• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.1
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• pp.1-7
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• 1999

In order to determine the mode I stress intensity factor ($K_I$) by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a paramagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effects of the magnetic flux and the demagnetization on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. The change in potential drop was linearly decreased with increasing the tensile load and was caused by the change in conductivity near the crack tip. The reason of decreasing the change in potential drop with increasing the tensile load was that the increase of the conductivity near the crack tip due to the tensile load caused the decreases of the resistance and internal inductance of the specimen The relationship between the change in potential drop and the change in $K_I$ was not affected by demagnetization and was independent of the crack length.

• Journal of the Korea Furniture Society
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• v.20 no.4
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• pp.358-373
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• 2009

Probability based design(PBD)method has some advantages against current design methods. First, it can provide the quantitative values for the structural safety or capacity through the reliability index, $^{\beta}$. That presented the certainty on the corresponding structure for the designer or user, also that permitted the broad consideration in the safety of structures. In addition, it can give the quantitative lifetime of the related structure in the calculation process of target reliability index. Also, incidental economical efficiency can be expected because decrease of required structural material can be obtained by using the practical material data. Unlikely current deterministic structural design methods, main advantage is the reflection of real condition in the structural design process by application of the data with not small clear specimen but structural size material. Advanced countries, namely America, Canada, Europe, Australia and New Zealand already converted from allowable stress design(ASD) method to PBD method and used as a standard wooden structures code in the late 1980s and 1990s. Other domestic constructions standards such as the steel or concrete constructions accepted and used the PBD methods already. Accordingly, wooden structural design method also should be converted from deterministic ASD to probabilistic LRFD(Load and resistance factor design) in order to keep pace with worldwide demands for PBD. Hence, to suggest the reason of introduction the PBD in domestic wooden structural design and analysis, a brief example was used to show the different reliability index by using the different design methods. Definition, merits and demerits of deterministic ASD and probabilistic LRFD were followed. Also the three examples were presented to show the similarity and differences between ASD and LRFD. Finally, connection problems that might cause a disputation in wooden structural design and analysis were broadly examined.

• Structural Engineering and Mechanics
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• v.59 no.5
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• pp.933-950
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• 2016

Decks, interior beams, edge beams and girders are the parts of a steel floor system. If the deck is optimized without considering beam optimization, finding best result is simple. However, a deck with higher cost may increase the composite action of the beams and decrease the beam cost reducing the total cost. Also different number of floor divisions can improve the total floor cost. Increasing beam capacity by using castellated beams is other efficient method to save the costs. In this study, floor optimization is performed and these three issues are discussed. Floor division number and deck sections are some of the variables. Also for each beam, profile section of the beam, beam cutting depth, cutting angle, spacing between holes and number of filled holes at the ends of castellated beams are other variables. Constraints include the application of stress, stability, deflection and vibration limitations according to the load and resistance factor (LRFD) design. Objective function is the total cost of the floor consisting of the steel profile cost, cutting and welding cost, concrete cost, steel deck cost, shear stud cost and construction costs. Optimization is performed by enhanced colliding body optimization (ECBO), Results show that using castellated beams, selecting a deck with higher price and considering different number of floor divisions can decrease the total cost of the floor.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2954-2966
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• 1994

The characteristics and good corrosion resistance at room and elevated temperatures led to increasing application of Ti-alloys such as aircraft, jet engine, turbine wheels. In forging of Ti-alloy at high temperature, die chilling and die speed should be carefully controlled because the flow stress of Ti-alloy is sensitive to temperature, strain and strain-rate. In this study, the forging of turbine disk was numerically simulated by the finite element method for hot-die forging process and isothermal forging process, respectively. The effects of the temperature changes, the die speed and the friction factor were examined. Also, local variation of process parameters, such as temperature, strain and strain-rate were traced during the simulation. It was shown that the isothermal forging with low friction condition produced defect-free disk under low forging load. Consequently, the simulational information will help industrial workers develope the forging of Ti-alloys including 'preform design' and 'processing condition design'. It is also expected that the simulation method can be used in CAE of near net-shape forging.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.1
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• pp.63-69
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• 2006

New design equations for calculating the lateral-torsional buckling moment resistances of singly stepped I-section beams subjected to general loading on the top flange are suggested based on the investigations of elastic finite-element analyses. The new equations presented in this study are compared with current moment gradient modifiers presented by other researchers and specifications. The study considered almost loading cases on buildings and bridges. The proposed equations should be easily used to calculate the lateral-torsional buckling moment resistance of stepped I-beams.

• Steel and Composite Structures
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• v.46 no.4
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• pp.497-512
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• 2023

Using light weight concrete as infill material in conventional cold-formed steel (CFS) shear wall systems can considerably increase their load bearing capacity, ductility, integrity and fire resistance. The compressive strength of the filler concrete is a key factor affecting the structural behaviour of the composite wall systems, and therefore, achieving maximum compressive strength in lightweight concrete while maintaining its lightweight properties is of significant importance. In this study a new type of optimum polystyrene lightweight concrete (OPLC) with high compressive strength is developed for infill material in composite CFS shear wall systems. To study the seismic behaviour of the OPLC-filled CFS shear wall systems, two full scale wall specimens are tested under cyclic loading condition. The effects of OPLC on load-bearing capacity, failure mode, ductility, energy dissipation capacity, and stiffness degradation of the walls are investigated. It is shown that the use of OPLC as infill in CFS shear walls can considerably improve their seismic performance by: (i) preventing the premature buckling of the stud members, and (ii) changing the dominant failure mode from brittle to ductile thanks to the bond-slip behaviour between OPLC and CFS studs. It is also shown that the design equations proposed by EC8 and ACI 318-14 standards overestimate the shear force capacity of OPLC-filled CFS shear wall systems by up to 80%. This shows it is necessary to propose methods with higher efficiency to predict the capacity of these systems for practical applications.

• Journal of Korean Society of Steel Construction
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• v.19 no.6
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• pp.633-642
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• 2007

Although the Load and Resistance Factor Design (LRFD) method is an advanced design approach, it does not accurately capture the interaction between individual members and structural system. A nonlinear inelastic analysis for the entire structure is required to solve this problem. According to many design codes of advanced countries, a nonlinear inelastic analysis can be applied to predict the structural behavior and strength reasonably. In this study, an LRFD design method using practical nonlinear inelastic analysis was proposed. Design examples using the proposed method waspresented, and the economical efficiency and adequacy of the proposed method was investigated by comparing the design results with that of the AISC-LRFD. It has been consequently demonstrated that the proposed method can reduce the construction cost through savings in steel.

• Journal of the Korean GEO-environmental Society
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• v.16 no.1
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• pp.5-16
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• 2015

In the long span bridge construction, construction cost portion of large scale marine foundation is about 40% (KICTEP, 2007). In this study, designs for deep water depth large composite foundation of a super long span cable-stayed girder bridge of prototype were performed by three design methods (ASD, LRFD, Eurocode) and the behaviors of a large diameter drilled shaft were analyzed and the 3D numerical analysis was performed. As a result, the soft rock socket lengths in allowable stress design estimation method were the longest. The soft rock socket lengths estimated by the design approach 2 among Eurocode and the LRFD were similar. The longer the socket length socketed in the soft rock was, the smaller the axial force acting on a large-diameter drilled shaft head was and the smaller the settlement of drilled shaft was.

• Structural Engineering and Mechanics
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• v.56 no.4
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• pp.667-694
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• 2015

The suspended dome system is a new structural form that has become popular in the construction of long-span roof structures. Suspended dome is a kind of new pre-stressed space grid structure that has complex mechanical characteristics. In this paper, an optimum topology design algorithm is performed using the enhanced colliding bodies optimization (ECBO) method. The length of the strut, the cable initial strain, the cross-sectional area of the cables and the cross-sectional size of steel elements are adopted as design variables and the minimum volume of each dome is taken as the objective function. The topology optimization on lamella dome is performed by considering the type of the joint connections to determine the optimum number of rings, the optimum number of joints in each ring, the optimum height of crown and tubular sections of these domes. A simple procedure is provided to determine the configuration of the dome. This procedure includes calculating the joint coordinates and steel elements and cables constructions. The design constraints are implemented according to the provision of LRFD-AISC (Load and Resistance Factor Design-American Institute of Steel Constitution). This paper explores the efficiency of lamella dome with pin-joint and rigid-joint connections and compares them to investigate the performance of these domes under wind (according to the ASCE 7-05), dead and snow loading conditions. Then, a suspended dome with pin-joint single-layer reticulated shell and a suspended dome with rigid-joint single-layer reticulated shell are discussed. Optimization is performed via ECBO algorithm to demonstrate the effectiveness and robustness of the ECBO in creating optimal design for suspended domes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.263-274
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• 2018

In this study, the applicability and external/internal stability of a MSEW abutment with a slab were investigated. Structural analysis of slab bridges between 10 ~ 20.0 m and thicknesses of 0.7 ~ 0.9 m was carried out to calculate the reaction forces due to dead and live loads acting on the bridge supports. The slab bridge with a length of 20.0 m satisfied the allowable contact pressure of 200 kPa for the true MSEW abutment. Because the external stability of the true MSEW abutment was dominated by the geometry of the MSE wall, the change in the factor of safety due to the load of the super-structure is small. Because the stiffness of the foundations is fixed and the load of the super-structure is increased, the factor of safety of the bearing capacity was reduced. As the load of the super-structure was increased, the horizontal earth pressure of the true MSEW abutment increased greatly. As a result, the pullout and fracture of the uppermost reinforcement, which are the factors of safety, did not meet the design criteria. Therefore, it is necessary to increase the pullout resistance and the long-term allowable tensile force of the reinforcement placed on the top of the reinforced soils to ensure efficient design and performance of a true MSEW abutment.