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Re: Nailed board diaphragm with gap between boards and framing

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Nels,
John Kariotis conducted cyclic loading tests on wood diaphragms including board sheathing, about 1981. I don't have the reference on the report, but I believe it was done for NSF.  You could contact him for further info and a reference, or maybe borrow a copy.
John Rose
APA (retired)
Tacoma, WA

"Nels Roselund, SE" wrote:

Buddy [or anyone else who cares to jump in], I' working on an existing historic building with a single board floor diaphragm.  I'm evaluating it using the Guidelines for Seismic Evaluation of Existing Buildings [GSREB published by ICBO, the strength-version of the Uniform Code for Building Conservation -- UCBC].  No allowable values are given for a single board floor, unless the sheathing boards are tongue-in-groove, which they are not, in this case.  I'm planning to install a second layer of boards over the first, joints offset in each direction, in order to attain a diaphragm that is given allowable values, in both the GSREB and the UCBC. The floor was built with battens of lath [1/4" x 1-1/2"] laid across the joists before installing the boards, board edges centered over the battens.  This was probably done to keep dirt on the floor from falling through the floor boards into the rooms below.  The result is that there is are 1/4" gaps between the floor sheathing boards and the tops of the floor joists.  The nails pass through those gaps.  Is there a way of evaluating what that gap does to the strength and the rigidity of the diaphragm? For example, is there a way of adjusting the yield mode formulas of the NDS, Section 12.3.1 to find an effective nail strength?  Is there a way of adjusting the nail-slip component of the diaphragm deflection calculation of Section 23.222 of the 1997 UBC? I'm not looking for precision.  I'm looking for a rational approach, a reasonable method that makes sense. The project is in a National Park.  This is important because of historic preservation; for authenticity; for that one-in-a-hundred [or a-thousand] person who will look up, see the battens and the gaps under the floor boards, and say, "Wow, I think I know why they did that!" Nels Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net