Aerodynamic Coefficients and Risk‐consistent Design

A simple procedure is presented for estimating the reliability of windsensitive structures whose orientation is not specified. The procedure is based on a second moment reliability approach and makes use of: (1) Aerodynamic coefficients obtained experimentally as functions of wind direction, and (2) climatological data consisting of sets of largest annual speeds associated with winds blowing from each of the 8 (or 16) compass directions. An illustration of the procedure, based on sets of actual data, is presented. It is then shown that the tools presented in the paper can be applied to develop, from directional, aerodynamic, and climatological data, nominal aerodynamic coefficients which in effect reduce wind loads with respect to those inherent in current U.S. practice, in a manner that reflects the directional dependence of both the aerodynamic behavior of structures and the extreme wind climate, while being consistent with respect to failure risk. These tools are first developed for the general case where the orientation of the structure is not known. It is then shown that criteria for risk‐consistent design for buildings with specified orientation can be derived immediately as a particular case from the criteria applying to structures whose orientation is unknown.