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RE: SEAW Wind Procedure

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I was not aware that the method being derived in Washington was an approved method as yet. It was suggested by another California Engineer active in SEA that a group from California, Oregon and Washington (not excluding your area or Nevada and Utah) form an alliance to work on a simplified method that can be presented for approval and submission for legislative approval in each state.


I was sent a beta version of a piece of software that is being worked on by the Wood Truss Council of America (WTCA) and have notices that they have a similar problem updating from the 2003 IBC and the IRC to the current code requirements. They are partially there while I am working on my own Multi-Lat™.


I’ll take a stab at it (although I do not have a copy of their design methodology) is that they are looking at the uplift on the tributary width of each truss (2 sounds like it might be trusses spaced at 24” o.c.) times the length of the truss and the dead load applied to the truss to calculate the required ties necessary to avoid uplift (if it occurs based on the resisting force of the truss. If the length of the truss or framing member is assumed to be 50-feet then the dead load acting on it is compared to the uplift depending on whether or not it is an open building, partially open building or a closed building with the uplift acting on the eave.  I’m guessing here so don’t hold it against me if I am wrong but if the roof framing were spaced at 24” o.c. then the tributary area of the roof member is the length times 1’-0” on each side or 2-feet which would give you a member with a tributary area in square feet. The uplift acting on it must be determined from what type of exposure the interior of the building receives (open, partially open or closed).


Let me know if you verify this.




From: Joseph R. Grill [mailto:jrgrill(--nospam--at)]
Sent: Saturday, February 09, 2008 8:00 AM
To: seaint(--nospam--at)
Subject: SEAW Wind Procedure


As a lot of you are doing, I am trying to study the new wind provisions.  I have a copy of the "SEAW's  handbook of a Rapid-Solutions Methodology for Wind Design" and I am trying to see if it will be beneficial to me.


Most of the work I do is for small fairly simple structures.  I am hoping there is someone out there (in the Washington area) that can explain something to me.


I am looking at the Application Problem 2 in Appendix B1.  I am looking at the uplift loading at the roof, which is a low slope roof.  When they are finding the uplift coefficient from Figures 3-4EB and 3-4ED they are taking into account a tributary area, "TA".  In the example that I am looking at they have determined that TA = (9/2)(50)=225 square feet.  I can't find (in any of the three books in the set) a definition of "TA".  I don't see where this particular "TA" comes from.  This tributary area doesn't seem to correlate to that which is calculated at the roof in example 4.


Is there anyone out there that is familiar with the SEAW methodology that can explain?



Joe Grill