2514 RAINIER AVE 2022-03-01 - Laserfiche WebLink

1.10 In Plane Diaphragm Flexibility AASC _5' � i i DECK Skew Cut Diaphragm Boundary At skew cut conditions, the minimum number of fasteners is determined based on the location of the fasteners in the ribs per the perpendicular attachment schedule. The average spacing of the fastener per sheet shall not be greater than the spacing of the parallel boundary fasteners. Fasteners may need to be doubled up in some flutes to achieve this. (See figure 1.10.1) Figure 1.10.1: SKEW DIAPHRAGM Diaphragm Shear Zoning Steel deck diaphragms may be zoned based on shear demand on the diaphragm to create the most economical roof structure. This may not be practical for every building, but many rectangular large roof structures lend themselves to zoning. The deck panel along the collectors will have the highest shear demand dropping off toward the middle of the diaphragm. The deck gage and attachment pattern can be reduced as the shear demand in the diaphragm diminishes (see Figure 1.10.2). Figure 1.10.2: DIAPHRAGM SHEAR ZONING Diaphragm Deflection Diaphragms in plane deflections should be based on the shear deflection of the diaphragm. For diaphragms that do not have a large aspect ratio of length to depth, flexural deflec- tion should not be considered. Flexural deflection equations based on slender beams do not apply to deflection of deep beams, which are generally considered beams with a length to depth ratio of 5:1 or less. Diaphragms with length to depth ratios greater than 5:1 probably do not meet the requirements for flexural deflections because the diaphragm, acting as the web of the beam, is orders of magnitude more flexible than the diaphragm cords, acting as the flanges of the beam. Typical lengths of steel deck panels that are safe and efficient for erection are in the 20 to 35 foot range. For erection safety, 3 span sheets are the desirable minimum sheet length. A mini- mum 3 span condition should not be specified because sin le and doublespans are required for layout in most buildin s. For design purposes a ratio of span to length, R, from '/3 to 15 is appropriate for general design. F=#.#+#.# R R L F = Diaphragm stiffness in micro inches per Ibs L = Vertical load span, which is the support spacing L = Deck panel length, which is a multiple of the vertical load span Example: DG13-36, 20 gage, 36/7/4 attachment pattern, DeltaGrip® spacing of 12 inches, Vertical load span of 5 feet F=7.1+19.6R Assume R = 1/5, a 25 foot long panel with 5 foot vertical load span F=7.1+19.6R=7.1+19.6(1/5)=11 Figure 1.10.3: DIAPHRAGM STIFFNESS FACTOR Diaphragm Deflection Concept The deflection of a diaphragm that is zoned for shear can be approximated by summing the deflection of each deck zone, based on the diaphragm stiffness of each zone (see Figure 1.10.4). For zone 3 in the figure, the diaphragm stiffness of the least stiff zone is applied to the entire building depth. 14 L 0-1 Atotai A' 1 A, +A3 Atotal= Al + 62+ A, Figure 1.10.4: DIAPHRAGM DEFLECTION CONCEPT 24 V1.0 • Roof Deck Catalog www.ascsd.com SC - 5