Problem 8.20

 

Given

 

Application	joists in flat roof
Spacing	24 in. OC
Load	D = 8 psf S = 100 psf
Type of panel	APA rated sheathing (plywood or nonveneer panel)
Orientation	strong direction

 

 

Deflection Limits  (IBC table 1604.3)

 

Roof members	L (100 psf)	S or W (100 psf)	D + L (108 psf)
supporting plaster ceiling	L/360	L/360	L/240
supporting non-plaster ceiling	L/240	L/240	L/180
not supporting ceiling	L/180	L/180	L/120

 

 

Span Rating  (Load-Span Tables for APA Structural-Use Panels)

 

Try a 40/20 with joists supporting a plaster ceiling.

L	L/360	108 psf > 100 psf  ✓
S or W	L/360	108 psf > 100 psf  ✓
D + L	L/240	163 psf > 108 psf  ✓
Bending		1.15(130 psf) = 149.5 psf > 108 psf  ✓
Shear		1.15(218 psf) = 250.7 psf > 108 psf  ✓

 Try a 40/20 with joists supporting a non-plaster ceiling.

L	L/240	163 psf > 100 psf  ✓
S or W	L/240	163 psf > 100 psf  ✓
D + L	L/180	217 psf > 108 psf  ✓
Bending		1.15(130 psf) = 149.5 psf > 108 psf  ✓
Shear		1.15(218 psf) = 250.7 psf > 108 psf  ✓

 Try a 40/20 with joists not supporting a ceiling.

L	L/180	217 psf > 100 psf  ✓
S or W	L/180	217 psf > 100 psf  ✓
D + L	L/120	?? psf > 108 psf  - probably okay since above (more-conservative) ceiling options were okay
Bending		1.15(130 psf) = 149.5 psf > 108 psf  ✓
Shear		1.15(218 psf) = 250.7 psf > 108 psf  ✓

 ∴ A 40/20 span rating or larger would work for APA rated plywood sheathing.

 

Try a 48/24 with joists supporting a plaster ceiling.

L	L/360	174 psf > 100 psf  ✓
S or W	L/360	174 psf > 100 psf  ✓
D + L	L/240	260 psf > 108 psf  ✓
Bending		1.15(208 psf) = 239.2 psf > 108 psf  ✓
Shear		1.15(222 psf) = 255.3 psf > 108 psf  ✓

 Try a 48/24 with joists supporting a non-plaster ceiling.

L	L/240	260 psf > 100 psf  ✓
S or W	L/240	260 psf > 100 psf  ✓
D + L	L/180	347 psf > 108 psf  ✓
Bending		1.15(208 psf) = 239.2 psf > 108 psf  ✓
Shear		1.15(222 psf) = 255.3 psf > 108 psf  ✓

 Try a 48/24 with joists not supporting a ceiling.

L	L/180	347 psf > 100 psf  ✓
S or W	L/180	347 psf > 100 psf  ✓
D + L	L/120	?? psf > 108 psf  - probably okay since above (more-conservative) ceiling options were okay
Bending		1.15(208 psf) = 239.2 psf > 108 psf  ✓
Shear		1.15(222 psf) = 255.3 psf > 108 psf  ✓

 ∴ A 48/24 span rating or larger would work for APA rated OSB sheathing.

 

 

Thickness  (Panel Design Specification)

 

 ∴ A 19/32 in. thickness or larger would work for APA rated plywood sheathing.  A 23/32 in. thickness or larger would work for APA rated OSB sheathing.

 

 

Edge Support  (ASD-LRFD Manual)

 

∴ Edge support is not required for a 24 in. span.

 

 

Conclusion

 

Minimum grade	APA rated plywood sheathing	APA rated OSB sheathing
Span rating	40/20	48/24
Thickness	19/32 in. or greater	23/32 in. or greater
Edge support	not required	not required