• International conference on construction engineering and project management
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• 2007.03a
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• pp.509-519
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• 2007

Private financing is playing an increasing role in public infrastructure construction projects worldwide. However, private investors/operators are exposed to the financial risk of low profitability due to the inaccurate estimation of facility demand, operation income, maintenance costs, etc. From the operator's perspective, a sound and thorough financial feasibility study is required to establish the appropriate capital structure of a project. Operators tend to reduce the equity amount to minimize the level of risk exposure, while creditors persist to raise it, in an attempt to secure a sufficient level of financial involvement from the operators. Therefore, it is important for creditors and operators to reach an agreement for a balanced capital structure that synthetically considers both profitability and repayment capacity. This paper presents an optimal capital structure model for successful private infrastructure investment. This model finds the optimized point where the profitability is balanced with the repayment capacity, with the use of the concept of utility function and multi-objective GA (Generic Algorithm)-based optimization. A case study is presented to show the validity of the model and its verification. The research conclusions provide a proper capital structure for privately-financed infrastructure projects through a proposed multi-objective model.

• Ecology and Resilient Infrastructure
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• v.9 no.2
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• pp.130-130
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• 2022

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.3
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• pp.267-276
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• 2021

Community infrastructure contains national facilities that directly affect the quality of life of citizens. They need to be evenly supplied to every one of citizens. However, the services provided by infrastructure differ by region. In this paper, we propose a method to analyze the current status of the supply of community infrastructure consisting of accessibility and capacity. Accessibility can be evaluated by the time between residence blocks and facilities, which is an indicator of the convenience of citizens. Capacity is assessed by the area supplied for the local population, to assess whether facilities are being sufficiently supplied to the region. The method presented in this paper was applied on a case region to test the applicability. The analysis method of the supply status of community infrastructure in this study is considered to be used as a basic framework for regional supply plan of community infrastructure and urban planning.

• Steel and Composite Structures
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• v.20 no.2
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• pp.379-397
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• 2016

Due to creep and shrinkage of the concrete core, concrete-filled steel tubular (CFST) arches continue to deform in the long-term under sustained loads. This paper presents analytical investigations of the effects of geometric nonlinearity on the long-term in-plane structural performance and stability of three-pinned CFST circular arches under a sustained uniform radial load. Non-linear long-term analysis is conducted and compared with its linear counterpart. It is found that the linear analysis predicts long-term increases of deformations of the CFST arches, but does not predict any long-term changes of the internal actions. However, non-linear analysis predicts not only more significant long-term increases of deformations, but also significant long-term increases of internal actions under the same sustained load. As a result, a three-pinned CFST arch satisfying the serviceability limit state predicted by the linear analysis may violate the serviceability requirement when its geometric nonlinearity is considered. It is also shown that the geometric nonlinearity greatly reduces the long-term in-plane stability of three-pinned CFST arches under the sustained load. A three-pinned CFST arch satisfying the stability limit state predicted by linear analysis in the long-term may lose its stability because of its geometric nonlinearity. Hence, non-linear analysis is needed for correctly predicting the long-term structural behaviour and stability of three-pinned CFST arches under the sustained load. The non-linear long-term behaviour and stability of three-pinned CFST arches are compared with those of two-pinned counterparts. The linear and non-linear analyses for the long-term behaviour and stability are validated by the finite element method.

• Smart Structures and Systems
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• v.24 no.3
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• pp.303-317
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• 2019

Magneto-rheological fluid (MRF) rotatory dampers are normally used for controlling the constant rotation of machines and engines. In this research, such a device is proposed to act as variable stiffness device to alleviate the rotational oscillation existing in the many engineering applications, such as motor. Under such thought, the main purpose of this work is to characterize the nonlinear torque-angular displacement/angular velocity responses of an MRF based variable stiffness device in oscillatory motion. A rotational hysteresis model, consisting of a rotatory spring, a rotatory viscous damping element and an error function-based hysteresis element, is proposed, which is capable of describing the unique dynamical characteristics of this smart device. To estimate the optimal model parameters, a modified whale optimization algorithm (MWOA) is employed on the captured experimental data of torque, angular displacement and angular velocity under various excitation conditions. In MWOA, a nonlinear algorithm parameter updating mechanism is adopted to replace the traditional linear one, enhancing the global search ability initially and the local search ability at the later stage of the algorithm evolution. Additionally, the immune operation is introduced in the whale individual selection, improving the identification accuracy of solution. Finally, the dynamic testing results are used to validate the performance of the proposed model and the effectiveness of the proposed optimization algorithm.

• Journal of The Korean Society of Agricultural Engineers
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• v.64 no.1
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• pp.79-89
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• 2022

Soil moisture is significantly related to crop growth and plays an important role in irrigation management. To predict soil moisture, various process-based model has been developed and used in the world. Various models (Land surface model) may have different performance depending on the model parameters and structures that causes the different model output for the same modeling condition. In this study, the three land surface models (Noah Land Surface Model, Soil Water Atmosphere Plant, Community Land Model) were used to compare the model performance (soil moisture prediction) and develop the multi-model simulation. At first, the genetic algorithm was used to estimate the optimal soil parameters for each model, and the parameters were used to predict soil moisture in the study area. Then, we used the multi-model approach based on Bayesian model averaging (BMA). The results derived from this approach showed a better match to the measurements than the results from the original single land surface model. In addition, identifying the strengths and weaknesses of the single model and utilizing multi-model methods can help to increase the accuracy of soil moisture prediction.

• Journal of the Korean Geosynthetics Society
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• v.22 no.2
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• pp.47-54
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• 2023

In this paper, we propose the technique of optimal search keyword extraction and retrieval for news article classification. The proposed technique was verified as an example of identifying trends related to North Korean construction. A representative Korean media platform, BigKinds, was used to select sample articles and extract keywords. The extracted keywords were vectorized using word embedding and based on this, the similarity between the extracted keywords was examined through cosine similarity. In addition, words with a similarity of 0.5 or higher were clustered based on the top 10 frequencies. Each cluster was formed as 'OR' between keywords inside the cluster and 'AND' between clusters according to the search form of the BigKinds. As a result of the in-depth analysis, it was confirmed that meaningful articles appropriate for the original purpose were extracted. This paper is significant in that it is possible to classify news articles suitable for the user's specific purpose without modifying the existing classification system and search form.

• Steel and Composite Structures
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• v.50 no.4
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• pp.383-401
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• 2024

The research comprehensively studies the axial compression performance of T-shaped concrete-filled thin-walled steel tubular (CTST) long columns after fire exposure. Initially, a series of tests investigate the effects of heating time, load eccentricity, and stiffeners on the column's performance. Furthermore, Finite Element (FE) analysis is employed to establish temperature and mechanical field models for the T-shaped CTST long column with stiffeners after fire exposure, using carefully determined key parameters such as thermal parameters, constitutive relations, and contact models. In addition, a parametric analysis based on the numerical models is conducted to explore the effects of heating time, section diameter, material strength, and steel ratio on the axial compressive bearing capacity, bending bearing capacity under normal temperature, as well as residual bearing capacity after fire exposure. The results reveal that the maximum lateral deformation occurs near the middle of the span, with bending increasing as heating time and eccentricity rise. Despite a decrease in axial compressive load and bending capacity after fire exposure, the columns still exhibit desirable bearing capacity and deformability. Moreover, the obtained FE results align closely with experimental findings, validating the reliability of the developed numerical models. Additionally, this study proposes a simplified design method to calculate these mechanical property parameters, satisfying the ISO-834 standard. The relative errors between the proposed simplified formulas and FE models remain within 10%, indicating their capability to provide a theoretical reference for practical engineering applications.

• International conference on construction engineering and project management
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• 2022.06a
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• pp.1130-1137
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• 2022

The Industry Foundation Classes (IFC) provides standardized product models for the building construction domain. However, the current IFC schema has limited representation for infrastructure. Several studies have examined the data schema for road and highway modeling, but not in a sufficiently comprehensive and robust manner to facilitate the overall integrated project delivery of road projects. Several discussions have focused on slope engineering for road projects, but no solution has been provided regarding the formalized parametric modeling up to now. Iterative design, analysis, and modification are observed during the process of slope design for road projects. The practitioners need to carry out the stability analysis to consider different road design alternatives, including horizontal, vertical, and cross-section designs. The procedure is neither formalized nor automated. Thus, there is a need to develop the formal representation of the product and process of slope analysis for road design. The objective of this research is to develop a formal representation (i.e., an IFC extension data schema) for slope analysis. It consists of comprehensive information required for slope analysis in a structured manner. The deliverable of this study contributes to both the formal representation of infrastructure development and, further, the automated process of slope design for road projects.

• Journal of the Korean Society of Industry Convergence
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• v.21 no.6
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• pp.317-327
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• 2018

The perception of earthquake in Korea has changed due to the earthquake that occurred in Gyeongju and Pohang, and the earthquake has become an important factor in infrastructure management. Damage to infrastructures in the event of an earthquake is extensive. In particular, damage to infrastructures that perform public function used to spread to the whole area. From the point of view of earthquake disaster prevention, it is very important for the public to define what infrastructures are important management targets and to prepare a countermeasure. In this study, we propose a method to evaluate the importance of infrastructure to effectively manage infrastructures for earthquakes. For this purpose, important factors for the railway bridges, power generation and electric power facilities, and apartment complexes are suggested. AHP analysis is conducted to suggest priorities. In addition, the evaluation criteria for infrastructure importance are presented.