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Nailed board diaphragm with gap between boards and framing
- To: <seaint(--nospam--at)seaint.org>
- Subject: Nailed board diaphragm with gap between boards and framing
- From: "Nels Roselund, SE" <njineer(--nospam--at)att.net>
- Date: Tue, 7 Jan 2003 16:46:25 -0800
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
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!"