風荷重を受けるクーリングタワーの動的挫屈解析

概要

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A new method for analysis of response of cooling towers due to wind loads is presented based on the finite element method. This method avoids the direct finite element analysis of nonlinear effects and also takes advantage of the important feature that structure response is primarily due to several basic lateral vibration modes, reducing the number of unknowns to a few in contrast to the direct finite element approach. The two in-plane displacements u and v are obtained compatible with the assumed lateral displacement ω composed of free vibration modes and the unknowns, the generalized modal displacements, are determined based on Hamilton's Principle and the governing cquations for the modal displacements are numerically solved by Newmark's β scheme. A cooling tower due to a wind load of step type goes snapped at the upper rim and the dynamic buckling load is just the same as the predicted value from the experiment by Der, T. J. and Filder, R.. In the present case, the critical head at throat, H=113.76m, is 1.068t/m^2 for R/t=159, which corresponds to C=0.058 in Der's experimental formula. The assumed wind composed from Davenport's spectrum for random winds, with an ordinary speed V_<max>=80 m/sec at throat, does not give the cooling tower any nonlinear effect but the dynamic effect of wind increases the dynamic response at throat about 60% larger than that in static response.
1976-05-30