• Structural Engineering and Mechanics
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• v.71 no.1
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• pp.1-12
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• 2019

This study investigates optimum designs of steel space truss towers under seismic loading by using Jaya optimization algorithm. Turkish Earthquake Code (2007) specifications are applied on optimum designs of steel space truss towers under the seismic loading for different local site classes depending on different soil groups. The proposed novel algorithm does not have any algorithm-specific control parameters and depends only a simple revision equation. Therefore, it provides a practical solution for structural optimization problems. Optimum solutions of the different steel truss examples are carried out by selecting suitable W sections taken from American Institute of Steel Construction (AISC). In order to obtain optimum solutions, a computer program is coded in MATLAB in corporated with SAP2000-OAPI (Open Application Programming Interface). The stress and displacement constraints are applied on the design problems according to AISC-ASD (Allowable Stress Design) specifications. Firstly, a benchmark truss problem is examined to see the efficiency of Jaya optimization algorithm. Then, two different multi-element truss towers previously solved with other methods without seismic loading in literature are designed by the proposed algorithm. The first space tower is a 582-member space truss with the height of 80 m and the second space tower is a 942-member space truss of about 95 m height. The minimum optimum designs obtained with this novel algorithm for the case without seismic loading are lighter than the ones previously attained in the literature studies. The results obtained in the study show that Jaya algorithm is a practical and robust optimization method for structural optimization problems. Moreover, incorporation of the seismic loading causes significant increase in the minimum design weight.

• Progress in Medical Physics
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• v.29 no.4
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• pp.101-105
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• 2018

In this paper, a neutron moderation system for boron neutron capture therapy (BNCT) based on a $^{252}Cf$ neutron source is proposed. Different materials have been studied in order to produce a high percentage of epithermal neutrons. A moderator with a construction mixture of $AlF_3$ and Al, three reflectors of $Al_2O_3$, BeO, graphite, and seven filters (Bi, Cu, Fe, Pb, Ti, a two-layer filter of Ti+Bi, and a two-layer filter of Ti+Pb) is considered. The MCNPX simulation code has been used to calculate the neutron and gamma flux at the output window of the neutronic system. The results show that the epithermal neutron flux is relatively high for four filters: Ti+Pb, Ti+Bi, Bi, and Ti. However, a layer of Ti cannot reduce the contribution of ${\gamma}$-rays at the output window. Although the neutron spectra filtered by the Ti+Bi and Ti+Pb overlap, a large fraction of neutrons (74.95%) has epithermal energy when the Ti+Pb is used as a filter. However, the percentages of the fast and thermal neutrons are 25% and 0.5%, respectively. The Bi layer provides a relatively low epithermal neutron flux. Moreover, an assembly configuration of 30% $AlF_3+70%$ Al moderator/$Al_2O_3$ reflector/a two-layer filter of Ti+Pb reduces the fast neutron flux at the output port much more than other assembly combinations. In comparison with a recent model suggested by Ghassoun et al., the proposed neutron moderation system provides a higher epithermal flux with a relatively low contamination of gamma rays.

• Convergence Security Journal
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• v.18 no.1
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• pp.33-42
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• 2018

CFD analysis is an analytical technique that applies a computer to the design and development of products across the entire industry for heat or fluid flow. This technology is used to shorten the development period and reduce costs through computerized simulation. However, the software used for CFD analysis is now required to use expensive foreign software. The Opensource CFD analysis software used in the proposed system has reliability of commercial CFD analysis software and has various user groups. However, for users who have expert knowledge, Opensource CFD software which supports only text interface environment, We have developed an environment that enables the construction of a CFD analysis environment for beginners as well as professionals. In addition, the proposed system supports the pre-processing (design and meshing) environment for CFD analysis and the environment for post-processing (result analysis & visualization), enabling the integrated CFD analysis process in one platform.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.34 no.2
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• pp.23-31
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• 2018

In recent years, as the development of construction technology and population increase, buildings are becoming more complex and high-rise. These large scale buildings are difficult to secure fire and evacuation safety when fire occurs. So it is necessary to prepare specific measures. According to this situation, in 2011, Republic of Korea officially launched Performance-based Design in "Fire-fighting system Installation business Act". But even 6 years passed since the enforcement, there are still faces manifold problems in the course of implementation. In order to examine the necessary improvements, in this study, I conducted interviews and questionnaires with experts, investigated the improvement items under current laws. And draw up a measures for that items. The subjects of the survey were fire-fighting officer, professional engineer fire fighting, fire protection planner and professor in Daegu. As a result of twice surveys, a total of 19 items are derived. And then compared and analyzed the criteria of overseas countries, and suggested improvement directions for final items. In addition, conducted a third questionnaire survey on the proposed improvement direction to verify the appropriateness of the alternative. The results of this study will be used as basic data to deal with the general problems of performance-based design in future, and further study on each item will be needed.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.11
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• pp.63-72
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• 2018

In this study, we analyzed high-performance building technologies through a case study of 65 high-performance buildings in the U.S., Europe, Asia and Oceania. In detail, we reviewed the international trend of building energy-saving technology and energy consumption per unit area by analyzing buildings constructed within a 10 year period(2008-018). The primary energy consumption was $48-440kWh/m^2$, and the average value was calculated as $169.3kWh/m^2$. Although some buildings received high certification ratings, they did not meet either Korean or international energy evaluation standards. The system analysis revealed that many energy-saving technologies show various application rates in different countries because the technologies possess different properties. Furthermore, small-area building groups tended to have less primary energy consumption than the medium and large-area buildings, but the area-energy relationship $R^2$ value was analyzed as 0.3161, indicating no clear proportional relationship. Therefore, we propose that it is necessary to maximize the energy savings of buildings by taking into consideration a region's code, climate, building usage, area and space-using patterns to reduce energy and greenhouse gas emissions.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.2
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• pp.29-40
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• 2018

Strength design wind loads for the wind resistance design of structures shall be evaluated by the product of wind loads calculated based on the basic wind speed with 100 years return period and the wind load factor 1.3 specified in the provisions of load combinations in Korean Building Code (KBC) 2016. It may be sure that the wind load factor 1.3 in KBC(2016) had not been determined by probabilistic method or empirical method using meteorological wind speed data in Korea. In this paper, wind load factors were evaluated by probabilistic method and empirical method. The annual maximum 10 minutes mean wind speed data at 69 meteorological stations during past 40 years from 1973 to 2012 were selected for this evaluation. From the comparison of the results of those two method, it can be found that the mean values of wind load factors calculated both probability based method and empirical based method were similar at all meteorological stations. When target level of reliability index is set up 2.5, the mean value of wind load factors for all regions should be presented about 1.35. When target level of reliability index is set up 3.0, wind load factor should be presented about 1.46. By using the relationship between importance factor(conversion factor for return period) and wind load factor, the return periods for strength design were estimated and expected wind speeds of all regions accounting for strength design were proposed. It can be found that return period to estimate wind loads for strength design should be 500 years and 800 years in according to target level of reliability index 2.5 and 3.0, respectively. The 500 years basic wind speed map for strength design was suggested and it can be used with a wind load factor 1.0.

• Journal of the Korean Society of Systems Engineering
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• v.18 no.2
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• pp.94-107
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• 2022

Accidents prevention and mitigation is the highest priority of nuclear power plant (NPP) operation, particularly in the aftermath of the Fukushima Daiichi accident, which has reignited public anxieties and skepticism regarding nuclear energy usage. To deal with accident scenarios more effectively, operators must have ample and precise information about key safety parameters as well as their future trajectories. This work investigates the potential of machine learning in forecasting NPP response in real-time to provide an additional validation method and help reduce human error, especially in accident situations where operators are under a lot of stress. First, a base-case SGTR simulation is carried out by the best-estimate code RELAP5/MOD3.4 to confirm the validity of the model against results reported in the APR1400 Design Control Document (DCD). Then, uncertainty quantification is performed by coupling RELAP5/MOD3.4 and the statistical tool DAKOTA to generate a large enough dataset for the construction and training of neural-based machine learning (ML) models, namely LSTM, GRU, and hybrid CNN-LSTM. Finally, the accuracy and reliability of these models in forecasting system response are tested by their performance on fresh data. To facilitate and oversee the process of developing the ML models, a Systems Engineering (SE) methodology is used to ensure that the work is consistently in line with the originating mission statement and that the findings obtained at each subsequent phase are valid.

• Steel and Composite Structures
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• v.44 no.3
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• pp.295-307
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• 2022

The objective of this research is to study experimentally the behavior of stiffened steel tubes (CFSTs). Considered parameters are stiffening methods by through-bolts or shear connectors with different configurations. In addition, the effect of global (ratio between length to diameter) and local (proportion between diameter to thickness) slenderness ratios are investigated. Load application either applied on steel only or both steel and concrete is studied as well. Case of loading on steel only happens when concrete inside the column shrinks. The purpose of the research is to improve the behavior of CFSTs by load transfer between them and different stiffening methods. A parametric experimental study that incorporates thirty-three specimens is carried out to highlight the impact of those parameters. Different outputs are recorded for every specimen such as load capacities, vertical deflections, longitudinal strains, and hoop strains. Two modes of failure occur, yielding and global buckling. Shear connectors and through-bolts improve the ultimate load by up to 5% for sections loaded at steel with different studied global slenderness and local slenderness equal 63.5. Meanwhile, shear connectors or through bolts increase the ultimate load by up to 6% for global slenderness up to 15.75 for sections loaded on composite with local slenderness equals 63.50. Recommendations for future design code development are outlined.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.3
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• pp.129-137
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• 2023

This study presents a dry precast concrete (PC) beam-column connection, and its target seismic performance level is set to be emulative to the reinforced concrete (RC) intermediate moment resisting frame system specified in ACI 318 and ASCE 7. The key features include self-sustaining ability during construction with the dry mechanical splicing method, enabling emulative connection performances and better constructability. Test specimens with code-compliant seismic details were fabricated and tested under reversed cyclic loading, which included a PC beam-column connection specimen with dry connections and an RC control specimen. The test results showed that all the specimens failed in a similar failure mode due to plastic deformations in beam members, while the hysteretic response curve of the PC specimen showed comparable and emulative performances compared to the RC specimen. Seismic performance evaluation was quantitatively addressed, and on this basis, it confirmed that the presented system can fully satisfy all the required performance for the intermediate RC moment resisting frame.