Estimation of along-wind moments in RC chimneys

This paper reviews the prevailing international codal recommendations to determine the design along-wind moments in reinforced concrete (RC) chimneys and towers. A comparative study reveals significant disparities among the various codal estimates of the design moments, given the same basic wind speed and terrain condition. These disparities are a matter of concern to practising chimney designers and approving authorities in many countries. The relative accuracy of these differing estimates, which are based on different gust factor methods, have been quantitatively assessed with reference to rigorous stochastic dynamic analyses. This study covers a number of linearly tapered RC chimneys with heights in the range 100-400 m, located in different terrain conditions and subject to the range of wind speeds encountered in practice. It is observed that the estimates of the design moments are generally conservative in varying degrees, and are unconservative only in some cases. In very rough terrains, the lack of appropriate design provisions results in extremely conservative designs. With a view to improving the accuracy in the predictions, modifications to the gust factor method have been proposed in this paper. Copyright © 1996 Elsevier Science Ltd.