• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.279-288
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• 2016

The present study simplified the moment-curvature relationship to straightforwardly determine the flexural behavior of reinforced concrete (RC) columns. For the idealized column section, moments and neutral axis depths at different stages(first flexural crack, yielding of tensile reinforcing bar, maximum strength, and 80% of the maximum strength at the descending branch) were derived on the basis of the equilibrium condition of forces and compatibility condition. Concrete strains at the extreme compression fiber beyond the maximum strength were determined using the stress-strain relationship of confined concrete, proposed by Kim et al. The lateral load-displacement curves converted from the simplified moment-curvature relationship of columns are well consistent with test results obtained from column specimens under various parameters. The moments and the corresponding neutral axis depth at different stages were formulated as a function of longitudinal reinforcement and transverse reinforcement indices and/or applied axial load index. Overall, curvature ductility of columns was significantly affected by the axial load level as well as concrete compressive strength and the amount of longitudinal and transverse reinforcing bars.

• Composites Research
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• v.14 no.3
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• pp.1-9
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• 2001

A new non-destructive fatigue prediction model of the composite laminates is developed. The natural frequencies of fatigue-damaged laminates under extensional loading are related to the fatigue life of the laminates by establishing the equivalent flexural stiffness reduction as a function of the elastic properties of sublaminates. The flexural stiffness is derived by relating the 90-ply elastic modulus reduction, and using the laminate plate theory to the degraded elastic modulus and the intact elastic modulus of other laminates. The natural frequency reduction model, in which the dominant fatigue mode can be identified from the sensitivity scale factors of sublaminate elastic properties, provides natural frequency vs. fatigue cycle curves for the composite laminates. Vibration tests were also conducted on $[{90}_2/0_2]_s$ carbon/epoxy laminates to verify the natural frequency reduction model. Correlations between the predictions of the model and experimental results are good.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.285-299
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• 1993

The objective of the present study is to analyze material flow in the metal forming processes by using computer simulation and experiment with model material, plasticine. A UBET program is developed to analyze the bulk flow behaviour of various metal forming problems. The elemental strain-hardening effect is considered in an incremental manner and the element system is automatically regenerated at every deforming step in the program. The material flow behavior in closed-die forging process with rib-web type cavity are analyzed by UBET and elastic-plastic finite element method, and verified by experiments with plasticine. There were good agreements between simulation and experiment. The effect of corner rounding on material flow behavior is investigated in the analysis of backward extrusion with square die. Flat punch indentation process is simulated by UBET, and the results are compared with that of elastic-plastic finite element method.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.8
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• pp.653-660
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• 2015

In this study, we conduct power performance and load analyses of two different types of vertical-axis tidal-current turbines using the computational fluid dynamics (CFD) method. To analyze the power output and loads, we perform transient CFD simulations considering the cavitation model using ANSYS CFX. The averaged power output of an H-type rotor was 7.47 kW and 67.6 kW in normal and extreme operating conditions, respectively, which did not satisfy the initial design conditions. However, in the case of the helical-type rotor, the power output under normal and extreme conditions were close to the expected values. The cavitation, which may cause instantaneous power fluctuation, occurred repeatedly at the suction side of the rotors. In order to guarantee a more stable power supply and to prevent fatigue failure, we require a design that minimizes cavitation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.665-674
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• 2015

A TSL (Thin Spray-on Liner) which consists of polymers has a higher initial strength, faster construction time and higher waterproofing performance than the conventional cementitious shotcrete. Main supporting mechanism of TSL is the adhesion and tensile strength which is distinct from the conventional shotcrete. Even though highly in demand due to its outstanding characteristics, TSL is not yet well-known support material. In this study, to evaluate contact behavior of TSL, numerical analysis was performed with comparing result from laboratory tests. From the analysis, cohesive behavior at the contact surface between TSL and rock can be evaluated by using combination of cohesive and the damage model. In addition, results show that the cohesive stiffness controled slope between force and displacement, the fracture energy controled level of force at the contact.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.6
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• pp.463-470
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• 2013

In this paper, 2D simple analyses were performed in order to predict the large torsional oscillations in a suspension bridge based on Makenna and Tuama model(2001). The existing model(Makenna and Tuama, 2001) has shown unrealistic results as the wind speed increases and frequency decreases. Furthermore, resonance could not be simulated by the existing model. Therefore, in this study, new model was proposed with a consideration of the torsional resistance. The vertical and rotational behaviors of the deck in the suspension bridge were analyzed. Analysis results showed that at first vertical oscillations were observed and it was gradually transformed to the rotation oscillations. With the consideration of the torsional resistance, it was shown that vertical behavior were stabilized as time passed. However, the rotational behavior was not stabilized and was kept until the end of analysis. Beat periods decreased while the wind speed increased. The resonance of the rotational mode was dependent to the rotational resistance. Obtained results could be applied for the design of the suspension bridge under the wind load.

• Tunnel and Underground Space
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• v.8 no.3
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• pp.200-208
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• 1998

This research is intended to investigate the behavior of the jointed rock under various loading conditions: static or dynamic load. The distributed state concept (DSC) is based on the idea that the response of the joint can be related to and expressed as the response of the reference states : relative intact (RI) and fully adjusted (FA) states. In the DSC, an initially RI joint modifies continuously through a process of natural self-adjustment, and a part of it approaches the FA state at randomly disturbed locations in the joint areas. In this study, based on the DSC concept, RI state, FA state, and disturbance function (D) are defined for characterizing the behavior of rock joint. From the results of this research, it can be stated that DSC model is capable of capturing the physical behavior of jointed rock such as softening and hardening and considering the size of joint and roughness of joint surface.

• Tunnel and Underground Space
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• v.17 no.5
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• pp.381-388
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• 2007

The regular RC structures have been transformed into irregular RC structures by alternate load of RC structures during explosive demolition. Numerical simulation programs have contributed to a better understanding of large displacement collapse behavior during explosive demolition, but there remain a number of problems which need to be solved. In this study, the 1/5 scaled 1, 3 and 5 stories RC structures were designed and fabricated. To consider the collapse possibility of upper dead load, fabricated RC structures were demolished by means of felling method. To observe the collapse behavior of the RC structures during felling, displacement of X-direction (or horizontal), displacement of Z-direction (or vertical) md relative displacement angle from respective RC structures were analyzed. Finally explosive demolition on the scaled RC structures using felling method are carried out, collapse behavior by felling method is affected by upper dead load of scaled RC structures. Displacement of X and Z direction increases gradually to respective 67ms and 300ms after blasting. It is confirmed that initial collapse velocity due to alternate load has a higher 3 stories RC structures than 5 stories.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1077-1082
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• 2013

To improve cycling performance, the power output of the rider and the sources of resistance (e.g., air resistance, frame stiffness, and cycle mass) must be considered. From a mechanical viewpoint, we consider how the bike frame performance can be increased while decreasing the resistance. First, to improve the competitive ability of a racing track cycle, we should consider the stiffness of the bike frame including the pedal loading and aerodynamic effects when riding. Therefore, we obtained the cross-sectional area of each part of the bike frame and then aimed to minimize the drag force through an aerodynamic parametric study. In addition, the frame should remain safe under the loading applied by the rider. Under the guidelines of the UCI (union Cycliste Internationale) regulations, the bike frame has been evaluated under the proposed loading condition, and we developed a racing track cycle for elite cyclists.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.164-170
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• 2016

The initial urban railway was only required to perform its role as means of transportation. As the time of staying in an underground platform was extended, it has been faced with the issues of environmental improvement as a living space. Therefore, the sliding automatic door, which is the basis of the screen door, is used widely for large distribution stores, hospitals, restaurants, and public offices for customers' convenience and as a convenient method to control access. Therefore, screen doors are required for the purpose of customers' convenience, securing safety, establishing pleasant station buildings, and energy savings. It would be also necessary to develop the optimal design technology for a screen door system through the design of element parts and to ensure reliability. Therefore, this paper calculated, interpreted, and verified the theoretical weight of the composition parts to verify the design drive hardness of the motor for screen doors necessary for the safety of subways.