Actual ground-exposure determination and its influences in structural analysis and design

Wind exposure categories are currently used to account for the influences of different ground roughness in wind profile that is fundamentally important to wind-resistant structural analysis and design. Since each classified exposure covers a relatively large spectrum of ground roughness with constant indices such as exponent a. this results in uncertain wind-resistant structural analysis and design for structures in each and every categorized exposure. More importantly, such an uncertainty is not only quantitative but also qualitative in terms of aerodynamic instability assessment and economic loss estimation. This study proposes a method to determine the actual wind exposure and estimates its influences in wind-resistant structural analysis and design. In particular, this paper first provides a review of wind exposure categories and illustrates the shortcomings of its use in structural analysis and design. It then introduces a method to determine the actual ground exposure. The method generates formulae for the actual ground roughness exponent on the basis of measured data from both wind-tunnel and full-scale experiments, of ground roughness-induced wind energy dissipation analysis, as well as of current Chinese and other countries' loading codes. Through examples of hypothetical and practical engineering projects, this study finally investigates the influences of the actual ground roughness exponent on wind-induced structural responses and economic loss estimation, as well as on wind-resistant structural design. (C) 2001 Published by Elsevier Science Ltd.