ud83dudcda Wood Deck Build Log u2014 23 of 45
u2190 Detail #7: Floor Joist Strength u00b7 Series Index u00b7 Detail #9: Beam Strength Calc u2192
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Decking Board (u30c7u30c3u30adu6750) Strength Calculation
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Hi, I’m DIY Dad. ^ ^
After the floor joists, next up is the decking boards u2014 the visible surface you actually walk on. The member is SPF 2u00d74 lumber (38 u00d7 89 mm u00d7 6 ft).
u2191 Decking board layout
Material Properties (SPF Grade 1 framing, bending)
- Long-term allowable stress: 8.14 N/mmu00b2
- Short-term allowable stress: 14.8 N/mmu00b2
- Modulus of elasticity: 10,000 N/mmu00b2
- Section modulus: Z = bhu00b2 / 6 = 89 u00d7 38u00b2 / 6 = 21,419 mmu00b3
- Second moment of area: I = bhu00b3 / 12 = 89 u00d7 38u00b3 / 12 = 406,967 mmu2074
Calculation
Clear span = joist-to-joist spacing = 361.25 mm, rounded to 362 mm.
Total design load: 240 kg. Since at least 2 decking boards share the load, each board carries 1/2.
W = 240 u00d7 0.5 u00d7 9.8 = 1,176 N
M = WL / 4 = 1,176 u00d7 362 / 4 = 106,428 Nu00b7mm
u03c3 = M / Z = 106,428 / 21,419 = 4.97 N/mmu00b2 < 8.14 N/mmu00b2 u2192 OK
u03b4 = WLu00b3 / (48EI) = 1,176 u00d7 362u00b3 / (48 u00d7 10,000 u00d7 406,967) = 0.29 mm < 1.2 mm (L/300) u2192 OK
Both stress and deflection are within allowable limits. ^ ^
Next up: the beams (u6881).
That’s all for today! (^^)/~~~
ud83dudcda Wood Deck Build Log u2014 23 of 45
u2190 Detail #7: Floor Joist Strength u00b7 Series Index u00b7 Detail #9: Beam Strength Calc u2192
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