• Title/Summary/Keyword: admissible limit

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Dynamic response of functionally graded annular/circular plate in contact with bounded fluid under harmonic load

  • Yousefzadeh, Sh.;Jafari, A.A.;Mohammadzadeh, A.;Najafi, M.
    • Structural Engineering and Mechanics
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    • v.65 no.5
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    • pp.523-533
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    • 2018
  • In this study, the dynamic response of a functionally graded material (FGM) circular plate in contact with incompressible fluid under the harmonic load is investigated. Analysis of the plate is based on First-order Shear Deformation Plate Theory (FSDT). The governing equation of the oscillatory behavior of the fluid is obtained by solving Laplace equation and satisfying its boundary conditions. A new set of admissible functions, which satisfy both geometrical and natural boundary conditions, are developed for the free vibration analysis of moderately thick circular plate. The Chebyshev-Ritz Method is employed together with this set of admissible functions to determine the vibrational behaviors. The modal superposition approach is used to determine the dynamic response of the plate exposed to harmonic loading. Numerical results of the force vibrations and the effects of the different geometrical parameters on the dynamic response of the plate are investigated. Finally, the results of this research in the limit case are compared and validated with the results of other researches and finite element model (FEM).

Stability assessment of tunnel face in a layered soil using upper bound theorem of limit analysis

  • Khezri, Nima;Mohamad, Hisham;Fatahi, Behzad
    • Geomechanics and Engineering
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    • v.11 no.4
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    • pp.471-492
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    • 2016
  • Underground tunnelling is one of the sustainable construction methods which can facilitate the increasing passenger transportation in the urban areas and benefit the community in the long term. Tunnelling in various ground conditions requires careful consideration of the stability factor. This paper investigates three dimensional stability of a shallow circular tunnel in a layered soil. Upper bound theorem of limit analysis was utilised to solve the tunnel face stability problem. A three dimensional kinematic admissible failure mechanism was improved to model a layered soil and limiting assumptions of the previous studies were resolved. The study includes calculation of the minimum support pressure acting on the face of the excavation in closed-face excavations. The effects of the characteristics of the layers on the minimum support pressure were examined. It was found that the ratio of the thickness of cover layers particularly when a weak layer is overlying a stronger layer, has the most significant influence on the minimum tunnel support pressure. Comparisons have been made with the results of the numerical modelling using FLAC3D software. Results of the current study were in a remarkable agreement with those of numerical modelling.

Analysis of the Corner Cavity of Axisymmetric Backward Extrusion by the Upper Bound Approach (상계해석을 이용한 축대칭 후방압출 공정의 Corner Cavity 해석)

  • 박재훈;변홍석;김영호
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.2
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    • pp.144-150
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    • 2000
  • In this paper, the formation of a corner cavity in the final stage of axisymmetric backward extrusion process is studied by means of upper bound analysis using kinematically admissible velocity. The quantitative relationships between corner cavity formation and process parameters are studied. And analytical results are compared with those of experiment to which plasticine is used. It is found that the analytical results agree well with experimental one. In addition, to restrict the formation of a corner cavity, driven container is applied to backward extrusion and the results are compared with those of FEM. The critical thickness of the bottom of the billet decreases with increase in reduction of area, and increases with decrease in friction. To prevent the formation of corner cavity, the concept of moving container was applied. Throughout this process, the occurrence of a corner cavity is delayed and forming limit area is enlarged.

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Assessment of Tunnel Collapse Load by Closed-Form Analytical Solution and Finite Element Analysis (근사적인 해석법과 유한요소해석에 의한 터널붕괴하중 평가)

  • Lee, Yong-Joo
    • Journal of the Korean Geotechnical Society
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    • v.23 no.4
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    • pp.185-197
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    • 2007
  • Limit analysis of upper and lower bound solutions has been well developed to provide the stability numbers for shallow tunnels in cohesive soil ($c_u$ material), cohesive-frictional soil (c'-$\phi$' material) and cohesionless soil ($\phi$'material). However, an extension of these methods to relatively deep circular tunnels in the cohesionless soil has been explored rarely to date. For this reason, the closed-form analytical solutions including lower bound solution based on the stress discontinuity concept and upper bound solution based on the kinematically admissible failure mechanism were proposed for assessing tunnel collapse load in this study. Consequently, the tunnel collapse load from those solutions was compared with both the finite element analysis and the previous analytical bound solutions and shown to be in good agreement with the FE results, in particular with the FE soil elements located on the horizontal tunnel axis.

New J Testing Method Using Load-COD Curve for Circumferential Through-Wall Cracked Pipes under Bending (하중-균열열림변위를 이용한 굽힘하중이 작용하는 원주방향 관통균열 배관의 새로운 J 실험법)

  • Huh Nam-Su;Kim Yun-Jae;Kim Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.1 s.244
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    • pp.60-65
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    • 2006
  • The present paper provides experimental J estimation equation for the circumferential through-wall cracked pipe under four-point bending, based on the load-crack opening displacement (COD) record. Based on the limit analysis and the kinematically admissible rigid-body rotation field, the plastic ${\eta}$-factor for the load-COD record is derived and is compared with that for the load-load line displacement record. Comparison with the J results from detailed elastic-plastic finite element (FE) analysis shows that the proposed method based on the load-COD record provides reliable J estimates even for shallow cracks, whereas the conventional approach based on the load-load line displacement record gives erroneous results for shallow cracks. Thus, the proposed J estimation method could be recommended for testing the circumferential through-wall cracked pipe, particularly with shallow cracks.