風を受ける鋼製煙突の楕円変形に関する構造力学的考察

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タイトル別名
  • SOME STRUCTURAL CONSIDERATIONS ON OVALLING OF STEEL STACKS UNDER THE WIND ACTION
  • カゼ オ ウケル コウセイ エントツ ノ ダエン ヘンケイ ニ カンスル コウゾウ リキガクテキ コウサツ
  • Structural dynamical consideration of the ovalling deformation of steel stacks under wind

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On a large steel stack, with poor lining, its circular cross-section tends to deform under the wind action. This phenomenon is treated in the field of aeroelasticity, which is discussed generally as the problem of ovalling. At first, in this paper, Reynolds numbers which play an important roll on that problem are found. The relation of the wind pressure distributions around the stack to Reynolds numbers is obtained from the experimental reports published by other authors. Secondarily, from the viewpoint of structure, the deformation due to the static pressure is derived. To avoid the resonance, we get the natural frequency of a stack in simple fomula. Conclusions are as follows: 1) The wind pressure distribution around the circular section depends on Reynolds numbers. 2) In the case of large steel stacks, which are found often in power stations, Reynolds numbers are included in the range of 10^6〜10^7 corresponding to the wind velocity of 10 60m/s. 3) If the cylindrical shell of the steel stack should resist against the oval deformation, without lining or other stiffeners, the shell thickness must be more than 1/170〜1/180 of the radius of the stack. Moreover, since the displacement in this case comes to 10 or 20 percents of the radius, the resistant strength to the local buckling of the cylindrical shell reduces by half. 4) To avoid the cylindrical shell becoming thicker, the considerably strong lining or the longitudinal ribs on the outer-surface must be set up. 5) The approximation of the natural frequency for ovalling is obtained from Flugge's equations. Its first term in the former corresponds to the frequency of a ring and other for a membrane. Calculating the periods of some actual steel stacks without lining from our equation, it is found that in ovalling the resonance wind velocity is usually of 13〜18m/s, which will be lower than in cantilever vibration.

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