IBC 2006 Code 3

[JOHNPIA2]

I would appreciate some clarifications on wind speed and exposure categories, per IBC 2006.
For hurricane-prone regions, exposure C is to be used, with the appropriate wind speed. What about tornadoes? Is the max. wind speed limited to 90mph, and the exposure D, for tornado-prone regions? This does not look right to me.

 

[JAE]

Tornados are typically between 150 mph and 250 mph IF...and I say if....you are specifically designing a tornado shelter. You can get a free copy of FEMA 361 by calling. This document outlines required design guidelines for tornado/storm shelters (including hurricanes).

In most areas of the country where tornados are frequent, the design is usually set at 90 mph. Statistically, the odds of a building getting hit by a tornado are small and the cost/benefit ratio to actually tornado-proof a building is quite large.

 

[UcfSE]

Basically tornadoes are considered an extreme event, something we don't typically design for unless the structure must remain functional after the event, such as a hospital or tornado shelter, or if damage to the structure would be hazardous to the public, such as a nuclear power plant. The ASCE provides a wind speed map for tornadic gust wind speeds that go up to 200 mph for a recurrence interval of 100,000 years. As JAE stated, tornado-proofing a building will be disproportionately exspensive, to the point you may not be able to afford a building to tornado proof.

 

[Bagman2524]

ICC has a new standard (IS-STM/ICC-500)for storm shelters that covers tornado design. These are the only structures (other than nukes) that I know of that are required to be designed for tornados.

http://www.iccsafe.org/cs/standards/is-stm/index.html