• Composites Research
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• v.21 no.4
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• pp.22-28
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• 2008

The composite joint has become an important research area because the structural efficiency of a structure with a joint is determined by its joints rather than by its basic structure since the joints are often the weakest areas in composite structures. In this paper, the strengths of adhesive joints consisting of metal and composites were predicted and tested by the maximum strain theory and damage zone theory. Nonlinear finite element analyses of adhesive Joints considering the material nonlinearity of the adhesive layer were performed. From the tests and analyses, the strengths of the adhesive joints could be predicted to within 22.2% using the damage zone ratio.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.765-770
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• 2014

This paper describes the study on a method for improving the structural durability of bolted joints applied to a composite bogie frame. In this study, three bolted joints with and without inserts and screw threads were selected for determining the effect of the inserts, using experiment and analysis. The structural performances of the proposed bolted joints were compared and evaluated using the test method prescribed by the ASTM D5961 standard. The results revealed that the bolted joint having an insert shape without the screw thread offered improved durability for application to a composite bogie frame. Furthermore, the structural integrity of the frame comprising the bolted joints was evaluated using finite element analysis according to the JIS E 4207 standard. The Tasi-Wu and Von-Mises failure criteria were used for determining the failure of the composite structure and bolted joints, respectively. A sub-modeling technique was introduced for investigating the performance of the bolted joints in greater detail. The analysis results demonstrated that the Tasi-Wu failure index of the composite structure near the bolted joints was reduced by approximately one-half after applying an insert without the screw thread. This implies that the structural durability of the bolted joints of a composite bogie frame could be improved by using a metal insert without the screw thread.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.517-520
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• 2017

In this paper, we represented the structural design parameter effect on the sealing gap behavior of solid rocket motor case and nozzle connection under penetrated pressure through the sealing path between insulation rubber and the ablative FRP bonded on the inside convergent wall of nozzle. It is important to keep the good sealing capacity during all the combustion time of SRM. To achieve the crucial role of sealing system of SRM, designers must consider design factors for stable sealing clearance gap as the nearly unchanged initial design state as possible for sufficient compression rate of O-ring under sealing gap pressure.

• Composites Research
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• v.37 no.3
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• pp.238-245
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• 2024

In this study, as part of the development of a monitoring system for the efficient maintenance of steel pipes, an experimental study was conducted to evaluate the performance of steel pipes treated with modified polyethylene coating. In the case of the conventional mechanical pre-coating method, there was a deterioration in polyethylene adhesion during expansion testing, which led to the application of a chemical pre-treatment process using a calcium-mixed phosphate zinc film to resolve this issue. SEM and EDX analyses showed that the densest structure was observed at a Zn/Ca ratio of 1.0, and improved heat resistance compared to the conventional method was confirmed. Additionally, to prevent coating detachment during expansion, an evaluation of adhesion and elongation was conducted on steel pipes with modified polyethylene coating, incorporating materials such as elastomers based on maleic anhydride grafting, metal oxides, blocking agents, and slip agents. Experimental results showed that the specimen (S4) containing all modified materials exhibited more than a 25% performance improvement compared to the specimen (S2) containing only metal oxides. Lastly, the development and performance evaluation of wedge-shaped socketing and pressing wheels, which are part of the pipe fixing accessories, were conducted to prevent surface coating damage on the completed pipes.

• Journal of Aerospace System Engineering
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• v.12 no.1
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• pp.35-41
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• 2018

Unmanned Aerial Vehicles (UAV) have been used for various purposes in multiple fields, such as observation, communication relaying, and information acquisition. Nowadays, UAVs must have high performance in order to acquire more precise information in larger amounts than is now possible while performing for long periods. At present, domestically, a high-altitude long-endurance UAV (HALE UAV) for long-term flight in the stratosphere has been developed in order to replace some functions of the satellite. In this study, as a part of structural soundness evaluation of the aircraft structure developed for the HALE UAV, the structural soundness of the fasteners of the fuselage and tail is evaluated by calculating the margin of safety(M.S). The result confirms the validity of the design of the fasteners in the aircraft structure of the UAV.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.4
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• pp.38-47
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• 2013

For the joint connection of the precast steel grid composite decks, the prefabricated joint which is composed of concrete shear key and high-tension bolts was already proposed. In this study, for the purpose of increasing the bending stiffness and bending strength of the proposed prefabricated joint section details of the proposed joint are modified, and through experimental tests the bending performance, such as stiffness and strength of a modified joint, is compared with those of the proposed joint. Test and analysis results show that the shear cracks in the concrete shear key are clearly reduced by the strengthening of the shear key using shear studs and additional rebars. According to analysis results of the moment-curvature relationship, bending stiffness of the modified joint is about 47% greater than the stiffness of the proposed joint. Furthermore, the modified joint has about 32% greater bending strength than the proposed joint. Compared to specimens without the joint the modified joint has same or slightly higher bending strength, but about 37% lower bending stiffness.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.158-158
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• 2011

통상 교량구조물은 차도부와 보도부 및 그 부속시설로서 난간 및 연석부 등으로 구성되는데, 자동차 전용도로의 경우 보도부가 설치되지 않게 되고, 국내의 국도 및 지방도상의 많은 교량이 차도부와 보도부의 별도의 구분이 없이 보행자가 연석부 위로 통행하거나 여의치 않을 경우 난간에 기대어 통행하는 경우가 일반적이어서 안전사고의 위험에 직접 노출되는 경우가 많다. 이에 국토해양부에서는 최근 "도로의 구조 및 시설기준에 관한 규칙"을 개정하여 국내의 보행자 관련 교통사고로 인한 사망자가 전체 교통사고 사망자의 약 절반을 차지하는 실정을 고려하여 보행자의 안전한 통행로 확보를 통해 보행공간의 근본적인 개선이 불가피한 실정임을 시사 하였다. 이에 국내에서는 교량 보도부의 확장에 대한 관심이 높은 실정이며, 현재 보도부 확장에 대한 시공이 활발하게 이뤄지고 있다. 그러나 기존 교량에 보도부를 신설 혹은 확장함에 있어서 보도부 부재의 설치 간격 및 필요한 앵커볼트의 수량 및 부재의 성능 평가에 대한 기준이 명확하게 이뤄지지 않은 상태에서 설치되어져 왔었다. 기존에 시공되던 H-형강의 브라켓 단면의 경우 브라켓 단면의 중량이 커서 안정성 및 시공성이 떨어지며 과다한 앵커볼트의 체결 및 브라켓 단면의 과다설계로 인한 공사기간 및 비용의 증대를 가져오는 문제점이 있었다. 이에 본 연구에서는 교량 보도부의 확장 및 신설에 있어서 보도부 부재의 설치간격의 적정성 및 브라켓의 최적화를 위한 브라켓의 성능평가 시험을 수행하였다. 브라켓의 성능평가 시험은 1차 2차 3차 시험으로 나누어 진행되었으며, 1차시험은 H-형강의 브라켓단면을 원형강관으로서의 대체 가능성을 확인하였고, 2차 시험에서는 원형강관의 브라켓 단면의 앵커볼트수량의 최적화에 대한 시험을 수행하였으며, 3차 시험은 최적화된 브라켓 단면에 프리스트레싱의 도입으로 반력 및 인발력의 감소효과를 확인하는 연구를 수행하였다. 본 연구의 수행결과 기존의 설계 및 시공방법이 과다 설계가 이뤄졌음을 판단하였고, 브라켓 단면의 최적화를 통하여 기존 시공방법에 비해 시공성, 안전성, 경제성을 높일수 있을 것으로 판단된다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.4
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• pp.221-232
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• 2023

This paper presents a novel convolutional neural network (CNN)-based approach for predicting bolt clamping force in the early bolt loosening state of bolted structures. The approach entails tightening eight bolts with different clamping forces and generating frequency responses, which are then used to create a similarity map. This map quantifies the magnitude and shape similarity between the frequency responses and the initial model in a fully fastened state. Krylov subspace-based model order reduction is employed to efficiently handle the large amount of frequency response data. The CNN model incorporates a regression output layer to predict the clamping forces of the bolts. Its performance is evaluated by training the network by using various amounts of training data and convolutional layers. The input data for the model are derived from the magnitude and shape similarity map obtained from the frequency responses. The results demonstrate the diagnostic potential and effectiveness of the proposed approach in detecting early bolt loosening. Accurate bolt clamping force predictions in the early loosening state can thus be achieved by utilizing the frequency response data and CNN model. The findings afford valuable insights into the application of CNNs for assessing the integrity of bolted structures.

• Journal of Bio-Environment Control
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• v.29 no.4
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• pp.473-479
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• 2020

In this study, the structural experiment was conducted with two types of specimens to investigate the mechanical behavior of the column-rafter-purlin connection of an arch-type greenhouse under monotonic loading. Based on the experimental results, the flexural performance was analyzed for two types of connections, and connection classification was attempted. Type B showed 77% of flexural performance compared to Type A, and both types showed that the rigidity and flexural strength did not reach the level of the full rigid. The behavior of the column-rafter-purlin connection was dominated by local buckling due to deformation of the weld and fasteners. As a result of connection classification by AISC standard, both Type A and B connections showed a result that did not meet the rigid connection performance assumed during design, and were classified as simple connection. Therefore, the connection performance evaluation and classification results show that the greenhouse design should be made in consideration of connection performance and in order to design a reliable greenhouse structure, a study on establishing clear design standards for the greenhouse connection is necessary.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.427-438
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• 2016

This study is experimental research for the effect of gap at the end plate on the performance of extended end-plate type splice. For this research, simple beam type specimens by using extended end-plate type splice are planned. Main variables are the initial gap between end-plates, the installation of finger shim plate before the installation of high tension bolts, the final gap between end-plates, and the installation of finger shim plate after the installation of high tension bolts. The static loading tests results show that the maximum bending strength of splice is not dependent on the gap, but the vertical displacement, initial stiffness and elastic stiffness are affected by the gap. In addition to that, the possibility of brittle fracture is increased when the torque of high tension bolt is used to control the gap. Thus, careful consideration is needed in this case.