ABSTRACT
Spectrum of horizontal gustiness Since the energy in the wind impinges on a structure through the mechanism of an interaction of gusts of wind with the structure, then it is important to know how much energy is present as a function of frequency. A spectrum may be generated directly from windspeed data. Alternatively, the spectrum of pressures may be presented through a linear transformation, or the ordinates may be weighted by the frequency to produce a nS(n) spectrum in which the power in the signal is represented as a function of frequency or of reduced frequency. The reason for presenting the data in this fashion is basically that in the nS(n) form the value of the energy in the wind can be fed directly into a formulation for the calculation of the response of a structure to such a wind. Indeed, the selection of a single value from such a representation at a frequency appropriate to a resonance of a structure can be used for a direct calculation of the response in that mode of vibration. An example is the formulation:
where 0.577
(5.10)
This equation implies that the response of a structure to a wind load can be thought of in terms of two basic parts. The first is essentially quasi-static and may be thought of as the response to the mean wind. The second part is the dynamic response and is the structure's response to the sub-inertial part of the spectrum at higher frequencies. The approach using equations (5.10) and (5.11) is that taken by the Engineering Sciences Data Unit in Item 76001. An example of its use is given in Appendix E.
