this paper are constructed as follows: The second section observes the recent trend of the economic development of Korea and related Korean articles, which might help in clearly defining the scope and analytic methodology of this study. The third section provides an analysis model to be used in this study, which is Structural VAR as mentioned above. Variables used, estimation equations, and identification conditions of impacts are explained. The fourth section reports estimation results derived by the previously introduced model, and the fifth section concludes.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.4
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• pp.363-371
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• 2023

To construct a ship, blocks of various sizes must be moved and erected . In this process, lugs are used such that they match the block fastening method and various functions suitable for the characteristics of each shipyard facility. The sizes and shapes of the lugs vary depending on the weight and shape of the block structures. The structure is reinforced by welding the doubling pads to compensate for insufficient rigidity around the holes where the shackle is fastened. As for the method of designing lugs according to lifting loading conditions, a simple calculation based on the beam theory and structural analysis using numerical modeling are performed. In the case of the analytical method, a standardized evaluation method must be established because results may differ depending on the type of element and modeling method. The application of this ambiguous methodology may cause serious safety problems during the process of moving and turning-over blocks. In this study , the effects of various parameters are compared and analyzed through numerical structural analysis to determine the modeling conditions and evaluation method that can evaluate the actual structural response of the lug. The modeling technique that represents the plate part and weld bead around the lug hole provides the most realistic behavior results. The modeling results with the same conditions as those of the actual lug where only the weld bead is connected to the main body of the lug, showed a lower ulimated strength compared with the results obtained by applying the MPC load. The two-dimensional shell element is applied to reduce the modeling and analysis time, and a safety working load was verified to be predicted by reducing the thickness of the doubling pad by 85%. The results of the effects of various parameters reviewed in the study are expected to be used as good reference data for the lug design and safe working load prediction.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.727-735
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• 2012

Recently, a high-strength strand of 2400 MPa was developed using domestic technologies. In 2011, KS D 7002 was revised to cover the newly developed high-strength strands to support their practical usage. Presently, however, discussions and evaluations are not sufficient on the mechanical properties of the strands and their performance in structural members. Also, there were no detailed reviews on the need to revise the current design code for practical use of the high-strength strands. In this study, flexural behavior of a member with the high-strength strands was estimated through sectional analysis and a review and comparison of the domestic and foreign design codes were conducted considering the analysis results. Also, the need for the revision of the design code was discussed. Such discussion especially focused on the estimation of the stress in strand, which related with various issues such as determination methods for yield point of strands, time-dependent loss of prestressing force, estimation of stress in strand at member failure, and net strain limit for ductile failure of member. The discussion revealed that some parts in the design code need a revision and the further studies are required.

• Journal of Life Science
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• v.14 no.3
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• pp.478-483
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• 2004

In a model reaction using lysyl oxidase purified partilally from bovine aorta, effect of L-ascorbic acid AsA on the oxidative reaction of lysine in collagen was investigated. Addition of Ash to the reaction mixture under aerobic conditions resulted in the decrease of enzymatic activity. In order to examine the specificity of AsA in the oxidative reaction of lysine, other reductants including A derivatives instead of AsA were added to the reaction mixture. Thiol such as glutathione had no effect on the activities of lysyl oxidase. on the other hand, it was observed that erythorbic acid, which was a stereoisomer of AsA, had the same inhibitory effect on this oxidative reaction as AsA. Moreover, by the addition of 3,4-dihydroxybenzoate, which was structural analog of AsA, the activities decreased in a similar manner to that of AsA. These results indicate that the regulatory effect of AsA on lysyl oxidase is attributed to characteristics of the structure. From the determination of Ash remained in the reaction mixture, it is shown that AsA concentration remarkably decreased by lysyl oxidase of the reaction mixture. It is hypothesized that endiol groups reduces the enzyme-bound $Cu^{+2}$ required for further progress of the reaction, and suggests that AsA regulates specifically the reduction of $Cu^{+2}$ required to oxidize lysyl oxidase. This findings support that AsA has an important regulatory role on the oxidative reaction of lysine and on changes of collagen cross-links with aging.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.782-788
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• 2002

Several non-destructive test methods have been developed to estimate compressive strength of concrete in other countries. However, their applications are limited in domestic concrete due to their inaccuracies. The purpose of this study is to propose an aging coefficient of compressive strength of structural concrete in rebound number method and ultrasonic pulse velocity method for domestic concrete. The test variables include type of aggregate, curing condition, and compressive strength. Two approaches are used to estimate aging coefficient. One is evaluated by uniform linear regression equation for all ages and shows uniform strength reduction coefficient regardless of material properties and the other is evaluated by individual regression equation for each ages and shows nonuniform strength reduction and rebound increasing coefficients which decrease with increasing of rebound number and compressive strength. The latter result which can include the effect of rebound number and compressive strength is more resonable than the former.