Wood Diaphragm Unit Shear and Chord Force (SDPWS)
The flexible wood diaphragm as a deep horizontal beam: the end reaction V = wL/2, the maximum unit shear v = wL/(2b) the sheathing nailing must carry, the moment wL^2/8, and the chord force T = C = M/b the perimeter members resolve it into. A 192 x 120 ft roof at 516 plf runs 413 plf of unit shear -- the published WoodWorks value -- and 19.8 kip of chord force; narrow the diaphragm to 60 ft and both exactly double. Simple-span flexible (tributary) distribution; collectors, deflection, and openings are separate. A design aid, not a substitute for the engineer of record's stamped lateral design.
Formula and source
V = w L / 2; v = w L / (2 b); M = w L^2 / 8; chord T = C = M / b.
The AWC Special Design Provisions for Wind and Seismic (SDPWS) simple-span flexible-diaphragm deep-beam model, as compiled in the AWC/APA engineered-wood-diaphragm design guides, by name.
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