• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.15-27
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• 2007

Over the past decade, labor costs have increased relative to the cost of material hardware according to analysts in the construction industry. Therefore, the minimum weight design, which has been widely adopted in the literature for the optimal design of steel structures, is no longer the most economical construction approach. Presently, although connection- related costs is crucial in determining the most cost-effective steel structures, most studies on this subject focused on minimum-weight design or engaged in higher analysis. Therefore, in this study, we proposed a fabrication scheme for the most cost-effective moment-resisting steel frame structures that resist lateral loads without compromising overall stability. The proposed approach considers the cost of steel products, fabrication, and connections within the design process. The optimal design considered construction realities, with the optimal trade-off between the number of moment connections and total cost was achieved by reducing the number of moment connections and rearranging them using the combination of analysis that includes shear, displacement and interaction value based on the LRFD code and optimization scheme based on genetic algorithms. In this study, we have shown the applicability and efficiency in the examples that considered actual loading conditions.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.7
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• pp.992-1001
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• 2023

OWEC (Overtopping Wave Energy Converter) is a wave power generation system using the wave overtopping. The performance and safety of the OWEC are affected by wave characteristics, such as wave height, period. To mitigate this issue, optimal OWEC designs based on wave characteristics must be investigated. In this study, the environmental conditions along the Ulleungdo coast were used. The hydraulic efficiency of the OWEC was calculated using SPH (Smoothed Particle Hydrodynamics) by comparing 4 models that changed the substructure. As a result, it was possible to change the substructure. Through design optimization, a new truss-type structure, which is a substructure capable of carrying the design load, was proposed. Through a case study using member diameter and thickness as design variables, structural safety was secured under allowable stress conditions. Considering wave load, the natural frequency of the proposed structure was compared with the wave period of the relevant sea area. Harmonic response analysis was performed using wave with a 1-year return period as the load. The proposed substructure had a reduced response magnitude at the same exciting force, and achieved weight reduction of more than 32%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.397-407
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• 2013

Recently, a great progress has been made in bridge construction technology through the development of high performance materials and new structural types. However, most of attention has been paid to the cast-in-place technologies and material cost saving. The cast-in-place method is always subject to some environmental damages in construction sites, which frequently causes conflicts with residents. To overcome the disadvantages, a lot of fabrication construction method was developed. Most fabrication construction methods developed up to now have been applied for superstructure of bridges. In contrast, such fabricable methods developed for substructures are extremely rare. A fabricated column using ICH CFT(Internally Confined Hollow CFT) column was developed in a series of previous researches. Included in the previous studies are design and construction methods for the precast segmental coping, the column-coping connection, the column-segment connection, column-foundation connection. In this paper, seismic performance of the fabricated ICH CFT columns was extensively investigated experimentally. Two test specimens were prepared depending on the connection methods of segments; one by mortar-grouting method and the other by reinforcement method using stiffeners.

• Journal of Korean Society of Steel Construction
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• v.19 no.6
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• pp.737-749
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• 2007

Flexural design of double composite box girder over the interior pier for three-span continuous bridge was performed by the LRFD method. The maximum span length of the continuous bridge ranged from 80m to 120m and the relative ratio of the span length was assumed to be 1:1.25:1. The girder section was designed for the strength limit state and service limit state with additional design check for constructibility. Before the bottom concrete and compression flange showed a complete composite action, the buckling of lower compression flange was checked. The flexural stiffness and flexural resistance characteristics for the section and for the constituent members such as tension flange, compression flange, and web were analyzed for different thicknesses of the bottom concrete on top of the compression flange. The effect of the distribution ratio of steel between the top and bottom flanges was investigated by analyzing ductility behavior and stress distribution through the girder's depth for several different relative area ratios of steel between the top and bottom flanges. It was found that a total amount of 15% of steel can be saved by applying the double composite system compared with that of the conventional composite system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.1-7
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• 2013

Structural design and analysis of a coiling arm unloading machine for submarine cable have been originally conducted in this study. Three-dimensional CAD modeling process is practically applied for the structural design in detail. Finite element method(FEM) and multi-body dynamics(MBD) analyses are also used to verify the safety and required motions of the designed coiling arm structure. The effective moving functions of the designed coiling arm with respect to rotational and radial motions are achieved by adopting bearing-roller mechanical parts and hydraulic system. Critical design loading conditions due to its self weight, carrying cables, offshore wind, and hydraulic system over operation conditions are considered for the present structural analyses. In addition, possible inclined ground conditions for the installation of the designed coiling arm are also considered to verify overturn stability. The present hydraulic type coiling arm system is originally designed and developed in this study. The developed coiling arm has been installed at a harbor, successfully tested its operational functions, and finished practical unloading mission of the submarine cable.

• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.29-41
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• 2007

Structural design, like other complex decision problems, involves many trade-offs among competing criteria. Although mathematical programming models are becoming increasingly realistic, they often have design limitations, that is, there are often relevant issues that cannot be easily captured. From the understanding of these limitations, a decision-support system is developed that can generate some useful alternatives as well as a single optimum value in the optimization of steel frame structures. The alternatives produced using this system are "good" with respect to modeled objectives, and yet are "different," and are often better, with respect to interesting objectives not present in the model. In this study, we created a decision-support system for designing the most cost-effective moment-resisting steel frame structures for resisting lateral loads without compromising overall stability. The proposed approach considers the cost of steel products and the cost of connections within the design process. This system makes use of an optimization formulation, which was modified to generate alternatives of optimum value, which is the result of the trade-off between the number of moment connections and total cost. This trade-off was achieved by reducing the number of moment connections and rearranging them, using the combination of analysis based on the LRFD code and optimization scheme based on genetic algorithms. To evaluate the usefulness of this system, the alternatives were examined with respect to various design aspects.

• Composites Research
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• v.36 no.6
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• pp.454-460
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• 2023

Recently, regulations on greenhouse gas emissions have been strengthened, and the International Maritime Organization (IMO) has been strengthening greenhouse gas regulations with a goal of net 'zero' emissions by 2050. In addition, in the shipbuilding/offshore sector, it is important to reduce operating costs, such as improving propulsion efficiency and lightening structures. In this regard, research is currently being conducted on topology optimization using 3D printed composite materials to satisfy structural lightness and high rigidity. In this study, three topology shapes (hexagonal, square, and triangular) were applied to the interior of a rudder, a ship structure, using 3D printed composite materials. Structural analysis was performed to determine the appropriate shape for the rudder. CFD analysis was performed at 10° intervals from 0° to 30° for each rudder angle under the condition of 8 knots, and the load conditions were set based on the CFD analysis results. As a result of the structural analysis considering the internal topology shape of the rudder, it was confirmed that the triangular, square, and hexagonal topology shapes have excellent performance. The rudder with a square topology shape weighs 78.5% of the rudder with a triangular shape, and the square topology shape is considered to superior in terms of weight reduction.