3x Tongue and groove diaphragm

[burtc]

What are the 2006 IBC allowable stress wind and seismic diaphragm design values for 3x6 T & G decking? It will be nailed to 4x12 floor joists at 30" o.c. A diagonal orientation is possible but not preferred. Wind controls teh design; v(asd,wind) = 205 plf. The previous posts on a closed thread were in 2004. Thanks - Any input is much appreciated!

 

[msquared48]

You won't find it in the IBC or AITC. Maybe the NDS, but I doubt it. It is generally not an accepted practice now structurally, particularly at floors. Older publications of the Douglas-Fir Use Book or Wood Book may have such a table, but that would have been with better wood than we have now.

Professionally speaking, I would not use such a diaphragm. It's too flexible.

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

 

[msquared48]

I did find this in my 1958 version of the Douglas-Fir Use Book, but it is not specific to T&G material. Appears to be planking. The material though is over 50 years old. Personally, I would not rely on it.

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

 

[mmillerpe]

Generally, I have seen a 1/2" or 5/8" layer of sheathing applied over the top of the T&G heavy timber roof decking, and I have done this on one project several years ago. I believe I was able to find information that if you do this, use can use the blocked diaphragm values from the IBC or NDS in the design of the diaphragm. You would need to specify the connection between the Heavy Timber decking to the frames or shear wall lines to transfer the diaphragm loads.

 

[woodman88]

In the 2009 IBC it states in Section 2306.2.2 that "Single diagonally sheathed lumber diaphragms shall be designed and constructed in accordance with AF&PA SDPWS"
Which is the ANSI / AF&PA SDPWS-2008 - Special Design Provisions for Wind and Seismic standard with Commentary covers materials, design, and construction of wood members, fasteners, and assemblies to resist wind and seismic forces. Engineered design of wood structures to resist wind or seismic forces is either by allowable stress design (ASD); or load and resistance factor design (LRFD). The most notable new provisions of the 2008 Wind and Seismic standard include criteria for wood structural panels designed to resist combined shear and uplift from wind.

Garth Dreger PE
AZ Phoenix area

 

[burtc]

Thanks to all of you. Woodman88, I will pursue the ANSI reference document, and will also contact the WWPA and AF&PA folks on Monday. My client has thousands of board feet of 3x6 T & G material on hand and did not want to add sheathing if possible, for a number of reasons. The longest spans of the diaphragm are 30', and it is approx. 20' deep. Wind controls the design, and v (asd) is only about 240-245 plf depending on some architectural options.