Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

224 Chapter Nine
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Bending Deflection in Plyform Sheathing
For a maximum permissible deflection of l/360, but no greater than
2 × 4 ¹⁄16 in., and plywood with three or more spans, Eqs. (5-57a) and
(5-57b) from Table 9-6 can be used to calculate the allowable span
length for bending deflection.
From Eq. (5-57a): l d
= [1,743EI/360w d
] 1/3 for ∆=l/360
= [1,743(1,6500,000)(0.199)/360(713)] 1/3
= 13.1 in.
From Eq. (5-57b): l d
= [1,743EI/16w d
] 1/4 for ∆=¹⁄16 in.
= [1,743(1,650,000)(0.199)/16(713)] 1/4
= 14.9 in.
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Summary of Allowable Span Lengths for the Sheathing
For bending, the maximum span length of sheathing = 12.1 in.
For shear, the maximum span length of sheathing = 14.5 in.
For bending deflection, the maximum span length of sheathing = 13.1 in.
For this design, bending stress controls the maximum span length of
the Plyform sheathing. The studs that support the Plyform must be placed
at a spacing that is no greater than 12.1 in. For uniformity and constructability,
choose a maximum stud spacing of 12.0 in., center to center.
Check Total Deflection in Plyform
Calculate the total deflection, including bending deflection and shear
deflection and compare it to the maximum permissible deflection of l/360
and ¹⁄16 in. For bending deflection with 2-in. nominal studs for support
the effective span length is the clear span + ¼ in. (refer to Figure 5-10):
l d
= 12 in. – 1.5 in. + ¼ in.
= 10.75-in.
Calculate bending deflection from Eq. (5-51) as follows:
∆ d
= w d
l d4
/1,743EI
= 713(10.75) 4 /(1,743)(1,650,000)(0.199)
= 0.017 in.
For shear deflection with 2-in. nominal studs to support the effective
span length is the clear span (refer to Figure 5-10).
l s
= 12 in. – 1.5 in.
= 10.5 in.
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