• Title/Summary/Keyword: local imperfection

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Ultimate Axial Strength of Longitudinally Stiffened Cylindrical Steel Shell for Wind Turbine Tower (풍력발전 타워용 종방향 보강 원형단면 강재 쉘의 극한압축강도)

  • Ahn, Joon Tae;Shin, Dong Ku
    • Journal of Korean Society of Steel Construction
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    • v.29 no.2
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    • pp.123-134
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    • 2017
  • Ultimate axial strength of longitudinally stiffened cylindrical steel shells for wind turbine tower was investigated by applying the geometrically and materially nonlinear finite element method. The effects of radius to thickness ratio of shell, shape and amplitude of initial imperfections, area ratio between effective shell and stiffener, and stiffener spacing on the ultimate axial strength of cylindrical shells were analyzed. The ultimate axial strengths of stiffened cylindrical shells by FEA were compared with design buckling strengths specified in DNV-RP-C202. The shell buckling modes obtained from a linear elastic bifurcation FE analysis as well as the weld depression during fabrication specified in Eurocode 3 were introduced in the nonlinear FE analysis as initial geometric imperfections. The radius to thickness ratio of cylindrical shell models was selected to be in the range of 50 to 200. The longitudinal stiffeners were designed according to DNV-RP-C202 to prevent the lateral torsional buckling and local buckling of stiffeners.

Ultimate Strength Analysis of Connections of Floating Pendulum Wave Energy Converter (부유식 진자형 파력발전장치의 연결부 최종강도해석)

  • Sohn, Jung Min;Cheon, Ho Jeong;Shin, Seung Ho;Hong, Key Yong
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.17 no.1
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    • pp.36-41
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    • 2014
  • A floating offshore structure has high tendency to occur the buckling when compressive, bending and shear loads applied. When the buckling is occurred, in-plane stiffness of structure is remarkably decreased. And it has a harmful effect on the local structural strength as well as global structural strength. In the present study, it has been investigated the ultimate strength of tubular members which is located between a floater and a damping plate of the floating pendulum wave energy converter. Nonlinear finite element method is conducted using the initial imperfection according to 1st buckling mode which is obtained from the elastic buckling analysis. It is also noted the ultimate bending strength characteristic varying with a diameter, thickness and stiffeners of the tubular member.

Inelastic Analysis of Steel-Concrete Composite Column with Non-Compact Steel Section (비조밀단면을 가진 SC 합성 기둥의 비선형 해석)

  • Oh, Myoung Ho;Jang, Tae Young;Kim, Myeong Han;Kim, Dae Joong;Kim, Sang Dae
    • Journal of Korean Society of Steel Construction
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    • v.17 no.1 s.74
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    • pp.63-71
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    • 2005
  • There were already several studies conducted on the steel-concrete (SC) composite column, which was developedcomplement the weaknesses and maintain the advantages of previous composite columns. The axial compressive capacity of the SC composite column was estimated by the tests in previous studies, but the experiments for the large-scale column could not be performed because of the limitation with the laboratory's capacity. In this study, the analytical study was performed using the general finite element analysis program to reflect the interaction of concrete and steel and the local buckling of steel flange composed of the non-compact section. The appropriateness of the analytical model was verified by the comparison between experimental and analytical results. The nonlinear behavior of full-scale SC composite column was analyzed using the verified analytical model. From these analytical studies, it was concluded that the width-to-thickness ratio of the steel cross-section of the SC composite column should not exceed 25:0. The section area of the link is best when it is over 0.025 dt, and the link distance is to be less than D/2 or 300mm.

Flexural Strength of HSB Steel Girders Due to Inelastic Lateral-Torsional Buckling - Sections with Slender Web (HSB 강거더의 비탄성 횡비틂좌굴에 의한 휨강도 - 세장 복부판 단면)

  • Cho, Eun-Young;Shin, Dong-Ku
    • Journal of Korean Society of Steel Construction
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    • v.24 no.2
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    • pp.217-231
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    • 2012
  • The flexural behavior of HSB I-girder with a non-slender web attributed to inelastic lateral-torsional buckling under uniform bending was investigated using nonlinear finite element analysis of ABAQUS. The girder was assumed to have a compact or noncompact web in order to prevent premature bend-buckling of the web. The unbraced length of the girder was selected so that inelastic lateral-torsional buckling governs the ultimate flexural strength. The compression flange was also assumed to be either compact or noncompact to prevent local buckling of the elastic flange. Both homogeneous sections fabricated from HSB600 or HSB800 steel and hybrid sections with HSB800 flanges and SM570-TMC web were considered. In the FE analysis, the flanges and web of I-girder were modeled as thin shell elements. Initial imperfections and residual stresses were imposed on the FE model. An elasto-plastic strain hardening material was assumed for steel. After establishing the validity of the present FE analysis by comparing FE results with test results in existing literature, the effects of initial imperfection and residual stress on the inelastic lateral-torsional buckling behavior were analyzed. Finite element analysis results for 96 sections demonstrated that the current inelastic strength equations for the compression flange in AASHTO LTFD can be applied to predict the inelastic lateral torsional buckling strength of homogeneous and hybrid HSB I-girders with a non-slender web.

Role, Change, Job Satisfaction and Obstacles in Carrying out the Role of Public Health Nurses in Health Center (보건소 보건간호사의 역할변화, 역할수행의 장애요인과 만족도)

  • Ahn, Kyeong-Sook;Jung, Moon-Sook
    • Journal of agricultural medicine and community health
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    • v.20 no.1
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    • pp.1-13
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    • 1995
  • Based on the questionnaires sent to 270 nurses of public health centers in kyungnam during the period of March 19 to April 11 in 1992, this study was written for the of finding out the grade of satisfaction, obstacles in carrying out duties concerned with nursing services and the change of nurses role needed according to the change of the local public health administration. The first-ranking tasks carried by nurses of public health center are believed to have been family planning activities before the 1970's, nursing services during the 1970's, mother-child health activities during the 1980's, and nursing services during the period of 1990 to 1992. As far as the priority order of all the family planning activities is concerned, the counseling of the insertion of intrauterine contraceptive device, the use of oral pill or the distribution of condom was placed emphasis on before 1970, and publicity activities of family planning after that time. The first priority order of mother-child health activities has been put on the registration of pregnant women since 1970, with prenatal examination and vaccination ranking next to it. The priority order for activities against tuberculosis was laid on finding out and registration of new T.B. patients every year, with patients' control, and medication or injection ranking next to it. As for the priority order of nursing services, traveling medical examination and treatment ranked the first-stressed activity before 1970, with medication and injection ranking next to it. The first priority order management activity of communicable diseases was put on vaccination before 1970, with medication and injection. ranking next. And consultation and education ranked second to it during 1990 to 1992. As for the health services of the aged, traveling examination and treatment ranked the order, with the assistance of medical examination ranking next to it. As far as troubles and obstacles shown in case of family planning, the rate of residents' lack understanding was 28.8%, that of lacking budget 13.6%, and the imperfection of public health administration system 11.9%. In the case of tuberculosis control, residents' lacking understanding was 32.5%, the deficiency of public health administration system 18.2%, over-duty(shortage of hands) 15.6%, and the insufficiency skill and know-how 13.0%. In the case of nursing services, the deficiency of public health administration system was 18.2%, each over-duty(the shortage of hands) and the shortage of facilities and equipment 15.6% respective, and residents' lacking understanding 13.0%. The rate of dissatisfaction with the chance or possibility of promotion for his or her career or capability was shown to be 49.2%, and 65.9% of the health nurses expressed their complaints of the deficiency of the chance of the promotion to a professional or expert. when the public health nurses were asked in the questionably whether they were satisfied or not with current state of equipment and facilities needed for public health service, 49.6% of them answered in the negative. The grade of the satisfaction with the current individual position was shown to be low as much as the status of his or her position was now. 37.6% of those asked in the research answered to have the readiness to switch jobs for the reasons of dissatisfaction and so on with lacking promotion chance as well as bad working condition. Significant correlation between the grade of job satisfaction and the current status of the po as found to be in this research, which showed that the lower the status of position was, the lower the grade of job satisfaction was. But little correlation between the grade of job satisfaction and his or her schooling and career was found. In order to carry out primary health care successfully, it can be said that more education and publicity activities to make public health nurses and residents see it in a new light are requested. In addition to it, it is suggested that the improvement of promotion system for public health nurses and the enlargement of job province should also be taken in consideration of the high dissatisfaction with and complaints of the chance of promotion and the system of position. In order words, it is important that considerations for system improvement enough to make nursing services pleasant and satisfactory should be taken into.

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