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Design wind speeds for various return periods are provided in most national design codes throughout the world (e.g., NBCC 2010, ASCE 7-10). The design wind speeds are often based on an extreme value analysis of historical data obtained from a number of meteorological stations distributed over the region of interest. However, only the extreme wind speed magnitude is typically available to the designer, which does not provide information on the directional characteristics or underlying probability distribution of the wind. These parameters of the local wind characteristics may be useful for designers of directionally-sensitive structures or for higher-order reliability-based design. This paper describes an analysis of wind records obtained from discrete meteorological stations and the methods used to develop estimates of wind speed and directionality. The trends in wind speed and direction for a set of stations are also discussed. Following this, statistical wind parameters (including wind speed and direction) can be extracted for a number of locations within the study area. These values can be subsequently used to assess the reliability of one or more point structures, or a distributed system. The results are compared with those based on a traditional Gumbel (Type I) extreme value analysis for the same set of station data.

Transmission towers play a vital role in power distribution networks and are often subject to strong wind loads. Lattice tower design is often based on a linear elastic response to wind loading using methodology derived for atmospheric boundary layer (ABL) winds. A number of failures have been attributed to high intensity wind (HIW) events such as downbursts and tornadoes. This thesis investigates extreme winds on a self-supported lattice transmission tower and ultimately makes comparisons of the capacity under ABL and HIW. The force-deformation relation between the base shear and the displacement of the tip of the tower are used to represent the capacity curve of a structure under wind loading. Wind tunnel testing is used to evaluate the aerodynamic behaviour of a typical tower cross-arm section, which serves as the basis for selection of wind loading expressions for the numerical model. Recommendations are made for further investigation of lattice aerodynamics, including a more robust definition of the drag coefficient. Capacity estimates obtained using the incremental dynamic analysis (IDA) and nonlinear static pushover (NSP) procedures are compared, which indicate good agreement for ABL winds. The analyses consider both geometric and material nonlinearity. The NSP analysis is used to estimate the capacity of the tower under various wind profiles for the transverse and longitudinal wind directions, and it is shown that the capacity curve obtained under typical downburst scenarios can be approximately enveloped by those obtained under rectangular and ABL wind profiles. An uncertainty propagation analysis is carried out using the simple Monte Carlo technique, which shows that the coefficient of variation of the tower capacity is small compared to that associated with extreme wind load effects. Oblique wind directions are considered for ABL, rectangular and downburst wind loading, which associate critical wind speeds with direction. The resulting capacity curves are used to develop the capacity surface of the tower. It is shown that a conservative approximation of the tower capacity curve, or surface, under downburst wind is made if a fully correlated ABL wind loading profile is used as the wind load distribution.