×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Designing buildings for Tornadic Winds

Designing buildings for Tornadic Winds

Designing buildings for Tornadic Winds

(OP)
I am working on an steel-framed office building (5-6 stories) that has to be designed as an essential facility (requirement by client). I would really appreciate if anyone out here could through some light on designing such a building for Tornadic winds. I did a bit of code review on this and I am totally confused. Is it even practical to design such a building for such high wind velocities?? If yes, where can I find the design criteria. ASCE 7-05 commentary does have some information regarding tornadic wind velocities to be considered. But, I couldn't find any information on how to calculate pressures (both MWFRS and C&C) and load factors to be used in the final design. I would really appreciate your thoughts and comments on this. Thank you.

RE: Designing buildings for Tornadic Winds

It isn't very practical to design an entire building for tornadic winds.  The only thing that changes with the essential (Cat. IV) building category for wind is the importance factor.  If there is a storm shelter you need to include in your building, then that would need to be designed for tornadic winds per ICC-500 (I believe there is also a FEMA document that supplements this).  But for an entire MWFRS, the standard 90 mph wind is all that needs to be designed for (assuming you're in the 90 mph region).  Of course, you can always overdesign the hell out of everything, but it may not be practical from a budget standpoint especially when the mean recurrence interval is 100,000 years.

The issue with tornadoes isn't so much of the wind speed either, but more with the openings and penetrations that are created in your building by debris.  These then cause pressure buildups as you approach a partially enclosed building envelope.  But since they are not predictable, they are nearly impossible to design to.  I'm not sure ASCE-7 made any load combinations for a Volvo flying through your third story windows.

RE: Designing buildings for Tornadic Winds

Fema has some guidance on storm shelters.

This can be had at the link.

Maybe only critical items need to be placed in the safe room rather than design the entire building for a torndao.

As others have stated, internal pressures can be come significant for a direct hit by a tornado.

RE: Designing buildings for Tornadic Winds

I know that we bid on a job in our area to build a doppler radar facility where it had to stay operational during a tornado. We did not get the job but there was a special heavily reinforced concrete vault for the equipment and operators. I do not know what standard they built it.  

RE: Designing buildings for Tornadic Winds

As stated above, when a facility is designated 'essential', the only thing that changes is the wind importance factor in calculating the design wind pressure. This does not imply that the facility has to be designed for tornados.

If the owner wants the facility, or parts of the facility, designed to withstand a tornado, that is another issue. And a question that should be asked of the owner. What is he/she intetending when they say they want their facility to be 'essential'.

FEMA 361 is guidance for the design of tornado shelters. FEMA 453 mentioned above if for shelters offering protection from man-made events.

We have been asked many times if it is practical to design multi-story buildings to meet FEMA 361 guidance (we are located in the midwest, and tornados are an issue around here). Our response always is that yes, we can design a multi-story building to FEMA 361. The only problem is the owner likely cannot afford it.

The best solution is to locate the shelter underground. If that is not feasible, 1 story 'protected areas' on the ground floor are the only practical solution.

JMHO.

RE: Designing buildings for Tornadic Winds

Portions of Nuclear Power Plants are designed for tornadic winds.  There's the wind issue and the pressure drop.  The tornado moves at some speed (like 60 mph) and the circular wind at the edges is in the range of 240 mph as I remember. These combine for a maximum pressure of 300 mph. There's also the fact that due to the relative small size of a tornado, part of the building might have wind in one direction and part in another direction.
But designing a massive chunk of concrete with no openings for a tornado and an occupied building for a tornado are two different issues.  I'm not sure you could design a 5 story building for these forces.

RE: Designing buildings for Tornadic Winds

Quote:

FEMA 361 is guidance for the design of tornado shelters

lkjh345, as stated by bnickeson above, check out ICC 500.  This document is based upon FEMA 361 and essentially provides a "code-language" specification on shelter designs vs. 361's "guide-language".

 

RE: Designing buildings for Tornadic Winds

The International Code Council (ICC) was in the process of issuing a standard a couple of years ago that dealt with designing emergency shelters for tornados.  Try their website at iccsafe.org.

RE: Designing buildings for Tornadic Winds

Uh....ICC 500

 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources