Local governments usually have ultimate authority over local building codes. Nonetheless, with the exception of a few areas with very unique wind environments (New York City’s urban canyons and Miami’s hurricane-prone beach fronts, for example), most local building codes are built upon one of several standards that vary from one country to another.
As this portrait of global aerosols above shows, overall wind patterns are different at different latitudes. These differences are even greater as local effects are taken into account.
Generally speaking, wind codes are not mutually compatible because each code is built upon its own set of assumptions, the most obvious of which is wind speed basis. The calculations in ASCE/SEI 7-10, for example, are based on a three-second gust, which is a wind speed that:
Other wind codes use different wind speeds. For example, Eurocode’s calculations are built around a wind speed averaged for 10 minutes. Using Eurocode’s methods with a wind speed taken from ASCE/SEI 7-10 will yield inaccurate results.
Because wind codes are inherently generic, they usually (though not always) predict wind forces that are higher than what is seen in nature, when applied correctly. Wind tunnel testing more accurately characterizes the specific wind-related phenomena of interest to a specific structure and, in many cases, produces lower design loads than calculated using a wind code.
Originally published: December 28, 2014