• Tribology and Lubricants
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• v.38 no.5
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• pp.179-184
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• 2022

The power train of transmission for 21-ton grade wheel excavator makes use of a complex gear train composed of a planetary and helical gear system to drive the wheel excavator by transmitting power to the axle. The complex gear train with a shift mode is an important part of the transmission because of strength problems in an extreme environment. To calculate the specifications of the complex gear train and analyze the gear bending and compressive stresses of the complex gear train, this study analyzes gear bending and compressive stresses accurately for the optimal design of the complex gear train with respect to cost and reliability. In this article, the gear bending and compressive stresses of the complex gear train are calculated using the Lewes and Hertz equation. Evaluating the results with the data of the allowable bending and compressive stress from the stress and number of cycles curves of the gears verified the calculated specifications of the complex gear train. A computer structure analysis is performed with the 3D model of the planetary and helical gears to analyze the structure strength of the complex gear train. The results demonstrate that the durability and strength of the complex gear train are safe, because the safety factors of the bending and compressive stresses are more than 1.0.

• Journal of the Korean Geotechnical Society
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• v.25 no.1
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• pp.89-99
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• 2009

Compared to standard piling methods, micropile construction can be used in downtown areas since it generates less vibration and noise. Since it only causes less soil disturbance, it is commonly used as reinforcement to existing structures. In this study, a field wherein the bearing capacity and settlement of soil can not support the weight of the superstructure was selected and micropiles were implemented instead of ordinary piles. The deformation modulus of the micropile reinforced ground was determined and was directly reflected in the design. Loading testing was used to check whether or not the allowable bearing capacity satisfies the condition of the designed bearing capacity. The computed deformation modulus based from the test was used in the numerical analysis of soil to investigate the stability of the foundation and analysis method. And a method for controlling the bearing capacity and settlement was recommended.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.35 no.3
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• pp.49-56
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• 2023

The allowable mean overtopping discharge is used as a design parameter for coastal structures. The crest elevation of coastal structures should ensure the wave overtopping discharge within acceptable limits for structural safety and the safety of pedestrians, vehicles, operations, and so on. In this study, two-dimensional physical model tests on typical rubble-mound structure geometries were performed and the the mean wave overtopping discharges under various water depth and wave conditions were measrued. The various test conditions were applied to the tests with the change of the wave steepness, relative freeboard and relative wave height. An empirical formula from the experimental data was proposed to predict the mean wave overtopping volumes.

• Journal of the Korean Geotechnical Society
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• v.39 no.1
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• pp.5-14
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• 2023

The pile driving process may lead to ground heaving, causing additional positive skin friction to act on the piles, compromising their stability. This study proposes a new pile foundation type that can reduce positive skin friction. This was investigated by designing and constructing a pile with a hydraulic cylinder which actively responds to ground deformation. The newly proposed pile design was compared against traditional piles in multiple model tests where ground heaving was simulated. In the tests, base load and total shaft resistance were measured during ground heaving and with expansion of the hydraulic cylinder. As a result of the tests, a very small amount of expansion of the hydraulic cylinder member completely reduced the positive skin friction and increased the base load. Excessive expansion of the hydraulic cylinder, however, generates negative skin friction beyond the zero skin friction state. Therefore, it is necessary to estimate the appropriate level of hydraulic cylinder expansion, taking into account the amount of ground heaving and the allowable displacement of the pile.

• Transactions of Materials Processing
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• v.32 no.6
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• pp.311-320
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• 2023

Recently, lightweight of automotive parts has been required to solve environmental problems caused by global warming. Accordingly, research and development are proceeded on manufacturing of parts using aluminum that can replace steel for lightweight of the automotive parts. In addition, high strength aluminum can be applied to body parts in order to meet both requirements of lightening and improving crash safety of vehicle. In this study, hot blow forming of roof side rail is employed to manufacturing of the automotive parts with high strength aluminum tube. In hot blow forming, longer forming times and excessive thinning can be occurred as compared with conventional manufacturing processes. So optimization of process conditions is required to prevent excessive thinning and to uniformize thickness distribution with fast forming time. Mechanical properties of high strength aluminum are obtained from tensile test at high temperature. These properties are used for finite element(FE) analysis to investigate the effect of strain rate on thinning and thickness distribution. Variation of thickness was firstly investigated from the result of FE analysis according to tube diameter, where the shapes at cross section of roof side rail are compared with allowable dimensional tolerance. Effective tube diameter is determined when fracture and wrinkle are not occurred during hot blow forming. Also FE analysis with various pressure-time profiles is performed to investigate the their effects on thinning and thickness distribution which is quantitatively verified with thinning factor. As a results, optimal process conditions can be determined for the manufacturing of roof side rail using high strength aluminum.

• Journal of Korean Association for Spatial Structures
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• v.24 no.2
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• pp.31-41
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• 2024

This study aims to investigate the seismic response of a large span thin shell structures and assess their displacement under seismic loads. The study employs finite element analysis to model a thin shell structure subjected to seismic excitation. The analysis includes eigenvalue analysis and time history analysis to evaluate the natural frequencies and displacement response of the structure under seismic loads. The findings show that the seismic response of the large span thin shell structure is highly dependent on the frequency content of the seismic excitation. The eigenvalue analysis reveals that the tenth mode of vibration of the structure corresponds to a large-span mode. The time history analysis further demonstrates, with 5% damping, that the displacement response of the structure at the critical node number 4920 increases with increasing seismic intensity, reaching a maximum displacement of 49.87mm at 3.615 seconds. Nevertheless, the maximum displacement is well below the allowable limit of the thin shell. The results of this study provide insight into the behaviour of complex large span thin shell structures as elevated foundations for buildings under seismic excitation, based on the displacement contours on different modes of eigenvalues. The findings suggest that the displacement response of the structure is significant for this new application of thin shell, and it is recommended to enhance the critical displacement area in the next design phase to align with the findings of this study to resist the seismic impact.

• The Journal of the Convergence on Culture Technology
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• v.10 no.5
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• pp.687-692
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• 2024

Recently, electric skateboards have been used as a means of personal transportation due to their convenience and simplicity of operation, but the conventional skateboards driven by timing belts or hub motors have disadvantages such as low driving torque, high current and vibration. Therefore, in this paper, we propose a new type of electric skateboard that can run at high speeds for long periods of time so that it can be used as a auxiliary means of transportation. The planetary gear and motor unit are combined and installed inside one drive wheel, and power is supplied to the wheel through the integrated driving unit to prevent high currents and enable high-speed driving. First, the allowable current and running speed of the electric skateboard were set for efficient personal transportation and the appropriate reduction ratio, modules, and planetary gear dimensions were determined by comparing the torque required for the wheel axis and the maximum output torque of the motor. Additionally, an appropriate suspension device was added to reduce driving vibration for user convenience, and the feasibility of the proposed in-wheel gearbox was experimentally verified through fabrication.

• Steel and Composite Structures
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• v.53 no.1
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• pp.29-43
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• 2024

In this paper, the behavior of an innovative metallic a butterfly-shaped link as damper with shear and flexural mechanism was investigated experimentally and numerically. The damper is directly attached to the diagonal member of the Concentrically Braced Frame (CBF) to prevent buckling of the braces. Since it is expected that nonlinear behavior of the system is limited to the dampers, the other parts of structures remind elastic that the damper can replaced easily after a severe earthquake. The experimental outcomes indicated that both types of dampers (with shear or flexural mechanism) pertain to stable hysteresis loops without any significant degradation in stiffness or strength. Comparing the dampers indicated that the shear damper has a greater ultimate strength (4.59 times) and stiffness (3.58 times) than flexural damper but a lower ductility (16%) and ultimate displacement (60%). Also, the shear damper has a considerable dissipation energy 14.56 times greater than flexural dampers where dissipating energy are affected by ultimate strength, stiffness and ultimate displacement. Also, based on the numerical study, the effect of main plate slenderness on the behavior of the damper was considered and the allowable slenderness was suggested to the design of the dampers. Numerical results confirmed that the flexural damper is more sensitive to the slenderness than shear damper. Accordingly, as the slenderness is less than 50 and 30, respectively, for, shear and flexural damper, no degradation in ultimate strength is realized. By increasing the slenderness, the maximum reduction of the ultimate strength, stiffness, and energy dissipation capacity reached by 16%, 7%, and 17% for SDB dampers whereas it is 3%, 33%, 20%, and 45% for MDB.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.1125-1146
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• 2018

Segment lining applied to the TBM tunnel is mainly made of concrete, and it requires sufficient structural capacity to resist loads received during the construction and also after the completion. When segment lining is design to the Limit State Design, both Ultimate Limit State (ULS) and Service Limit State (SLS) should be met for the possible load cases that covers both permanent and temporary load cases - such as load applied by TBM. When design segment lining, it is important to check structural capacity at the joints as both temporary and permanent loads are always transferred through the segment joints, and sometimes the load applied to the joint is high enough to damage the segment - so called bursting failure. According to the various design guides from UK (PAS 8810, 2016), compression stress at the joint surface can generate bursting failure of the segment. This is normally from the TBM's jacking force applied at the circumferential joint, and the lining's hoop thrust generated from the permanent loads applied at the radial joint. Therefore, precast concrete segment lining's joints shall be designed to have sufficient structural capacity to resist bursting stresses generated by the TBM's jacking force and by the hoop thrust. In this study, bursting stress at the segment joints are calculated, and the joint's structural capacity was assessed using Leonhardt (1964) and FEM analysis for three different design cases. For those three analysis cases, hoop thrust at the radial joint was calculated with the application of the most widely used limit state design codes Eurocode and AASHTO LRFD (2017). For the circumferential joints bursting design, an assumed TBM jack force was used with considering of the construction tolerance of the segments and the eccentricity of the jack's position. The analysis results show reinforcement is needed as joint bursting stresses exceeds the allowable tensile strength of concrete. This highlights that joint bursting check shall be considered as a mandatory design item in the limit state design of the segment lining.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.152-161
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• 2023

In general, large-capacity hydrogen storage vessels, typically in the form of vertical cylindrical vessels, are constructed using steel materials. These vessels are anchored to foundation slabs that are specially designed to suit the environmental conditions. This anchoring method involves pre-installed anchors on top of the concrete foundation slab. However, it's important to note that such a design can result in concentrated stresses at the anchoring points when external forces, such as seismic events, are at play. This may lead to potential structural damage due to anchor and concrete damage. For this reason, in this study, it selected an vertical hydrogen storage vessel based on site observations and created a 3D finite element model. Artificial seismic motions made following the procedures specified in ICC-ES AC 156, as well as domestic recorded earthquakes with a magnitude greater than 5.0, were applied to analyze the structural behavior and performance of the target structures. Conducting experiments on a structure built to actual scale would be ideal, but due to practical constraints, it proved challenging to execute. Therefore, it opted for an analytical approach to assess the safety of the target structure. Regarding the structural response characteristics, the acceleration induced by seismic motion was observed to amplify by approximately ten times compared to the input seismic motions. Additionally, there was a tendency for a decrease in amplification as the response acceleration was transmitted to the point where the centre of gravity is located. For the vulnerable components, specifically the sub-system (support columns and anchorages), the stress levels were found to satisfy the allowable stress criteria. However, the concrete's tensile strength exhibited only about a 5% margin of safety compared to the allowable stress. This indicates the need for mitigation strategies in addressing these concerns. Based on the research findings presented in this paper, it is anticipated that predictable load information for the design of storage vessels required for future shaking table tests will be provided.