Wood Diaphragm Unit Shear and Chord Force (SDPWS)

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.

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.

AWC SDPWS is viewable free of charge through AWC's online reader; the deep-beam w L / (2 b) arithmetic is public.

Estimate. AHJ and licensed professional govern.

Field names used by the API: w_plf, l_ft, b_ft, v_end_lb, v_plf, m_ftlb, chord_kip

• Simple-span flexible model uniform load between two parallel resisting lines with tributary-area distribution; a rigid-diaphragm relative-stiffness distribution and multi-span or cantilever diaphragms are separate analysesAWC SDPWS
• Collectors and openings separate drag-strut / collector forces at intermediate lines, diaphragm deflection, and openings each have their own checksAWC/APA design guides
• Compare to the nailing schedule the unit shear is checked against the SDPWS nominal capacity for the sheathing and nailing, with the ASD reduction or seismic factor appliedAWC SDPWS Tables 4.2A-4.2D