Wind load design

[cmrdata]

Design wind pressure tables in the ASCE 7-05 and FM Data Sheet 1-28 are quite comparable, if you take into account the additional importance factor of 1.15 adopted by FM for the cladding and components.
With the adoption of ASCE 7-10 in which wind load is based on ultimate load, I gather for certain buildings we might have do it twice:

1. Proceed with ASCE 7-10, with wind load as ultimate load, to satisfy the Building Code.
2. If the building is insured by FM, run a separate analysis/design with FM 1-28, with wind load as service load.
3. Compare the results from two designs above, and the more conservative one governs.

This sounds silly and I'm not sure what I miss here. I appreciate any comments you might have.

 

[wannabeSE]

Why can't you determine the wind pressure using ASCE 7-10 (2012 IBC) ASD load combinations (0.6W) to get the wind pressure and compare this to FM?

 

[bhugey]

Just had the same discussion in our office. Haven't found anywhere within FM documents on how they are incorporating the ASCE 7-10 wind changes.
But, I suspect you could get there a couple ways.
I would take the approach of assuming that FM's intent still applies. They bump up the code prescribed wind by a 1.15 importance factor and use Exposure C or worse.
And, FM is only concerned with components and cladding.
As wannabeSE suggests, using ASD , you could use ASCE7-10 to get wind pressures and factor down to ASD, but then you would need to apply the importance factor 1.15.
Or, if you are in a Category II building, you could use the ASCE 7-10 maps for category III and IV, which would include the 1.15 factor.

Until FM provides clarity, and I intend to ask an FM representative, it seems we end up specifying C&C loading that is, in our judgement, equivalent to their intent.