2001 ASD Supplements - unprotected PDF - American Wood Council

ASD WOOD STRUCTURAL PANEL SHEAR WALL AND DIAPHRAGM SUPPLEMENTSW-5Subdiaphragm – A portion of a larger wood diaphragmdesigned to anchor and transfer local forces to primarydiaphragm struts and the main diaphragm.Tie-Down (Hold-Down) – A device used to resist upliftof the chords of shear walls.Wall Bracing – a building element that resists lateral loadsin conventional (non-engineered) applications; the configurationand connections are prescribed by the buildingcodes for light-framed wood structures.2.3 BackgroundWood Structural Panel – A panel manufactured fromveneers; or wood strands or wafers; or a combination ofveneer and wood strands or wafers; bonded together withwaterproof synthetic resins or other suitable bonding systems.Examples of wood structural panels are plywood,oriented strand board (OSB), or composite panels.2INTRODUCTIONShear walls and diaphragms are designed to transferin-plane forces. When using these two assemblies to resistlateral design forces of buildings, the structural systemis sometimes referred to as a “box system”. The shearwalls provide reactions for the roof and floor diaphragms,and transmit the forces into the foundation (see Figure2.1).With ordinary good construction practice, any sheathedelement in a building adds considerable strength to thestructure. Thus, if the walls and roofs are sheathed withpanels and are adequately tied together, and tied to thefoundation, many of the requirements of a diaphragmstructure are met. This fact explains the durability of woodstructural panel sheathed buildings in hurricane and earthquakeconditions even when they have not been engineeredas diaphragms or shear walls per se.There are various textbooks and other resources whichprovide in-depth coverage of this topic (see section A.2).Figure 2.1Distribution of Lateral Loads on Buildings (Wind Illustrated)Roof (horizontal diaphragm)carries load to end wallsLbvhwvTWind load, F(lb. per sq. ft.)wvCSide wall carries loadto roof diaphragm at topand to foundation at bottomEnd wall (vertical diaphragm or shearwall) carries load to foundationv (lb./ft. of diaphragm width) =w (lb./ft. of wall) = Fh2wL2bT (lb.) = C = vhAPA – The Engineered Wood Association