Wind Effects on Structures

After several spectacular collapses caused by wind, there has been increased interest in the accurate prediction of the wind loading to which buildings and structures are subjected. The reliability of these design wind loads depends to a very large extent on the accurate prediction of the most severe wind conditions to be experienced for many years into the future, and on the accuracy of the wind force and pressure coefficients applicable to the structure. Many factors influence these coefficients and hitherto many of these factors have not been reproduced in measurements on models in wind tunnels, so much of the existing data is of uncertain reliability. For many structures it is sufficient to regard the wind as causing static loadings and for this purpose to use time-averaged wind forces. However, the advent of modern design and fabrication of structures has rendered them more prone to respond to the dynamic action of wind. Increasing attention is therefore being given to the time-dependency of the wind forces resulting either from the fluctuations of speed caused by the turbulence of natural wind, or from some form of aerodynamic instability arising from the interaction of the structure with the airstream. The calculation of the dynamic response to turbulent winds involves the application of statistical theories to calculate the maximum amplitude of the response (stress or displacement) and the frequency of its occurrence, coupled with the concept of an acceptable degree of risk that the structure will not fulfil its functional requirements during its lifetime.