• International Journal of Ocean System Engineering
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• 제3권4호
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• pp.175-187
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• 2013

Moonpools are vertical wells in a floating body used onboard many types of vessels like Exploration and drilling vessels, Production barges, Cable-laying vessels, Rock dumping vessels, Research and offshore support vessels. Moonpool gives passage to underwater activities for different types of ships as per their mission requirements. It is observed that inside a moonpool considerable relative motions may occur, depending on shape, depth of the moonpool and on the frequency range of the waves to which the ship is exposed. The vessel responses are entirely different in zero and non-zero Froude number. Former situation is paid attention in this study as the mission requirement of the platform is to be in the particular location for long period of operation. It is well known that there are two modes of responses depending on the shape of the moonpool viz., piston mode for square shape and sloshing mode for rectangular shapes with different aspect ratios of opening like 1:1.5 and 1:2 ratios. Circular shaped moonpool is also tested for measuring the responses. The vessel moored using heavy lines are modelled and tested in the wave basin. The pretensions of the lines are varied by altering the touchdown points and the dynamic tensions on the lines are measured. The different modes of oscillations of water column are measured using wave gauge and the vessel response at a particular situation is determined. RAOs calculated for various situations provide better insight to the designer.

• Ocean Systems Engineering
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• 제3권2호
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• pp.137-147
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• 2013

Moonpools are vertical wells in a floating body used onboard many types of vessels like cable-laying vessels and offshore support vessels. Moonpool gives passage to underwater activities for different types of ships as per their mission requirements. It is observed that inside a moonpool considerable relative motions may occur, depending on shape, depth of the moonpool and on the frequency range of the waves to which the ship is exposed. The vessel responses are entirely different in zero and non-zero Froude number. Former situation is paid attention in this study as the mission requirement of the platform is to be in the particular location for long period of operation. It is well known that there are two modes of responses depending on the shape of the moonpool viz., piston mode for square shape and sloshing mode for rectangular shapes with different aspect ratios of opening like 1:1.5 and 1:2 ratios. Circular shaped moonpool is also tested for measuring the responses. The vessel moored using heavy lines are modeled and tested in the wave basin. The moored lines are provided with pre-tension and the dynamic tensions on the lines are measured. The different modes of oscillations of water column are measured using wave gauge and the vessel response at a particular situation is determined. RAOs determined for various situations provide better insight to the designer. The experiments done in the wave basin may also be compared with a software package meant for handling moored floating bodies.

• Steel and Composite Structures
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• 제12권1호
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• pp.73-92
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• 2012

The effect of element interaction and material nonlinearity on the ultimate capacity of stainless steel plated cross-sections is investigated in this paper. The focus of the research lies in cross-sections failing by local buckling; member instabilities, distortional buckling and interactions thereof with local buckling are not considered. The cross-sections investigated include rectangular hollow sections (RHS), I sections and parallel flange channels (PFC). Based on previous finite element investigations of structural stainless steel stub columns, parametric studies were conducted and the ultimate capacity of the aforementioned cross-sections with a range of element slendernesses and aspect ratios has been obtained. Various design methods, including the effective width approach, the direct strength method (DSM), the continuous strength method (CSM) and a design method based on regression analysis, which accounts for element interaction, were assessed on the basis of the numerical results, and the relative merits and weaknesses of each design approach have been highlighted. Element interaction has been shown to be significant for slender cross-sections, whilst the behaviour of stocky cross-sections is more strongly influenced by the material strain-hardening characteristics. A modification to the continuous strength method has been proposed to allow for the effect of element interaction, which leads to more reliable ultimate capacity predictions. Comparisons with available test data have also been made to demonstrate the enhanced accuracy of the proposed method and its suitability for the treatment of local buckling in stainless steel cross-sections.

• 대한전자공학회논문지
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• 제15권5호
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• pp.19-24
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• 1978

기계적 진동 주파수와 파형, 2점식별 thresho1d 치, 접촉자의 크기에 대한 피체 진동촉각의 기능적 성질을 심리물리실험에 의해 연구했다. 이의 실험 결과를 기초로 하여 압전 진동소자를 이용한 진동촉각 자극장치를 제작하여 한글을 인식하기 위한 맹인용 시각보조 장치로써 제안했다. 촉각출력상은 200 Hz의 구형파에 의해 진동하는 8열×l행의 소형 진동자열에 의해 집게 손가락에 표시했다. NOVA미니컴퓨터의 제어에 의해 한글 자모 24자중 하나를 택하여 진동자열의 8점에 왼쪽에서 오른쪽으로 제시하도록 했다. 한글 식별률실험은 설계한 실험시스템에 의해 학습효과없이 행했으며 측정된 평균식별률은 90%였다.

• Steel and Composite Structures
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• 제3권3호
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• pp.153-168
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• 2003

This paper discusses the results and observations from a large-scale fire test conducted on a slim floor system, comprising asymmetric beams, rectangular hollow section beams and a composite floor slab. The structure was subjected to a fire where the fire load (combustible material) was higher that that found in typical office buildings and the ventilation area was artificially controlled during the test. Although the fire behaviour was not realistic it was designed to follow as closely as possible the time-temperature response used in standard fire tests, which are used to assess individual structural members and forms the bases of current fire design methods. The presented test results are limited, due to the malfunction of the instrumentation measuring the atmosphere and member temperatures. The lack of test data hinders the presentation of definitive conclusions. However, the available data, together with observations from the test, provides for the first time a useful insight into the behaviour of the slim floor system in its entirety. Analysis of the test results show that the behaviour of the beam-to-column connections had a significant impact on the overall structural response of the system, particularly when the end-plate of one of the connections fractured, during the fire.

• Steel and Composite Structures
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• 제31권3호
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• pp.291-301
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• 2019

Pure torsion loading conditions were not frequently occurred in practical engineering, but the torsional researches were important since it's the basis of mechanical property researches under complex loading. Then a 3D finite element model with precise material constitutive models was established, and the effectiveness was verified with test data. Parametric studies with varying factors as steel yield strength, concrete strength and sectional height-width ratio, were performed. Internal stress state and the interaction effect between encased steel tube and the core concrete were analyzed. Results indicated that due to the confinement effect between steel tube and core concrete, the torsional strength of CFT columns was greatly improved comparing to plain concrete columns. The steel ratio would greatly influence the torque share between the steel tube and the core concrete. Then the torsional strength calculation formulas for core concrete and the whole CFT column were proposed. The proposed formula could be simpler and easier to use with guaranteed accuracy. Related design codes were more conservative than the proposed formula, but the proposed formula presented more satisfactory agreement with experimental results.

• Steel and Composite Structures
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• 제46권2호
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• pp.153-173
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• 2023

Rectangular concrete-filled steel tubular (RCFST) column, a type of concrete-filled steel tubular (CFST), is widely used in compression members of structures because of its advantages. This paper proposes a robust machine learning-based framework for predicting the ultimate compressive strength of RCFST columns under both concentric and eccentric loading. The gradient boosting neural network (GBNN), an efficient and up-to-date ML algorithm, is utilized for developing a predictive model in the proposed framework. A total of 890 experimental data of RCFST columns, which is categorized into two datasets of concentric and eccentric compression, is carefully collected to serve as training and testing purposes. The accuracy of the proposed model is demonstrated by comparing its performance with seven state-of-the-art machine learning methods including decision tree (DT), random forest (RF), support vector machines (SVM), deep learning (DL), adaptive boosting (AdaBoost), extreme gradient boosting (XGBoost), and categorical gradient boosting (CatBoost). Four available design codes, including the European (EC4), American concrete institute (ACI), American institute of steel construction (AISC), and Australian/New Zealand (AS/NZS) are refereed in another comparison. The results demonstrate that the proposed GBNN method is a robust and powerful approach to obtain the ultimate strength of RCFST columns.

• Computers and Concrete
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• 제33권3호
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• pp.285-299
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• 2024

Recently, many engineering computations have realized their digital transformation to Machine Learning (ML)-based systems. Predicting the behavior of a structure, which is mainly computed with structural analysis software, is an essential step before construction for efficient structural analysis. Especially in the seismic-based design procedure of the structures, predicting the lateral load capacity of reinforced concrete (RC) columns is a vital factor. In this study, a novel ML-based model is proposed to predict the maximum lateral load capacity of RC columns under varying axial loads or cyclic loadings. The proposed model is generated with a Deep Neural Network (DNN) and compared with traditional ML techniques as well as a popular commercial structural analysis software. In the design and test phases of the proposed model, 319 columns with rectangular and square cross-sections are incorporated. In this study, 33 parameters are used to predict the maximum lateral load capacity of each RC column. While some traditional ML techniques perform better prediction than the compared commercial software, the proposed DNN model provides the best prediction results within the analysis. The experimental results reveal the fact that the performance of the proposed DNN model can definitely be used for other engineering purposes as well.

• 한국구조물진단유지관리공학회 논문집
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• 제19권2호
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• pp.10-21
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• 2015

합성구조의 안전성의 보장을 위해 대부분의 설계기준은 경험적 사실을 기반으로 강재의 설계기준항복강도의 상한선을 제시하고 있다. 그러나 세장비가 큰 콘크리트충전강관기둥과 같이 탄성 좌굴하중에 영향을 받는 부재의 경우 설계강도를 크게 낮게 평가함에 따라 비경제적 설계가 수행될 경우가 발생한다. 따라서 세장한 기둥의 경제적 설계를 위해 현행 설계기준에서 제시하고 있는 강재의 설계기준항복강도 이상의 항복강도를 보유한 강재가 사용될 경우 설계기준의 안전성에 대한 평가를 수행하였다. 다양한 경우에서의 높은 설계기준항복강도의 적용성 평가를 위하여 유한요소해석을 사용한 변수분석을 계획하였으며, 680MPa 급의 항복강도를 보유한 강재가 적용된 세장한 직사각형 콘크리트 충전 강관기둥의 실험을 수행하여 유한요소해석 모델의 적합성 평가와 고강도 강재의 적용성 평가를 수행하였다. 변수분석에 적용된 변수는 강재의 항복강도, 콘크리트의 설계기준압축강도, 강재의 두께와 세장비로 구성되었다. 각 변수들은 KBC 2009에 의한 강도와 비교되었다. 54개의 모델에 대한 변수분석 결과와 기 수행 연구결과들을 통해 세장한 직사각형 콘크리트 충전 강관기둥은 KBC에서 제안하고 있는 강재항복강도의 제한을 초과할 경우에도 안전하게 설계될 수 있는 것으로 나타났다.

• 콘크리트학회논문집
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• 제13권1호
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• pp.46-53
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• 2001

본 연구에서는 PCI 방법으로 설계한 직사각형보의 댑 전단거동을 구명키 위해 실물 크기의 두 개의 보 네 개의 댑단부에 대하여 실험하였다. 적용된 설계 활하중 500kgf/$m^2$은 주차장, 1,200kgf/$m^2$은 매장을 위한 국내설계기준이다. 보의 하단폭은 5층 정도의 매장 또는 주차장건물의 하부 기둥크기와 동일하게 60cm로 하였고, 댑의 깊이는 PCI에서 허용하는 최대치 내에서 하부 플랜지높이의 절반을 적용하였다. 대상 실물 실험체는 PCI 설계에 충분히 만족하도록 설계하였으나, 네 개의 실험체중 활하중 1200kgf/$m^2$를 위한 두 개의 실험체는 사용하중이전에 초기균열이 발생되었고 예측강도에 훨씬 못 미치는 하중에서 니브의 수직 전단파괴에 의하여 종국파괴되었다. 니브 수직전단파괴를 일으킨 활하중 1200kgf/$m^2$실험체의 최종 파괴강도는 77.22tonf과 78.36tonf으로 PCI의 81.9tonf과 ACI의 65.62tonf 사이 값으로 ACI의 예측식에 상회하나 PCI 제안 값에 미달하여 발생하였으므로 ACI제안 방식이 안전적인 측면을 고려할 때 더 합리적인 것으로 사료된다. 모든 하중-변형률곡선에서 걸이철근(Ash)의 변형률이 항복변형률에 도달할 정도로 가장 두드러졌다. 강도를 개선하기 위하여 추가적인 경사 걸이 철근이 필요한 것으로 판단된다.