Building Codes such as ASCE 7, TIA-222, S37, and the Euro Codes stipulate that, in the absence of site specific studies, extreme wind assessment must assume that the extreme wind can occur from any direction. This assumption can be a severe over-estimate of the the actual wind loading on the structure when the site is situated in complex terrain or the airport observation site has non-standard exposure, as is often the case.
ICE Inc has produced site specific assessments for thousands of sites over the past 12 years and noted many cases where the airport observations are affected by directional exposure differences and even topographic enhancements. Also quite often there is a large directional variation in extreme winds making the interaction with topographic features highly specific to the location of the site.
In some of these cases special studies were required to determine the applicability of the code prescription for extreme wind. As a result of these studies ICE has developed the methodology for providing directional extreme winds using hourly observations segregated into 8 sectors followed by terrain and topographic corrections specific to each of the sectors. This provides extreme wind profiles for each sector for any specified recurrence interval which allows for comparison of wind pressures over the height of the structure for all sectors to ensure that the worst case design wind is applied.
ICE now offers the current standard wind profile assessment for simple situations and the new directional assessment for more complex meteorological and or topographic situations. When providing a quote for a site-specific report ICE can make a recommendation on the necessity for a directional assessment.