Risk Category IV wind speeds v. tornado wind speeds

It is my opinion that you are trying to compare apples & oranges. A straight line wind gust has got to be a different animal than a rotational wind that is also moving forward.

Tornado winds are ultimate aren't they?

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FEMA 361 and ICC 500 both treat tornado winds as an ultimate effect - using 1.0 as the load factor.

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I second the FEMA & ICC documents. Only thing to add is that if you truly are looking at tornado loading than you must satisfy the missile impact criteria not just the wind speeds. Keep in mind that your wall is only as good as your weakest link (doors, door hinges, windows, etc.) Once a projectile penetrations the enclosure then internal pressures can increase causing roofs to uplift or other issues. I only bring this up because I have also seen someone ask a similar question. The situation gets expensive once you start looking into pre-approved wall sections, speciality doors and roof hold downs. Probably worth clarify if they want a tornado shelter or simply a building able to take 157 mph wind speed (but not necessarily tornado resistant).

Thanks all.
Wind gusts and tornado winds are different animals and this was explained to the client.
They asked for a study after hearing our explanation.
Do the FEMA documents use the Fujita scale for the wind speeds?
This is strictly a study at this time. The missiles and internal pressures will all be considered if the client opts for a tornado shelter.

FEMA 361 based shelter design on a wind speed map for the USA - not a Fujita scale system.
(FEMA 361 is a free download found Here)

There are, however, various wind speed ranges given in this table from FEMA 361:




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