Applicability of Simplified Wind Method.

[BlastResistant]

Hi all,

IBC (03) 1609.1.1 says that wind loads shall be determined per ASCE 7 (02) with one of the exceptions being "Wind loads determined by the provisions of Section 1609.6," which is the simplified method. Section 1609.6.1.2 gives conditions under which the simplified method can be used for components and cladding. Well, ASCE 7 (02) Section 6.4.1.2 gives 5 conditions, all of which must be met in order to use the simplified method for components and cladding. All of these conditions can be found somewhere in the IBC except the last one which states, "the building is not subject to the topographic effects of Section 6.5.7 (i.e., Kzt = 1.0)."

It seems that the ASCE 7 is adding an additional requirement on top of the IBC. Is this correct? In my region, a location where Kzt = 1.0 is non-existent. Does that mean I can never use the simplified method? No one in my office ever noticed this before because if you can use the simplified method per the IBC, one would never bother to pick up the ASCE 7 in the first place!

Thanks in advance for your comments.

 

[msquared48]

You will find that the simplified method is very conservative, and I have personally found that it applies in the order of 25% more load to the structure in specific circumstances than the Equivalent Force Method. You may save on analysis time, but the owner will pay with the extra materials.

It is OK for simple projects, but for the more complicated and larger projects, use EFM.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

Sorry, I don't know what I was thinking - seismic is not wind. But the same thoughts of mine still apply. Senior moment.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[abusementpark]

I wouldn't use the simplified method. You can buy a piece software for probably $500 bucks that will run through Method 2 for you.

 

[woodman88]

You need to check the building code requirements and amendments to the code for the local jurisdiction. If it states the IBC and has no amendment sending you to a section of another standard then you use just the IBC section.
I have mostly used the simplified method for wind and the equivalent force method for siesmic.

Garth Dreger PE
AZ Phoenix area

 

[NFExp]

BlastResistant

The IBC 06 refers to the ASCE 7-05 only for determining wind loads. For the simplified method, the ASCE 7-05 does not have the condition that Kzt=1.0.

So in my opinion you are OK with using the simplified method.