• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.36-42
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• 1997

A prototype of 500Wh class flywheel energy storage device was designed and manufactured to check the previously predicted system performance. The system was intentionally designed to show rigid body behavior up to the maximum operating speed of 60000Tpm and to have its 2nd rigid critical mode, of which nodal point lies on the flywheel center of mass, around 4000 to 6000rpm with radial magnetic bearing stiffness of l.e+6 N/m. Numerous experiments an the system behavior showed that the PM axial bearing, designed utilizing a commercial code, acts as resonably as predicted and, most importantly, the system becomes stable after the 2nd critical speed. The EM radial bearing, however, was found out to have orthotropic property with much less radial stiffness values than expected, so that it was observed that the 2nd forward and backward critical modes were excited at 310 and 590rpm respectively with larger vibration amplitudes. Thus, in order to improve the system dynamic behavior, the EM radial bearing is currently being re designed so as to get bigger stiffness and, in turn, smoother operation of the system.

• Earthquakes and Structures
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• v.20 no.4
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• pp.389-403
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• 2021

Skewed bridges, being irregular structures with complicated dynamic behavior, are more susceptible to earthquake damage. Reliable seismic-resistant design of skewed bridges can be achieved by accurate determination of nonlinear seismic demands. However, the effect of geometric characteristics on the response modification factor (R-factor) is not accounted for in bridge design practices. This study attempts to investigate the effects of changes in the number of spans, skew angle and bearing stiffness on R-factor values and to assess the seismic fragility of skewed bridges. Results indicated that changes in the skew angle had no significant effect on R-factor values which were in consonance with code-prescribed R values. Also, unlike the increase in the number of spans that resulted in a decrease in the R-factor, the increase in bearing stiffness led to higher R-factor values. Findings of the fragility analysis implied that although the increase in the number of spans, as well as the increase in the skew angle, led to a higher failure probability, greater values of bearing stiffness reduced the collapse probability. For practicing design engineers, it is recommended that maximum demands on substructure elements to be calculated when the excitation angle is applied along the principal axes of skewed bridges.

• Earthquakes and Structures
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• v.16 no.1
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• pp.97-107
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• 2019

The frame structures investigated in this paper is composed of Concrete encased columns with L-shaped steel section and steel beams. The seismic behavior of this structural system is studied through experimental and numerical studies. A 2-bay, 3-story and 1/3 scaled frame specimen is tested under constant axial loading and cyclic lateral loading applied on the column top. The load-displacement hysteretic loops, ductility, energy dissipation, stiffness and strength degradation are investigated. A typical failure mode is observed in the test, and the experimental results show that this type of framed structure exhibit a high strength with good ductility and energy dissipation capacity. Furthermore, finite element analysis software Perform-3D was conducted to simulate the behavior of the frame. The calculating results agreed with the test ones well. Further analysis is conducted to investigate the effects of parameters including concrete strength, column axial compressive force and steel ratio on the seismic performance indexes, such as the elastic stiffness, the maximum strength, the ductility coefficient, the strength and stiffness degradation, and the equivalent viscous damping ratio. It can be concluded that with the axial compression ratio increasing, the load carrying capacity and ductility decreased. The load carrying capacity and ductility increased when increasing the steel ratio. Increasing the concrete grade can improve the ultimate bearing capacity of the structure, but the ductility of structure decreases slightly.

• Earthquakes and Structures
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• v.22 no.2
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• pp.203-218
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• 2022

In this paper, quasi-static tests were carried out on three prefabricated reinforced concrete column-steel beam (RCS) sub-assemblages with floor slabs and one comparison specimen without floor slab. The effects of axial compression and floor slab on the seismic performance were studied, and finite element simulations were conducted using ABAQUS. The results showed that the failure of prefabricated RCS sub-assemblages with floor occurred as a joint beam and column failure mode, while failure of sub-assemblages without floor occurred due to beam plastic hinge formation. Compared to the prefabricated RCS sub-assemblages without floor slab, the overall stiffness of the sub-assemblages with floor slab was between 19.2% and 45.4% higher, and the maximum load bearing capacity increased by 26.8%. However, the equivalent viscosity coefficient was essentially unchanged. When the axial compression ratio increased from 0.24 to 0.36, the hysteretic loops of the sub-assemblages with floor became fuller, and the load bearing capacity, ductility, and energy dissipation capacity increased by 12.1%, 12.9% and 8.9%, respectively. Also, the initial stiffness increased by 10.2%, but the stiffness degradation accelerated. The proportion of column drift caused by beam end plastic bending and column end bending changed from 35% and 46% to 47% and 36%, respectively. Comparative finite element analyses indicated that the numerical simulation outcomes agreed well with the experimental results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.130-140
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• 2018

An AU-composite beam based on U-shaped steel beams and steel plate anchors of type A was developed. The composite beam reduced the height of the building floor and construction cost. In addition, it decreased the length of construction work, and improved the flexural strength and stiffness as a form of tubes. In this study, AU-composite beams were tested directly and their performance was evaluated through bending experiments. The strength of the specimens was increased initially by linear loads and reached a maximum strength due to destruction of the concrete slab. All of the experiments showed more than 85% of the maximum stress and performed gentle movement. In addition, there was good composite behavior with the steel plate anchor that had excellent composite effects and reached full strength until the maximum strength was reached. When the thickness of the steel plate was increase, the flexural stiffness and strength of the specimen were improved. Therefore, the flexural strength of AU-composite beams can be estimated using the flexural strength formula according to the KBC 2016.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.151-161
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• 2009

This study was conducted to investigate the characteristics of the curling behavior of long-span pavement slabs under environmental loads. By developing and using finite element models of the long-span pavement slabs, the stress distribution and the effects of slab length, slab thickness, stiffness of underlying layers, and the restraints of the slab ends on the curling behavior were analyzed. In addition, the field experiments were performed with the actual long-span pavement slab to obtain the curling behavior of the real structure under environmental loads. As a result of this study, it was found that the vertical displacements of the long-span pavement slab along the centerline due to the curling behavior were zero except for the areas near the slab ends, and the curling stresses were maximum and constant where the displacements were zero. The slab length and the stiffness of underlying layers did not affect the maximum curling stresses. The restraints at the slab ends made the curling stresses occur near the slab ends, but did not much affect the maximum curling stresses.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.3
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• pp.45-54
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• 2009

This study was developed the metallic plate for bone fixation in the neurosurgery and general surgery and plates has a finn place in bone operating and treatment. The plates can be realized to bending strength and stiffness for strength estimation. Maximum point of bending curves has a bending point(P) with maximum load which to applied nearly 0.2% offset displacement. The device's sizing has a ${\Phi}13$ and ${\Phi}18$, and algorithm of strength estimation compared a plate(${\Phi}13$, ${\Phi}18$, ${\Phi}13-{\Phi}18$). The bending strength of the curved metallic plate has to evaluate maximum of a 311N, 387N, 410N, 474N. When a displacement preserve with a load, tensile stress through to press a plate is 274N, 324N, 382N, 394N. The algorithm of strength estimation can be used to support estimation of bending strength and stiffness. Their tool bring to settlement in the new basic algorithm for evidence with varied adjustment.

• Steel and Composite Structures
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• v.48 no.3
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• pp.305-320
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• 2023

The mechanical properties of polymeric composites are degraded under elevated temperatures due to the effect of temperature on the mechanical behavior of the resin and resin fiber interfaces. In this study, the effect of temperature on the impact response of the carbon fiber reinforced plastics (CFRP) was investigated at low-velocity impact (LVI) using a drop-weight impact tester machine. All the composite plates were fabricated using a vacuum infusion process with a stacking sequence of [45/0_2/-45/90_2]s, and a thickness of 2.9 mm. A group of the specimens was exposed to an environment with a temperature cycling at the range of -30 ℃ to 65 ℃. In addition, three other groups of the specimens were aged at ambient (28 ℃), -30 ℃, and 65 ℃ for ten days. Then all the conditioned specimens were subjected to LVI at three energy levels of 10, 15, and 20 J. To assess the behavior of the damaged composite plates, the force-time, force-displacement, and energy-time diagrams were analyzed at all temperatures. Finally, radiography, optical microscopy, and scanning electron microscopy (SEM) were used to evaluate the effect of the temperature and damages at various impact levels. Based on the results, different energy levels have a similar effect on the LVI behavior of the samples at various temperatures. Delamination, matrix cracking, and fiber failure were the main damage modes. Compared to the samples tested at room temperature, the reduction of temperature to -30 ℃ enhanced the maximum impact force and flexural stiffness while decreasing the absorbed energy and the failure surface area. The temperature increasing to 65 ℃ increased the maximum impact force and flexural stiffness while decreasing the absorbed energy and the failure surface area. Applying 200 thermal cycles at the range of -30 ℃ to 65 ℃ led to the formation of fine cracks in the matrix while decreasing the absorbed energy. The maximum contact force is recorded under cyclic temperature as 5.95, 6.51 and 7.14 kN, under impact energy of 10, 15 and 20 J, respectively. As well as, the minimum contact force belongs to the room temperature condition and is reported as 3.93, 4.94 and 5.71 kN, under impact energy of 10, 15 and 20 J, respectively.

• Journal of the Korea Society of Computer and Information
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• v.28 no.10
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• pp.171-178
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• 2023

In this paper, we propose a smart automated warehouse to maximize space utilization. Previous elevator-type automatic warehouses were designed with a maximum payload of 100kg on trays, which has the problem of extremely limiting the number of pallets that can be loaded within the space. In this paper, we design a smart warehouse that can maximize space utilization with a maximum vertical stiffness of 300kg. As a result of the performance evaluation of the implemented warehouse, the maximum payload was 500.6kg, which satisfied the original design and requirements, the lifting speed was 0.5m/s, the operating noise of the device was 67.1dB, the receiving and forwarding time of the pallet was 36.92sec, the deflection amount was 4mm, and excellent performance was confirmed in all evaluation items. In addition, the PLC control method, which designs the control UI and control panel separately, was integrated into the PC system to improve interoperability and maintainability with various process management systems. In the future, we plan to develop it into a fully automatic smart warehouse by linking IoT sensor-based logistics robots.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.4
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• pp.657-669
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• 2018

In recent years, the development of complex urban areas has become saturated and much attention has been focused on the development of underground space, and deep excavation is frequently performed in order to increase the utilization of underground space due to the enlargement of buildings and the high rise of buildings. Therefore, in this study, we tried to understand the behavior of the braced wall and the behavior of the tunnel adjacent to the wall according to the stiffness of the wall and the distance between the tunnel and wall. As a result of the study, the deformation of the braced wall tended to decrease with increasing the stiffness of the wall, and the axial force acting on the struts was also different according to the stiffness of braced wall. When the stiffness of the braced wall is small (2 mm), the point at which the axial force of the braces maximizes is near 0.3H of the wall. When the stiffness of the braced wall is large (5 mm), the axial force is maximum at around 0.7H of the wall. Also, the tunnel convergence occurred more clearly when the separation distance from the braced wall was closer, the stiffness of the wall was smaller, and the tunnel convergence was concentrated to the lower right part. The ground settlement due to the excavation of the ground tended to decrease as the distance between tunnel and braced wall was closer to that of the tunnel, which is considered to be influenced by the stiffness of the tunnel.