What is a Site Specific Wind Assessment

http://janrebel.eu/wp-content/plugins/reflex-gallery/admin/scripts/FileUploader/php.php The design of tall structures such as communication towers requires knowledge of the design pressure, both at the surface level (10 m) and as a profile with height above ground. The Building Codes which the engineer follows provide maps or tabulations of derived wind or pressure at the surface level (Basic Wind) with prescriptions for accounting for terrain characteristics, topographic effects, and vertical wind profiles.

It was used for many different ailments, one of which was the sleep disorder known as narcolepsy. Due to the large areas covered by the maps in the US or Canada encompassing many types of local meteorological effects which are not included in the maps, the codes recognize that such information and procedures are not adequate for producing credible wind pressure estimates for special wind zones and local meteorological situations. The codes then recognize the need for a Site Specific assessment of such situations, which are presumed to include recourse to local meteorological data and application of recognized procedures for deriving the wind profile for the tower.

This medication is also sometimes used to treat ocular neovascular glaucoma, a condition where new blood vessels grow in If the engineer then decides to obtain a site-specific wind for a tower site, he finds that the product denoted as “Site-Specific Wind and Ice Assessment” is interpreted differently by organizations which supply site specific studies, although the Building and Tower codes such as ASCE7 (in Section 26.5.3) and TIA 222 (Section 2.64 and explicitly in topographic category 5) require the use of meteorological data obtained at a nearby site and analysis using accepted statistical methods in the literature in order to treat them as site specific assessments. For example if the basic wind from the ASCE maps is used and the user calculates and applies the 4 profile factors specified in the pressure formula per the code prescription, then the user would not call it a site specific assessment.

buy Lyrical dance costumes online ICE Inc. obtains hourly wind and other meteorological data from a nearby airport with 30 or more years of record, as well as supporting meteorological data such as precipitation, temperature, humidity, and observations such as gust, freezing precipitation, cloud ceiling, and weather type codes. ICE then performs the statistical analysis to determine the extreme wind speed for any return period required by the user, applies the topographic and terrain corrections using the Simple Guidelines, and models the icing for each event in order to provide vertical profiles of wind for the extreme event, freezing rain and in-cloud icing dependent on tower height, location, and the elevation of the tower site.

Environment Canada uses as its starting point the mapped wind from the NBCC (National Building Code of Canada) in tabular form and applies an equation derived from the Simple Guidelines for topographic influences on the wind profile. Icing accumulation due to freezing rain is per NBCC table, and no rime icing estimate is produced. EC provides a service on this basis which it calls Site Specific.

The Checkwind software from Revolutio (Australia) interpolates the ASCE7 Map or other code wind map to a specific location and performs for the user the topographic and terrain corrections provided in the code. It also calls this a site specific wind.

The ATC (Applied Technology Council) Hazards by Location web site provides wind values by interpolating the ASCE7 wind maps for a specific geographic location, and the user is expected to apply the terrain and topographic correction factors to obtain a wind in accord with the code. They call this a Site Specific wind as well, although there is no charge for obtaining the interpolated wind from the web site presumably in recognition of the fact that the user can do the map interpolation on his own.

Ultimately it is up to the design engineer to decide which product serves his client’s needs. It is easy to see why the engineer would be uneasy about having to make the decision, given that he does not have the full picture of what these procedures entail. This is then compounded by the fact that the same name “Site Specific Wind” is being used for totally different products. As ICE is familiar with the EC data and procedures through numerous comparisons and discussions, the following sets out some of the differences between the ICE service and the EC service and the implications of the two approaches in practice. A more detailed discussion of the differences is provided in a paper available on our web site at ice-inc.co.

As a basic requirement, when different data and methods are compared it is important to establish the basis for comparison. This is particularly critical in the case of the return value for wind speed, because this is not a quantity that is measurable except by indirect statistical inference. In the design process the specifics of the derivation of the wind speed and profile of wind speed with height are essential, so that a comparison of the single value at 10 m is not sufficient to compare available alternatives.

There are several differences between the ICE and EC site specific approach which often produce large differences in the results provided to the engineer.

Read More in the following papers: