EWPAA Structural Plywood and LVL Design Manual - Engineered ...

7.4 Structural Plywood Flooring – Design MethodologyThe steps involved in the design of a plywood sheathed floor system are as follows:1. Select a joist spacing to suit standard plywood flooring sheet lengths :a. Standard sheet lengths are :i. 2400 - suitable joist spacings include 400, 600, 800 mmii. 2250 - suitable joist spacings include 375, 450, 750 mm (limited availability)iii. 2700 - suitable joist spacings include 450, 540, 675, 900 mmb. To optimise structural plywood performance ensure plywood is supportedcontinuously over a minimum of two spans.2. Set Deflection Limits:i. A typical deflection limit is span/200. Where the plywood flooring willbe an underlay to a rigid covering such as tiles, tighter deflectioncriteria are recommended. AS/NZS1170.1 Appendix C recommends adeflection limit of span/300.3. Determine floor imposed load requirements from AS/NZS 1170.1 for bothconcentrated and uniformly distributed loadsi. Typically, the load contribution of the plywood flooring itself isinsignificant when compared to the imposed loads and consequentlyis ignored in strength and stiffness calculations.4. Determine the capacity factor (Φ) and strength modification factors from AS1720.1-1997 for structural plywood flooring:The relevant factors are: Refer AS1720.1-1997orBending : (φk 1 k 19 g 19 )not found. of this manualError! Reference sourceShear : (φk1k 19g 19 )Deflection: (j2 j 6 g 19 )AS1720.1-1997Referenceφ = 0.9 for all structural elements in houses Table 2.6k 1 =0.94For concentrated loads assuming loads are applied at infrequentintervals such as might arise due to a pallet, jack or maintenance typeload. Effective duration of peak load = 5 days.k 1 = 0.80For uniformly distributed loads assuming loads are typical floor typeClause 2.4.1.1loads (crowd or vehicle or stored material. Effective duration of peakTable 2.7load = 5 months.k 19 = 1.0As it is not anticipated the plywood moisture content will exceed anaverage of 15% in a dry interior application. In a dry interior application, Table 5.9moisture content would be in the range 8 to 12 %.g 19= 1.0Direction of the face veneers is parallel with the span direction.Therefore, g19= 1.0 for bending, shear strength and deflection.Table 5.11Clausesj 2 = 1.0 for short term concentrated loads of less than 1 days duration.2.4.1.2j 2 = 2.0 for longer term uniformly distributed loads, such as stored materials. Table 5.13j 6 = 1.0average moisture content not anticipated to exceed 15%. (Refer k19above)Table 5.1555