Section 2.0 - Loads

ID #1110

As everyone is aware, many jurisdictions are now adopting the IBC 2012, which has updated wind speed maps. Regarding TIA-222-G, can the converted (Vasd) wind speeds from the IBC 2012 be used instead of the wind speeds listed in TIA-222-G, or do we need to take the more stringent of the two? I know this gets a little tricky when the risk category/structure class is something other than II, since the importance factors in TIA are more elaborate (wind speed with no ice, with ice, ice weight) than those in the IBC (who simply provide a number for the wind speed with no ice). We do a lot of work on the Atlantic coastline, and these changes would be most beneficial to our clients. Any interpretation of this would be greatly appreciated.

Per TIA-222-G Section 2.6.4.1 the wind maps per ASCE 7-10 may be used to determine the basic wind speeds. The ASCE 7-10 wind maps for Category I, II and III structures include the appropriate load and importance factors based upon the structure classification; therefore, the load factor and importance factor for use with TIA-222-G must be equal to 1.0. In addition, when ASCE 7-10 basic wind speeds are used, hurricane coastal areas must be considered as Exposure D as an exception to TIA-222-G Section 2.6.9.1 which allows the use of exposure C for hurricane coastal areas. ASCE 7-10 wind speeds have been reduced in the hurricane coastal areas based on new research. In addition, hurricane coastal areas are now considered as exposure D based on research which has indicated that the roughness of the ocean is more representative of exposure D conditions. In the current version of revision G and previous versions of ASCE 7 the roughness of the ocean was believed to be more representative of exposure C conditions.

Tags: 2.6.4.1, 2.6.9.1, ASCE 7-10, hurricane, importance factor, Wind maps

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Last update: 2012-07-30 17:12
Author: John Erichsen
Revision: 1.0

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