2001 ASD Supplements - unprotected PDF - American Wood Council

ASD WOOD STRUCTURAL PANEL SHEAR WALL AND DIAPHRAGM SUPPLEMENTSW-35Step 8.Drag Strut Forces and Drag Connections (East & West WallsOnly)Drag struts are required where there are openings inthe shear walls to distribute forces from the diaphragm tothe shear walls. The force in the drag strut equals the differencebetween the applied diaphragm shear and theresisting wall shear.East WallWest WallAMaximum force in Drag Strut:APPENDICES280 x 40 = 11,200 lb.Drag force is maximum of:VLLa 0 1L−L =0(280)(20)(45)110 −20= 2,800 lb. for two 2x8sVLLa 0 2L−L =0(280)(20)(45)110 −20= 2,800 lb. for two 2x8s= 1,400 lb. per 2x8Given that the maximum tensile capacity of a single2x8 wall plate is 8,500 lb., this is the maximum capacityat the splice of a double top plate of 2x8s. If the tensilestress exceeds 8,500 lb. at a splice location, then an additional(a third) 2x8 plate must be used. This will increasethe allowable tensile capacity at the splice to 17,000 lb.For this example, the following is used to determine thelocation along the wall plate where three 2x8s are required.On the South end of the East wall:8,500 11,200= , x = 30' ft.x 40On the North end of the East wall:8,500 11,200= , x = 53' ft.x 70In lieu of multiple 2x8s to provide continuity betweenwall plates, framing anchors/straps may be used. A single2x8 with straps at butt joints may be used above, withdouble 2x8s required only when the axial load is greaterthan 8,500 lb. and less than 17,000 lb. Where 2x8s aredoubled up, straps are required at splice locations.Be sure there is no more than one butt joint at each splice location.Space joints at least twice length of splice (or about 5 feet minimum).APA – The Engineered Wood Association