ABSTRACT
In practice, evaluation of gust action is commonly based on classification of ^o in three steps: £o = 0.003 m for very smooth surfaces typified by tundra or water (correction for sea surface roughness is possible as a function of storm strength), £o = 0.03 m for typical UK inland countryside, ^Q = 0.3 m for suburban housing and forests. Although higher values of ^o are possible (e.g. for city centres), the basic presumption of a generalized statistical pattern is unreliable (see buffeting, Section 3.2.6); an estimate of structural response based on the model for suburban roughness will give a conservative estimate of the mean load and probably of the peak gust response, but may underestimate the specifically dynamic action. An ad hoc wind tunnel test will give valuable additional information in such cases, but interpretation is beyond the scope of this chapter.
