• Advances in Computational Design
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• v.9 no.1
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• pp.39-52
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• 2024

If the governing differential equation arising from engineering problems is treated as an analytic, continuous and derivable function, it can be expanded by one point as a series of finite numbers. For the function to be zero for each value of its domain, the coefficients of each term of the same power must be zero. This results in a recursive relationship which, after applying the natural conditions or the boundary conditions, makes it possible to obtain the values of the derivatives of the function with acceptable accuracy. The elastoplastic analysis of an inhomogeneous thick sphere of metallic materials with linear variation of the modulus of elasticity, yield stress and Poisson's ratio as a function of radius subjected to internal pressure is presented. The Beltrami-Michell equation is established by combining equilibrium, compatibility and constitutive equations. Assuming axisymmetric conditions, the spherical coordinate parameters can be used as principal stress axes. Since there is no analytical solution, the natural boundary conditions are applied and the governing equations are solved using a proposed new method. The maximum effective stress of the von Mises yield criterion occurs at the inner surface; therefore, the negative sign of the linear yield stress gradation parameter should be considered to calculate the optimal yield pressure. The numerical examples are performed and the plots of the numerical results are presented. The validation of the numerical results is observed by modeling the elastoplastic heterogeneous thick sphere as a pressurized multilayer composite reservoir in Abaqus software. The subroutine USDFLD was additionally written to model the continuous gradation of the material.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.73-84
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• 1993

In this research, configuration design optimization of plane truss structure has been tested by using decomposition technique. In the first level, the problem of transferring the nonlinear programming problem to linear programming problem has been effectively solved and the number of the structural analysis necessary for doing the sensitivity analysis can be decreased by developing stress constraint into member stress approximation according to the design space approach which has been proved to be efficient to the sensitivity analysis. And the weight function has been adopted as cost function in order to minimize structures. For the design constraint, allowable stress, buckling stress, displacement constraint under multi-condition and upper and lower constraints of the design variable are considered. In the second level, the nodal point coordinates of the truss structure are used as coordinating variable and the objective function has been taken as the weight function. By treating the nodal point coordinates as design variable, unconstrained optimal design problems are easy to solve. The decomposition method which optimize the section areas in the first level and optimize configuration variables in the second level was applied to the plane truss structures. The numerical comparisons with results which are obtained from numerical test for several truss structures with various shapes and any design criteria show that convergence rate is very fast regardless of constraint types and configuration of truss structures. And the optimal configuration of the truss structures obtained in this study is almost the identical one from other results. The total weight couldbe decreased by 5.4% - 15.4% when optimal configuration was accomplished, though there is some difference.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.581-586
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• 2018

Cast iron manhole lids cause environmental pollution during the manufacturing process, and the work environment is very poor. In addition, if the height of the manhole cover does not match the height of the road surface, it causes considerable inconvenience and safety problems. This study proposes a height - adjustable steel manhole cover that can replace cast iron manhole covers and easily match the road surface with the upper surface of the manhole cover. Structural analysis was performed to grasp the design variable of the structure of the manhole cover, satisfying the required quality performance. To fabricate a manhole cover that satisfies the required load capacity, the optimal design for the U-shaped reinforcement structure was made. The cylindrical shape of the height adjustment part and the low frame were formed by bending the steel sheet into a circular shape and then welding. Reinforcing bars were also made by bending a steel plate. The height adjustment groove was machined by a CNC milling machine. Four prototypes were fabricated and a load bearing test was carried out, and new manhole cover was made reflecting results of the test. In the load bearing test, there was no breakage of the welded part, and deformation occurred mainly at the contact area between the groove and gusset plate. Deformation of 1 to 2.7mm occurred due to a load of 450kN. On the other hand, after removing the load, there was almost no residual deformation, and the load bearing evaluation was judged to be satisfactory because the manhole cover could be disassembled and reassembled.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.230-236
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• 2020

A trash screen is installed in front of the inflow channel of a drainage pumping station, sewage treatment plant, and a power plant to block floating contaminants. The bottleneck phenomenon, which decreases the water inflow, causes damage to the damper as a result of clogging in between the screen if string type obstacles are not removed. In this paper, the apron was removed, and the screen was expanded, to prevent breakage of the bottleneck phenomenon and string type obstacles. This was designed using an extended rake by adding an inner rake in between the screen interspace to remove the bottleneck phenomenon and string type obstacles. To design the inner rake that satisfies the allowable stresses of the existing damper rake, the experiment points were determined according to the experimental design method using the inner rake vertical length and the thickness of the reinforced section as parameters. The use of the ANSYS static structural module and statistical analysis tool R software gives the optimized shape according to the response surface method. The relative error between the response surface analysis results and the simulation results was 1.63% of the determined optimal design-point rake length of 210.2 mm and the reinforcement section thickness of 2 mm. Through empirical experiments, a test rake was constructed to the actual size, and approximately 97% of the bottleneck phenomenon and string type obstacles could be removed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.130-137
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• 2013

This research was performed through the experimental design to get the statistical analysis on foamed concrete mixed plaster with hydrogen peroxide. In this experiment, we set the ratio of each material, which part of lightweight concrete, as experimental factors and evaluated on the mechanical properties by statistical analysis for response variables obtained from experiments. Experimental factors are plaster replacement, water binder ratio, and hydrogen peroxide ratio. Response variables are dry density, compressive strength, and flexural strength. Mixing design of the foamed concrete set up a total of 15 experimental points by Box-Behnken (BB) method of the response surface analysis. Thus, the results of a study were summarized as follows. Values of the probability in experimental factors (plaster replacement, water binder ratio and hydrogen peroxide ratio) on the response variables were estimated to be significant at the 95% of confidence limit. On response surface analysis for dry density of foamed concrete, water binder ratio and hydrogen peroxide ratio were estimated to be significant (${\alpha}$ = 0.05), and the relationship between the amount of void and the water content for dry density is inverse proportional. On response surface analysis for the compressive strength of foamed concrete, water binder ratio, hydrogen peroxide ratio and (hydrogen peroxide ratio)$^2$ was estimated to be significant (${\alpha}$ = 0.05). On response surface analysis for the flexural strength of foamed concrete, water binder ratio, hydrogen peroxide ratio was estimated to be significant (${\alpha}$ = 0.05). Through multi response surface analysis, we found the optimal area that meets performance goals.

• Korean Journal of Construction Engineering and Management
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• v.13 no.1
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• pp.118-128
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• 2012

As the bearing wall structure, which has been widely applied to domestic apartment buildings since the 1980s, cause many problems during remodeling of buildings, the government encourages constructors to adopt flat plate or rahmen structure through legal incentives. In line with such a trend, the green frame, an eco-friendly rahmen structure that has removed the shortcomings of previous structures, was developed to enhance structural safety, constructability, and eco-friendliness. The construction of green frame can reduce the labor cost and facilitate the composition of iron bars to reduce rebar loss through calculating the quality and establishing the bar bending schedule automatically on the precast concrete member data collected over the design phase. Therefore, the purpose of this study is to develop the algorithm to automate the calculation of iron bar volume for the green frame designed on composite precast concrete members. Automated algorithm to calculate concrete structural design information and design information. Practices through the application site should prove efficacy. The database established by the developed algorithm will automate the establishment of iron bar processing map and bar cutting list and the calculation of optimal composition and order volume to minimize the rebar loss. This will also reduce the expenses on management staff and overall construction cost through the minimization of rebar loss.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.333-340
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• 2004

The use of the othotropic steel deck is steadily increased due to the advance of the technology in the steel bridges which recently have been longer. But the othotropic steel deck bridge is the structure that is very fragile to the fatigue, especially, the fatigue crack at the cross of the longitudinal rib and transversal rib is one of the biggest problems that othotropic steel deck bridges have. The causes of these fatigue cracks come from the secondary stress on out-plane behavior of transversal rib. In this study, we conducted the experiment to find the optimal details to improve fatigue strength on intersection between longitudinal rib and transversal rib in the othotropic steel deck bridge through numerical analysis using the experiment of the fatigue in the 3-dimensional real structure and program LUSAS. As a result of study, it is showed that the details of the korean standard section attached with a curved bulkhead plate is the most profitable. And, it is indicated that the stress which is generated when the reform improved section by parametic study can be reduced by about 50% at most or more. Along with the reduced stress and the longer interval between transversal ribs(G=400), the decreased steel amount by 4% and the shortened welding length by 34% make it possible to produce the othotropic steel deck bridge which is strong against fatigue.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.4
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• pp.249-256
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• 2019

This paper presents an optimization framework of electrical impedance tomography for characterizing electrical conductivity profiles of concrete structures in two dimensions. The framework utilizes a partial-differential-equation(PDE)-constrained optimization approach that can obtain the spatial distribution of electrical conductivity using measured electrical potentials from several electrodes located on the boundary of the concrete domain. The forward problem is formulated based on a complete electrode model(CEM) for the electrical potential of a medium due to current input. The CEM consists of a Laplace equation for electrical potential and boundary conditions to represent the current inputs to the electrodes on the surface. To validate the forward solution, electrical potential calculated by the finite element method is compared with that obtained using TCAD software. The PDE-constrained optimization approach seeks the optimal values of electrical conductivity on the domain of investigation while minimizing the Lagrangian function. The Lagrangian consists of least-squares objective functional and regularization terms augmented by the weak imposition of the governing equation and boundary conditions via Lagrange multipliers. Enforcing the stationarity of the Lagrangian leads to the Karush-Kuhn-Tucker condition to obtain an optimal solution for electrical conductivity within the target medium. Numerical inversion results are reported showing the reconstruction of the electrical conductivity profile of a concrete specimen in two dimensions.

• Journal of the Korean GEO-environmental Society
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• v.12 no.3
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• pp.5-12
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• 2011

In this paper, after studying structural performance for the representative corrugated steel plate used in Korea, we proposed the optimum shape for section of corrugated steel plate considering a width of steel plates that can be produced currently in the factory. Using AISI(1986) in examination for the performance of the corrugated steel plate, we determined the mechanical limit of the optimum sections considering shear force and bending moment of corrugated steel plate and also determined the geometric limit of them considering formability, shapes and ratio between width of steel plate before forming and that after forming. As a result of examination for performance of steel plate applying algorithm for searching optimal sections algorithm developed in this study to the existing representative corrugated steel plate, allowable force and moment of inertia indicated the maximum values at bending radius 76mm and internal bending angle $50^{\circ}$. And as an application result of the optimum design system that used SS490 with 1,550mm of width and 4,700mm of length considering current production situation in Korea, we developed the new section with more than 2 times of structural performance comparing with existing corrugated steel plate.

• Korean Journal of Construction Engineering and Management
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• v.6 no.5 s.27
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• pp.89-101
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• 2005

The early phase of construction projects, communication among the related participants has great influence on the further transaction of the projects. However, important decision making are made by the experience of the field managers in practice without the method for systematic analysis. For example, in building construction project, selection process for construction method has been executed by decision making of some architects dependent on their experience. As a result, there have been frequent construction method alterations during the construction process and delay of duration, addition of cost, etc have followed accordingly. The main reasons of such a mal-functional transaction are due to the absent of the reasonal procedure of decision making reflecting the characteristics of construction project. Therefore, there is a need for an supporting tool and production design for the selection of rational construction method. The objective of this study is to propose production design process and decision making model in relation to various influent factors at the early phase of construction projects. To achieve these objectives, this study 1)analyzes the prior theory about production design, 2)we have studied about selection process for optimal construction method through constraint analysis in structural works, 3)performs a case study to embody the problems of the production design, and 4)proposes a cooperative committee model for supporting production design by analyzing the results of case study and interviewing experts. It is anticipated that the effective tool of proposed model would be able to improve communication among the related participants and systematically accumulate data that might be used in similar construction projects.